- Hypertrophic cardiomyopathy (HCM) is a myocardial disorder characterized by ventricular hypertrophy, diminished LV cavity dimensions, normal or enhanced contractile function, and impaired ventricular relaxation.
- The idiopathic form of HCM has an early onset (as early as the first decade of life) without associated HTN.
- An acquired form also occurs in elderly patients with chronic HTN.
- The pathophysiologic change in HCM is myocardial hypertrophy that is typically predominant in the ventricular septum (asymmetric hypertrophy) but may involve all ventricular segments equally.
- Many cases of HCM have a genetic component, with mutations in the myosin heavy-chain gene that follow an autosomal-dominant transmission with variable phenotypic expression and penetrance.
- HCM can be classified according to the presence or absence of LV outflow tract obstruction.
- LV outflow obstruction may occur at rest, but is enhanced by factors that increase LV contractility or decrease ventricular volume.
- Delayed ventricular diastolic relaxation and decreased compliance are common and may lead to pulmonary congestion.
- Myocardial ischemia is frequently secondary to a myocardial oxygen supply-demand mismatch.
- Systolic anterior motion of the anterior leaflet of the mitral valve often is associated with MR and may contribute to LV outflow tract obstruction.
- Presentation varies but may include dyspnea, angina, arrhythmias, syncope, cardiac failure, or sudden death.
- Sudden death is most common in children and young adults between the ages of 10 and 35 years and often occurs during periods of strenuous exertion.
- Family history of HCM is suggestive of the familial subtype.
- Physical findings include bisferious carotid pulse (in the presence of obstruction).
- Forceful double or triple apical impulse and a coarse systolic outflow murmur localized along the left sternal border that is accentuated by maneuvers that decrease preload (e.g., standing, Valsalva maneuver) may also be found.
Imaging and Diagnostic Studies
- The ECG may show conduction system disease or low voltage, in contrast to the increased voltage seen with ventricular hypertrophy.
- Two-dimensional echocardiography and Doppler flow studies can establish the presence of a significant LV outflow gradient at rest or with provocation.
- Additional risk stratification should be pursued with 24- to 48-hour Holter monitoring and exercise testing.
- Management is directed toward relief of symptoms and prevention of endocarditis, arrhythmias, and sudden death.
- Treatment in asymptomatic individuals is controversial, and no conclusive evidence has been found that medical therapy is beneficial.
- All individuals with HCM should avoid strenuous physical activity, including most competitive sports.
- Î²-Adrenergic antagonists may reduce symptoms of HCM by reducing myocardial contractility and heart rate. However, symptoms may recur during long-term therapy.
- Calcium channel antagonists, particularly verapamil and diltiazem, may improve the symptoms of HCM, primarily by augmentation of diastolic ventricular filling.
- Therapy should be initiated at low doses, with careful titration in patients with outflow obstruction. The dose should be increased gradually over several days to weeks if symptoms persist. Dihydropyridines should be avoided in patients with LV outflow tract obstruction as a result of their vasodilatory properties.
- Diuretics may improve pulmonary congestive symptoms in patients with elevated pulmonary venous pressures. These agents should be used cautiously in patients with severe LV outflow obstruction because excessive preload reduction worsens the obstruction.
- Nitrates and vasodilators should be avoided because of the risk of increasing the LV outflow gradient.
- Atrial and ventricular arrhythmias occur commonly in patients with HCM.
- Supraventricular tachyarrhythmias are tolerated poorly and should be treated aggressively; cardioversion is indicated if hemodynamic compromise develops.
- Digoxin is relatively contraindicated because of its positive inotropic properties and potential for exacerbating ventricular outflow obstruction.
- Atrial fibrillation should be converted to sinus rhythm when possible, and anticoagulation is recommended if paroxysmal or chronic atrial fibrillation develops.
- Diltiazem, verapamil, or Î²-adrenergic antagonists can be used to control the ventricular response before cardioversion. Procainamide, disopyramide, or amiodarone may be effective in the chronic suppression of atrial fibrillation.
- Patients with NSVT detected on ambulatory monitoring are at increased risk for sudden death. However, the benefit of suppressing these arrhythmias with medical therapy has not been established, and the risk of a proarrhythmic effect of antiarrhythmic drugs exists.
- ICD placement should be considered in high-risk patients: those with genetic mutations associated with SCD; prior SCD or sustained ventricular tachyarrhythmia; a history of syncope or near-syncope, recurrent or exertional, in young patients; multiple nonsustained episodes of VT on Holter recordings; hypotensive response to exercise; LV hypertrophy with a wall thickness >30 mm in young patients; and a history of sudden, premature death in close relatives.33 There is very limited benefit for invasive electrophysiologic testing in the risk stratification of patients with HCM.
- Dual-chamber pacing (see Chapter 7, Cardiac Arrhythmias) improves symptoms in some patients with HCM.34 Alteration of the ventricular activation sequence via right ventricular (RV) pacing may minimize LV outflow tract obstruction secondary to asymmetric septal hypertrophy.
- Only 10% of the patients with HCM meet the criteria for pacemaker implantation, and the effect on decreasing the left ventricular outflow tract (LVOT) gradient is only 25%. Dual chamber pacing has not been demonstrated to decrease morbidity and mortality in patients with HCM.
- Surgical therapy is useful in the treatment of symptoms but has not been shown to alter the natural history of HCM.
- The most frequently used operative procedure involves septal myotomy-myectomy with or without mitral valve replacement (MVR).
- Alcohol septal ablation, a catheter-based alternative to surgical myotomy-myectomy, seems to be equally effective at reducing obstruction and providing symptomatic relief when compared to the gold standard surgical procedure.
- Cardiac transplantation should be reserved for patients with end-stage HCM with symptomatic HF.