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The potentially lifesaving impact of ICDs is not without device-associated morbidity Forty percent of children may experience an ICD-related complication (29% inappropriate shock).231 The majority of patients who received an inappropriate shock had either sinus tachycardia (48%) or supraventricular tachycardia (19%) Although there was no difference in the frequency of inappropriate shock among patients on medication at the time of ICD implantation, it is unclear whether more aggressive medical therapy may mitigate this risk There are promising early data using subcutaneous ICDs in adults with HCM, but further study is needed before this approach can be recommended.263 Disease-Modifying Therapy Greater understanding of the molecular pathways underlying HCM has led to greater interest in the potential of disease-modifying therapy Thus far, trials exploring the use of medical therapy have been negative.97,264 Recruitment is ongoing for the VANISH99 and LIBERTY-HCM98 trial investigating the role of valsartan and eleclazine in medical therapy for HCM Exercise restrictions in HCM are largely based on expert guidelines; it remains unclear if there is an appropriate level of activity that may help to maintain long-term cardiovascular health while minimizing the risk of cardiac events Preliminary evidence suggests moderate-intensity monitored exercise may be safe and associated with improvement in exercise capacity265; however, this topic requires far more scrutiny and evaluation before the current exercise recommendations can be modified Dilated Cardiomyopathy Definition DCM is defined as left ventricular dilation and systolic dysfunction in the absence of coronary artery disease, pericardial disease, or abnormal loading conditions sufficient to cause functional impairment.2 DCM may be primary or secondary; however, the phenotype is a common final response to genetic or environmental injury Epidemiology The overall annual incidence of DCM in children is 0.6 to 0.7 cases per 100,000 population per year, although there is an age-dependent risk, with the highest incidence in patients less than 1 year of age.266–270 There is also age-dependent penetrance, with a much higher prevalence of DCM and asymptomatic dysfunction in the community.271 There is no gender predominance; however, there is obviously an increased frequency of males affected among patients with X-linked disease (e.g., neuromuscular disease).266–269,272 Clinical Outcomes Although the overall 1- and 5-year freedom from death or transplant is about 70% and 60%, respectively, the clinical outcomes vary by cause (Fig 61.7).266,270,272,273 Overall survival has improved with time; however, the majority of the survival benefit is secondary to the increased utilization of heart transplantation.274,275 Older age (>5 to 6 years of age), worse systolic function, and greater left ventricular dilation are risk factors for adverse outcomes (composite outcome of death or transplantation).272,276 Approximately one-third of patients will experience normalization of function, with higher rates of recovery among younger patients and patients with better initial systolic function.273,277,278 The rates of recovery in patients with myocarditis have been alternately described as higher and lower than those of patients with idiopathic or familial DCM.273,277,278 There appear to be no differences in outcome among patients with idiopathic and those with familial DCM.276 FIG 61.7 Freedom from death or transplantation in children with dilated cardiomyopathy according to underlying cause DCM, Dilated cardiomyopathy Etiology DCM is associated with a number of genetic causes (see Table 61.1) Approximately 30% to 50% of all patients with DCM have familial disease.279 Data from the Pediatric Cardiomyopathy Registry and National Australian Childhood Cardiomyopathy Study classify approximately 10% to 15% of patients as having familial disease, whereas individual centers describe a slightly higher yield (approximately 25%).267,276,280,281 Studies examining the frequency of a positive genetic test range from 15% to 50%.281–283 The discrepancy in the results is likely due to differences in the population (especially age) as well as variable criteria used to assess pathogenicity Estimates regarding the yield are also complicated by the evolving assessment of mutation pathogenicity The yield of genetic testing may be increased by as much as 70% through the use of multidisciplinary clinics, including cardiology and genetics.280 ... DCM is associated with a number of genetic causes (see Table 61.1) Approximately 30% to 50% of all patients with DCM have familial disease.279 Data from the Pediatric Cardiomyopathy Registry and National Australian Childhood Cardiomyopathy Study classify approximately 10% to 15% of... yield of genetic testing may be increased by as much as 70% through the use of multidisciplinary clinics, including cardiology and genetics.280