Hypertrophic obstructive cardiomyopathy (HOCM) is a relatively common disorder. Historically, it has been referred to as idiopathic hypertrophic subaortic stenosis. HOCM is a significant cause of sudden cardiac death in young people, including well-trained athletes, affecting men and women equally across all races. In most patients, it results from asymmetric septal hypertrophy causing outflow obstruction of the left ventricle. It is difficult to diagnose and presents a challenge to medical health professionals in evaluating at-risk athletes. Unfortunately, hypertrophic obstructive cardiomyopathy is often not diagnosed until a significant cardiac event has occurred.
The familial form of HOCM is an autosomal dominant genetically transmitted disorder. It is the most common genetically transmitted cardiomyopathy. It can also occur in individuals without family history secondary to de novo mutations. HOCM results from a mutation in genes that encode for one of the nine sarcomere proteins, such as B-myosin heavy chain, troponin, actin, and titin. The mutations cause structural abnormalities in myofibril and myocytes that have the potential to lead to abnormal force generation and conduction abnormalities. The consequences of which are a phenotype for asymmetric left ventricular hypertrophy in the absence of other causes.
Hypertrophic obstructive cardiomyopathy occurs in men and women with equal distribution across all races. Females tend to be more symptomatic causing more disability and present at a younger age. A 1995 study by Maron et. Al. concluded that it occurs at a rate of 1:500 in the general adult population. In the United states alone, there are fewer than 100 deaths per year due to HOCM at a rate of 1:220,000 athletes.
HOCM can be classified as obstructive or non-obstructive. There is some degree of asymmetric left ventricular hypertrophy. The degree of obstruction and clinical presentation is dependent upon the extent of hypertrophy. It most commonly affects the ventricular septum (about 2/3 of patients), although any portion of the left ventricle can be affected.
Dynamic outflow obstruction in HOCM is due to systolic anterior motion(SAM) of the anterior leaflet of the mitral valve. This is due to impingement of the mitral valve leaflets on the hypertrophied basal septum. The outflow tract obstruction is dynamic and caused by a pressure gradient which pulls the anterior leaflet of the mitral valve anteriorly further leading to outflow tract obstruction. The degree of obstruction is dependent upon contractility and loading conditions. In 25% of patients, the obstruction can exist at rest, but about 70% of patients can be brought about with provocative maneuvers.
Most patient’s with HOCM have an abnormal diastolic function. This increases left ventricular pressures impairing ventricular filling which further exacerbates obstruction. Because the coronary vessels are filled during diastole in combination with outflow tract obstruction and ventricular stiffness, there is an increased risk for myocardial ischemia. This may be responsible for ventricular arrhythmias and sudden death. In severe cases, this can occur at rest. More commonly, it occurs with provocative maneuvers such as exercise during increased myocardial demand.
A thorough history and physical should be performed. All patients should be asked about family history of HOCM and of sudden cardiac death. A majority of patients are asymptomatic. Dyspnea is the most common complaint among symptomatic patients. Patients may also complain of presyncope, syncope, angina, palpitations (secondary to arrhythmia), or dizziness. Symptoms will frequently be exacerbated by exertion. Severe cases will present like congestive heart failure with paroxysmal nocturnal dyspnea, leg edema, and orthopnea. The most devastating presentation is sudden cardiac death.
Physical Exam will not provide a definitive diagnosis, but it should provide clues to increase clinical suspicion. Patients may present with a jugular venous pulse with prominent A wave, S4 heart sound, split second heart sound (may paradoxically split in severe outflow tract obstruction), double carotid pulse, systolic ejection crescendo-decrescendo murmur, laterally displaced apical precordial impulse that may be abnormal forceful or enlarged, and/or a holosystolic murmur at the apex and axilla of mitral regurgitation with systolic anterior wall motion. Lung exam should be normal.
Lab studies should be normal, but with severe disease, BNP may be elevated. Genetic testing is available and diagnostic but is reserved for patients with significant family histories or those who exhibit clear symptoms. The American Heart Association is currently opposed to routine screening for genetic markers.
A chest x-ray may be normal but left ventricular hypertrophy may be seen.
EKG may show LVH. It may also show arrhythmias such as a.fib or non-sustained v-tach. EKG can frequently be normal.
2D-echocardography is the primary imaging modality to make the diagnosis of HCM. Echo has an 80% diagnostic accuracy for HOCM. There can be direct visualization and relatively accurate measurements of the septum and left ventricular wall sizes. It will be able to show increased flow velocity along left ventricular outflow tract. Color flow Doppler can show mitral valve regurgitation. Reduced LV compliance can be seen in diastolic dysfunction.
Cardiac MRI is considered the gold standard for diagnosis of LV wall properties and should be performed in patients suspected of having HOCM with a normal or inconclusive echocardiogram.
Cardiac catheterization is not required for diagnosis but may be performed to determine accurately the degree of outflow tract obstruction, LV anatomy, the degree of mitral valve regurgitation, and the patency of the coronary arteries.
Treatment is based on the severity of symptoms. Mild disease is treated with lifestyle modifications. Patients should be strongly advised to avoid strenuous exercise and heavy lifting. First lime medical treatment for symptomatic HOCM is beta blockers though cardiac selective calcium channel blockers may be used. ACE inhibitors and nitrates should be avoided as these medications decrease afterload which would lead to worsening LV outflow tract obstruction.
Surgical intervention is reserved for patients who are resistant to lifestyle and medical management or those who have outflow gradient of 50mmhg or more. Septal myectomy is the surgical treatment of choice in young healthy patients. Alcohol septal ablation is a newer percutaneous technique usually limited to older patients for whom an open procedure would be considered risky.