Hypertrophic Cardiomyopathy (HCM) is a genetic condition where the heart muscle, particularly the walls of the left ventricle, becomes abnormally thick. This thickening makes the heart stiffer, reducing the size of the pumping chamber and making it harder for the heart to fill with blood and pump it effectively. The disease is complex and highly variable, affecting roughly one in 500 people, though many remain undiagnosed. Because of its subtle presentation and serious potential complications, including sudden cardiac death, a systematic diagnostic process is necessary to identify the condition.
Recognizing the Need for Testing
Suspicion of hypertrophic cardiomyopathy often begins when a person reports specific symptoms or during a routine physical exam. Common complaints that prompt further investigation include shortness of breath, especially during physical activity, chest discomfort, or episodes of lightheadedness or fainting. These symptoms occur because the thickened heart muscle struggles to meet the body’s demand for blood flow.
The initial assessment includes gathering a thorough medical and family history. Since HCM is often inherited (typically in an autosomal dominant pattern), a history of the condition in close relatives or unexplained sudden cardiac death is a significant red flag. During the physical examination, the doctor will listen for a heart murmur. This swishing sound may indicate that blood flow is partially blocked as it leaves the heart, a feature known as left ventricular outflow tract obstruction (LVOT).
Core Diagnostic Tools: ECG and Echocardiogram
The diagnostic process moves to two non-invasive tests: the Electrocardiogram (ECG) and the Echocardiogram. The ECG measures the electrical activity of the heart and provides early clues about the muscle’s structure and function. Abnormalities are present in over 90% of people with the condition, often showing signs of ventricular hypertrophy, which means the electrical signals are traveling through an abnormally large amount of muscle.
The ECG may also reveal deep, narrow “dagger-like” Q waves or ST and T wave abnormalities. These electrical patterns reflect the abnormal way the heart muscle is structured and activated. An abnormal ECG result, even without clear symptoms, frequently prompts the next step in the diagnostic sequence: the echocardiogram.
The echocardiogram, an ultrasound of the heart, is considered the primary tool for diagnosing HCM. It provides detailed images of the heart’s structure and function, allowing doctors to measure the thickness of the heart muscle walls. A diagnosis is typically confirmed in adults if the wall thickness is 15 millimeters or greater in any segment of the left ventricle, provided other causes like high blood pressure are absent.
The echocardiogram assesses how the heart is functioning. It can visualize if the thickened wall is causing obstruction of blood flow out of the heart, a feature called hypertrophic obstructive cardiomyopathy (HOCM). The test also checks for systolic anterior motion (SAM) of the mitral valve, where the valve leaflet is pulled into the outflow tract, contributing to the obstruction. If initial measurements are inconclusive, a stress echocardiogram may be performed during exercise to reveal a “latent” obstruction that only appears under physical exertion.
Confirming the Diagnosis: Advanced Imaging and Genetics
When the echocardiogram is inconclusive or a more detailed view is needed, Cardiac Magnetic Resonance (CMR) imaging is used. CMR offers superior tissue characterization and a three-dimensional view of the heart, which is particularly helpful for visualizing areas of hypertrophy hard to see with an ultrasound, such as the apex. This advanced imaging accurately measures the full extent and pattern of wall thickening, helping to distinguish HCM from other conditions that cause a thickened heart muscle.
A CMR scan using a contrast dye called gadolinium can also reveal areas of myocardial scarring, known as Late Gadolinium Enhancement (LGE). The presence and extent of this scarring help doctors determine the person’s risk for serious complications, such as sudden cardiac death. Exercise stress testing, separate from an echocardiogram, provides valuable functional information by measuring the heart’s electrical and blood pressure response to exertion, assessing functional capacity and risk.
Genetic testing confirms the hereditary nature of the disease and guides the screening of family members. HCM is most commonly caused by mutations in genes that code for sarcomere proteins responsible for muscle contraction, with MYH7 and MYBPC3 being the most frequent culprits. While genetic testing detects a pathogenic variant in 30% to 65% of cases, a negative result does not rule out the condition. When a specific mutation is identified, it allows for “cascade screening,” meaning only first-degree relatives who carry that same mutation need regular monitoring.