Causes of wide QRS complex tachycardia in children

INTRODUCTION — 

Wide QRS tachycardia may be due to ventricular tachycardia (VT), supraventricular tachycardia (SVT) with aberrant conduction, or atrioventricular reentrant tachycardia (AVRT) with an accessory pathway. Children with wide QRS complex tachycardia may present with hemodynamic instability, and if not urgently treated, serious morbidity or death may occur. (See "Pediatric advanced life support (PALS)".)

Causes of wide QRS complex tachycardia in children will be reviewed here. The evaluation and management of wide QRS complex tachycardia in children are discussed separately. (See "Management and evaluation of wide QRS complex tachycardia in children".)

DEFINITIONS — 

The following terms are used throughout this topic:

●Tachycardia – Tachycardia in children is generally defined as a heart rate above the normal range for age (ie, >160 beats per minute for infants under age 2, >140 beats per minute for children 2 to 12 years, and >100 beats per minute for adolescents and adults (table 1))

●Wide QRS complex – Wide QRS complex is defined by a QRS duration >80 milliseconds in younger children and >100 milliseconds in adolescents

SUPRAVENTRICULAR TACHYCARDIA — 

Supraventricular tachycardia (SVT) originates above the ventricles and usually presents as a narrow QRS complex tachycardia. However, SVT can also produce a wide QRS complex through the following mechanisms:

●Aberrant conduction – Conduction through the His-Purkinje system can be delayed or blocked, which results in a wide QRS complex. (See "Basic approach to delayed intraventricular conduction".)

●Atrioventricular reentrant tachycardia (AVRT) with an accessory pathway – AVRT requires the presence of an extranodal accessory pathway connecting the atrium and ventricle. This allows direct electrical communication between the two chambers.

During AVRT tachycardia, QRS complexes can be either narrow or wide depending upon the direction of conduction through the reentrant pathway. If the ventricles are activated antegrade via the accessory pathway, followed by retrograde conduction over the atrioventricular node/His-Purkinje system, the QRS complex will be wide. This is known as antidromic reciprocating tachycardia (waveform 1 and waveform 2).

In the more common orthodromic form with a narrow QRS complex, the ventricles are activated antegrade through the atrioventricular node, followed by retrograde conduction back to the atria via the accessory pathway.

SVT is discussed in greater detail separately. (See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children".)

VENTRICULAR TACHYCARDIA — 

Ventricular tachycardia (VT) originates from the ventricular myocardium or Purkinje cells below the bifurcation of the bundle of His. It is reported to occur in 3 percent of healthy children [1,2].

VT may be associated with sudden cardiac death. As a result, patients who develop VT or are at risk for developing VT must be identified, evaluated, and treated if necessary. Some forms of VT found primarily in infants and young children may be benign, but this conclusion is reached only after other more serious causes of VT are excluded. (See "Sudden cardiac arrest (SCA) and sudden cardiac death (SCD) in children".)

VT is defined as three or more consecutive beats of ventricular origin on electrocardiogram (ECG). It can occur in patients with congenital heart disease (CHD), an inherited disorder that affects cardiac electrical or myocardial function, acquired heart disease, or in the setting of a structurally and functionally normal heart.

In one retrospective review from a single Swiss center, 27 children with spontaneous episodes of VT were observed from 1995 to 2005: 13 had no structural heart disease, and the remaining 14 patients had a wide range of underlying cardiac disease [3]. Five patients died, all of whom had underlying cardiac disease.

In a school-based screening study from Japan, resting ECGs demonstrated an incidence of VT at 2 to 8 per 100,000 children [4]. Among the 48 children with VT detected on screening ECG, two had structural heart disease and the other 46 patients had idiopathic ventricular tachycardia.

Congenital heart disease — Arrhythmias, including VT, are seen as a late complication in children and adults with CHD. This finding is associated with increased risk of mortality and serious morbidity. The electrical pathophysiology in CHD is based upon a complex interplay between gross cardiac anatomy, chamber enlargement from abnormal pressure and volume loads, cellular injury from hypoxia and cardiopulmonary bypass, fibrosis at the site of suture lines, prosthetic material, and direct trauma to the specialized conduction tissues [5].

●Risk factors for VT – In general, the risk of experiencing VT among patients with CHD increases with age. Onset of arrhythmic complications of CHD most commonly occurs in adulthood. Other factors that influence the risk of VT in this setting include:

•The nature of the specific CHD defect – Ventricular arrhythmias are a leading cause of morbidity and mortality in patients with CHD as they reach adulthood. VT is most frequently associated with tetralogy of Fallot (TOF), although it may occur in patients with other congenital defects (eg, D-transposition of the great arteries, Ebstein malformation of the tricuspid valve, and lesions with left ventricular outflow obstruction) [5-9]. Most studies of VT and CHD focus on a specific lesion and often favor the study of more common lesions with a surgical outcome good enough to provide reasonable patient numbers. Thus, many studies focus on TOF [10]. This issue is discussed in greater detail separately. (See "Tetralogy of Fallot (TOF): Long-term complications and follow-up after repair", section on 'Arrhythmias and sudden cardiac death'.)

•Residual cardiac defects after repair – In individuals with repaired or palliated CHD including TOF, the presence of residual cardiac defects, volume overload, or cardiac dysfunction has been associated with an increased risk of VT [11]. In adults with repaired TOF, left ventricular failure has been associated with sudden death following surgical repair [12]. In fact, moderate to severe left ventricular systolic dysfunction on echocardiogram has proven to be a stronger predictor of serious cardiac events than any right ventricular variable [10].

•Widened QRS postoperatively – Several studies have also reported that postoperative patients with a QRS duration that is greater than or equal to 180 milliseconds were more likely to develop VT or sudden cardiac death [12-14].

•Other factors – Other reported risk factors for VT following surgical repair for TOF include older age at repair and increased length of time from repair [12], a history of palliative shunts, inducible VT at electrophysiology (EP) testing, and high-grade ventricular ectopy [5]. A later age at repair seems to correlate with the development of left ventricular dysfunction, possibly due to prolonged periods of time with ventricular volume overload and hypoxia.

●Presentation – Although patients may experience slow VT and are hemodynamically stable at presentation, some patients present with rapid VT that results in syncope or cardiac arrest. Ventricular arrhythmias are the most common cause of sudden death in patients following surgical repair for TOF; however, atrial arrhythmias and atrioventricular block may also have catastrophic outcomes in adults with CHD, including death [5]. (See "Tetralogy of Fallot (TOF): Long-term complications and follow-up after repair", section on 'Management of VT and prevention of SCD'.)

●EP testing – EP testing with programmed ventricular stimulation is useful in identifying postoperative patients with CHD who are at increased risk of developing serious arrhythmias, including VT. The induction of VT at EP testing is an imperfect but powerful predictor, independent of ECG and other clinical variables [15].

This was illustrated in a study of 252 postoperative patients with TOF (mean age 16 years) who had programmed ventricular stimulation at the time of EP testing [9]. Sustained monomorphic VT was induced in 30 percent and polymorphic VT in 4.4 percent of patients. There was a threefold increase in the incidence of symptomatic VT or sudden death in patients with a positive EP study compared with those with a negative study.

Additional details on the role of EP testing in patients with repaired TOF are provided separately. (See "Tetralogy of Fallot (TOF): Long-term complications and follow-up after repair", section on 'Indications for EPS'.)

The management of VT in patients with CHD is discussed separately. (See "Management and evaluation of wide QRS complex tachycardia in children", section on 'Patients with underlying congenital heart disease'.)

Genetic disorders — With molecular genetic advances, several genetic disorders that are associated with VT have been identified. They can be classified as channelopathies or cardiomyopathic disorders.

Channelopathies — Inherited channelopathies associated with VT are briefly reviewed here and are discussed individually in detail separately. These disorders affect the movement of ions (eg, sodium, potassium, and calcium) through channels within the cardiac cell membrane and include the following:

Long QT syndrome (LQTS) — LQTS is a disorder of myocardial repolarization characterized by a prolonged QT interval and T-wave abnormalities on the ECG, syncope, and sudden cardiac death.

Variants in a number of cardiac ion genes and genes that affect ion channel function have been identified in patients with congenital LQTS (table 2); most patients have a loss of function of a potassium channel (eg, KCNQ1 and KCNH2) or a gain of function of a sodium channel (eg, SCN5A). The clinical phenotypes of congenital LQTS include the common autosomal dominant form and the autosomal recessive form (Jervell and Lange-Nielsen syndrome), which is also associated with sensorineural deafness and has a more malignant clinical course. Other rare forms of LQTS include Timothy syndrome (characterized by profound QT prolongation, structural cardiac disease, and noncardiac manifestations) [16] and Andersen-Tawil syndrome (characterized by LQTS, noncardiac features, and periodic paralysis) [17]. The genetics and diagnosis of congenital LQTS are discussed in greater detail separately. (See "Congenital long QT syndrome: Pathophysiology and genetics" and "Congenital long QT syndrome: Diagnosis".)

LQTS is associated with an increased risk of a life-threatening arrhythmia referred to as torsades de pointes (waveform 3). Causes of acquired prolonged QTc duration (eg, drugs, hypokalemia, and hypomagnesemia) can also precipitate ventricular arrhythmia in patients with congenital LQTS (table 3). (See 'Acquired QTc prolongation' below and "Acquired long QT syndrome: Definitions, pathophysiology, and causes".)

Patients with LQTS may present with syncope, seizures, or cardiac arrest. A family history of sudden death, seizures, recurrent syncope, or unexplained drowning should heighten the suspicion of LQTS. A link between LQTS and sudden infant death syndrome (SIDS) has been reported, though it likely accounts for a very small subset of SIDS cases [18]. (See "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Sudden infant death syndrome: Risk factors and risk reduction strategies", section on 'Genetic factors'.)

The clinical features, diagnosis, and management of congenital LQTS are discussed in greater detail separately. (See "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Congenital long QT syndrome: Diagnosis" and "Congenital long QT syndrome: Treatment".)

Brugada syndrome — Brugada syndrome is an uncommon channelopathy that is associated with characteristic ECG findings of ST segment elevation in leads V1 to V3 and a right bundle branch block-like pattern in the right precordial leads, which can be triggered by the fever (waveform 4 and waveform 5) and certain drugs including cannabis. (See "Brugada syndrome: Epidemiology and pathogenesis", section on 'Fever'.)

Brugada syndrome is characterized by variable expression. SCN5A gene variants, which encode for the subunit of a cardiac sodium channel, resulting in a loss of sodium channel function, have been found in 10 to 30 percent of patients with Brugada syndrome. It is likely that in many patients, Brugada syndrome is an oligogenic disease and that the coinheritance of several genetic risk variants contribute to the disease [19]. (See "Brugada syndrome: Epidemiology and pathogenesis", section on 'Genetics'.)

Affected patients may present with life-threatening ventricular arrhythmias. Sudden cardiac death may be the first and only clinical event in Brugada syndrome, occurring in as many as one-third of patients. Death usually occurs during sleep and in the early morning hours. A family history of sudden death at a young age is commonly found. In some patients, the typical ECG findings of Brugada are present intermittently but may be unmasked by fever, increased core body temperature, or the administration of medications.

The clinical features, diagnosis, and management of Brugada syndrome are discussed in greater detail separately. (See "Brugada syndrome: Clinical presentation, diagnosis, and evaluation".)

Catecholaminergic polymorphic VT (CPVT) — Patients with CPVT are at risk for VT (specifically, bidirectional VT), supraventricular arrhythmias, ventricular fibrillation, and sudden cardiac death, especially in association with adrenergic stress or exercise (waveform 6). Like LQT1, there are increasing data to suggest that some drowning and near-drowning events and sudden infant death syndrome are associated with CPVT [20].

At rest, the ECG typically is normal, although bradycardia and a prominent U wave have been reported. With adrenergic influence, there is the appearance of frequent premature ventricular contractions (PVCs) and nonsustained polymorphic VT. The ventricular ectopy is described as bidirectional. The QT interval is normal, which distinguishes it from LQTS, and there are no ST segment changes differentiating it from Brugada syndrome.

This disorder is inherited in an autosomal dominant or autosomal recessive pattern and also occurs in sporadic cases as a de novo mutation. Various variants of gene loci that encode proteins involved in calcium regulation across the sarcoplasmic reticulum have been identified in patients with CPVT. These include mutations of the RyR2 gene (which encodes the human cardiac ryanodine receptor) and the calsequestrin 2 gene (which encodes a major calcium reservoir protein within the sarcoplasmic reticulum). Mutations in the CALM1 gene, which encodes calmodulin, result in compromised calcium binding and have been associated with familial ventricular fibrillation and sudden cardiac death [21,22].

CPVT is typically a disease of childhood and adolescence, but it can present at any age. One possible explanation for the peak in childhood/adolescence is that the intensity of exercise and physical activity is typically higher at this age compared with infancy and later adulthood. Approximately 30 percent of patients have a family history of sudden death in childhood and adolescence. Prognosis is guarded, even in patients in whom the disease is identified and treatment instituted. The mainstay of therapy includes beta blockers, with emerging encouraging results from flecainide. There are increasing data about the superiority of nadolol over other beta blockers for CPVT [23]. ICD or LCSD have been used for high-risk patients and those with symptoms despite medical therapy. The emerging recognition of the risk of ICD storm in this population is negatively influencing the decision for ICD implantation in children with CPVT. LCSD has proven an effective antifibrillatory intervention for these patients. Whenever syncope occurs despite optimal medical therapy, LCSD could be considered the next step rather than an ICD and could complement the ICD in patients with recurrent shocks [24]. These therapies and the clinical features of CPVT are discussed in greater detail separately. (See "Catecholaminergic polymorphic ventricular tachycardia".)

Calcium release deficiency syndrome (CRDS) — CRDS is a rare inherited arrhythmia syndrome that is newly described. It is caused by loss-of-function variants in the cardiac RyR2 gene. Unlike CPVT, which is caused by gain-of-function RyR2 variants, patients with CRDS are predisposed to VT and sudden death in the absence of adrenergic stimulation [25]. In CRDS, there are no electrical abnormalities during stress electrocardiography, which makes establishing this diagnosis challenging. Arrhythmic events are rarer than in CPVT, and when they do occur, they are often lethal. An invasive electrophysiologic test appears to be effective in unmasking the phenotype, called the long-burst, long-pause, short-coupled ventricular extra-stimulus protocol. Optimal therapies for patients with CRDS have not been established, although flecainide appears to be a promising candidate drug.

Cardiomyopathy — VT can often be associated with inherited cardiomyopathic disorders and, less commonly, with more generalized inherited myopathic diseases, such as myotonic dystrophy. (See "Myotonic dystrophy: Etiology, clinical features, and diagnosis", section on 'Cardiac abnormalities'.)

The following is a brief review of the inherited cardiomyopathies associated with ventricular arrhythmias, which are discussed in greater detail separately.

Hypertrophic cardiomyopathy (HCM) — HCM is a genetic disease caused by variants in genes that encode the myocardial contractile proteins of the cardiac sarcomere (figure 1). Variants in the cardiac myosin binding protein-C gene and cardiac beta-myosin heavy chain gene are the most common, but numerous other variants have been identified. Thus, there is a wide variation in the clinical presentation and course of this disorder and makes standardization of therapy difficult. (See "Hypertrophic cardiomyopathy: Gene mutations and clinical genetic testing".)

The clinical manifestations and management of pediatric patients with HCM are discussed separately. (See "Hypertrophic cardiomyopathy in children: Clinical manifestations and diagnosis" and "Hypertrophic cardiomyopathy in children: Management and prognosis".)

In patients with HCM, ventricular arrhythmias are thought to be due to electrically unstable myocardium resulting from myocellular disarray, fibrosis, and ischemia. Ventricular arrhythmias and risk of sudden cardiac arrest in HCM are discussed in greater detail separately. (See "Hypertrophic cardiomyopathy: Management of ventricular arrhythmias and sudden cardiac death risk".)

Arrhythmogenic cardiomyopathy (ACM) — ACM is defined by a clinical presentation with documented or symptomatic arrhythmia and myocardial structural and functional abnormalities.

●Arrhythmogenic right ventricular cardiomyopathy (ARVC) – ARVC is the best characterized of the ACMs. ARVC is a characterized by fatty or fibrofatty replacement of the right ventricular myocardium, resulting in myocardial thinning, aneurysm formation, and wall motion abnormalities. In some cases, there may also be left ventricle involvement, with relative sparing of the ventricular septum. (See "Arrhythmogenic right ventricular cardiomyopathy: Anatomy, histology, and clinical manifestations".)

ARVC was thought to be rare but is now thought to account for 3 to 5 percent of unexplained sudden deaths in adolescents and young adults and up to 10 percent in certain regions (eg, northern Italy). Both autosomal dominant and recessive forms of ARVC have been reported, with identified variants in several desmosomal protein genes. Autosomal recessive ARVC is less common and can be part of a syndrome called Naxos disease, which also includes hyperkeratosis of the palms and soles and wooly hair. (See "Arrhythmogenic right ventricular cardiomyopathy: Pathogenesis and genetics", section on 'Genetics'.)

Affected patients generally present between 10 and 50 years of age with dizziness, palpitations, and syncope due to VT. The characteristic VT has a left bundle branch pattern that should lead one to consider a right ventricular origin.

Physiologic cardiac adaptation to regular exercise, including biventricular dilation and T-wave inversion, may create diagnostic overlap with ARVC [26,27]. The T-wave changes and balanced biventricular dilation are thought likely to represent benign manifestations of training in asymptomatic athletes without relevant family history. Diagnostic criteria for ARVC were nonspecific in such individuals, and comprehensive testing using widely available techniques may be needed to differentiate these entities.

Other ECG findings of ARVC as well as the clinical findings, diagnostic evaluation, and treatment of ARVC are discussed in greater detail separately. (See "Arrhythmogenic right ventricular cardiomyopathy: Anatomy, histology, and clinical manifestations" and "Arrhythmogenic right ventricular cardiomyopathy: Diagnostic evaluation and diagnosis" and "Arrhythmogenic right ventricular cardiomyopathy: Treatment and prognosis".)

●DSP cardiomyopathy – ACM is not a purely right ventricular entity. Pathogenic variants in desmoplakin (DSP) can cause ACM with a presentation that mimics acute myocarditis. Thus, it is important to consider genetic causes in the differential diagnosis of myocarditis. (See "Myocarditis: Causes and pathogenesis", section on 'Arrhythmogenic cardiomyopathy'.)

Affected patients typically have left ventricular manifestations of ACM. They can have subepicardial left ventricular fibrosis, left ventricular dysfunction, arrythmias, and discrete episodes of chest pain/myocarditis with elevated troponin levels [28,29].

Duchenne muscular dystrophy — With improved management, patients with Duchenne muscular dystrophy are surviving into their 20s, and cardiomyopathy has emerged as an important cause of morbidity and mortality in adolescence and adulthood. Heart failure and associated fibrosis in patients with Duchenne muscular dystrophy predisposes patients to ventricular arrhythmias, which is associated with a risk of sudden cardiac death [30,31]. (See "Duchenne and Becker muscular dystrophy: Clinical features and diagnosis", section on 'Cardiomyopathy'.)

Barth syndrome — Barth syndrome is an X-linked disorder characterized by a noncompaction of the left ventricle, a form of a dilated cardiomyopathy, cyclic neutropenia, skeletal myopathy, and growth delay. Ventricular arrhythmias and sudden death can occur in this population, and monitoring for this should be undertaken in these patients [32]. Typically, Barth syndrome is due to a genetic variant in the Tafazzin gene. (See "Inherited syndromes associated with cardiac disease", section on 'Barth syndrome'.)

Acquired heart disease — Acquired heart diseases that can result in VT in children include:

Coronary heart disease — In contrast to adults, VT is rarely caused by coronary heart disease in children. Structural coronary artery abnormalities (eg, left coronary arising from the right sinus) are an important cause of arrhythmic sudden death in the young, especially in association with sports [33]. (See "Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features" and "Congenital and pediatric coronary artery abnormalities".)

Myocarditis — Viral infections of the myocardium cause myocardial inflammation and edema, which can precipitate ventricular ectopy, complex VT, and sudden death. Viral myocarditis is a recognized contributor to unexplained death in the first two decades of life. (See "Sudden cardiac arrest (SCA) and sudden cardiac death (SCD) in children", section on 'Etiology'.)

Acute myocarditis and ventricular arrhythmias can occur in severe COVID-19, as discussed separately. (See "COVID-19: Arrhythmias and conduction system disease".)

The clinical manifestations, diagnosis, and treatment of myocarditis are discussed separately. (See "Clinical manifestations and diagnosis of myocarditis in children" and "Treatment and prognosis of myocarditis in children".)

Chagas disease — Chagas disease is caused by the parasite Trypanosoma cruzi, which resides primarily in Central and South America. Although uncommon in children, dilated cardiomyopathy can develop and is associated with heart failure, heart block, and VT during the chronic phase of the infection. (See "Chronic Chagas cardiomyopathy: Clinical manifestations and diagnosis", section on 'Arrhythmias'.)

Acquired QTc prolongation — Like congenital LQTS, patients with acquired QTc prolongation are at risk for developing polymorphic VT. QTc prolongation can be caused by the following (table 3):

●Metabolic disturbances – Hypokalemia, hypomagnesemia, or anorexia nervosa. (See "Anorexia nervosa in adults and adolescents: Medical complications and their management", section on 'Cardiovascular'.)

●Myocardial infarction or ischemia.

●Intracranial disease – Stroke.

●Drugs – Antiarrhythmic drugs (eg, quinidine or procainamide), some nonsedating antihistamines (eg, terfenadine or astemizole), macrolide antibiotics, antipsychotic and antidepressant medications, ondansetron, and methadone.

The clinical features, diagnosis, and management of acquired QTc prolongation are discussed in greater detail separately. (See "Acquired long QT syndrome: Clinical manifestations, diagnosis, and management".)

Cardiac tumors — Rarely, VT may be caused by primary cardiac tumors. In a retrospective study of 173 children with primary cardiac tumors (including 106 rhabdomyomas, 25 fibromas, 14 myxomas, 6 vascular malformations, 4 teratomas, 3 lipomas, and 15 other tumors), approximately one-quarter had clinically significant arrhythmias, with VT being the most common [34]. VT was particularly common in patients with fibromas, occurring in two-thirds of that subset. Approximately one-third of the entire cohort (62 patients) underwent surgical excision, and control of arrhythmia was an indication for surgery in 20 patients. Postoperatively, arrhythmias resolved in 18 of these 20 patients. In a later study from the same group that included 18 children with VT due to cardiac fibromas, sustained arrhythmia episodes were found to correlate with diffuse myocyte interdigitation and entrapped myocardium [35]. All four patients who underwent complete tumor resection were cured of arrhythmias. However, 2 of the 14 with subtotal resections had recurrence. These findings suggest that the interdigitating myocardium represents a potential histopathologic substrate for VT.

BENIGN FORMS OF VT — 

Relatively benign forms of VT can be seen in children without demonstrable pathology. They include accelerated ventricular rhythm, right ventricular outflow tract (RVOT) tachycardia, and idiopathic left VT.

Accelerated ventricular rhythm — It is important to differentiate accelerated ventricular rhythm from VT because the prognosis is different. Accelerated ventricular rhythm is a relatively slow monomorphic ventricular rhythm. The rate tends to be just slightly faster than the sinus rate (15 to 20 percent faster) and so varies with age, but most often it is <120 beats per minute [36]. Although most commonly seen in newborns, accelerated ventricular rhythm may be present in older children and adolescents [37,38].

Accelerated ventricular rhythm is distinguished from VT because of its slower rate and the absence of symptoms. In addition, accelerated ventricular rhythm is usually suppressed by exertion, whereas VT from other causes may persist or degenerate into ventricular fibrillation during exercise, and/or results in progressive myocardial dysfunction over time. Accelerated ventricular rhythm is generally diagnosed only in patients with a structurally and functionally normal heart, although rare cases have been seen in children with CHD [39].

The ECG typically shows sinus rhythm followed by fusion beats at the onset of the ventricular rhythm and at its termination. The EP mechanism is unknown and may include triggered activity or abnormal automaticity.

Accelerated ventricular rhythm is usually a benign condition that often occurs in newborn infants [40]. It most often resolves spontaneously and should not be treated [40]. Thus, it is important to differentiate this rhythm disturbance from pathologic VT to avoid potentially toxic antiarrhythmic agents. Patients should be followed until resolution to monitor cardiac function because a decline in cardiac function may rarely occur in patients with frequent ventricular ectopy [41]. Accelerated ventricular rhythm is thought to be due to enhanced automaticity of the myocardium or His-Purkinje fibers. Although typically benign, in the setting of metabolic disarray, ischemia, or myocardial disease, it may be a harbinger of more malignant ventricular arrhythmias [41].

Right ventricular outflow tract tachycardia — One of the most common ventricular arrhythmias in young patients is RVOT tachycardia, a generally benign condition that may resolve spontaneously. Even in those in whom it persists, the arrhythmia burden often declines over time. The tachycardia is monomorphic with left bundle branch block QRS morphology and an inferior axis. There is often a late transition (after lead V3) in the precordial leads [41].

This rhythm disturbance is thought to be a cAMP-mediated triggered activity, and as such, it may be responsive to termination with vagal maneuvers, adenosine, calcium channel blockers, and beta blockers. Rarely, RVOT tachycardia may be due to automaticity or reentry that may or may not be sensitive to verapamil. It is characterized by relatively slow rates (140 to 190 beats per minute) with a monomorphic QRS pattern of left bundle branch block and an inferior axis.

Children with RVOT may be asymptomatic and present because of an incidental finding [37]. A retrospective review of 48 Canadian children with RVOT tachycardia who presented at a median age of 8.2 years showed that 41 of the 48 patients (82 percent) presented with an incidental finding of an irregular heart rhythm or abnormal ECG [37]. Seven patients were referred because of syncope or near syncope. Reported symptoms obtained from interviews of patients included abdominal pain, asthma-related complaints, fatigue, fever, limb pain, and rash. In other series, palpitations and near syncope were noted in ≥50 percent of patients [41,42]. RVOT tachycardia that is incessant and longstanding can result in arrhythmia-induced cardiomyopathy. Syncope is uncommon in RVOT tachycardia and should raise suspicion of another diagnosis or an associated cardiomyopathy [41].

Magnetic resonance imaging (MRI) may reveal subtle abnormalities of the right ventricle, including thinning of the ventricular free wall, fatty infiltration, and wall motion abnormalities [37]. In the previously mentioned Canadian study, 13 of the 25 patients studied by MRI had abnormalities of the right ventricle [37].

A major challenge for the clinician is to distinguish children with RVOT tachycardia from the more serious ARVC, discussed above, which has a high risk of sudden cardiac death. (See 'Arrhythmogenic cardiomyopathy (ACM)' above.)

Rigorous diagnostic criteria must be employed before arriving at the diagnosis of ARVC as many patients with minor criteria have been inappropriately diagnosed with ARVC [43]. An incidental presentation and slow VT generally are more characteristic of patients with RVOT compared with those with ARVC. The VT associated with ARVC is usually due to reentry and not responsive to vagal maneuvers or adenosine [44]. However, further diagnostic testing including MRI, EP testing, and/or signal-averaged ECG may further differentiate the two entities [37]. (See "Arrhythmogenic right ventricular cardiomyopathy: Anatomy, histology, and clinical manifestations", section on 'RVOT tachycardia'.)

Treatment for RVOT tachycardia is indicated for symptomatic patients and those rare patients who develop arrhythmia-induced cardiomyopathy [45]. Therapy includes antiarrhythmic agents and catheter ablation [37]. Catheter ablation has proven highly successful, and the application of novel mapping systems, noncontact, and electroanatomical techniques increase efficacy [45].

Prognosis for this condition is excellent, and there is no related mortality in patients with structurally and functionally normal hearts up to an 80-month follow-up period [37,42]. VT can originate from the left ventricular outflow tract and is similar to RVOT tachycardia in its clinical manifestations, prognosis, and management. In patients with left ventricular outflow tract tachycardia, the ECG demonstrates monomorphic VT with a right bundle branch block and inferior axis. (See "Ventricular tachycardia in the absence of apparent structural heart disease", section on 'Repetitive monomorphic VT'.)

Idiopathic left ventricular tachycardia — Idiopathic left VT (also referred to as left ventricular fascicular tachycardia, Belhassen tachycardia, or verapamil sensitive tachycardia) is a benign VT. In affected patients, the ECG demonstrates a right bundle branch block with a superior or left axis.

Idiopathic left VT originates from the left posterior fascicle and occurs in the absence of structural disease, although it may be related to a false tendon that extends from the posteroinferior left ventricle to the septum.

The mechanism of VT is thought to be due to a reentry circuit in the vicinity of the left posterior fascicle. As a reentrant tachycardia, it can be initiated with atrial and ventricular pacing. The VT is sensitive to verapamil and occasionally adenosine but not vagal maneuvers. Although catheter ablation is an effective cure, even without therapy, this form of VT has a good prognosis with occasional spontaneous remissions and rare reports of tachycardia-induced cardiomyopathy [41,46]. (See "Ventricular tachycardia in the absence of apparent structural heart disease", section on 'Idiopathic left ventricular tachycardia'.)

The application of noncontact mapping strategies to both RVOT tachycardia and idiopathic left VT has increased the ability to provide a cure for these problems in children, even when the tachycardia is not sustained [47].

ARRHYTHMIA-INDUCED CARDIOMYOPATHY — 

Idiopathic VT and, more commonly, frequent PVCs can lead to left ventricular dysfunction in patients without structural heart disease and can exacerbate cardiomyopathy in patients with heart disease. The mechanism of PVC-mediated cardiomyopathy is not fully understood in adult patients, and less is known about this in pediatric patients. Potential mechanisms include ventricular dyssynchrony especially related to a left bundle branch block morphology, abnormal calcium handling from the short coupling intervals, and abnormal ventricular filling from the pause after the ectopic beat [48].

In a study involving 72 children with ventricular ectopy and asymptomatic VT, six patients (8 percent) had left ventricular dysfunction (defined as a shortening fraction of ≤28 percent) at presentation [49]. Patients with left ventricular dysfunction had a higher burden of ectopy, higher number of couplets, and higher prevalence of VT. Following treatment of the arrhythmia (with medication [n = 2] or ablation [n = 5]), left ventricular function normalized in five of six patients. This small pediatric study suggests that the left ventricular dysfunction is reversible with termination of culprit arrhythmia, a finding that is consistent with clinical studies in adults and animal studies [48].

Arrhythmia-induced cardiomyopathy is discussed in greater detail separately. (See "Arrhythmia-induced cardiomyopathy".)

SUMMARY AND RECOMMENDATIONS

●Importance – Wide QRS tachycardia may be due to ventricular tachycardia (VT), supraventricular tachycardia (SVT) with aberrant conduction, or atrioventricular reentrant tachycardia (AVRT) with an accessory pathway. Children with wide QRS complex tachycardia may present with hemodynamic instability, and if not urgently treated, serious morbidity or death may occur. (See 'Introduction' above and "Management and evaluation of wide QRS complex tachycardia in children", section on 'Initial management'.)

SVT is discussed in greater detail separately. (See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children".)

●VT in congenital heart disease – VT is often seen as a late surgical complication in patients with congenital heart disease (CHD) and is associated with increased risk of mortality and serious morbidity. (See 'Congenital heart disease' above.)

●Genetic causes of VT – Patients with inherited disorders that affect the cardiac muscle and/or function and can present with life-threatening ventricular arrhythmias or a history of unexplained death in a young family member. These include channelopathies and inherited causes of cardiomyopathy (see 'Genetic disorders' above):

•Congenital long QT syndrome (LQTS) (see "Congenital long QT syndrome: Pathophysiology and genetics" and "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Congenital long QT syndrome: Diagnosis")

•Brugada syndrome (see "Brugada syndrome: Epidemiology and pathogenesis" and "Brugada syndrome: Clinical presentation, diagnosis, and evaluation")

•Catecholaminergic polymorphic VT (CPVT) (see "Catecholaminergic polymorphic ventricular tachycardia")

•Hypertrophic cardiomyopathy (see "Hypertrophic cardiomyopathy in children: Clinical manifestations and diagnosis")

•Arrhythmogenic cardiomyopathy (see "Arrhythmogenic right ventricular cardiomyopathy: Pathogenesis and genetics" and "Arrhythmogenic right ventricular cardiomyopathy: Anatomy, histology, and clinical manifestations")

•Duchenne muscular dystrophy (see "Duchenne and Becker muscular dystrophy: Clinical features and diagnosis", section on 'Cardiomyopathy')

•Barth syndrome (see "Inherited syndromes associated with cardiac disease", section on 'Barth syndrome')

●VT in acquired heart disease – Acquired heart diseases associated with VT include myocarditis and acquired QTc prolongation. In contrast with adults, coronary artery disease is a rare cause of VT in children. (See 'Acquired heart disease' above and "Clinical manifestations and diagnosis of myocarditis in children" and "Acquired long QT syndrome: Definitions, pathophysiology, and causes".)

●Benign forms of VT – Relatively benign forms of VT can be seen in children structurally normal hearts. They include accelerated ventricular rhythm, right ventricular outflow tract (RVOT) tachycardia, and idiopathic left VT. These diagnoses are only made after other more serious causes of VT are excluded. (See 'Benign forms of VT' above.)

●Arrhythmia-induced cardiomyopathy – Idiopathic VT and frequent premature ventricular contractions (PVCs) can lead to left ventricular dysfunction in patients without structural heart disease and can exacerbate cardiomyopathy in patients with heart disease. In most cases, left ventricular dysfunction is reversible with termination of culprit arrhythmia. (See 'Arrhythmia-induced cardiomyopathy' above and "Arrhythmia-induced cardiomyopathy".)