What is the diagnosis and treatment for Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Hypertrophic Obstructive Cardiomyopathy (HOCM): Diagnosis and Management

Diagnosis of HOCM

HOCM is characterized by:

• Left ventricular hypertrophy (typically ≥15 mm in adults) in the absence of other cardiac or systemic diseases capable of producing such hypertrophy 1
• Dynamic left ventricular outflow tract (LVOT) obstruction caused by systolic anterior motion (SAM) of the mitral valve and mitral-septal contact 1
• Genetic inheritance pattern that is typically autosomal dominant, caused by mutations in genes encoding sarcomere proteins 1

Diagnostic criteria include:

• Echocardiography showing asymmetric septal hypertrophy with dynamic LVOT obstruction (resting or provocable gradient ≥30 mm Hg) 1
• LVOT gradients ≥50 mm Hg (either at rest or with provocation) are considered significant and may warrant intervention in symptomatic patients 1
• Cardiac MRI may provide additional diagnostic information, particularly when echocardiographic images are suboptimal 1

Pathophysiology

HOCM leads to symptoms through several mechanisms:

• LVOT obstruction causing increased LV systolic pressure 1
• Prolonged ventricular relaxation and elevated LV diastolic pressure 1
• Mitral regurgitation due to SAM 1
• Myocardial ischemia from supply-demand mismatch 1
• Diastolic dysfunction from increased chamber stiffness and impaired relaxation 1

Management Algorithm

First-Line Medical Therapy

Beta-blockers are the mainstay of pharmacologic therapy for symptomatic patients with HOCM and should be titrated to achieve a resting heart rate of 60-65 bpm 2, 1. Benefits include:

• Negative inotropic effects reducing LVOT obstruction 1
• Attenuation of adrenergic-induced tachycardia 1
• Prolonged diastolic filling period improving diastolic function 1

Second-Line Medical Therapy

For patients unable to tolerate beta-blockers or with persistent symptoms:

• Non-dihydropyridine calcium channel blockers (verapamil or diltiazem) may be used 1, 2
• Caution: Verapamil is potentially harmful in patients with severe dyspnea at rest, hypotension, very high resting gradients (>100 mm Hg), or in infants <6 weeks of age 1, 2

For patients with obstructive HCM who remain symptomatic despite beta-blockers and calcium channel blockers:

• Disopyramide combined with a beta-blocker or verapamil may be effective 1, 2
• Disopyramide should be titrated to 400-600 mg/day in divided doses with QTc monitoring 2

Medications to Avoid in HOCM

• Dihydropyridine calcium channel blockers (e.g., nifedipine) due to vasodilatory effects that may worsen obstruction 1, 2
• Vasodilators (ACE inhibitors, ARBs) may exacerbate outflow obstruction 1, 2
• High-dose diuretics may decrease preload and worsen obstruction 1

Invasive Treatment Options

For patients with severe symptoms (NYHA class III-IV) despite optimal medical therapy and LVOT gradient ≥50 mm Hg, septal reduction therapy should be considered 1:

1. Surgical Myectomy (preferred option):

   • Gold standard for treatment of refractory HOCM 1, 3
   • Particularly appropriate for younger patients, those with extreme hypertrophy, or with concomitant cardiac conditions requiring surgery 1, 4
   • Mortality <1% at experienced centers 3

   • 90% of patients experience improvement by at least two functional classes 3

2. Alcohol Septal Ablation:

   • Alternative for patients with high surgical risk, advanced age, or significant comorbidities 1, 4
   • Should be performed only at experienced centers 1
   • May have higher risk of complete heart block requiring permanent pacemaker 1

Septal reduction therapy should NOT be performed in asymptomatic patients with normal exercise capacity, regardless of gradient severity 1, 2.

Special Considerations

• Patients with atrial fibrillation and HCM should receive anticoagulation regardless of CHA₂DS₂-VASc score 2
• Low-intensity aerobic exercise is reasonable, but strenuous activity and competitive athletics should be avoided 2
• Careful monitoring for complications including heart failure, arrhythmias, and sudden cardiac death is essential 5, 6

Pitfalls to Avoid

• Using verapamil in patients with severe obstruction (>100 mmHg), hypotension, or severe dyspnea at rest 1, 2
• Using disopyramide as monotherapy in patients with atrial fibrillation 2
• Delaying septal reduction therapy in appropriate candidates with refractory symptoms 1
• Performing septal reduction procedures at inexperienced centers 1, 3

With optimal management following current guidelines, patients with HOCM can achieve near-normal life expectancy and significantly improved quality of life 5, 3.