Hypertrophic cardiomyopathy (HCM) is a complex, yet relatively common, genetic heart disease that occurs in approximately 1 in 500 individuals. It affects both genders and all races. The disease results in excessive thickening of the heart muscle—referred to as “hypertrophy”—which occurs most commonly in the septum (i.e. the muscular wall that separates the left and right lower chambers of the heart). In the majority of patients, this thickening begins during puberty, with little to no change in the thickness beyond early adulthood. However, symptoms from HCM can develop or worsen at any age, but most commonly occur during mid-life.
Types of HCM
Almost two-thirds of HCM patients have the obstructive form of the disease. This means their mitral valve moves abnormally, causing it to come in contact with the thickened septum, and therefore partially obstructing flow of blood out of the heart. This obstruction of blood creates higher pressure in the left lower chamber of the heart, which can be reliably measured with an echocardiogram. In some patients, this obstruction to blood flow is present at rest. In other patients it occurs only during exercise, requiring an exercise stress test be performed at the time of the clinical evaluation.
The obstruction to blood flow and the resulting increase in pressure in the heart is responsible for what we call “limiting” symptoms, that include: shortness of breath with activity, exertional fatigue, chest pain (or “heart pounding”) and occasionally lightheadedness. These symptoms can often be managed with appropriate medications. However, when medications are not effective, patients can then become candidates for invasive treatment options to relieve the obstruction—via either surgical myectomy or alcohol ablation.
The remaining one-third of HCM patients has the non-obstructive form of the disease. This means their heart muscle is thickened but there is no obstruction to blood flow out of the heart at rest or with exercise. Symptoms of non-obstructive HCM are often controlled well with medications. Given the absence of a pressure gradient (i.e. obstruction), these patients do not benefit from invasive treatments such as surgical myectomy or alcohol septal ablation.
Severity of symptoms and risk of complications vary greatly between HCM patients. Many individuals with HCM never experience serious problems or symptoms. In contrast, others develop symptoms similar to other forms of heart disease including:
- Shortness of breath (with exertion)
- Chest pain or pressure (occurring with exertion or at rest)
- Fatigue and excessive tiredness (either related or unrelated to exertion)
- Palpitations (sudden, forceful heart beats)
- Lightheadedness, dizziness, or fainting
- Loss of consciousness
Tests & diagnosis
In addition to a comprehensive physical exam, your doctor will request some of the following tests to confirm your HCM diagnosis:
Risk of sudden cardiac death
For the last 15 years, it has been possible to prevent sudden cardiac death in hypertrophic cardiomyopathy using the implantable defibrillator. Prophylactic use of defibrillators has eliminated the vast majority of sudden death events in this disease. It is now possible to identify those patients who will likely benefit from defibrillators using a process called risk stratification, in which disease related markers are identified that target those patients who should receive defibrillators. Many patients live into advanced age having never experienced a symptom or complication.
We have fortunately been able to identify several non-invasive clinical markers to help determine if an HCM patient is at high risk in the future for the development of ventricular arrhythmias (i.e. abnormal heartbeats which can cause loss of consciousness or potentially be fatal). If you are found to be high risk, we will discuss with you implanting a cardioverter defibrillator (ICD), designed to sense and automatically terminate these arrhythmias. This has proven highly effective at re-establishing normal heart rhythms via electrical pulses, thus preventing sudden cardiac death events.
We should emphasize that only a very small proportion of patients with HCM are at increased risk for sudden cardiac death.