Pediatric Hypertrophic Cardiomyopathy Clinical Presentation

Patients with hypertrophic cardiomyopathy (HCM) may be asymptomatic. When present, symptoms may include dyspnea, syncope, presyncope, angina, palpitations, orthopnea, paroxysmal nocturnal dyspnea, congestive heart failure, and dizziness. Some children may present with sudden cardiac death as their first manifestation.

Sudden cardiac death

Sudden cardiac death is the most devastating presenting manifestation and, unfortunately, may be the first clinical manifestation of the disease, even among asymptomatic patients. ^[7] It has the highest incidence in preadolescent and adolescent children and is typically associated with sports or vigorous exertion. Indeed, HCM has been identified as the most common cause of sudden death in the athlete following physical activity. ^{[11, 12, 13]}

In more than 80% of individuals with HCM, the arrhythmia that causes sudden death is ventricular fibrillation. Many patients with HCM develop ventricular fibrillation after atrial fibrillation, atrial flutter, supraventricular tachycardia associated with Wolff-Parkinson-White syndrome, ventricular tachycardia, or low-cardiac-output hemodynamic collapse.

Early diagnosis is of prime importance if death is to be prevented by prescription of an appropriate level of safe activity, medications, surgery, or an implantable cardioverter defibrillator. ^[14] Because this is an autosomal dominantly inherited disease, screening of first-degree relatives with physical examination, electrocardiography (ECG), and echocardiography is useful to identify additional family members with HCM before the onset of significant symptoms or sudden death.

Dyspnea

Dyspnea is the most common presenting symptom, occurring in as many as 90% of symptomatic patients. It is largely a consequence of elevated left ventricular diastolic filling pressures and transmission of those elevated pressures back into the pulmonary circulation. The elevated left ventricular filling pressures principally result from impaired diastolic compliance as a result of marked hypertrophy of the ventricle.

Syncope

Syncope is a common symptom of HCM, resulting from inadequate cardiac output on exertion or from cardiac arrhythmia (either tachycardia or bradycardia). Syncope is more common in children and young adults with small left ventricular chamber size and evidence of ventricular tachycardia on ambulatory monitoring. Some patients have abnormalities in sinus node function, leading to sick sinus syndrome. Syncope identifies children with HCM who are at significantly increased risk of sudden death and warrants an urgent evaluation and aggressive treatment.

Presyncope

Presyncope refers to “graying out” spells that occur in the erect posture and can be relieved by the individual immediately lying down. These symptoms are exacerbated by vagal stimulation. Presyncope may also occur with nonsustained atrial or ventricular tachyarrhythmias.

Presyncope occurs commonly in patients with HCM and identifies a subgroup of patients who may be at increased risk for sudden death. Like syncope, presyncope warrants a directed evaluation to rule out malignant arrhythmias. However, dizziness and presyncope are common symptoms in teenagers and may simply represent vasodepressor reaction or a common faint. A thorough investigation is warranted to rule out potential malignant etiology of presyncopal symptoms.

Angina

Typical symptoms of angina are seen in children with HCM and occur in the absence of detectable coronary atherosclerosis. Impaired diastolic relaxation and markedly increased myocardial oxygen consumption due to ventricular hypertrophy result in subendocardial ischemia, particularly during exertion.

Palpitations

Palpitations are common in HCM. They are usually due to arrhythmia, such as premature atrial and ventricular beats, sinus pauses, intermittent atrioventricular (AV) block, atrial fibrillation, atrial flutter, supraventricular tachycardia, or ventricular tachycardia. Nonsustained ventricular tachycardia is another marker for a higher risk of sudden death.

Orthopnea and paroxysmal nocturnal dyspnea

Although orthopnea and paroxysmal nocturnal dyspnea are uncommon in children, these early signs of congestive heart failure are observed in individuals with severe cases of HCM. They occur when impaired diastolic function and elevated left ventricular filling pressure result in pulmonary venous congestion.

Congestive heart failure

Although relatively uncommon in children, congestive heart failure is present in 10% of children at initial presentation, most commonly in infants younger than 1 year. It is observed in individuals with severe cases of HCM. Congestive heart failure may occur as a result of a combination of impaired diastolic function and subendocardial ischemia. Systolic function in children with HCM is almost always well preserved, at least until the late stages of the disease.

Patients with congestive heart failure have a high likelihood of recurrent heart failure, as a consequence of both mitral regurgitation and profound diastolic dysfunction.

Dizziness

Dizziness is common in children with HCM who have elevated pressure gradients across the left ventricular outflow tract. Worsened by exertion, dizziness may be exacerbated by hypovolemia after high levels of exertion or increased insensible fluid loss (eg, during or after exposure to extreme heat).

Dizziness may be caused by medications or maneuvers (eg, rapid standing or a Valsalva maneuver during defecation) that decrease preload and afterload and increase the pressure gradient across the left ventricular outflow tract.

Dizziness also may be caused by arrhythmia-related hypotension and decreased cerebral perfusion. Nonsustained arrhythmias often cause symptoms of dizziness and presyncope, whereas sustained arrhythmias more likely lead to syncope, collapse, and sudden cardiac death.

Most children with hypertrophic cardiomyopathy (HCM) do not have outflow tract obstruction and, therefore, may have completely normal physical examination findings. Abnormalities related to heart sounds, cardiac impulses, or murmurs may, however, be noted.

Heart sounds

The first heart sound (S₁) is normal in patients with HCM. The second heart sound (S₂) is usually split; however, in some patients with HCM and extreme outflow gradients, S₂ is split paradoxically. A third heart sound (S₃) or gallop is common in children with HCM but does not have the same ominous significance as in patients with valvular aortic stenosis or in adults. A fourth heart sound (S₄) is frequently heard and is due to the impact of atrial systole against a highly noncompliant left ventricle.

Cardiac impulse

The apical precordial impulse is frequently displaced laterally and is usually abnormally forceful and increased. A double apical impulse, resulting from a forceful left atrial contraction against a highly noncompliant left ventricle, occurs commonly in children with HCM. A triple apical impulse, resulting from a late systolic bulge that occurs when the heart is almost empty and is performing near-isometric contraction, is highly characteristic but is less frequent than a double apical impulse.

Murmur

The outflow murmur typically heard is a systolic ejection, crescendo-decrescendo murmur that is heard best between the apex and left sternal border; it radiates to the suprasternal notch but not to the carotid arteries or neck. The intensity of the murmur directly varies with the subaortic gradient across the left ventricular outflow tract.

Because obstruction is dynamic and directly related to volume status, left ventricular outflow tract obstruction and murmur diminish with any increase in preload (eg, that elicited by a Valsalva maneuver, a Mueller maneuver, or squatting) or increase in afterload (eg, that elicited by a handgrip). The murmur and the gradient increase with any decrease in preload (eg, that elicited by nitrate medications, diuretics, or standing) or with any decrease in afterload (eg, that elicited by vasodilators).

A holosystolic murmur of mitral regurgitation is heard at the apex and left axilla in patients with systolic anterior motion of the mitral valve and significant left ventricular outflow gradients.

A diastolic decrescendo murmur of aortic regurgitation is heard in 10% of children with HCM, although mild aortic regurgitation can be detected by Doppler echocardiography in 33% of patients with the disorder.

Other findings

The jugular venous pulse reveals a prominent ‘a’ wave due to diminished right ventricular compliance secondary to massive hypertrophy of the ventricular septum.

A double carotid arterial pulse may occur. The carotid pulse rises quickly because of increased velocity of blood through the left ventricular outflow tract into the aorta. The carotid pulse then declines in mid-systole as the gradient develops, followed by a secondary rise in carotid pulsation during systole.