Hypertrophic cardiomyopathy on ECG

What it looks like on ECG

There is no specific "HCM ECG pattern", but abnormalities are detected in the majority of patients, with various estimates placing it at 75–95%. Most commonly, these are signs of left ventricular hypertrophy: increased R-wave amplitude in the left precordial leads (V5–V6) and I, aVL; increased S-wave amplitude in V1–V2; and positive voltage criteria — the Sokolow–Lyon index (SV1 + RV5 or SV1 + RV6 >35 mm, i.e., 3.5 mV) or the Cornell criterion (RaVL + SV3 >28 mm in men, >20 mm in women). The sensitivity of these criteria in HCM is limited; normal voltages do not rule out the diagnosis. A pattern of "LVH with systolic strain" is frequently associated — downsloping ST-segment depression and asymmetrical negative T waves in the leads exhibiting high R-wave amplitudes.

Special attention must be paid to pseudoinfarct Q waves — narrow (<40 ms) and deep, located in the inferior (II, III, aVF) or lateral (I, aVL, V5–V6) leads, and occasionally present across multiple leads simultaneously. These are assessed using standard approaches for pathological Q waves: depth and width, presence in two contiguous leads, and accounting for the known caveats regarding an isolated Q wave in lead III or aVL, which can be a normal variant. Altered initial septal depolarization vectors resulting from marked hypertrophy, myofibrillar disarray, and fibrosis account for such Q waves in HCM; however, an ECG alone cannot reliably exclude concomitant or prior myocardial infarction — ischemic heart disease may also coexist in a patient with HCM. Such Q waves require comprehensive clinical and instrumental evaluation: symptoms, serial ECGs, high-sensitivity troponin, and imaging as indicated.

The apical variant of HCM (more frequently described in Japanese patients, but observed worldwide) is characterized by deep, occasionally giant (≥10 mm) negative T waves, predominantly in V3–V6, with variable extension to other precordial, inferior, or lateral leads. Their magnitude and localization fluctuate; in some cases, ST-segment depression and negative T waves predominate without pronounced J-point changes. If not sufficiently scrutinized, this presentation may be mistaken for anterior wall ischemia.

Atrial abnormalities — signs of left atrial enlargement (broad, notched P wave in lead II, biphasic P wave with a deep negative terminal phase in V1) secondary to elevated left ventricular filling pressures. Atrial fibrillation frequently develops subsequently.

Mechanism

Mutations in sarcomere protein genes (beta-myosin heavy chain, myosin-binding protein C, and others) lead to hypertrophy, chaotic arrangement of muscle fibers (myofibrillar disarray), and patchy fibrosis, most prominently in the interventricular septum. Increased muscle mass generates high QRS amplitudes (LVH voltage criteria). Septal fiber disarray and fibrosis alter the trajectory of initial depolarization, which can produce narrow, deep Q waves in the absence of true necrosis, although this mechanism does not rule out concurrent coronary artery disease. Repolarization abnormalities in the hypertrophied and ischemic (due to microvascular dysfunction) myocardium result in deep T-wave inversion, which is most pronounced when hypertrophy is localized to the apex. Fibrosis and fiber disarray also provide the arrhythmogenic substrate for ventricular arrhythmias.

Causes

• Mutations in cardiac sarcomere protein genes (autosomal dominant inheritance) — the primary cause of classic HCM; a causative variant is not identified in a subset of patients
• Storage diseases and metabolic disorders (HCM phenocopies): Fabry disease, Danon disease (LAMP2 gene), PRKAG2 syndrome (PRKAG2 gene), and others
• Mitochondrial diseases
• Syndromic forms (Noonan syndrome and other RASopathies) in pediatric patients
• Cardiac amyloidosis — occasionally clinically and echocardiographically mimics HCM (pseudohypertrophy)

Differential diagnosis

• Hypertensive heart disease (secondary LVH): differentiated solely by echocardiography/MRI and clinical history (history of hypertension), with a similar ECG presentation
• Athlete's ECG: high voltage typically unaccompanied by deep negative T waves or pathological Q waves; when in doubt — echocardiography and cardiac MRI
• Myocardial infarction (inferior, anterior): pathological Q waves in HCM do not rule out prior or acute infarction per se; clinical assessment, ECG evolution, and troponin levels are required
• Apical HCM vs. anterior wall ischemia / Wellens' syndrome: giant T waves in apical HCM are usually stable in the setting of an established diagnosis, but any new symptoms or dynamic changes mandate the exclusion of ACS rather than attributing findings to "known baseline status"
• PRKAG2 syndrome, Danon disease, and other phenocopies with pre-excitation: true pre-excitation and a short PR interval in the presence of hypertrophy are atypical for sarcomere-mediated HCM and warrant targeted evaluation for these conditions, as well as differentiation from pseudo-delta waves caused by septal hypertrophy

Clinical significance and management

HCM is a major cause of sudden cardiac death in young individuals and athletes, driven by ventricular tachyarrhythmias occurring against the background of fibrosis and ischemia of the hypertrophied myocardium. Upon detecting suspicious ECG findings (unexplained LVH, pathological Q waves without clinical signs of MI, giant T waves), the physician must order an echocardiogram to assess wall thickness, left ventricular outflow tract (LVOT) obstruction, and systolic anterior motion (SAM) of the mitral valve. In confirmed cases, risk stratification for sudden death is performed (wall thickness, family history of SCD, unexplained syncope, nonsustained VT on Holter monitoring, obstruction gradient, late gadolinium enhancement on cardiac MRI for fibrosis), alongside decisions regarding implantable cardioverter-defibrillator (ICD) placement, follow-up monitoring, and screening of first-degree relatives. Regarding physical activity, the contemporary approach avoids automatic bans in favor of individualized decision-making at a specialized center, taking into account the phenotype, risk profile, and type of exertion; moderate recreational activity is generally recommended for the majority of patients.

Common interpretation errors

• Interpreting pathological Q waves as a prior myocardial infarction without considering the clinical presentation and medical history, or conversely, automatically assuming they represent a benign "pseudoinfarct" pattern without ruling out concomitant coronary artery disease
• Failing to evaluate for acute coronary syndrome (clinical assessment, serial ECGs, high-sensitivity troponin) in the presence of new symptoms, chest pain, or dynamic ECG changes, while dismissing findings based on a known stable apical pattern
• Considering a normal ECG sufficient to rule out HCM in a young patient with a family history of sudden cardiac death
• Disregarding signs of left atrial enlargement as an indirect marker of diastolic dysfunction
• Confusing pseudo-delta waves in marked septal hypertrophy with true WPW syndrome and failing to search for phenocopies (PRKAG2, Danon disease) in the presence of genuine pre-excitation

Frequently asked questions

Related terms

More in the «Channelopathies and Cardiomyopathies» section

Entire section

Sources

• Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, 6th ed.
• Goldberger A.L. Clinical Electrocardiography: A Simplified Approach
• Orlov V.N. Guide to Electrocardiography
• 2023 ESC Guidelines for the management of cardiomyopathies

Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.