Ventricular tachycardia in the absence of apparent structural heart disease

INTRODUCTION — The evaluation and management of ventricular tachyarrhythmias are uniquely challenging due to the unpredictable and potentially lethal nature of the events. When evaluating patients with ventricular tachycardia (VT) and ventricular fibrillation (VF), several initial distinctions should be made. These include:

●Arrhythmia duration – Sustained or nonsustained

●Arrhythmia morphology – Monomorphic VT, polymorphic VT, or VF

●Associated symptoms – Ranging from none to hemodynamic collapse and sudden cardiac arrest

●Associated cardiac disease

Malignant arrhythmias usually occur in the presence of significant structural heart disease (eg, coronary heart disease with prior myocardial infarction, dilated cardiomyopathy, or hypertrophic cardiomyopathy). In this setting, ventricular arrhythmias carry a high risk of sudden cardiac death (SCD).

Less commonly, VT and VF occur in hearts that appear normal. In many such cases, however, the heart is in fact not normal, but rather has less visible abnormalities including derangements of cardiac ion channels or structural proteins. In these patients, ventricular arrhythmias also carry a high risk of SCD. Thus, a significant majority of patients with VT or VF have some form of underlying cardiac disease, are at increased risk for SCD, and require a thorough cardiac evaluation to exclude structural abnormalities and nonstructural disorders. (See "Cardiac evaluation of the survivor of sudden cardiac arrest".)

There are, however, some VT syndromes which occur in normal hearts that have a more benign prognosis [1,2]. These arrhythmias are sometimes referred to as idiopathic VT. Terminology and classifications vary, but three commonly cited syndromes are:

●Repetitive monomorphic VT, which is also referred to as right ventricular outflow tract (RVOT) VT. This arrhythmia is due to triggered activity and is sensitive to adenosine. An arrhythmia with similar characteristics that originates from the left ventricular outflow tract has also been described.

●Paroxysmal sustained VT, which is sometimes considered a variant of RVOT VT.

●Idiopathic left ventricular tachycardia, which originates from the posterior septum, is due to reentry, and is sensitive to verapamil.

These arrhythmias have substrate and mechanisms that are different from the malignant arrhythmias that occur in both abnormal and apparently normal hearts. Thus, they should be considered distinct syndromes rather than well-tolerated forms of other ventricular arrhythmia syndromes. The diagnosis, characterization, and management of these monomorphic VTs will be reviewed here.

Sustained and nonsustained ventricular arrhythmias in patients with heart disease, and malignant ventricular arrhythmias in the absence of apparent structural heart disease are discussed in detail separately. (See "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis" and "Approach to sudden cardiac arrest in the absence of apparent structural heart disease" and "Nonsustained VT in the absence of apparent structural heart disease".)

IDIOPATHIC VENTRICULAR ARRHYTHMIAS — Although the term idiopathic VT is widely used for the monomorphic VT syndromes described here, use of "idiopathic" can be misleading. Historically, both VT and VF that occur in the absence of apparent heart disease have been referred to as idiopathic. However, with continual improvements in both the understanding of arrhythmia mechanisms and diagnostic methods, an increasing percentage of patients are now given a diagnosis (eg, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy [ARVC], and catecholaminergic polymorphic VT). In contrast to the syndromes discussed here, these disorders have an increased risk of sudden cardiac death (SCD). (See "Catecholaminergic polymorphic ventricular tachycardia" and "Arrhythmogenic right ventricular cardiomyopathy: Anatomy, histology, and clinical manifestations", section on 'Ventricular arrhythmias' and "Brugada syndrome: Clinical presentation, diagnosis, and evaluation".)

Previously reported series of idiopathic VT and VF are likely to include a heterogeneous group of patients with various diagnoses and prognoses. Currently, idiopathic VT generally refers to one of the three benign syndromes described here and excludes patients with other diagnoses.

Sites of origin — Idiopathic VT, or VT not associated with structural organic heart disease, can arise in several locations:

●Right ventricular outflow tract (also called repetitive monomorphic VT)

●Tricuspid annulus

●Right ventricle

●Left ventricle

●Inferoapical septum

●Left ventricular outflow tract

●Aortic cusps

These arrhythmias, not as rare as previously thought, are susceptible to radiofrequency ablation [3]. (See 'Radiofrequency ablation' below.)

Classification — Multiple classification schemata for idiopathic VT appear in the literature. Investigations of idiopathic VT syndromes have focused for the most part on individual aspects of the syndrome (eg, clinical presentation, electrocardiographic appearance, electrophysiologic mechanism, response to antiarrhythmic agents); this approach has yielded a bewildering amount of often conflicting information. Despite this confusion, most investigators acknowledge the existence of at least three syndromes of idiopathic monomorphic VT:

●Repetitive monomorphic VT, also called right ventricular outflow tract (RVOT) VT, is a triggered arrhythmia that is characterized by frequent short "salvos" of nonsustained VT. Less commonly, arrhythmias with similar characteristics and mechanisms originate from the LVOT, and these are considered a variant of RVOT VT.

●Paroxysmal sustained VT, which also arises from the RV, and is sometimes considered a sustained variant of repetitive monomorphic VT.

●Idiopathic left ventricular tachycardia, which differs from the LVOT variant of RVOT VT in both the mechanism (reentry) and site of origin (inferoapex or midseptum).

These three syndromes effectively characterize the majority of patients with idiopathic monomorphic VT and often unite clinical presentation, ECG morphology, and anatomic location into recognizable syndromes (table 1) [1,2]. In fact, however, idiopathic VT can arise from virtually any area of the heart, and other typical locations include the RV and LV inflow areas and the papillary muscles. The syndromes discussed in this section are by far the most frequently observed.

Bundle branch reentrant VT is a special form of monomorphic VT that typically occurs in patients with structural heart disease. Patients with BBRVT often have a baseline nonspecific conduction delay or left bundle branch block, and most have a prolonged His-to-ventricle time (ie, HV interval). (See "Bundle branch reentrant ventricular tachycardia".)

Idiopathic VT — Idiopathic VT has accounted for approximately 10 percent all patients referred for evaluation of VT [1]. The mean age of patients with idiopathic VT is less than that of patients with VT secondary to underlying heart disease.

It is important to recognize that not all VT that occurs in the apparent absence of structural heart disease is idiopathic VT. Distinguishing idiopathic VT from other monomorphic VT syndromes is important for several reasons:

●Idiopathic VT is generally considered to have an excellent prognosis in terms of freedom from both the development of structural heart disease and arrhythmic death [4-10]. There are several exceptions to this generalization, however, and episodes of SCD can occur [7].

●Idiopathic VT often responds to antiarrhythmic drugs that would be unhelpful or even contraindicated in VT occurring in the setting of coronary heart disease.

●Most idiopathic VT syndromes are now amenable to cure with catheter ablation techniques.

Other ventricular tachyarrhythmias — In addition to monomorphic VT, both polymorphic VT and VF can occur in the absence of structural heart disease. In contrast to the generally good prognosis associated with idiopathic monomorphic VT, these syndromes are associated with an increased risk of SCD. (See "Approach to sudden cardiac arrest in the absence of apparent structural heart disease".)

●Polymorphic VT in the absence of structural heart disease occurs in two settings: with a prolonged QT interval in acquired or inherited long QT syndrome; and with a normal QT interval in usually familial disease, which is also called catecholaminergic polymorphic VT. (See "Congenital long QT syndrome: Epidemiology and clinical manifestations" and "Catecholaminergic polymorphic ventricular tachycardia".)

●VF in the absence of structural heart disease or other reversible arrhythmic triggers (eg, ischemia or metabolic derangements) is also referred to as idiopathic. The diagnosis of idiopathic VF is considered only after all other causes of VF have been rigorously excluded. The rationale for this approach comes from autopsy studies of SCD in previously healthy individuals. These studies found an appreciable incidence of coronary heart disease (most without a previous history of chest pain), hypertrophic cardiomyopathy, myocarditis, and ARVC. Brugada syndrome is a specific cause of lethal ventricular arrhythmias in patients without structural heart disease; it is characterized by ST elevation in the anterior precordial leads on the resting surface electrocardiogram. (See "Brugada syndrome: Clinical presentation, diagnosis, and evaluation" and "Approach to sudden cardiac arrest in the absence of apparent structural heart disease", section on 'Idiopathic VF'.)

DIAGNOSTIC EVALUATION — By definition, patients with idiopathic monomorphic VT have no detectable structural heart disease [1,2,4-9]. Thus, the assessment of these patients focuses upon establishing the presence of a normal heart. The evaluation of the patient with sustained ventricular arrhythmias and sudden death is reviewed in detail separately. (See "Sustained monomorphic ventricular tachycardia: Clinical manifestations, diagnosis, and evaluation", section on 'Additional diagnostic evaluation' and "Cardiac evaluation of the survivor of sudden cardiac arrest".)

General approach — For the purposes of this review, the following summarizes findings that may be seen in patients with idiopathic monomorphic VT:

●The resting ECG is typically normal between arrhythmia episodes, although some patients have temporary ECG repolarization abnormalities immediately after VT termination.

●The signal averaged ECG recorded during sinus rhythm is usually normal, although abnormalities may be seen during VT [6,11].

●Functional studies of left ventricular (LV) and right ventricular (RV) performance during sinus rhythm are normal, although segmental wall motion abnormalities may be seen immediately after VT termination. In patients who have not had a recent episode of VT, abnormalities in ventricular function should suggest an alternative diagnosis. (See "Cardiac evaluation of the survivor of sudden cardiac arrest", section on 'Echocardiography'.)

However, in rare cases, LV dysfunction can occur as a consequence of idiopathic VT, due to a tachycardia-induced cardiomyopathy. Such a myopathy can develop without persistent tachycardia if there are very frequent PVCs (ie, >20,000 per day) [12]. This is a very important condition to recognize, as the LV dysfunction is reversible with treatment of the arrhythmia. (See "Arrhythmia-induced cardiomyopathy", section on 'Frequent ventricular ectopy'.)

●The exercise stress test should be normal. Coronary angiography, which is considered in patients with minimally symptomatic arrhythmias only if the stress test suggests ischemia, should also be normal.

●Cardiovascular magnetic resonance imaging (CMR) may reveal mild structural abnormalities of the RV in patients with RMVT, primarily involving the free wall (focal thinning, fatty infiltration, and wall motion abnormalities) [13-15]. The significance of these changes is unclear, since there is a poor correlation between the origin of the RMVT and the site of the CMR abnormalities unless they are also present in the RVOT.

●Limited data suggest that RV radionuclide myocardial perfusion imaging can distinguish between idiopathic monomorphic VT and VT due to an organic cause such as dilated cardiomyopathy, myocarditis, or ARVC [16].

●RV biopsy, which is rarely performed, is usually normal, although a number of studies have reported abnormalities that are nonspecific and of no significant value [17-19].

Distinction from ARVC — RMVT can be particularly difficult to distinguish from the more serious disorder, ARVC. Although ARVC is unlikely in patients who have a normal signal averaged electrocardiogram and normal imaging studies of RV size and function, the "development" of ARVC in patients thought to have idiopathic VT at presentation has been reported [9,20].

Thus, the clinical boundaries between idiopathic RV tachycardia and ARVC may be difficult to establish in atypical cases. The findings on the ECG, signal averaged ECG, and electrophysiology (EP) studies may be helpful in making this distinction:

●The resting ECG can be normal at presentation in approximately 40 percent of patients with ARVC. However, characteristic abnormalities of ARVC develop in almost all patients within six years of presentation [21]. In a cohort of 59 patients (17 with ARVC, 42 with RMVT), ECG features suggestive of ARVC included longer mean QRS duration in lead I (150 versus 123 msec in RMVT), precordial transition in lead V6 (18 versus 0 percent in RMVT), and at least one lead with QRS notching (65 versus 21 percent in RMVT) [22].

●The signal averaged ECG in the time domain is typically abnormal in ARVC, but usually normal in idiopathic RV tachycardia [11].

●On EP study, four findings are seen in most patients with ARVC but are rare in idiopathic RV tachycardia: inducible VT by programmed stimulation; multiple VT morphologies; fractionated diastolic electrograms during VT or sinus rhythm at the VT site of origin or other RV sites; and regions of low amplitude and prolonged duration on intracardiac electrograms [23-25]. (See 'Electrophysiologic features' below.)

REPETITIVE MONOMORPHIC VT — Repetitive monomorphic VT (RMVT) is characterized by frequent short "salvos" of monomorphic nonsustained VT (waveform 1). It was first described by Gallavardin in 1922 and is variously described in the literature as RMVT, RV tachycardia, RVOT tachycardia, catecholamine-sensitive VT, adenosine-sensitive VT, and exercise-induced VT. Approximately 10 to 15 percent of cases arise from the left ventricular outflow tract [26-28].

Although RMVT is considered to occur in "normal" hearts, static and cine-magnetic resonance imaging often reveal mild structural abnormalities of the RV, primarily involving the free wall (focal thinning, fatty infiltration, and wall motion abnormalities) [13-15]. The functional significance of these changes is uncertain. In the few cases studied, DNA from myocardial biopsies of ventricular muscle has been normal [29].

Epidemiology and clinical features — RMVT occurs almost exclusively in young to middle-aged patients without structural heart disease [1,2,4-9]. There has generally been no predilection on the basis of sex, although a 2:1 female predominance was observed in one report [26]. A surprising number of competitive athletes (particularly cyclists) are identified in many series of RMVT.

The most common associated symptoms are palpitations and lightheadedness during episodes [5,6]. In one illustrative report of 18 patients, twelve had symptomatic arrhythmia, two of whom had syncope, and six were completely asymptomatic.

Most arrhythmias are nonsustained (usually 3 to 15 beats), but up to one-half of patients have some sustained episodes, and some patients have only sustained VT [6,9,13,30]. (See 'Paroxysmal sustained VT' below.)

Bursts of nonsustained VT are typically provoked by emotional stress or exercise, often occurring during the "warm-down" period after exercise, a time when circulating catecholamines are at peak levels [5,6,8]. There may also be a circadian pattern, with prominent peaks between 7 and 11 AM and 4 and 8 PM, correlating with periods of increased sympathetic activity [31]. In some patients, a critical "window" of heart rates (upper and lower thresholds) that result in occurrence of the arrhythmia can be defined [27].

The inducibility of RMVT by stress or catecholamine infusion is suggestive of an abnormality in cardiac sympathetic function. Consistent with this hypothesis is evidence of regional cardiac sympathetic denervation in some patients with RMVT and structurally normal hearts (five of nine compared with zero of nine controls in one report) [32]. Patients with RMVT may also have regions of impaired neuronal reuptake of norepinephrine, leading to increased local synaptic catecholamine concentrations and downregulation of myocardial beta adrenergic receptors [33].

There may also be sex-specific triggers. In a report of 47 men and women with RMVT, states of hormonal flux (premenstrual, gestational, perimenopausal, administration of birth control pills) were the most common trigger for RMVT in 59 percent of women and were the only recognizable triggers in 41 percent [34]. Men were more likely than women to identify exercise, stress, or caffeine as a trigger (92 versus 41 percent).

Site of origin — RV tachycardias usually originate from the septal aspect of the RVOT [6,26,28,35-38]. A nine site mapping schema of the septal RVOT has proven useful in localizing RVOT tachycardias on the basis of their 12 lead ECG morphology (figure 1) [39].

RV tachycardias typically arise from a very narrow area just inferior to the pulmonary valve in the anterior aspect of the RVOT [37]. Endocardial mapping in such patients shows that the earliest site of endocardial activation occurs in this region [6,9].

Less commonly, sites of origin have been mapped to the RV inflow tract, the free wall of the RVOT, the root of the pulmonary artery, the left and right aortic sinus of Valsalva, the left ventricle, the mitral annulus, and the papillary muscles [26,36,38,40-49].

Electrocardiographic features — The typical rate of RMVT ranges from 140 to 180 beats/min, and may fluctuate based upon catecholamine levels. The VT cycle length often prolongs prior to termination.

RV outflow tract — The majority of RMVT episodes have a characteristic ECG appearance with two main features [1,2,4-9,39]:

●Left bundle branch block

●Inferior axis

This morphology is consistent with the RVOT origin seen by catheter ablation and endocardial mapping [6,37]. This ECG "signature" accounts for at least 70 percent of all idiopathic VTs [1].

The ECG pattern of RV tachycardia initiation may provide information about the site of origin and the arrhythmogenic mechanism as illustrated by the following observations:

●In a series of 32 patients with exercise-induced RMVT, VT usually began without a change in cycle length. Arrhythmias that initiated in this manner had an inferior axis, and appeared to be related to triggered activity due to delayed afterpotentials [50]. By comparison, VT initiated with a long-short sequence was more often nonsustained and often had a superior axis, suggesting an origin in the body or septal region of the ventricle; the mechanism for this VT is probably early afterpotentials.

●In a report of 14 patients, those with septal compared with free wall sites were significantly less likely to have notching of the QRS complex (29 versus 95 percent) and more likely to show early precordial transition by lead V4 (79 versus 5 percent) [51]. In addition, a positive R wave in lead I distinguished posterior from anterior septal and free wall sites.

●The degree of similarity of 12-lead ECG waveforms between VT and a pace map can be used to estimate the likelihood of successful ablation at that site. (See 'Radiofrequency ablation' below.)

The majority of patients with RV tachycardia have a single ECG morphology [23]. However, occasional patients present with multiple tachycardia morphologies arising from discrete sites in the RVOT [52]. The presence of multiple left bundle VT morphologies, particularly during EP study, should suggest the possibility of ARVC [23,53,54]. (See 'Distinction from ARVC' above.)

LV outflow tract — Electrocardiographic criteria have also been described for RMVT originating in the LVOT [26,27]. In a series of 33 patients with RMVT, four (12 percent) had LV sites of origin that could be predicted by two patterns [26]:

●A right bundle, inferior axis morphology with a monophasic R wave in V1 that arose from the left fibrous trigone (waveform 2).

●A pattern similar to typical RMVT from the RVOT (left bundle, inferior axis) except that the precordial transition was earlier (at V2 for the LVOT as compared with V3 or later for the RVOT).

Other reports have characterized unique QRS morphologies for idiopathic VT arising from the sinuses of Valsalva [9,43,44]. Although there is some interindividual variability, premature ventricular complex/contraction (PVC; also referred to a premature ventricular beats or premature ventricular depolarizations) arising from the left aortic sinus tend to be negative in lead I and have a "w" pattern in V1, while PVC with a broad R wave in V1 is characteristic of a right aortic cusp origin. The precordial R wave transition is much earlier when VT originates from either aortic sinus of Valsalva compared with the RVOT, since the LVOT is posterior to the RVOT [44].

Electrophysiologic features — RMVT can be induced in the EP laboratory, although usually not with programmed stimulation [5,6,23,27,55]. In most patients, sustained or nonsustained episodes occur in response to burst atrial or ventricular pacing, and are greatly facilitated by isoproterenol or epinephrine infusion [5,6,27,30,55].

These electrophysiologic observations suggest that triggered activity due to delayed afterpotentials, rather than reentry, is the mechanism of RMVT. The response to "pharmacologic probes" further strengthens this hypothesis. RMVT has been terminated with adenosine, verapamil, and beta blockers, all of which interfere with the cAMP-mediated slow inward calcium current [29,40,56-58].

These observations are consistent with the hypothesis that RMVT results from triggered activity induced by cAMP-mediated delayed after depolarizations (DADs) [30,59]. The increase in cAMP activity may, at least in some patients, result from an acquired somatic cell mutation in the inhibitory G protein G-alpha-i2 at the site of the arrhythmogenic focus [59,60].

However, the lack of specificity of these probes and the absence of a uniform response supports the general consensus that the mechanism of RMVT is incompletely characterized and may vary among individuals. Additional support for other mechanisms is based upon the observation that the tachycardia may, in some patients, terminate with overdrive pacing, ventricular extrastimulation, or autonomic modulation using Valsalva maneuver or carotid sinus pressure [9].

EP studies may also help distinguish RMVT occurring in the absence of structural heart disease from that in ARVC [23,24]. (See 'Distinction from ARVC' above.)

Prognosis — The prognosis of RMVT is almost uniformly good [4-9,55]. The following observations from early studies illustrate the range of findings:

●Two initial series evaluated 30 and 18 patients [5,6]. The arrhythmia responded to a variety of antiarrhythmic drugs, including type I drugs and propranolol. At a mean of 30 months in one study and a range of 0.5 to 8 years in the other, there were no deaths or episodes of cardiac arrest [5,6].

●A third report consisted of 24 young patients, most of whom had RV tachycardia and two-thirds of whom were symptomatic [7]. At a mean follow-up of 7.5 years, three patients died suddenly; none was taking antiarrhythmic drugs at the time. The SCD events may have been due to RMVT itself, although patients with other syndromes now known to be malignant may have been included (eg, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy). Alternatively, a tachycardia-induced cardiomyopathy may have predisposed patients to additional arrhythmias. (See "Arrhythmia-induced cardiomyopathy".)

Malignant variant — More recent studies in which these other syndromes were unlikely have identified a malignant variant of RMVT. Polymorphic VT and VF, which are malignant arrhythmias, have been demonstrated in patients with RMVT [61,62]. In one series, three patients with RMVT later developed VF. In these patients, PVCs were more closely coupled to prior beats than is usual for RMVT [61]. It was postulated that relatively early triggered beats occurred in a vulnerable period during repolarization, resulting in VF.

In a subsequent report, 16 patients with frequent PVCs from the RVOT were noted to have polymorphic VT or VF that was initiated by one of the PVCs [62]. In contrast to the first study, the coupling interval of the PVCs in patients who developed malignant arrhythmias was not different from that in 85 other patients with RMVT who did not have malignant arrhythmias. Radiofrequency (RF) ablation successfully eliminated the RVOT PVCs in 13 patients and modified the PVCs in the other three. Over a mean follow-up of 54 months, none had recurrent VF or syncope. (See 'Radiofrequency ablation' below.)

The prevalence of this malignant variant, and whether it represents a distinct disorder from RMVT, is unclear. The high frequency in the above study (16 of 101 patients) is probably a substantial overestimate due to referral bias. In addition, it is possible that some cases categorized as polymorphic VT were simply the common form of RVOT VT in which QRS morphology varied during the tachycardia due to fluctuations in loading conditions. An editorial accompanying this report addressed the issue of whether RF ablation should now be considered in all patients with RMVT [63]. Due to the relatively high prevalence of RVOT PVCs, the rarity of malignant RVOT VT/VF, it is reasonable to focus concern on patients with the following higher risk characteristics:

●A history of syncope

●Very fast VT (>230 beats/min)

●Very frequent ectopy (>20,000 PVCs/day)

●PVCs with a short coupling interval

Treatment of RMVT — Therapeutic decisions for RMVT should consider that many patients are young and otherwise healthy. As a result, ablative therapy may be preferable to chronic administration of antiarrhythmic drugs.

Medical therapy — Medical therapy serves two roles in RMVT: termination of the arrhythmia; and prevention of recurrence. RMVT can be terminated with adenosine and beta blockers, all of which interfere with the cAMP-mediated slow inward calcium current [29,40,56-58].

For prevention of recurrence, beta blockers are often used as first-line agents. These drugs are attractive since their side effect profiles are mild in comparison with antiarrhythmic agents [64].

Propranolol has prevented recurrence in as many as 14 of 22 patients with a typical RVOT origin of RMVT [6,65]. However, other studies have found that these agents were much less likely to prevent recurrent RMVT, although the combination of a beta blocker with a class I drug may be useful [9,55].

Class I antiarrhythmic agents (table 2) alone are helpful in some patients. However, class III drugs (sotalol and amiodarone) may be preferred, especially in patients with arrhythmia that is refractory to other drugs [9].

Radiofrequency ablation — Due to the limited efficacy and potential side effects of antiarrhythmic drugs, there has been increasing use of radiofrequency (RF) ablation in patients with symptomatic RMVT. Professional society guidelines for the management of ventricular arrhythmias and the prevention of SCD indicate that there is evidence and/or general agreement supporting RF ablation in patients with symptomatic idiopathic VT that is drug-refractory, or in such patients who are intolerant of drugs or do not desire long-term drug therapy [64].

The 2019 HRS/EHRA/APHRS/LAHRS Expert Consensus Statement on Catheter Ablation of Ventricular Arrhythmias recommended catheter ablation in the following patients with idiopathic VT and without structural heart disease [66,67]:

●Severely symptomatic patients with monomorphic VT.

●Monomorphic VT in patients in whom antiarrhythmic drugs are not effective, not tolerated, or not desired.

●Patients with recurrent sustained polymorphic VT and VF (electrical storm) that is refractory to antiarrhythmic therapy when there is a suspected trigger that can be targeted for ablation.

Success rates for RF catheter ablation range from 80 to 100 percent [28,35,36,40,41,68]. The success rate depends in part upon the location of the focus; the success of catheter ablation for idiopathic VTs in atypical positions is generally not as high as for RVOT locations [36]. The degree of similarity of 12-lead ECG waveforms between VT and a pace map can be used to estimate the likelihood of successful ablation at that site [69]. A mean absolute deviation >12 percent suggests sufficient dissimilarity to dissuade ablation at that site.

Although successful ablation of LVOT tachycardia has been performed using an endocardial approach, coronary venous mapping and percutaneous approaches to the pericardial space have shown that some of these VTs arise from the LV epicardium [28,45,46,68,70]. There have also been several reports of successful ablation of RMVT from the left and right sinuses of Valsalva [43].

Radiofrequency ablation is generally associated with a low rate of procedural complications [28,35-38,40]. (See "Overview of catheter ablation of cardiac arrhythmias", section on 'Complications'.)

Long term follow-up of patients successfully treated with radiofrequency catheter ablation is limited. In two reports of 42 patients in whom all tachycardias were successfully ablated, only five (12 percent) had a detected recurrence during a 2 to 50 month follow-up [68,71].

The likelihood of successful ablation may be less when the site of origin is not endocardial or not definitively identified during mapping [68]. In a review of 75 patients with presumed RVOT VT, the inability to identify a focus, and therefore the success rate, correlated with the QRS duration in lead V2 [72]. The success rate was 95 percent when the QRS duration in V2 during pace mapping was ≥160 ms in duration compared with only 54 percent when the QRS duration was <160 ms. Left-sided and epicardial ablation strategies were not pursued in this experience.

Epicardial ablation — A possible explanation for failed radiofrequency ablation is that the arrhythmia arises from an epicardial rather than an endocardial focus. In one report of failed ablation (either acute failure of the procedure or late recurrence of arrhythmia) in 30 patients with VT (15 with apparently normal hearts), subxiphoid instrumentation of the pericardial space was used for both epicardial mapping and ablation [70]. Twenty-four of the VTs appeared to originate from the epicardium; 17 were successfully ablated, while the other seven had sites that were inaccessible primarily due to interference from the left atrial appendage. Six of these seven patients could be ablated from the left coronary cusp.

PAROXYSMAL SUSTAINED VT — Paroxysmal sustained VT is another clinical syndrome of idiopathic right ventricular tachycardia that resembles RMVT in many ways [6,9,13,73]. The most frequent QRS morphology is a left bundle branch block with an inferior axis, and the typical site of origin is the superior septal aspect of the RVOT. Furthermore, patients with paroxysmal sustained VT appear to respond to antiarrhythmic agents, particularly adenosine, in a manner similar to patients with RMVT, although data are limited [73].

Because of these similarities, it is not clear if paroxysmal sustained VT is a distinct clinical syndrome. Compared with nonsustained RMVT, this disorder is more often symptomatic and less often exercise-provoked. It is also more frequently induced by programmed stimulation, although isoproterenol may facilitate induction in some cases.

On the other hand, some investigators dispute the existence of paroxysmal sustained VT as a syndrome distinct from RMVT. One study, for example, found that 58 percent of patients with RMVT had at least one episode of sustained VT [9]. In addition, electrophysiologic studies may reproduce sustained VT in patients who present with only nonsustained VT (particularly during isoproterenol infusion) or vice versa. It has also been suggested that the incidence of sudden cardiac death in RMVT is actually due to overlap with paroxysmal sustained VT. For these reasons, the two syndromes are occasionally considered together as idiopathic right ventricular tachycardia, or simply as RMVT.

IDIOPATHIC LEFT VENTRICULAR TACHYCARDIA — Idiopathic left ventricular tachycardia (ILVT) was first described in 1979 [74]. Belhassen was the first to report the characteristic termination of this VT with intravenous verapamil [75], accounting for its two descriptive eponyms: Belhassen VT and verapamil-responsive VT.

Clinical features — The typical patient with ILVT presents at age 20 to 40, but often reports symptomatic episodes dating back to adolescence. The clinical characteristics of ILVT appear to be more uniform than those of the idiopathic RV tachycardias [10,75-80].

●It has a more variable association with physical activity, and is not usually provoked by exercise.

●It frequently produces symptoms such as palpitations and presyncope; syncope is uncommon.

●Cardiac arrest is rare, but isolated cases have been reported [78].

●Tachycardia-related cardiomyopathy has been reported, but is unusual since episodes are typically infrequent.

Site of origin — Endocardial mapping during the VT demonstrates that the site of earliest activation is the inferoseptal region of the left ventricle in patients with a left frontal axis [10]. Mapping for catheter ablation also consistently localizes this VT to the inferior aspect of the midseptal region [81]. By comparison, the anterosuperior left ventricle is the initial site in those patients with VT that has a right frontal axis [10,78,82].

Electrocardiographic features — Corresponding to its left ventricular origin, ILVT has a right bundle branch block morphology with a left superior frontal plane axis and a relatively narrow QRS duration (typically 0.12 to 0.14 sec) (waveform 3). A small subset of patients with ILVT has a right frontal plane (2 of 16 in one report) [10].

ILVT is often confused with supraventricular tachycardia because of its characteristic ECG morphology, and the response to verapamil (see below).

The signal averaged ECG in the time domain is usually normal during sinus rhythm. However, frequency analysis using fast Fourier transform has shown an abnormal high-frequency component of the initial portion of the QRS complex that may distinguish these patients from normals [83].

Electrophysiologic features — ILVT is typically reproduced in the electrophysiology laboratory using programmed stimulation employing extrastimuli and, on occasion, with rapid atrial or ventricular pacing [10,38,74-80]. In contrast to RMVT, ILVT is not usually provoked by isoproterenol infusion.

These observations, coupled with the response of ILVT to pacing (entrainment), support a reentrant mechanism [82]. Further support for a reentrant mechanism comes from several mapping studies:

●One report identified a mid-diastolic potential and a single fused presystolic Purkinje potential at the VT exit site during VT [84]. This observation suggests a macroreentry circuit involving the normal Purkinje system and abnormal Purkinje tissue that manifests decremental properties and verapamil sensitivity.

●A second study using electroanatomic mapping found that, during sinus rhythm, only patients with ILVT had a retrograde potential originating from the left posterior Purkinje fiber; diastolic potentials during ILVT coincided with the earliest retrograde Purkinje potential during sinus rhythm [81].

The His bundle is commonly activated early in a retrograde fashion during ILVT, and a distinct Purkinje spike typically precedes the onset of the QRS (image 1) [76]. However, the retrograde His bundle deflection can be dissociated from the QRS complex by premature stimulation in the ventricle, atrium, or His region, implying that the reentrant circuit does not require the His bundle [78,80]. These findings also suggest that the posterior fascicle of the left bundle branch may be a part of, or at least in close proximity to the VT circuit (figure 2A-B). The terms fascicular ventricular tachycardia and fascicular tachycardia been used to describe this arrhythmia [80,85,86].

Treatment of ILVT — Verapamil is usually effective in the treatment of ILVT, both for the termination of acute episodes and the prevention of recurrence [10,78-80,85]. Verapamil can be given 5 to 10 mg IV bolus over two minutes; if no response, an additional 10 mg IV bolus may be administered 15 to 30 minutes following the initial dose.

In one report, for example, intravenous verapamil terminated the arrhythmia in 13 of 14 patients and was effective in all five patients who required long-term oral therapy for symptom control [10]. By comparison, vagal maneuvers, beta blockers, and lidocaine are often ineffective. There is little reported experience with the use of other antiarrhythmic drugs; the class III agents are the most effective among those tested, while class I drugs are rarely of benefit [9].

Catheter ablation has been performed with efficacy rates of 85 to 100 percent in patients with resistant or incessant ILVT or those intolerant of medications [28,38,76,77,84,87]. Selection of ablation target sites focuses on pace mapping techniques and/or activation mapping, with particular attention to the mid-diastolic potential and/or presystolic Purkinje activation [76,84]. Electroanatomic mapping and identification of the earliest retrograde Purkinje potential can also be used for guiding ablation [81].

Reported series of catheter ablation for ILVT, although small, have demonstrated a high rate of chronic arrhythmia control and relative freedom from procedural complications [76,77,87]. In one report, for example, 17 successfully ablated patients were followed for a mean of seven months [77]. No patient had a recurrent symptomatic tachyarrhythmia, and in the six who were and underwent repeat electrophysiology study, the tachycardia could not be induced.

SPORADIC POLYMORPHIC VT IN THE STRUCTURALLY NORMAL HEART — Polymorphic VT may present in patients with no significant structural heart disease and no family history who do not have catecholaminergic polymorphic VT (CPVT). One study evaluated 15 such patients who presented with syncope, presyncope, or cardiac arrest [88]. The arrhythmia was induced by exercise in four and by coronary vasospasm in two.

Electrophysiologic similarities may exist between rapid polymorphic VT in the normal heart and idiopathic ventricular fibrillation (VF). As an example, idiopathic VF is often initiated by a PVC with a very short coupling interval; polymorphic VT may also be preceded by a short-long-short cardiac cycle. (See "Approach to sudden cardiac arrest in the absence of apparent structural heart disease", section on 'Idiopathic VF'.)

Prior to making this diagnosis, cardiac catheterization with coronary angiography is necessary to exclude the presence of obstructive coronary artery disease. Some individuals with sporadic disease have undergone genetic testing; some but not all of these patients have de novo mutations similar to mutations observed in patients with familial disease, and have therefore been classified as having CPVT [89-91].

Chronic therapy — There are presently no consensus treatment guidelines for the management of sporadic polymorphic VT in an otherwise normal heart. Therapy may be directed by the following observations:

●Chronic beta blocker administration may be effective in some patients whose polymorphic VT is reproducibly initiated by an infusion of isoproterenol or by exercise, a characteristic also seen with familial disease [88].

●The use of pacing, beta blockers, and calcium channel blockers alone or in combination may be effective if the arrhythmia is pause-dependent.

●Occasional patients with frequent uniform PVC triggering recurrent polymorphic VT or VF may be treated by catheter ablation of the PVCs when other methods fail.

However, an implantable cardioverter-defibrillator (ICD) is often the treatment of choice because patients with polymorphic VT and minimal or no structural heart disease are at risk for sudden death, and respond erratically to antiarrhythmic drugs [88,92]. Similar recommendations apply to patients with idiopathic VF. Pharmacologic or ablative therapy remains necessary in addition to the ICD for suppression of frequent arrhythmias (that result in ICD shocks). (See "Early repolarization".)

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: Inherited arrhythmia syndromes" and "Society guideline links: Ventricular arrhythmias" and "Society guideline links: Cardiac implantable electronic devices" and "Society guideline links: Catheter ablation of arrhythmias".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Catheter ablation for the heart (The Basics)")

●Beyond the Basics topic (see "Patient education: Catheter ablation for abnormal heartbeats (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Malignant ventricular arrhythmias usually occur in the presence of significant structural heart disease. Less commonly, ventricular tachycardia (VT) and ventricular fibrillation (VF) occur in hearts that appear normal but in fact, contain less visible abnormalities including derangements of cardiac ion channels or structural proteins. Idiopathic VT syndromes, including repetitive monomorphic VT, paroxysmal sustained VT, and idiopathic left ventricular tachycardia, occur in structurally normal hearts and have a more benign prognosis. (See 'Introduction' above.)

●Idiopathic VT syndromes account for approximately 10 percent all patients referred for evaluation of VT, with the mean age of patients with an idiopathic VT being less than that of patients with VT secondary to underlying heart disease. Distinguishing an idiopathic VT syndrome from other monomorphic VT syndromes is important given the far better prognosis, greater array of antiarrhythmic drug options, and amenability to cure with ablation. (See 'Idiopathic VT' above.)

●The diagnostic evaluation to establish the presence and type of heart disease in patients with sustained VT generally includes various invasive and noninvasive techniques, depending in part upon the clinical history and presentation. These include electrocardiography (ECG), echocardiography, exercise treadmill testing, signal averaged ECG, coronary angiography, endomyocardial biopsy, or magnetic resonance imaging. (See 'General approach' above and "Sustained monomorphic ventricular tachycardia: Clinical manifestations, diagnosis, and evaluation", section on 'Additional diagnostic evaluation'.)

●Repetitive monomorphic VT (RMVT), also called right ventricular outflow tract (RVOT) VT, is a triggered arrhythmia that is characterized by frequent short "salvos" of nonsustained VT. The most common symptoms associated with RMVT are palpitations and lightheadedness, typically occurring during or immediately after exercise or emotional stress, although a significant proportion of patients are asymptomatic. Most RMVT episodes have a characteristic ECG appearance with left bundle branch block appearance and an inferior axis. (See 'Repetitive monomorphic VT' above.)

●Treatment decisions for RMVT should consider that many patients are young and otherwise healthy, and as a result, ablative therapy may be preferable to chronic administration of antiarrhythmic drugs. RMVT can be terminated with adenosine, verapamil, and beta blockers, with beta blockers also often used as first-line agents to prevent recurrence. While class I and III antiarrhythmic drugs are effective in many patients, catheter ablation is frequently preferred given its high success rate and low rate of associated complications. (See 'Treatment of RMVT' above.)

●Paroxysmal sustained VT is another clinical syndrome of idiopathic VT that resembles RMVT in many ways. The QRS morphology on ECG is frequently a left bundle branch block pattern with an inferior axis, and patients typically respond to antiarrhythmic agents, particularly adenosine, in a manner similar to patients with RMVT. However, paroxysmal sustained VT is more often symptomatic and less often exercise-provoked than RMVT. (See 'Paroxysmal sustained VT' above.)

●Idiopathic left ventricular tachycardia (ILVT), also called Belhassen VT or verapamil-responsive VT, is not usually provoked by exercise and, while frequently associated with symptoms of palpitations and presyncope, is rarely associated with syncope of cardiac arrest. ILVT has a right bundle branch block morphology with a left superior frontal plane axis and a relatively narrow QRS duration (typically 0.12 to 0.14 sec). Verapamil is usually effective in the treatment of ILVT, both for the termination of acute episodes and the prevention of recurrence. Additionally, catheter ablation is highly successful in curing ILVT. (See 'Idiopathic left ventricular tachycardia' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Leonard Ganz, MD, FHRS, FACC, who contributed to an earlier version of this topic review.