A 22-year-old man is referred to a cardiologist after experiencing a brief loss of consciousness during basketball practice. He had been sprinting when he suddenly became lightheaded and collapsed. He regained consciousness within 1 minute without confusion, tongue biting, or urinary incontinence. He denies chest pain but reports occasional exertional palpitations. The patient takes no medications and denies stimulant or illicit drug use. His father died suddenly at age 38 while jogging. Temperature is 36.8°C (98.2°F), blood pressure is 118/70 mm Hg, pulse is 62/min, and respiratory rate is 14/min. Cardiac examination reveals a harsh systolic murmur best heard along the left lower sternal border. The murmur becomes louder when the patient stands from a squatting position and becomes softer with sustained handgrip. The lungs are clear. ECG demonstrates left ventricular hypertrophy with deep, narrow Q waves in the lateral leads. Transthoracic echocardiography shows asymmetric septal hypertrophy with a maximal septal thickness of 32 mm, systolic anterior motion of the mitral valve, and dynamic left ventricular outflow tract obstruction. Ambulatory ECG monitoring demonstrates several episodes of nonsustained ventricular tachycardia.
Which of the following is the most appropriate intervention to reduce this patient’s risk of sudden cardiac death?
The correct answer is:
B) Implantable cardioverter-defibrillator placement
This patient has hypertrophic cardiomyopathy with multiple major risk factors for sudden cardiac death, including unexplained exertional syncope, a first-degree relative who died suddenly at a young age, massive left ventricular hypertrophy with a septal thickness greater than 30 mm, and documented nonsustained ventricular tachycardia. Implantable cardioverter-defibrillator (ICD) placement is indicated for primary prevention because malignant ventricular arrhythmias are the principal cause of sudden death in high-risk patients with hypertrophic cardiomyopathy.
Hypertrophic cardiomyopathy is most often caused by an autosomal dominant mutation involving a cardiac sarcomere protein. Myocyte hypertrophy and disarray create an arrhythmogenic substrate, while asymmetric septal thickening and systolic anterior motion of the mitral valve can produce dynamic left ventricular outflow tract obstruction. The obstruction worsens when ventricular volume decreases or contractility increases. Therefore, the murmur becomes louder with standing or Valsalva, which reduce preload, and softer with squatting or handgrip, which increase ventricular filling or afterload.
Beta blockers are commonly used to reduce exertional symptoms by decreasing heart rate and contractility, thereby improving diastolic filling and reducing the outflow gradient. However, medications do not provide adequate protection against sudden arrhythmic death in a patient with this degree of risk. An ICD can detect and terminate ventricular tachycardia or ventricular fibrillation and is the most effective preventive intervention.
Patients should also avoid dehydration and intense competitive athletics, and first-degree relatives should undergo clinical screening because of the inherited nature of the disorder.
Answer choice A: Alcohol septal ablation alone, is incorrect.
Alcohol septal ablation produces a controlled infarction of the hypertrophied septum and can reduce left ventricular outflow obstruction in selected patients with severe symptoms despite medical therapy. However, it is a treatment for refractory obstruction, not a substitute for an ICD in a patient at high risk for sudden cardiac death. This patient’s syncope, family history, massive hypertrophy, and nonsustained ventricular tachycardia remain arrhythmic risk factors even if the outflow gradient is reduced.
Answer choice C: Metoprolol therapy alone, is incorrect.
Beta blockers are first-line therapy for exertional dyspnea, angina, and presyncope related to dynamic obstruction. They reduce contractility, prolong diastole, and improve ventricular filling. Metoprolol may therefore be appropriate as part of this patient’s treatment, but it does not provide reliable protection from ventricular fibrillation and should not be used as the sole intervention when multiple major sudden-death risk factors are present.
Answer choice D: Surgical septal myectomy alone, is incorrect.
Septal myectomy is considered for patients with severe obstructive symptoms that persist despite maximally tolerated medical therapy. Removing hypertrophied septal myocardium can substantially reduce the outflow gradient and improve symptoms. However, this patient’s principal management issue is prevention of sudden cardiac death, and myectomy does not eliminate the need for an ICD when major arrhythmic risk factors are present.
Answer choice E: Verapamil therapy alone, is incorrect.
Verapamil can improve symptoms in selected patients who cannot tolerate beta blockers by slowing the heart rate and improving diastolic relaxation. However, its vasodilatory effects can worsen obstruction in patients with severe gradients or hypotension. More importantly, verapamil does not adequately prevent sudden arrhythmic death in this high-risk patient.
Key Learning Point
Patients with hypertrophic cardiomyopathy who have major sudden-death risk factors—such as unexplained syncope, a family history of sudden cardiac death, massive ventricular hypertrophy, or nonsustained ventricular tachycardia—should receive an implantable cardioverter-defibrillator for primary prevention.
