From suspicion to diagnosis
Patients with any abnormal findings or features suggestive of HCM should be referred to a cardiologist for further work-up.13 Accompany the referral with an order for complete exercise restriction until a more detailed analysis has been completed or HCM has been ruled out.
2-dimensional echocardiogram shows LV wall hypertrophy
Diagnosis is primarily made on the basis of 2-dimensional echocardiography showing asymmetric LV wall hypertrophy without chamber dilation (in the absence of another condition that might cause hypertrophy, such as hypertension, valvular disease, or amyloidosis). The anterior septum is commonly thickened; abnormal systolic anterior motion of the mitral valve may be evident, as well.1
Although increased LV wall thickness (≥13 mm) is the most common finding in HCM—and thicknesses up to 60 mm have been recorded—this is not a universal sign. Many people with genetic evidence of HCM have normal LV wall thickness. Conversely, some patients have increased LV wall thickness but do not have HCM.
HCM or “athlete’s heart”? Mild concentric LV hypertrophy (13-14 mm)—a level of thickening often referred to as the “athlete’s heart”—may be present in healthy individuals who exercise strenuously. In borderline cases, calculation of the LV mass distribution index by 3-dimensional echocardiography has been shown to have 100% specificity in distinguishing HCM from both athlete’s heart and hypertensive cardiomyopathy.14
Cardiac magnetic resonance imaging (MRI). With gadolinium as the contrast agent, cardiac MRI is another diagnostic tool. Imaging may reveal certain delayed enhancement patterns that are highly suggestive of HCM.15 Cardiac MRI can accurately quantify LV wall thickness and LV mass distribution index and identify subtle areas of patchy LV wall thickness that echocardiography may miss.16
Ensure that family members undergo screening
When physical exam, medical history, and follow-up tests are highly suggestive of HCM, clinical screening of asymptomatic first-degree relatives is recommended. In screening family members, it is important to remember that a normal physical exam, echocardiogram, and EKG do not definitively rule out HCM, as many people who have genetic mutations for this condition do not develop physical abnormalities until they reach adulthood.1 In such cases, genetic screening—the most definitive means of HCM diagnosis—may be considered, in consultation with a specialist.
Recognize the limits of genetic testing. Genetic testing is not universally recommended, however, for a number of reasons. Cost (about $3000) is a key factor. In addition, the test for HCM is not widely available. Nor is it highly sensitive, identifying only 50% to 60% of those with genetic mutations associated with HCM.4 What’s more, the presence of a genetic mutation does not guarantee that cardiac abnormalities will ever develop. Lifestyle, coexisting hypertension, and modifier genes may all play a role in determining whether an individual is affected.1,4
Provide follow-up. When genetic screening is not available, is declined, or is negative, stress the need for periodic clinical follow-up of family members. If the first-degree relative is an adolescent, he or she will need a history and physical examination, 12-lead EKG, and 2-dimensional echocardiography annually from the age of 12 to 18 years. If the relative is older than 18, he or she should be evaluated every 5 years.6
For patients themselves, SCD risk assessment is the next step
While family physicians may be involved in the care of a patient with HCM, an assessment of the individual’s risk for SCD is best done by a specialist. Risk stratification is typically based on the presence (or absence) of LVOTO, atrial fibrillation (AF), and heart failure.
LVOTO. Defined as a subaortic gradient of 30 mm Hg or more, LVOTO is present at rest in 25% of HCM patients.17 Because the obstruction is typically dynamic, treadmill or bicycle exercise testing in conjunction with Doppler echocardiography may be needed to identify it.6 LVOTO is a strong risk factor for death due to heart failure or stroke (relative risk [RR], 4.4, compared with HCM patients who do not have LVOTO) and death from any HCM-related cause (RR=2.0). Patients with LVOTO and left atrial enlargement are also at increased risk for bacterial infective endocarditis.18
AF, which occurs in approximately 25% of those with HCM and is more common in patients with LVOTO,19 often presents clinically as acute heart failure because of the reduced diastolic filling. Although AF is not as ominous as ventricular arrhythmia, it increases the risk for embolic stroke, the likelihood of severe functional disability, and the risk of death from HCM.19
Heart failure. This is the most common complication of HCM. In some cases, patients progress to a dilated cardiomyopathy that resembles classic systolic heart failure—and responds well to conventional treatments for systolic failure. More often, the condition more closely resembles diastolic failure and responds best to negative inotropic agents and the avoidance of volume depletion, both of which increase cardiac filling.20