Atrial tachyarrhythmias in children

INTRODUCTION — Atrial tachyarrhythmias (ATs) are non-sinus arrhythmias that result in a heart rate above the 95^th percentile for age and that do not require the atrioventricular (AV) junction, accessory pathways, or ventricular tissue for initiation and maintenance of the elevated heart rate.

In pediatric patients, ATs are most commonly seen in children with structural congenital heart disease (CHD) who have undergone cardiac surgery; they can also occur in children without CHD and may result in significant morbidity.

Related topics include:

●(See "Atrial arrhythmias (including AV block) in congenital heart disease".)

●(See "Fetal arrhythmias".)

●(See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children" and "Management of supraventricular tachycardia (SVT) in children".)

TERMINOLOGY — AT is a subset of supraventricular tachycardia (SVT). SVT is a broad group of tachycardic disorders that includes any non-sinus rapid rhythm that arises from structures above the bundle branches, including the atrium (table 1).

ATs can be classified based on the P wave phenotype on electrocardiogram (ECG), whether a single or multiple foci are involved in the origin of the tachycardia, and the frequency and duration of tachycardia (ie, sporadic/paroxysmal, frequently recurrent, or persistent tachycardia). The tachyarrhythmia mechanism (macroreentry, microreentry, enhanced automaticity, and triggered) only loosely correlates with this schema and should be avoided as part of the classification nomenclature unless the mechanism is clearly known. For completeness sake, atrial flutter and fibrillation are also discussed in this review.

The following classification is used in this review:

●Primary atrial tachycardia – The term "primary atrial tachycardia" implies a non-sinus tachycardia with discrete and monotonous P waves. Beyond this general term, the nomenclature continues to evolve. Focal atrial tachycardias (FAT; also referred to as atrial ectopic tachycardia [AET] or ectopic atrial tachycardia [EAT]) arise from a single site within the left or right atrium. FAT can be automatic or nonautomatic (see "Focal atrial tachycardia"):

•Automatic FAT emanates from a single atrial focus, is mostly incessant, and has a variable rate over time that is influenced by the autonomic nervous system. Progressive rate acceleration over the first several beats is frequently observed. During periods of marked vagotonia, automatic FAT may be suppressed in some individuals. The P waves are discrete and non-sinus in appearance. As with all pathologic ATs, the PR interval may be inappropriately long relative to the atrial rate. This tachycardia occurs due to an area of enhanced automaticity.

•Nonautomatic FAT also due to a single focus, behaves in a paroxysmal manner, stopping and starting abruptly (waveform 1A). It may be a rare sporadic event or may recur frequently, even nearly incessantly. The rate is usually relatively constant within a given paroxysm. Microreentry or triggered activity are thought to be the most common mechanisms.

•Sinoatrial node reentry tachycardia (SANRT) is a form of nonautomatic FAT that is sometimes categorized separately. Like all reentry tachycardias, it starts and stops abruptly (waveform 2A-B). Its P waves are identical to sinus P waves as it emanates from the head of the sinoatrial node. Similar to FAT, the PR interval may be longer than expected for the tachycardia rate. It may be terminated with intravenous adenosine. (See "Sinoatrial nodal reentrant tachycardia (SANRT)".)

●Chaotic atrial tachycardia (CAT) – CAT (called multifocal atrial tachycardia in adults) is diagnosed when there are at least three different rapidly depolarizing, non-sinus P wave morphologies during a 10-second rhythm strip or ECG (waveform 3). Classically defined, there should be irregular P-P, P-R, and R-R intervals. The degree of persistence versus intermittency of the tachycardia is not implied by the name. (See "Multifocal atrial tachycardia".)

●Atrial fibrillation – Atrial fibrillation involves multiple, simultaneous atrial reentry wavelets that appear on a rhythm strip as a low-amplitude or choppy, irregular baseline with a variable R-R interval (waveform 4). (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation" and "Epidemiology, risk factors, and prevention of atrial fibrillation".)

●Atrial flutter – Atrial flutter is a macroreentry tachycardia in which the critical part of the large electrical circuit passes between the inferior vena cava and the tricuspid valve annulus, the cavotricuspid isthmus. It manifests as a sawtooth pattern on ECG, usually with 2:1 atrioventricular (AV) conduction (waveform 5A-B). There are two forms of atrial flutter: "counterclockwise" atrial flutter, which has a negative sawtooth pattern in leads II, II, and aVF, and "clockwise" atrial flutter, which has a positive sawtooth pattern in these leads. The pattern is often better observed when an intravenous bolus of adenosine is administered. In the absence of structural heart disease, pediatric atrial flutter most commonly occurs in the fetus and newborn. (See "Overview of atrial flutter".)

●Intraatrial reentrant tachycardia (IART) – IART, sometimes referred to as "atypical atrial flutter" or "incisional atrial tachycardia," implies a macroreentry mechanism and usually follows surgery for congenital heart disease (CHD). Its appearance and behavior are akin to atrial flutter, although, by definition, the anatomical substrate of IART is different than that of typical atrial flutter. (See "Atrial arrhythmias (including AV block) in congenital heart disease", section on 'Intraatrial reentrant tachycardia'.)

Descriptors of AT, such as "sporadic," "frequently recurrent," "nonsustained incessant," and "persistent," help communicate the tachycardia behavior but may also lead to confusion. These terms represent a continuum that describes the frequency and persistence of the arrhythmia, but the mechanism is not implied.

In some conditions, the above classification implies the underlying tachyarrhythmia mechanism (SANRT, IART, atrial flutter, atrial fibrillation) but not in others (FAT, CAT). Although the correlation of mechanism with rhythm strip phenotype is imperfect, there are some clinical features that are associated with specific mechanisms. (See "Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation", section on 'Automaticity and triggered activity' and "Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation", section on 'Mechanisms of reentry'.)

●Reentry always implies a sudden onset and termination of tachycardia. For single anatomic circuit reentrant mechanisms (eg, SANRT, IART, atrial flutter), the atrial rate is constant within an episode.

●Enhanced automaticity occurs when a small area of atrial muscle has depolarization properties that are faster than those of the underlying or normal atrial tissue and sinoatrial node. Such a site tends to depolarize at rates that vary over time and are influenced by changes in autonomic tone.

●Triggered activity occurs when a site suddenly and rapidly depolarizes in response to catecholamine surge and secondary intracellular calcium loading. The rate is also relatively constant within a given episode. This mechanism may be very difficult to prove.

The other important distinction that defines the classification of pediatric ATs is whether or not the child has undergone cardiac surgery. Atrial arrhythmias associated with CHD and cardiac surgery are discussed separately. (See "Atrial arrhythmias (including AV block) in congenital heart disease".)

Our approach is to use the above classification schema delineated by the rhythm strip, adding modifiers based upon the onset, frequency, and/or persistence of tachycardia episodes and, if known, the underlying mechanism (eg, sporadic nonautomatic FAT, nonsustained incessant CAT, or persistent automatic FAT).

EPIDEMIOLOGY

Prevalence — In children and infants without cardiac surgery, primary atrial tachycardia appears throughout infancy and childhood and accounts for 14 percent of supraventricular tachycardia (SVT) cases [1]. Since SVT occurs in approximately 1 in 200 to 400 children, the estimated prevalence of primary atrial tachycardia in children is approximately 1 in 1500 to 3000 children. By comparison, the prevalence of focal atrial tachycardia (FAT) in healthy adults in one report was 1 in 300 [2]. (See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children", section on 'Epidemiology'.)

Associated conditions

Congenital heart disease — The prevalence of ATs in patients with congenital heart disease (CHD) is discussed separately. (See "Atrial arrhythmias (including AV block) in congenital heart disease", section on 'Prevalence and incidence'.)

Cardiac tumors — Nearly any kind of cardiac tumor arising from or invading the atrial wall or annulus fibrosis can predispose to a variety of tachycardias, including ATs. Cardiac tumors most commonly seen in children are rhabdomyomas, fibromas, lymphoma, and myxomas. Their presence may be an important indicator of an underlying serious condition, especially tuberous sclerosis in the case of rhabdomyomas. (See "Tuberous sclerosis complex: Clinical features".)

Channelopathies — It is increasingly recognized that ATs also may occur in patients with heritable primary arrhythmia syndromes, including long and short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. Up to 30 percent of patients with these conditions experience ATs [3]. Certain variants in the sodium channel gene, SCN5A, have shown a particular predilection to cause ATs, often with other dangerous arrhythmias [4]. Thus, the presence of ATs that are not otherwise explained should prompt consideration of these syndromes. (See "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Brugada syndrome: Clinical presentation, diagnosis, and evaluation" and "Catecholaminergic polymorphic ventricular tachycardia".)

Neuromuscular disease — ATs are relatively common in individuals with neuromuscular diseases, especially Duchenne muscular dystrophy, Friedreich ataxia, some forms of Emery-Dreifuss and limb-girdle muscular dystrophy, and myotonic dystrophy type I [5]. In Duchenne muscular dystrophy, ATs are associated with diminished ejection fraction [6]. (See "Duchenne and Becker muscular dystrophy: Clinical features and diagnosis", section on 'Cardiomyopathy' and "Friedreich ataxia", section on 'Cardiomyopathy'.)

Other genetic disorders — ATs occur more frequently than expected in certain genetic conditions (eg, Noonan syndrome, Costello syndrome [and other RASopathies], and William syndrome), even in the absence of apparent structural heart disease [7].

CLINICAL FEATURES

Presenting symptoms — Signs and symptoms of ATs depend upon the duration and persistence of the tachycardia and the rate of ventricular response. The patient's age also impacts the presentation. Infants and toddlers cannot verbally describe symptoms and may present after a more prolonged duration of arrhythmia and, therefore, with more serious findings. Older children who can describe palpitations are generally detected earlier.

●Paroxysmal (sporadic) tachycardia – Sporadic nonautomatic focal atrial tachycardia (FAT) and atrial flutter are the most common ATs in this clinical category. The presentation of these paroxysmal ATs is similar to that of more common forms of supraventricular tachycardia (SVT; ie, atrioventricular [AV] reciprocating tachycardia and AV node reentrant tachycardia). They typically present with sudden palpitations, shortness of breath, presyncope, dizziness, and, sometimes, chest pain. Preverbal children may become irritable or suddenly quiet with associated pallor, diaphoresis, and feeding intolerance. In one report, ATs were more likely to present with fatigue and less likely with palpitations, dyspnea, or dizziness compared with other forms of SVT [8].

In some patients with rapid atrial flutter, these symptoms may initially be lacking if there is 2:1 AV conduction. In these patients, atrial flutter may become persistent and, if untreated, it can lead to tachycardia-induced cardiomyopathy (ie, the ventricular rate is slow enough that acute symptoms do not occur but fast enough to eventually impair ventricular function). Sporadic symptoms in such patients may represent moments of 1:1 AV conduction but within the context of a persistent arrhythmia.

Syncope is a relatively uncommon sign of AT, and it may be associated with increased risk of sudden death, especially in children who have undergone cardiac surgery.

●Sustained tachycardia – As a group, sustained ATs ("persistent" or "nonsustained incessant," using the nomenclature above) are more likely to represent automatic FAT, incessant or frequently recurring nonautomatic FAT, and, in infants, chaotic atrial tachycardia (CAT). They usually are associated with a slower ventricular rate than the more common types of SVT (ie, AV reciprocating tachycardia and AV node reentrant tachycardia) and other types of AT (eg, sporadic nonautomatic FAT).

Affected patients may not recognize palpitations or may be unable to verbalize symptoms and may only come to medical attention after the development of heart failure. This is called tachycardia-induced cardiomyopathy. FAT is the most common cause of tachycardia-induced cardiomyopathy, accounting for approximately 60 percent of cases [9]. Affected patients have left ventricular (LV) dilatation and impaired LV function [10]. The atrial rate at which this is likely to develop is not well defined. In our experience, adolescents seem to tolerate average heart rates of 110 to 120 beats per minute (bpm) with normal cardiac function for up to eight years.

Clinical manifestations of tachycardia-induced cardiomyopathy vary depending upon the patient's age:

•Infants present with nonspecific signs of heart failure including tachypnea, poor feeding, sweating, and failure to thrive. These symptoms are more common when the infants increase their exertion, such as during feeding.

•Older children and teenagers present with complaints of palpitations and/or classic symptoms of heart failure including dyspnea, fatigue with an inability to keep up with peers, respiratory distress, and diaphoresis (sweating). Symptoms are more severe and common with exertion.

Clinical improvement is expected to occur after ablation therapy for FAT [11], with normalization of LV contractility and, later, reduction in LV volume within 7 to 10 weeks of the procedure [9]. However, patients may have persistent derangement in diastolic function and cardiac interstitial fibrosis, thought to represent permanent damage, has been reported one year after resolution of the tachycardia [12].

Clinical features of specific atrial tachyarrhythmias

Focal atrial tachycardia

●Presentation – In children, the presentation of FAT can range from sporadic episodes (more likely nonautomatic FAT) of mild symptoms of palpitations and dizziness to sustained tachycardia with heart failure from tachycardia-induced cardiomyopathy (more likely automatic FAT) [10]. They can occur at any age and are most commonly of idiopathic origin.

Patients with congenital heart disease (CHD) are at increased risk of developing FAT, particularly following surgical repair. In one study, FAT occurred postoperatively in 2.5 percent of all CHD surgeries in infants <1 year old [13]. (See "Atrial arrhythmias (including AV block) in congenital heart disease", section on 'Ectopic/focal atrial tachycardia'.)

FAT has also been reported in association with cardiomyopathy, myocarditis, myocardial infarction, respiratory infection, chronic pulmonary disease (eg, bronchopulmonary dysplasia, pulmonary hypertension), and lung transplantation [14-16].

●Anatomic substrate – In children without CHD, the anatomic substrate for nonautomatic FAT is most commonly along the crista terminalis of the right atrium, the ostium of the coronary sinus, the tricuspid or mitral valve annuli, or the atrial appendages. There are several reports of FAT associated with right atrial appendage aneurysms [17-19]. However, FAT can arise from virtually anywhere in the atrial mass, including the atrial septum [20,21], the noncoronary cusp of the aortic valve [22], and the muscular sleeves of the proximal superior and inferior vena cavae and pulmonary veins. FAT may also arise from atrial tumors, notoriously from rhabdomyomas. (See "Cardiac tumors".)

●Electrocardiogram (ECG) findings – ECG findings are described below. (See 'Electrocardiogram findings' below.)

●Natural history – Affected infants and young children are generally responsive to medical therapy, and there is a reasonable likelihood of spontaneous resolution after a few months or years [23,24]. In one report of infants <6 months of age, the arrhythmia spontaneously resolved within one year in 14 of 15 patients (93 percent) [23]. In contrast, older children (>3 years of age) are less likely to respond to medical therapy and have a lower resolution rate. In several case series, spontaneous remission rates vary from 34 to 75 percent for patients up to 18 years of age within 10 to 28 months of diagnosis [14,24-27]. (See "Focal atrial tachycardia".)

Chaotic atrial tachycardia — CAT (also referred to as multifocal atrial tachycardia in adults) is an uncommon arrhythmia in children. (See "Multifocal atrial tachycardia".)

●Presentation – It usually occurs as a transient disorder during early infancy with mild ventricular dysfunction, often associated with a respiratory illness [28]. CAT can also occur in patients with structural heart disease and in infants with the RASopathies (especially Costello and Noonan syndromes) with or without underlying ventricular hypertrophy [29-31]. (See "Noonan syndrome" and "Hypertrophic cardiomyopathy in children: Clinical manifestations and diagnosis".)

●Anatomic substrate – Anecdotal reports suggest that this arrhythmia emanates from multiple pulmonary veins, similar to the origin of atrial fibrillation in adults [32]. However, in some cases, CAT may emanate from a single ectopic focus [33]. The mechanisms of CAT are poorly understood, and it likely involves multiple mechanisms.

●ECG findings – ECG findings are described below. (See 'Electrocardiogram findings' below.)

●Natural history – When CAT occurs in infancy, it typically resolves completely after six months [15,34-37]. Late arrhythmias are unlikely to occur, and the prognosis for long-term outcome is excellent in children with no underlying abnormality. If this rhythm persists or recurs late, there is evidence that it may be a manifestation of an underlying channelopathy, especially catecholaminergic polymorphic ventricular tachycardia, a heritable channelopathy caused by mutations in the RYR2 gene [28]. (See "Catecholaminergic polymorphic ventricular tachycardia".)

When associated with structural heart disease, the outcome is dependent upon the underlying condition. When associated with Costello and Noonan syndrome, CATs may have a malignant course and can be difficult to treat [28]. (See "Noonan syndrome", section on 'Prognosis' and "Hypertrophic cardiomyopathy in children: Management and prognosis", section on 'Prognosis'.)

Atrial fibrillation — Atrial fibrillation is uncommon in children. It can occur in the following settings [38,39]:

●Patients with underlying cardiac disease, including:

•Structural CHD (see "Atrial arrhythmias (including AV block) in congenital heart disease", section on 'Atrial fibrillation')

•Cardiomyopathies, especially hypertrophic cardiomyopathy [40] (see "Hypertrophic cardiomyopathy in children: Clinical manifestations and diagnosis")

•Wolff-Parkinson-White syndrome (see "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis", section on 'Atrial fibrillation')

•Channelopathies – Some channelopathies, previously thought to only potentiate sudden cardiac death from ventricular tachyarrhythmias (eg, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia), may also manifest with atrial fibrillation [40,41] (see "Brugada syndrome: Clinical presentation, diagnosis, and evaluation" and "Catecholaminergic polymorphic ventricular tachycardia")

●Following a triggering event – Paroxysmal atrial fibrillation may occur in a biologically predisposed but otherwise completely healthy individual during a hypervagal event or after drinking a cold or alcoholic beverage.

●Following an episode of a more common form of SVT – There is a growing appreciation of adolescent patients who develop atrial fibrillation immediately following a more common SVT, so-called "tachycardia-induced-tachycardia" [42].

●Hyperthyroidism – In rare cases, atrial fibrillation may be seen in a child with hyperthyroidism; however, in this setting, assessment should include an evaluation for a possible structural heart lesion. (See "Clinical manifestations and diagnosis of Graves disease in children and adolescents".)

●Familial cases – There have been reported rare familial cases of atrial fibrillation; both autosomal dominant and recessive forms have been identified. This is discussed in greater detail separately. (See "Epidemiology, risk factors, and prevention of atrial fibrillation", section on 'Monogenic inheritance'.)

●Athletes – Atrial fibrillation can sometimes be observed in the hyper-conditioned adolescent athlete. (See "Athletes with arrhythmias: Electrocardiographic abnormalities and conduction disturbances", section on 'Atrial fibrillation and atrial flutter'.)

●Idiopathic atrial fibrillation in the young – It is increasingly recognized that atrial fibrillation can rarely occur in otherwise healthy adolescents and young adults in the absence of structural heart disease, prior surgery, cardiomyopathy, ventricular pre-excitation, family history, or other risk factors (hypertension, thyroid disease). This has sometimes been called "lone atrial fibrillation" [43].

The ECG findings for atrial fibrillation are briefly summarized below (see 'Electrocardiogram findings' below) and are described in detail separately. (See "The electrocardiogram in atrial fibrillation".)

Atrial flutter and intraatrial reentry tachycardia — Atrial flutter is rare in children. It can occur in the following settings:

●Atrial flutter and intraatrial reentrant tachycardia (IART) following cardiac surgery – Atrial flutter and IART are primarily seen in children with a history of previous cardiac surgery, particularly following the Mustard, Senning, or Fontan procedures [44-47]. (See "Atrial arrhythmias (including AV block) in congenital heart disease" and "D-transposition of the great arteries (D-TGA): Management and outcome", section on 'Arrhythmias' and "Management of complications in patients with Fontan circulation", section on 'Arrhythmias'.)

●Neonatal atrial flutter – Atrial flutter can occur in fetuses and neonates with structurally normal hearts. This usually occurs in an otherwise uncomplicated pregnancy; however, cases of atrial flutter associated with maternal lithium treatment [48] and neonatal Coxsackie myocarditis [49] have been described. The mechanism for atrial flutter in this setting is thought to be similar to adults, involving macroreentry around the tricuspid valve, although definitive studies have not been performed. Neonatal atrial flutter rarely recurs following cardioversion with or without medical treatment.

●Atrial flutter in children with structurally normal hearts – Atrial flutter is exceedingly rare in older children with structurally normal hearts. Similar to atrial fibrillation, some patients may develop atrial flutter immediately following a more common SVT. Thus, a child without structural heart disease who presents with atrial flutter should be evaluated for more common forms of SVT (ie, AV reentrant tachycardia and AV nodal reentrant tachycardia) or subclinical channelopathic, neuromuscular, or other genetic disorders. (See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children".)

The ECG findings for atrial flutter and intraatrial re-entry tachycardia are briefly summarized below (see 'Electrocardiogram findings' below) and are described in detail separately. (See "Electrocardiographic and electrophysiologic features of atrial flutter".)

Electrocardiogram findings — In all ATs, the ECG demonstrates an inappropriately rapid heart rate for age (ie, above the 95^th percentile) and narrow QRS complex.

Specific ECG characteristics are as follows:

●FAT – The QRS complexes appear normal and occur at regular intervals (other than possible "warmup" at the onset of some FATs). The P wave has a uniform morphology, but its appearance usually differs from sinus rhythm and is dependent on the location of the focus (waveform 1A). The relationship of the P wave with the next QRS tends to be constant, unless there is second-degree AV block (waveform 1B). Although the P-R interval is inappropriately long relative to the atrial rate, the P-R interval does tend to be shorter than the ensuing R-P interval. The P wave may be difficult to discriminate if it is buried in the prior T wave. (See "Focal atrial tachycardia", section on 'Electrocardiographic features'.)

Algorithms have been developed to help the clinician estimate the anatomic source of the atrial tachycardia based on the P wave morphology, but these are derived mostly from adults [50,51].

Automatic versus nonautomatic FAT cannot easily be distinguished based on surface ECG.

●Sinoatrial node reentry tachycardia (SANRT) – SANRT, which is a form of nonautomatic FAT, is a paroxysmal arrhythmia with P wave morphology identical to that during sinus rhythm and a longer PR interval than would be expected for exercise-induced sinus tachycardia at the same heart rate (waveform 2A-B). As with other FATs, the P waves may even be partially superimposed on the previous T wave. (See "Sinoatrial nodal reentrant tachycardia (SANRT)".)

●CAT – The following ECG findings are required for the diagnosis of CAT (waveform 3) [52,53] (see "Multifocal atrial tachycardia"):

•Discrete P waves with at least three different morphologies (including the normal sinus P wave) in any single lead. P wave morphology is generally best seen in leads II, III, and V1.

•The P-P intervals, the P-R duration, and the R-R intervals vary.

•Atrial rate >100 bpm (usually 250 to 600 bpm).

•The P waves are separated by isoelectric intervals, albeit brief, which discriminates this rhythm from atrial fibrillation.

●Atrial fibrillation – Atrial fibrillation is an irregular rhythm without regular or organized atrial activity (waveform 4). Multiple reentrant circuits within the atrial myocardium generate multiple mobile wavelets, which often compete with or even extinguish each other. As a result, no uniform activation of the atrial tissue and no distinctive P waves are generated or recognized on the surface ECG. Since these multiple wavelets generate rapid and localized impulses, the sinus node is suppressed or not able to be expressed, as it cannot activate the atrium. (See "The electrocardiogram in atrial fibrillation".)

●IART – This arrhythmia usually has a 2:1 AV conduction relationship. The atrial rate is generally 260 to 320 bpm and results in a ventricular rate usually between 100 and 150 bpm (waveform 5A). The flutter waves usually have a monotonously repeating saw tooth pattern due to a constantly undulating or zigzag baseline. This pattern either represents continuous depolarization and repolarization of the atria, or right followed by left atrial depolarization. (See "Electrocardiographic and electrophysiologic features of atrial flutter".)

In some cases in which 2:1 AV block makes it difficult to recognize atrial flutter, persistent flutter waves can be demonstrated by vagal maneuvers or the use of intravenous adenosine (waveform 5B).

The 12-lead ECG can also help to discriminate between sinus tachycardia due to decompensated dilated cardiomyopathy and tachycardia-induced cardiomyopathy caused by tachyarrhythmia emanating from a focus near the sinus node. Features that favor tachycardia-induced cardiomyopathy include absence of second-degree AV block or a negative P wave in both leads V1 and V2 [54].

APPROACH TO DIAGNOSIS

Initial evaluation — The general approach to diagnosing an AT in pediatric patients is as follows:

●Electrocardiogram (ECG) – The first step in the evaluation is to obtain a 12-lead surface ECG. ECG findings for specific types of AT are described above (see 'Electrocardiogram findings' above). ECG findings in more common forms of supraventricular tachycardia (SVT; ie, atrioventricular [AV] reciprocating tachycardia and AV node reentrant tachycardia) are reviewed separately. (See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children", section on 'Electrocardiogram'.)

●Ambulatory monitoring – For patients with paroxysmal symptoms, the AT may not be present during routine ECG and ambulatory monitoring is required to make the diagnosis.

•Monitoring with smart mobile devices – The burgeoning industry of smartphones and smartwatches has made home monitoring more available and less expensive than it was when traditional medical devices were all that were available. However, at least to date, the rhythm recordings from these devices are limited to a single lead (usually limb lead I or inverted I). In addition, they afford limited recording time, usually missing the onset or termination of an abnormal rhythm. While these limitations usually do not preclude identification of irregular atrial tachycardias (eg, atrial fibrillation) or common forms of SVT, these devices may be less reliable for identifying focal atrial tachycardia (FAT). This is because detecting FAT relies upon a combination of identifying non-sinus P waves and sudden onset or termination. Nevertheless, these devices may suggest an FAT if the PR interval is inappropriately long relative to the atrial rate.

•Attached event recorders – Traditional ambulatory recording strategies still have a role when smart mobile devices are not helpful. These devices can be used for up to one month. They record extended rhythm strips associated with clinical tachycardic events that are either patient-triggered or based on preprogrammed criteria. They have been downsized and can be hidden beneath the child's shirt, making them more acceptable to young patients. The recording time of events enables documentation of event onset and/or termination, and more than one channel is available, so that comparison with the pre- or post-event sinus P wave can be made. Some devices will continuously record for up to two weeks. (See "Ambulatory ECG monitoring".)

●Insertable loop recorders – Children with very infrequent but very severe symptoms may benefit from placement of an insertable loop recorder. New generation devices are small and can be injected under the skin of the chest with a battery life of >3 years. Clinical events can be recorded using an external activator or automatically according to programmed criteria. In addition to the very long surveillance period, its advantages over attached recorders include better quality signals, longer recording duration per event, and a better opportunity to record an event onset or termination [55]. Its ability to discriminate AT from sinus tachycardia is otherwise the same as an attached monitor because it only records a single ECG channel.

●Exercise testing – For patients in whom symptoms primarily occur during exercise, formal exercise testing while being attached to a 12-lead ECG can establish the diagnosis, determine the hemodynamic effects, and even possibly localize the source of the tachycardia. Unfortunately, the yield of this testing is low. (See "Exercise testing in children and adolescents: Principles and clinical application".)

Subsequent testing — Once the diagnosis of an AT has been established, additional testing may include:

●Echocardiogram – Transthoracic echocardiography is used to assess myocardial function and to identify any structural cardiac defects that may have precipitated the rhythm disturbance, including congenital defects (ie, congenital heart disease [CHD]) or acquired lesions (ie, atrial tumors). Transesophageal echocardiography may be necessary in some patients as it provides better anatomic detail of the atrial appendages and is necessary to identify intracavitary clot. This is especially important in patients with CHD or cardiomyopathy associated with atrial flutter, atrial fibrillation, or intraatrial reentry tachycardia.

●Cardiac magnetic resonance imaging – Cardiac magnetic resonance imaging may be especially helpful to identify cardiac tumors and to evaluate the form and function of the atrial appendages. Newer techniques can identify regions of fibrosis, even in the thin-walled atria. (See "Clinical utility of cardiovascular magnetic resonance imaging".)

●Electrophysiology study – An electrophysiology study is used to confirm the underlying arrhythmia, determine its mechanism, identify site(s) of origin (focus or foci), and guide therapeutic decisions (eg, ablation or change in antiarrhythmic drug therapy). Catheter ablation can be performed as a therapeutic intervention at the same time as the diagnostic electrophysiology study. (See 'Chronic management' below and "Invasive diagnostic cardiac electrophysiology studies".)

●Evaluation for channelopathy – For children diagnosed with ATs (particularly atrial fibrillation and atrial flutter) without an identified etiology, a heritable primary arrhythmia syndrome should be considered (eg, long and short QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia). While these syndromes are characteristically associated with increased risk of ventricular arrhythmias, up to 30 percent of affected patients experience ATs [3]. The initial step to evaluating for these syndromes is to obtain a detailed family history, including a three-generation pedigree. Additional details of the evaluation are discussed separately. (See "Congenital long QT syndrome: Diagnosis" and "Short QT syndrome" and "Brugada syndrome: Clinical presentation, diagnosis, and evaluation" and "Catecholaminergic polymorphic ventricular tachycardia".)

MANAGEMENT

Acute management — The acute management of an infant or child who presents with narrow complex tachyarrhythmia is challenging because the exact mechanism of tachycardia is often unknown. The acute management is dependent on the patient's presentation and clinical status. The goal of therapy is to initially stabilize any patient with hemodynamic instability and to terminate the arrhythmia. Emergency management of narrow complex tachycardia is summarized in the algorithm (algorithm 1) and discussed in detail separately. (See "Pediatric advanced life support (PALS)", section on 'Tachycardia algorithm'.)

Most children who present with acute onset of narrow complex tachyarrhythmia have a common form of supraventricular tachycardia (SVT; ie, atrioventricular [AV] reentrant tachycardia or AV nodal reentrant tachycardia). The acute management of SVT in children is summarized in the table (table 2) and discussed in detail separately. (See "Management of supraventricular tachycardia (SVT) in children", section on 'Acute management'.)

An important consideration in the acute management of ATs is that while cardioversion is effective for many forms of AT (including most forms of nonautomatic focal atrial tachycardia [FAT], atrial flutter, atrial fibrillation, and intraatrial reentry tachycardia), it is not effective for automatic FAT. For children with automatic FAT that is associated with signs of congestive heart failure and low cardiac output, the goal of acute management is the same as for any SVT (namely, rapid reduction of heart rate). However, since first-line interventions for SVT (adenosine, electrical cardioversion) are generally ineffective for automatic FAT, other pharmacologic agents are usually necessary. Consultation with a pediatric cardiologist is advised. Traditional medications such as intravenous esmolol, procainamide, and amiodarone are variably efficacious in this setting. However, intravenous amiodarone can cause cardiovascular collapse, particularly when given rapidly [56]. Thus, extreme caution should be used when administering amiodarone in this setting. Newer pharmacologic options include intravenous sotalol [57] and enteral ivabradine [58,59]; however, experience with these agents is limited. Anecdotal experience supports the use of dexmedetomidine as a temporizing means of rate control until antiarrhythmic medications can be loaded. Intravenous digoxin is generally not effective, though it may nominally lower heart rate. If a child's cardiovascular status is too tenuous to tolerate days of varying antiarrhythmic drug trials, support with extracorporeal membrane oxygenation may be required until the tachyarrhythmia is suppressed with medications or its focus (foci) can be ablated in the electrophysiology laboratory.

Chronic management — After the acute episode is terminated, chronic management for AT is dependent upon the specific arrhythmia, age and size of the child, likelihood of spontaneous resolution, and severity of symptoms. In most cases, options include pharmacologic therapy and catheter ablation. The optimal approach is uncertain since there are few data to inform decision-making. Management varies from institution to institution. In general, treatment is chiefly pharmacologic for young/small patients (ie, <15 kg) with catheter ablation reserved for patients in whom pharmacologic options have been exhausted [60]. This is because of size considerations and safety concerns of catheter ablation in small patients. By contrast, catheter ablation is used more often as a first-line treatment in older/larger children with atrial ATs [60].

The following sections outline our initial approach for more common pediatric scenarios based on the underlying specific arrhythmia, likelihood of resolution, response to medical therapy, and severity of symptoms.

Focal atrial tachycardia — As noted above, the rate of spontaneous resolution of FAT is age dependent, and symptoms may vary from mild symptoms of episodic palpitations to sustained tachycardia with congestive heart failure from tachycardia-induced cardiomyopathy. (See 'Focal atrial tachycardia' above.)

Management of these arrhythmias is complicated by the fact that cardioversion is generally ineffective for automatic FAT because of its mechanism (enhanced automaticity). Patients presenting acutely with severe manifestations (eg, low cardiac output) generally require acute intervention to lower the heart rate, as discussed above (see 'Acute management' above). In children with less severe presentations and those who require ongoing therapy after the acute episode has been treated, the general approach to chronic management is as follows:

●Infants and young children – In infants with tachycardia-induced cardiomyopathy, pharmacologic therapy is the initial approach because of the high likelihood of eventual spontaneous resolution. The optimal choice of medication for initial treatment and for resistant arrhythmias is uncertain [25,61-66]. Agents that are used for complete suppression of the tachyarrhythmia include oral beta blockers, amiodarone [25,67], propafenone [61-63], flecainide [64,67], sotalol [66], and ivabradine [58]. A combination of two drugs (eg, propafenone and amiodarone, sotalol and propafenone) may be required in some cases [23,68]. However, it should be stressed that patients should not be treated simultaneously with two drugs from the same class (eg, propafenone and flecainide). In patients with reduced ventricular function, flecainide, propafenone, and beta blockers should be avoided or used with caution.

If the arrhythmia is suppressed, drug therapy is tolerated, and cardiac function normalizes, the drug is usually discontinued after one year since the arrhythmia is expected to resolve in most cases.

For very young children with tachycardia-induced cardiomyopathy who fail drug therapy, an ablation procedure should be considered since the potential risks associated with ablation are likely to be low relative to the risks of progressive cardiomyopathy associated with the arrhythmia.

●Older/larger children (≥15 kg) – In older children, if ventricular function is still preserved, medical management may be initiated with a beta blocker to lower the ventricular rate. However, in children weighing ≥15 kg, catheter ablation has become widely accepted as the treatment of choice rather than pharmacologic therapy due to the marginal safety profiles of antiarrhythmic drugs [60]. If there is evidence of tachycardia-induced cardiomyopathy, catheter ablation is generally performed as soon as the patient is considered sufficiently stable to undergo the procedure [69].

Catheter ablation, usually using radiofrequency energy, is the primary therapy for automatic FAT in older children (ie, 15 ≥kg) and has been used to treat patients with AT with any the following:

•Symptomatic tachyarrhythmia

•Tachycardia-induced cardiomyopathy

•Ineffective response to antiarrhythmic drugs

•Recurrence of tachycardia after drug discontinuation

In a report of 376 foci of automatic FAT (as also called atrial ectopic tachycardia [AET]) from the Pediatric Radiofrequency Catheter Ablation Registry, ablation was initially successful in 88 percent of cases [70]. However, the recurrence rate following ablation for automatic FAT is probably higher than for other forms of SVT. This is because sedation for the procedure may suppress automatic foci so that tachycardias may be quiescent and thus not treatable. In another report of 36 patients, the initial success rate for ablation of FAT was 97 percent, with a recurrence rate of 20 percent [71]. Recurrences were more likely if there were multiple foci.

Complications are uncommon. In the report from the Registry, complications occurred in 3 percent of cases, including stenosis of the superior cavoatrial junction, pulmonary vein ostial stenosis, phrenic nerve damage, and sinus node damage [70]. Complications are more likely to occur in small atria. Catheter ablation of foci near the AV node carries the risk of heart block; cryoablation techniques are preferred in that region due to a better safety profile.

Catheter ablation is usually performed using transvenous access (typically via the femoral vein). However, in some cases, alternative approaches are preferred because of the location of the focus. An epicardial FAT focus can be especially challenging, and percutaneous pericardial access is performed in some centers. When FAT foci are in the atrial appendages, a minimally invasive surgical approach using thoracoscopy may be used [72].

Catheter ablation is discussed in greater detail separately. (See "Overview of catheter ablation of cardiac arrhythmias".)

Chaotic atrial tachycardia — As noted above, pediatric chaotic atrial tachycardia (CAT) is most often seen as a transient condition in infants, with resolution in 50 percent within five months [37]. (See 'Chaotic atrial tachycardia' above.)

Medical treatment of CAT is challenging because typical maneuvers aimed at converting to sinus rhythm (eg, adenosine, overdrive pacing, or synchronized cardioversion) are often not successful. As a result, therapy is directed at controlling the ventricular response rate with a combination of oral digoxin, beta blockers, and calcium channel blockers. If this strategy is unsuccessful, and especially if tachycardia-induced cardiomyopathy is present, pharmacologic cardioversion is attempted with oral amiodarone [73], flecainide [74], or propafenone [36,75]. Once sinus rhythm is established and ventricular function normalizes, we usually continue therapy for an additional six months to a maximum of one year for responsive patients.

Patients are followed with ambulatory rhythm monitoring and echocardiography every month until ventricular function normalizes and then less frequently. It is reasonable to follow these patients periodically until school age.

Given the natural history of CAT in pediatric patients, catheter ablation usually does not play a role in management. However, successful use of catheter ablation in this setting has been described in single case reports [32,33]. This suggests that, in some cases, CAT may emanate from a single ectopic focus.

Neonatal atrial flutter — In the newborn with atrial flutter, direct current cardioversion is the usual primary therapy [76]. An alternative to electrical cardioversion is the use of esophageal pacing at a cycle length 50 to 100 milliseconds less than that of the atrial rate, which is also used in children with atrial flutter or intraatrial reentrant tachycardia (IART) after cardiac surgery [77]. Beta blocker therapy or digoxin are also reasonable options for initial therapy; however, most practitioners are moving away from using digoxin in this setting. Unlike older children and adults, intravenous calcium channel-blocking agents should be avoided in infants due to substantial risk of potentially fatal cardiovascular collapse. This same caveat also applies to intravenous beta blockers other than esmolol. Once there is resolution of the arrhythmia, patients are followed for an additional 6 to 12 months with electrocardiogram (ECG) and ambulatory rhythm monitoring. Parents/caregivers are taught how to measure their infant's heart rate and how to recognize signs of early congestive heart failure. Wearable heart rate monitors designed for infants are in development and may be an option in the future. Recurrence is rare, and an evaluation for intrinsic structural, functional, or channelopathic conditions should be performed if there is a repeat event.

Support for this treatment approach comes from a case series of 50 infants with atrial flutter, of whom 13 (26 percent) had spontaneous conversion to sinus rhythm [76]. Of the remaining 37 infants, 22 underwent attempted transesophageal pacing, which was successful in 32 percent; 23 infants underwent direct current cardioversion, which was successful in 87 percent; and 7 patients (14 percent of the entire cohort) required antiarrhythmic therapy. Atrial flutter recurred in six infants (12 percent); five of the recurrences occurred within 24 hours of the first episode, and all of these patients had additional episodes of arrhythmia.

Other atrial tachyarrhythmias — Management of ATs that occur mostly in patients who have undergone surgery for congenital heart disease (CHD; eg, atrial flutter, atrial fibrillation, or intraatrial reentry tachycardia) is discussed separately. (See "Atrial arrhythmias (including AV block) in congenital heart disease", section on 'Management'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Arrhythmias in children" and "Society guideline links: Supraventricular arrhythmias".)

SUMMARY AND RECOMMENDATIONS

●Terminology and classification – Atrial tachyarrhythmias (ATs) are non-sinus arrhythmias that result in a heart rate above the 95^th percentile for age and that do not require the atrioventricular (AV) junction, accessory pathways, or ventricular tissue for initiation and maintenance of the elevated heart rate. ATs are classified based upon of P wave morphology on electrocardiogram (ECG), number of foci (single versus multiple), and the frequency and duration of tachycardia (ie, sporadic/paroxysmal versus persistent) (table 1). (See 'Terminology' above.)

●Epidemiology – ATs are commonly seen in children with congenital heart disease (CHD) who have undergone cardiac surgery; however, they also occur in children without cardiac surgery or CHD and can result in significant morbidity and mortality. Primary atrial tachycardias account for approximately 15 percent of pediatric supraventricular tachycardia (SVT). (See 'Epidemiology' above and "Atrial arrhythmias (including AV block) in congenital heart disease".)

●Presentation – The signs and symptoms of ATs depend upon the duration and persistence of the tachycardia, ventricular response rate, and age of the patient (see 'Presenting symptoms' above):

•Paroxysmal tachycardia often presents with acute symptoms of palpitations, shortness of breath, presyncope, dizziness, fatigue, and sometimes chest pain. In the preverbal child, findings include irritability, pallor, diaphoresis, and feeding intolerance.

•Patients with persistent tachyarrhythmia can develop tachycardia-induced cardiomyopathy, which may present with signs and symptoms of heart failure. Symptoms in infants may include poor feeding, sweating, failure to thrive, and tachypnea. Older children may present with dyspnea, fatigue on exertion, and diaphoresis.

•Because infants and toddlers cannot verbally describe symptoms, they are more likely to present after a prolonged duration of arrhythmia with signs and symptoms of heart failure. Older children who can describe palpitations are generally detected earlier.

●Clinical features – The clinical features of specific ATs are summarized in the table (table 1) and discussed above. (See 'Clinical features of specific atrial tachyarrhythmias' above.)

●ECG findings – The following are representative examples of ECG tracings for different types of AT. The ECG findings are discussed in greater detail above and in separate topic reviews. (See 'Electrocardiogram findings' above and "The electrocardiogram in atrial fibrillation" and "Electrocardiographic and electrophysiologic features of atrial flutter".)

•Focal atrial tachycardia (FAT; also called atrial ectopic tachycardia [AET] or ectopic atrial tachycardia [EAT]) (waveform 1A-B)

•Sinoatrial node reentry tachycardia (SANRT) (waveform 2A-B)

•Chaotic (or multifocal) atrial tachycardia (CAT) (waveform 3)

•Atrial fibrillation (waveform 4)

•Atrial flutter and intraatrial reentrant tachycardia (IART) (waveform 5A-B)

●Diagnosis – The diagnostic evaluation begins with a 12-lead surface ECG. For patients with paroxysmal symptoms, the AT may not be present during routine ECG and ambulatory monitoring is required to make the diagnosis. For patients in whom symptoms occur primarily during exercise, formal exercise testing may help establish the diagnosis. (See 'Approach to diagnosis' above.)

Following a presumptive diagnosis based on 12-lead ECG and/or ambulatory monitoring, additional cardiac testing may include echocardiography to assess cardiac function and anatomy as well as an electrophysiology study to confirm the underlying arrhythmia, determine its mechanism and site of origin, and to guide therapeutic decisions. (See 'Subsequent testing' above.)

●Acute management – Emergency management of a child presenting with narrow complex tachycardia summarized in the algorithm (algorithm 1) and discussed in detail separately. (See "Pediatric advanced life support (PALS)", section on 'Tachycardia algorithm'.)

Most children who present with acute onset of narrow complex tachyarrhythmia have a common form of SVT. The acute management of SVT in children is summarized in the table (table 2) and discussed in detail separately. (See "Management of supraventricular tachycardia (SVT) in children", section on 'Acute management'.)

An important consideration in the acute management of ATs is that while cardioversion is effective for many forms of AT (including most forms of nonautomatic FAT, atrial flutter, atrial fibrillation, and IART), it is not effective for automatic FAT. In extreme cases, cardiovascular support with extracorporeal membrane oxygenation may be necessary until automatic FAT can be suppressed with medications, or its focus (foci) can be ablated in the electrophysiology laboratory.

●Chronic management – After the acute episode is terminated, chronic management is dependent upon the underlying arrhythmia, likelihood of resolution, severity of symptoms, and age/size of the child. The optimal approach is uncertain, and management varies from institution to institution. Treatment options generally include pharmacologic therapy and catheter ablation. (See 'Chronic management' above.)

In general, because of safety concerns with the use of catheter ablation in infants and small children, pharmacologic therapy is more often used for this age group. By contrast, catheter ablation is often the first-line treatment in older/larger children with ATs. Our general approach is as follows:

•FAT – In infants with tachycardia-induced cardiomyopathy, pharmacologic therapy is the initial approach because of the high likelihood of eventual spontaneous resolution. A number of antiarrhythmic drugs have been used in this setting, and there is little evidence that any one agent is superior to another. For older children (ie, >15 kg) with FAT, we suggest catheter ablation as the primary therapy (Grade 2C). (See 'Focal atrial tachycardia' above.)

•CAT – Pediatric CAT is most often seen as a transient condition in infants, and it typically resolves within 6 to 12 months. For most patients, we suggest initial therapy to control the ventricular response rate (eg, with oral digoxin, beta blocker, or calcium channel blocker) rather than antiarrhythmic therapy (Grade 2C). However, if rate control is unsuccessful, it is reasonable to attempt pharmacologic cardioversion with an antiarrhythmic agent (eg, oral amiodarone, flecainide, or propafenone). Given the natural history of pediatric CAT, catheter ablation usually does not play a role in management, although successful catheter ablation has been described. (See 'Chaotic atrial tachycardia' above.)

•Neonatal atrial flutter – For most neonates with atrial flutter, we suggest primary electrical cardioversion (Grade 2C). However, overdrive esophageal pacing or medical therapy (eg, with a beta blocker or digoxin) are reasonable alternatives. Intravenous calcium channel-blocking agents should be avoided in infants, due to substantial risk of potentially fatal cardiovascular collapse. (See 'Neonatal atrial flutter' above.)

•Other ATs – Management of ATs that occur mostly in patients who have undergone surgery for CHD (eg, atrial flutter, atrial fibrillation, or IART) is discussed separately. (See "Atrial arrhythmias (including AV block) in congenital heart disease", section on 'Management'.)