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September 25, 2018 Circulation. 2018;138:e272–e391. DOI: 10.1161/CIR.0000000000000549 e336

CLINICAL STATEMENTS AND GUIDELINES sensitive.S8.3-1–S8.3-3 These VTs are typically sustained with a QRS that has a right bundle-branch block configuration with a superior axis. Less frequently an inferior axis VT or a relatively narrow QRS VT occurs as a result of alternate reentry paths, also involving a part of the Purkinje system. Beta blockers or verapamil typically terminate these arrhythmias, but they fail to prevent recurrences in some patients.S8.3-1–S8.3-3 The target of catheter ablation for the most common form is usually the distal insertion of the anterograde limb of the Purkinje system along the inferior portion of the LV septum near its junction with the left posterior fascicle. Catheter ablation is acutely successful in >90% of patients with a risk of recurrence of approximately 10%. This VT may resemble fascicular VA that are due to a focal mechanism in the left anterior or left posterior fascicles of the LV His-Purkinje system. These fascicular arrhythmias usually have a focal mechanism with the target of catheter ablation being the site of earliest electrical activation recorded with a presystolic fascicular potential. Catheter ablation is highly effective for intrafascicular and fascicular VA. Serious complications are infrequent and include bleeding at the site of arterial or venous access and a small risk of bundle branch block or atrioventricular block. 2.	 Idiopathic LVT is based on reentrant mechanism involving tissue with slow conduction properties along the LV septum as the anterograde limb and the normal left posterior fascicle of the His- Purkinje system as the retrograde limb. The slow conduction zone is verapamil-sensitive.S8.3-3–S8.3-6 These arrhythmias typically have a right bundlebranch block morphology with superior axis, though reversal of the circuit may produce a relatively narrow QRS during VT. Verapamil typically terminates these arrhythmias in the anterograde slow conduction zone.S8.3-3–S8.3-6

3.	 Although no RCTs have been published, the chronic use of oral verapamil for verapamil-sensitive idiopathic LVT has been reported to control this tachycardia in many patients, including both adults and children.S8.3-5,S8.3-8–S8.3-10

8.4 Idiopathic Polymorphic VT/VF

Recommendations for Idiopathic Polymorphic VT/VF References that support the recommendations are summarized in Online Data Supplement 49.

COR LOE Recommendations

I B-NR 1. In young patients (<40 years of age) with unexplained SCA, unexplained near drowning, or recurrent exertional syncope, who do not have ischemic or other structural heart disease, further evaluation for genetic arrhythmia syndromes is recommended.S8.4-1–S8.4-8 I B-NR 2. In patients resuscitated from SCA due to idiopathic polymorphic VT or VF, an ICD is recommended if meaningful survival greater than 1 year is expected.S8.4-9–S8.4-13

I B-NR 3. For patients with recurrent episodes of idiopathic VF initiated by PVCs with a consistent QRS morphology, catheter ablation is useful.S8.4-11,S8.4-14

Recommendation-Specific Supportive Text

1.	 When combined with clinical evaluation, genetic testing can provide a diagnosis in up to 13% to 60% of younger (<40 years of age) survivors of SCA,S8.4-3 with the most common genotypes identified associated with long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and Brugada syndrome.S8.4-8 Drowning/ near drowning events are particularly associated with LQT1 and catecholaminergic polymorphic ventricular tachycardia; genetic mutations in long QT syndrome and catecholaminergic polymorphic ventricular tachycardia have been identified in 23% of patients with unexplained near-drowning episodes.S8.4-15 In 1 study,S8.4-6 exertion-related cardiac arrest, particularly in children, may be related to long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, or to calmodulin/triadin-mediated long QT syndrome/ catecholaminergic polymorphic ventricular tachycardia mutations, which may require additional specialized genetic testing.S8.4-1,S8.4-2,S8.4-4,S8.4-16–S8.4-18 Single-driver auto crashes should prompt the consideration of arrhythmic causes. The yield of genetic testing is higher if a family history of SCD at a young age is present. Referral to specialized genetic testing centers is important if local expertise is unavailable. 2.	 VF in the absence of identifiable structural heart disease or known genetic arrhythmia syndromes such as catecholaminergic polymorphic ventricular tachycardia, long QT syndrome, short QT syndrome, Brugada syndrome, or J wave syndromes is usually the result of short coupled PVCs arising from the Purkinje system in either the right or left ventricles or, less commonly, from the ventricular myocardium.S8.4-9–S8.4-13 The recurrence risk after resuscitation of idiopathic VF is very high.S8.4-12 Among 38 consecutive patients from 6 different centers who underwent ablation of primary idiopathic VF initiated by short coupled PVC, 87% had experienced ≥2 VF episodes in the preceding year.S8.4-12 Because idiopathic VF is associated with

Recommendations for Idiopathic Polymorphic VT/VF (Continued)

COR LOE Recommendations

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