Chapter 23

Note: Not all criteria are needed for diagnosis of hypertrophic cardiomyopathy.

• Asymmetric hypertrophied nondilated ventricle with septal to posterior wall end-diastolic thickness ≥ 1.3 cm not explained by other etiologies.
• Ejection murmur that increases with Valsalva with or without concomitant mitral regurgitation murmur and preserved aortic second sound.
• Increased gradients causing obstruction across left ventricular outflow tract and/or mid ventricle with characteristic late peaking “dagger”-shaped Doppler velocity profile.
• Mitral systolic anterior motion with varying degree of mitral regurgitation.
• Midsystolic aortic valve closure.
• Impaired diastolic function with decrease in tissue Doppler (early diastolic velocity [E′]) and longitudinal strain.

### Definition & Prevalence

Hypertrophic cardiomyopathy (HCM) is a disorder of the myocardium caused by mutations of the sarcomere or sarcomere-associated proteins. It mainly manifests as symmetric or asymmetric left ventricular hypertrophy (LVH) > 1.5 cm (Figure 23–1) in a nondilated ventricle unexplained by other cardiac or systemic causes of hypertrophy (see Table 23–1 for differential diagnosis of LVH). HCM has numerous alternate names such as idiopathic hypertrophic subaortic stenosis (IHSS) or asymmetrical septal hypertrophy (ASH). However, HCM is the widely preferred term for this condition as segmental hypertrophy can occur in any segment of the ventricle, not just the septum. Coexistent right ventricular (RV) hypertrophy and RV outflow obstruction occur less commonly in biventricular involvement.

###### Figure 23–1.

Parasternal long axis view in diastole showing asymmetric septal hypertrophy (white arrow) compared to the inferolateral wall.

Table 23–1. Differential Diagnosis of Left Ventricular Hypertrophy

HCM is relatively common (1 in 500) in the general population with about 750,000 people affected in the United States. Although it is the most common cause of sudden death in the young (< 35 years old) in North America, most people afflicted with HCM live a normal life. Contrary to the long mistaken notion that HCM was a uniformly fatal disease associated with a shortened life span, HCM patients may live well into their sixth to eighth decades, with patients older than age 90 with HCM being reported. Moreover, the first clinical recognition of HCM may occur when patients are in their sixth to eighth decade of life; usually these patients have milder forms of the disease with the most serious complications being uncommon after age 60. The natural history of HCM can take many paths: sudden cardiac death, symptomatic HCM heart failure, end-stage cardiomyopathy, atrial fibrillation, and stroke. However, if intervened upon in a timely manner, HCM can potentially have no effect on normal longevity.

### Genetics & Histopathology

The genetics of HCM involve an autosomal dominant pattern of inheritance, with 60–70% of patients having an affected family member. HCM is more common in males than females. Common genes affected include β-myosin heavy chain, myosin binding protein C, troponin I, and troponin T, but numerous others have been described. Mutations of the sarcomeric proteins lead to histopathologic evidence of myocardial disarray, which then leads to pathologic hypertrophy and patchy fibrosis of the myocardium. Intramural vessels are also frequently abnormal in HCM with thrombotic obliteration causing ischemia, which may propagate fibrosis regardless of presence of epicardial coronary disease. The genetic basis of ventricular hypertrophy does not always correlate with prognosis. Patients with tropomyosin mutations have only a mild degree of ventricular hypertrophy, with little or no left ventricular (LV) outflow tract obstruction, ...

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