Pediatric Hypertrophic Cardiomyopathy Treatment & Management

Medical management of hypertrophic cardiomyopathy (HCM) in children should focus on the following:

• Ruling out secondary causes
• Following for progression of disease and identifying those with obstruction
• Controlling symptoms and restricting activity (with avoidance of volume depletion)
• Identifying those at risk for sudden cardiac death
• Screening family members

Evaluation of the patient with HCM can usually be conducted on an outpatient basis. Inpatient studies and treatment may be necessary as well. Admit patients with HCM for testing, electrophysiology procedures, and/or surgical intervention.

Ruling out secondary causes

Evaluation, especially in children, should be performed to rule out the following secondary causes of cardiac hypertrophy:

• Athlete’s heart: Long-term athletic conditioning can result in ventricular hypertrophy but typically results in a concentric hypertrophy with an associated increase in left ventricular diastolic dimension, unlike primary hypertrophic cardiomyopathy.
• Inborn errors of metabolism
• Mitochondrial disorders
• Neuromuscular disorders

Following for disease progression

Children are at particular risk for development or progression of outflow tract obstruction and should be followed yearly with serial echocardiography during puberty.

Controlling symptoms and restricting activity

Medical and surgical therapy are used to reduce ventricular contractility or increase ventricular volume, to increase ventricular compliance and outflow tract dimensions, and, in obstructive HCM, to reduce the pressure gradient across the left ventricular outflow tract.

Patients with symptoms or evidence of outflow tract obstruction are generally started on calcium channel blocker or beta blocker therapy. Disopyramide has been used in adults, but has potential proarrhythmic effects and is not typically used in children. Carefully monitor medication dose and adverse effects.

Patients with severe outflow tract obstruction may be candidates for surgical myectomy. Alternative therapies, such as alcohol septal ablation or pacemaker insertion, are less commonly performed in children.

Patients should be advised not to participate in competitive sports or strenuous activity.

Identifying risk factors for sudden death

Reduction of the risk of sudden death is paramount to any therapy for HCM. Although no strict guidelines are available, suggested risk factors for sudden cardiac death include a history of previous arrest, unexplained syncope, ventricular arrhythmias, a family history of sudden cardiac death, abnormal blood pressure response during exercise stress testing, and a markedly enlarged septum (> 3 cm in adult studies). The amount of outflow obstruction has not been shown to be a risk factor for sudden death.

Screening family members

All first-degree family members of the patient must be informed and screened for HCM. This entails a detailed history, physical examination, electrocardiography (ECG), and echocardiography. If a genetic defect is known, asymptomatic family members should be gene tested.

Subacute bacterial endocarditis prophylaxis is not required. Beta-blockers and calcium channel blockers (eg, verapamil or diltiazem) are used to treat children with HCM. In individuals with significant tachyarrhythmias, amiodarone and other class III-type antiarrhythmic agents have also been used.

Avoid administration of inotropic drugs. Avoid nitrates and sympathomimetic amines except in patients with HCM and concomitant coronary artery disease. Avoid digitalis because glycosides are contraindicated, except in patients with uncontrolled atrial fibrillation. Avoid diuretics because of their effect on left ventricular myotomy and ventricular volume.

Left ventricular myectomy is sometimes performed in HCM patients who have severe symptoms refractory to therapy and an outflow gradient of more than 50 mm Hg either with provocation or at rest.

The procedure is typically successful in abolishing the outflow gradient; most patients have symptomatic improvement for at least 5 years. However, the reduction in left ventricular outflow gradient may not correlate with a reduction in the risk of sudden death or overall mortality. Furthermore, the outflow gradient may gradually increase over time and return to the same level as before, necessitating a repeat myectomy or additional medical therapy.

Transvenous dual-chamber pacing has been used for patients with HCM, although this is not current clinical practice. The right ventricular septal preexcitation induced by right ventricular apical pacing leads to a “pulling away” of the septum from the outflow region, allowing for an increase in flow with a decrease in left ventricular outflow tract obstruction.

Many patients with HCM and pacemaker implantation feel that their symptoms improve, allowing a reduction in prescribed medication. However, a reduction in left ventricular outflow tract gradient does not necessarily mean a reduction in vulnerability to ventricular arrhythmias and sudden death.

Recommendations for pacing in patients with hypertrophic cardiomyopathy have been made by the American College of Cardiology (ACC) and the American Heart Association (AHA).^[4]

Some investigators have used permanent pacing in selected HCM patients as adjunctive rather than primary treatment. The reported results vary considerably, with a significant placebo effect and a wide range of patient outcomes. Implantable cardioverter defibrillators (ICDs) have now essentially replaced pacemakers as cardiac rhythm management devices for HCM (see Implantable Cardioverter Defibrillator).^{[5, 6, 7, 8]}

Transvenous catheter ablation of the septal region has been performed by using selective arterial ethanol infusion to destroy myocardial tissue in patients with HCM. The procedure is analogous to a surgical myectomy, in that it attempts to decrease the amount of septal ventricular myocardium, thereby reducing the left ventricular outflow tract gradient.

The main drawbacks include the risk of inadvertent atrioventricular (AV) block and extension of the alcohol-induced infarct, leading to myocardial dysfunction or iatrogenic ventricular septal defects. Studies have demonstrated a higher rate of complications for alcohol septal ablation than for surgical myectomy.^[9]

The ICD has been used for prevention of sudden arrhythmic death. Transvenous placement is similar in technique to permanent pacemaker implantation. An ICD automatically detects, recognizes, and treats tachyarrhythmias and bradyarrhythmias using tiered therapy (ie, bradycardia pacing, overdrive tachycardia pacing, low-energy cardioversion, and high-energy shock defibrillation).

ICD therapy has been demonstrated to be lifesaving in children with HCM who receive appropriate shocks for ventricular tachycardia and ventricular fibrillation, even among those on appropriate antiarrhythmic drug therapy.

Smaller studies in children, as well as personal and anecdotal experience, appear to strongly favor using the ICD in HCM patients who have arrhythmias, aborted sudden death, malignant genotype or family history, and other factors that may increase mortality, particularly sudden arrhythmic death risk.^{[5, 6, 7, 8]}

Clearly, in patients who have had an aborted sudden death event or documented sustained ventricular tachyarrhythmias, the ICD is indicated as secondary prevention.

In adults, teenagers, and children, primary prevention is also employed for patients with HCM but without a documented ventricular tachyarrhythmia or aborted sudden death event. Although this is a reasonable indication, the appropriate shock rate is significantly lower in these primary prevention patients.

Additional markers of higher risk (eg, left ventricular wall thickness, nonsustained ventricular tachycardia, abnormal exercise blood pressure response, malignant family history, and other stratifying tests) are useful in identifying patients who have greater ventricular arrhythmia vulnerability.

The main drawbacks to implanting an ICD include the relatively high rate of inappropriate shocks (for sinus tachycardia, supraventricular tachycardia, or lead problems) and a high lead fracture rate, particularly in younger patients.

ICDs last approximately 4-5 years; device failure is usually the result of either battery depletion or lead failure. Young patients require multiple ICD device replacements and lead extraction procedures, which carry additional surgical risks.

No special diet is required in individuals with HCM; however, patients should be instructed to avoid volume depletion, as this can increase pressure gradients across the left ventricular outflow tract. They should also be advised to avoid excessive weight gain.

Strenuous and anaerobic exercise should be avoided. Competitive-level sports are not advised if any of the following are present:

• Significant outflow gradient
• Significant ventricular or supraventricular arrhythmia
• Marked left ventricular hypertrophy
• History of sudden death in relatives with HCM

Consultations may be indicated with the following:

• Cardiologist
• Cardiothoracic surgeon
• Cardiac electrophysiologist
• Geneticist