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PATIENT CASE

A 17-year-old adolescent boy presented to the general cardiology clinic for family screening after a maternal aunt had been diagnosed with hypertrophic cardiomyopathy (HCM). He had no history of chest pain, breathlessness, or syncope. He reported mild symptoms of postural hypotension. Examination revealed normal first and second heart sounds with an audible and palpable fourth heart sound, but no murmurs. His electrocardiogram (ECG) demonstrated left ventricular hypertrophy (LVH) with repolarization abnormalities, and echocardiographic and cardiac magnetic resonance imaging (MRI) features of severe asymmetric LVH are noted in this patient (Figure 10-1). He had no evidence of arrhythmia on ambulatory Holter monitoring, but exercise testing demonstrated an abnormal blood pressure response on exercise. Familial genetic testing was performed and identified a pathogenic mutation in the sarcomere gene MYL3. Given his risk factor profile for sudden cardiac death (SCD), an automatic implantable cardioverter defibrillator (AICD) was implanted for primary prevention.

Figure 10-1

Classic asymmetric left ventricular hypertrophy (LVH) in hypertrophic cardiomyopathy (HCM). Marked hypertrophy (*) of the interventricular septum is noted on both echocardiography (upper panel) and cardiac magnetic resonance imaging (MRI) (lower panel).

EPIDEMIOLOGY

  • HCM represents the most common inherited cardiac disorder and is a global disease with no racial or ethnic preponderance.1 A reported prevalence of approximately 0.2% (1:500) has been reported consistently in epidemiological studies.1

  • Age-related penetrance is a key feature of the disease, with onset and progression of hypertrophy occurring at virtually any age.

  • Importantly, it is the most common cause of SCD in young people (<35 years of age) and athletes.2

CLINICAL DEFINITION

  • HCM represents a primary disease of the myocardium. The hallmark of the disease is the presence of increased left ventricular (LV) wall thickness in the absence of another cardiac or systemic disease that could result in a similar degree of myocardial hypertrophy.

  • On a microscopic level there is extensive disarray of myocytes and myofibrils, as well as thickening of the intramural microvessels and interstitial fibrosis.

ETIOLOGY

  • In adults and adolescents, the disease typically exhibits an autosomal dominant pattern of inheritance. In around 40% to 60% of cases, a mutation in 1 of the genes encoding sarcomeric proteins is identified.

  • In up to 10% of cases in adults another underlying genetic disorder may be the cause of the HCM phenotype. In addition, nongenetic causes also account for some cases of unexplained LVH.3,4

DIFFERENTIAL DIAGNOSIS

  • LVH can represent either a physiologic (athlete’s heart) or pathologic cardiac response that can occur in a variety of cardiac, genetic, and systemic diseases (Figure 10-2), or in response to hemodynamic loading of the ventricle (arterial hypertension and aortic stenosis).

  • Accurate identification of the underlying etiology is critical given that HCM is a ...

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