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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 12/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate 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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 13/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate 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]. https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 14/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate 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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 15/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate 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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 16/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate 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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 17/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." th th The Basics patient education pieces are written in plain language, at the 5 to 6 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 th th sophisticated, and more detailed. These articles are written at the 10 to 12 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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 18/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate 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 https://www.uptodate.com/contents/ventricular-tachycardia-in-the-absence-of-apparent-structural-heart-disease/print 19/39 7/6/23, 3:40 PM Ventricular tachycardia in the absence of apparent structural heart disease - UpToDate The UpToDate editorial staff acknowledges Leonard Ganz, MD, FHRS, FACC, who contributed to an earlier version of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Brooks R, Burgess JH. Idiopathic ventricular tachycardia. A review. Medicine (Baltimore) 1988; 67:271. 2. Belhassen B, Viskin S. 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