To determine cardiac involvement, a 12-lead ECG and echocar- diogram are important for the initial clinical assess- ment, independent of symptom status. In general, the more extensive the cardiac involvement, includ- ing evidence of distal conduction disease, ven- tricular dysfunction, and atrial arrhythmias, the more likely a VA will occur. The initial evaluation for myotonic dystrophy patients includes ambula- tory monitoring. In asymptomatic patients, some experts advocate for annual follow-up during the concealed phase of the disease with an annual Table 9. Neuromuscular Disorders Associated With Heart Disease Muscular Dystrophy Inheritance Gene/Protein Affected Primary Cardiac Pathology Frequency of Cardiac Involvement Causes of Death Associated With Sudden Death? Duchenne X-linked recessive Dystrophin NICM >90% Respiratory, HF Yes, uncertain etiology Becker X-linked recessive Dystrophin NICM 60% 75% HF, respiratory Yes, uncertain etiology Limb-girdle type 1B Autosomal dominant Lamin A/C Conduction system disease and NICM >90% Sudden, HF Yes Limb-girdle type 2C-2F Autosomal recessive Sarcoglycan NICM <25% Respiratory, HF Uncertain Limb-girdle type 2I Autosomal recessive Fukutin-related protein NICM 20% 80% Respiratory, HF Uncertain Myotonic type 1 Autosomal dominant CTG repeat expansion Conduction system disease and NICM sudden, HF 30% of deaths, uncertain bradycardia versus tachycardia Myotonic type 2 Autosomal dominant CCTG repeat expansion Conduction system disease 10% 25% Normal causes Reported Emery-Dreifuss X-linked and autosomal dominant or recessive Emerin, Lamin A/C Conduction system disease and NICM >90% Sudden, HF Yes Facioscapulohumeral Autosomal dominant D4Z4 repeat contraction Possibly conduction disease 5% 15% Normal causes, respiratory rarely Not reported HF indicates heart failure; and NICM, nonischemic cardiomyopathy. Adapted with permission from Groh, et al.S7.8 15 CLINICAL STATEMENTS AND GUIDELINES 12-lead ECG to screen for development of conduc- tion abnormalities. 