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September 25, 2018 Circulation. 2018;138:e272–e391. DOI: 10.1161/CIR.0000000000000549 e324

CLINICAL STATEMENTS AND GUIDELINES 12-lead ECG to screen for development of conduction abnormalities. However, the optimal frequency of electrocardiographic screening is unknown.S7.8-18 Once cardiac involvement is present, either on the basis of conduction delay, atrial arrhythmias, or ventricular dysfunction, a low threshold for investigating symptoms or electrocardiographic findings by the clinician to determine the need for pacemaker implantation, invasive electrophysiological studies, or ICD implantation is optimal. 4.	 Up to one third of deaths in myotonic dystrophy patients are sudden.S7.8-9 Although commonly attributed to conduction block and asystole, SCD due to VT/VF has been recognized in patients with functioning permanent pacemakers, and spontaneous VA have been documented in some.S7.8-13,S7.8-19 The risk of SCD in patients with pacemakers suggests that an ICD may be preferred to a pacemaker. However, these patients are also at high risk of respiratory failure as a competing cause of death. Therefore, in patients with severe skeletal muscle involvement, a pacemaker or ICD may not improve outcomes.S7.8-15 A shared decision-making approach to selecting ICD or pacing therapy is warranted. Compared with myotonic type 1 patients, myotonic dystrophy type 2 patients are not well studied but may also benefit from the same approach.

7.9 Cardiac Channelopathies

Recommendations for Cardiac Channelopathies References that support the recommendations are summarized in Online Data Supplement 39.

COR LOE Recommendations

I B-NR 1. In first-degree relatives of patients who have a causative mutation for long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, short QT syndrome, or Brugada syndrome, genetic counseling and mutation-specific genetic testing are recommended.S7.9-1–S7.9-6

I B-NR 2. In patients with a cardiac channelopathy and SCA, an ICD is recommended if meaningful survival of greater than 1 year is expected.S7.9-7–S7.9-13

Synopsis

Implantation of an ICD in asymptomatic low-risk patients with a cardiac channelopathy for a positive family history of SCD as the sole indication is unsupported by published data.S7.9-13–S7.9-18

Recommendation-Specific Supportive Text

1.	 Clinical screening of first-degree relatives of patients with inherited arrhythmia syndromes is crucial to identifying affected family members. Due to the increased risk of adverse cardiac events in genotype positive patients with long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and Brugada syndrome, targeted screening for the identified family-specific mutation can identify individuals who are at risk for these adverse outcomes.S7.9-

2–S7.9-5 Screening ECGs may be insufficient for diagnosis, because the resting ECG in patients with catecholaminergic polymorphic ventricular tachycardia is normal, and as many as 25% of genotype-positive patients with long QT syndrome have QTc intervals  ≤440 ms.S7.9-2 Due to the increased risk of adverse cardiac events in young patients with long QT syndrome and catecholaminergic polymorphic ventricular tachycardia,S7.9-2,S7.9-19–S7.9-22 screening infants and young children is particularly important to guide therapy and institute preventive measures, including the avoidance of possible provocative medications (www.crediblemeds.org).S7.9-23 However, because up to 15% of mutations previously associated with catecholaminergic polymorphic ventricular tachycardia do not appear to cause disease,S7.9-24 caution is advised to avoid unnecessary treatment or sports restriction in phenotype-negative catecholaminergic polymorphic ventricular tachycardia mutation positive individuals. Notably, some patients may prefer not to undergo genetic testing, so genetic counseling should focus on this issue. 2.	 Patients with cardiac channelopathies (ie, long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, early repolarization syndrome, and short QT syndrome) and prior SCA have a significantly increased risk of subsequent SCA or SCD.S7.9-7–S7.9-13,S7.9-25–S7.9-28 Implantation of an ICD reduces the risk of death in high-risk patients.S7.9-9,S7.9-29–S7.9-31 Appropriate ICD therapy for VF/fast VT is reported in 8% to 33% of channelopathy patients, while inappropriate shocks and device complications are reported in 8% to 35%.S7.9-10,S7.9-29,S7.9-30,S7.9-32–S7.9-36 To minimize inappropriate shocks, concurrent beta blockers in long QT syndrome and catecholaminergic polymorphic ventricular tachycardia patients, optimal device programming, and appropriate lead selection are necessary. Ventricular pacing without ICD implantation was associated with a significant risk of recurrent SCA or SCD in long QT syndrome patients.S7.9-37–S7.9-39 In selected patients with LQT1 in whom the SCA occurred in the absence of beta-blocker treatment, betablocker therapy is offered as an alternative to ICD

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