Hypertrophic cardiomyopathy (HCM) is a genetic condition characterized by a thickening of the heart muscle, specifically the left ventricle. This thickening occurs without an obvious cause, such as high blood pressure, and can hinder the heart’s ability to pump blood effectively. The diagnostic process for HCM is a multi-step investigation, moving from initial patient assessment to advanced imaging and molecular confirmation.
Initial Clinical Evaluation and Screening
The diagnostic journey begins with a thorough clinical evaluation, where a physician gathers information about a patient’s symptoms and family medical history. Common symptoms that prompt an evaluation include shortness of breath, chest pain, palpitations, or fainting, especially during physical activity. Since HCM is often inherited, a detailed family history of heart disease or unexplained sudden death in relatives is a significant piece of information.
The physical examination includes listening to the heart, where the physician may detect a specific type of heart murmur. This murmur, often described as an ejection systolic murmur, is particularly suggestive of an obstruction in the left ventricular outflow tract (LVOT), a common feature of HCM. The murmur’s intensity can change dynamically with certain maneuvers, such as the Valsalva maneuver, which helps distinguish it from other heart murmurs.
Initial objective screening is performed using an Electrocardiogram (ECG), which records the heart’s electrical activity. While not definitive for diagnosis, the ECG is abnormal in over 90% of patients with HCM and serves as an effective screening tool. Common findings include voltage criteria for left ventricular hypertrophy and deep, narrow Q waves, often referred to as “dagger” Q waves, in the lateral leads.
The Role of Echocardiography
Echocardiography, which uses sound waves to create a moving picture of the heart, is the primary and most accessible tool for establishing a structural diagnosis of HCM. This non-invasive imaging technique allows for precise measurement of the heart muscle’s thickness and assessment of its function. The definitive criterion for diagnosis in adults is an unexplained maximal left ventricular wall thickness of 15 millimeters or greater at any point in the chamber.
In first-degree relatives of individuals with confirmed HCM, a lower measurement of 13 millimeters may be sufficient to establish a diagnosis. The echocardiogram also reveals the pattern of thickening, which is often asymmetrical, with the wall between the two lower chambers, the interventricular septum, being most commonly affected. This asymmetric hypertrophy is a characteristic finding of the condition.
Doppler echocardiography is used to assess blood flow dynamics and is crucial for identifying the obstructive subtype of HCM. This technique measures the speed of blood flow as it leaves the left ventricle, specifically looking for a pressure gradient in the left ventricular outflow tract (LVOT). The presence of a dynamic LVOT obstruction, defined as a gradient of 30 mmHg or greater, is often caused by the mitral valve’s anterior leaflet being pulled toward the thickened septum during contraction, a phenomenon known as systolic anterior motion (SAM).
Advanced Imaging and Functional Assessment
When echocardiography results are inconclusive or technically limited, advanced imaging is employed. Cardiac Magnetic Resonance (CMR) imaging is often considered the gold standard for morphological assessment due to its superior spatial resolution. CMR provides accurate measurements of wall thickness and helps differentiate HCM from other conditions that cause heart muscle thickening.
A unique feature of CMR is its ability to perform tissue characterization using a technique called Late Gadolinium Enhancement (LGE). After an intravenous contrast agent is administered, LGE highlights areas of myocardial fibrosis, or scarring, within the heart muscle. The presence and extent of this scarring are important for refining the diagnosis and for assessing a patient’s risk of developing dangerous heart rhythms.
Stress testing, frequently performed with an echocardiogram or nuclear imaging, assesses the heart’s function under exertion. This testing is valuable for revealing a latent LVOT obstruction, which may not be present when the patient is at rest. Continuous ambulatory ECG monitoring, such as a 24-hour Holter or an event recorder, is also used to detect abnormal heart rhythms common in HCM, aiding in overall risk assessment.
Genetic Testing
Genetic testing does not provide the structural diagnosis of HCM but is an important component for confirming the underlying cause and guiding family screening. The condition is primarily caused by mutations in genes that encode sarcomere proteins, the basic contractile units of the heart muscle. The two most commonly implicated genes are MYH7 and MYBPC3, which together account for a majority of the genetically identifiable cases.
Genetic testing is recommended for all individuals with a clinical diagnosis of HCM, using targeted panels that screen for these and other associated genes. Identifying a pathogenic mutation confirms the molecular etiology and facilitates cascade screening, which is the process of testing first-degree relatives for the same specific gene variant. This allows for the early identification of individuals at risk, often before they show any symptoms.
A positive genetic test guides family members toward appropriate surveillance, but a negative result does not completely rule out the condition. This is because some HCM cases are caused by mutations in genes that have not yet been identified, or the mutation may be unique to that family. Genetic testing is thus used alongside clinical and imaging data to establish a comprehensive diagnosis.