What are the ECG (electrocardiogram) findings in patients with Hypertrophic Cardiomyopathy (HCM)?

ECG Findings in Hypertrophic Cardiomyopathy (HCM)

The 12-lead ECG is abnormal in 75-95% of patients with phenotypic HCM, showing various characteristic findings including left ventricular hypertrophy, repolarization abnormalities, and pathological Q waves. 1

Key ECG Findings in HCM

Common Abnormalities

• Left ventricular hypertrophy (LVH) voltage criteria - one of the most common findings, though not reliably correlated with the severity or pattern of hypertrophy 1
• Repolarization abnormalities (ST-segment and T-wave changes) 1
• Pathological Q waves or QS patterns, which may mimic myocardial infarction patterns, especially in the inferior and lateral leads 1, 2
• T-wave inversions, particularly in lateral and inferior leads 3

Less Common Findings

• Persistent ST-segment elevation that may simulate acute myocardial infarction, variant angina, or acute pericarditis 4
• Left atrial enlargement 1
• Conduction abnormalities including left bundle branch block 1, 3
• Wolff-Parkinson-White pattern, which may suggest specific phenocopies of HCM 1

Clinical Significance and Monitoring

Diagnostic Value

• A 12-lead ECG is recommended in the initial evaluation of all patients with suspected HCM (Class I recommendation) 1
• ECG abnormalities may precede echocardiographic evidence of hypertrophy, making the ECG valuable for early detection 1, 5
• ECG should be performed as part of periodic follow-up every 1-2 years in established HCM patients 1

Risk Stratification

• 24-48 hour ambulatory ECG monitoring is recommended in the initial evaluation and periodic follow-up (every 1-2 years) to identify patients at risk for sudden cardiac death (SCD) 1
• Non-sustained ventricular tachycardia (NSVT) on ambulatory monitoring identifies patients at higher risk for SCD 1
• Extended monitoring (>24 hours) is recommended for patients with palpitations or lightheadedness 1

Screening

• A 12-lead ECG is recommended as a component of the screening algorithm for first-degree relatives of patients with HCM 1
• ECG screening should be performed every 12-18 months in adolescent first-degree relatives without echocardiographic evidence of hypertrophy 1

Important Caveats and Pitfalls

• Despite its importance, up to 6% of patients with echocardiographically confirmed HCM may have a normal ECG at presentation 6
• Recent research suggests that the prevalence of abnormal ECGs in participants with suspected HCM detected during screening echocardiography may be less than 25%, indicating that ECG alone is not sufficiently sensitive for HCM detection 3
• Patients with normal ECGs tend to have a less severe phenotype with better cardiovascular outcomes and lower risk of cardiac death 6
• ECG findings may help differentiate HCM from phenocopies such as cardiac amyloidosis and glycogen storage diseases 5
• The pattern of ECG abnormalities may correlate with the distribution of hypertrophy - isolated septal hypertrophy is more commonly associated with pathological Q waves, while combined ventricular hypertrophy shows more voltage criteria for LVH 2

Monitoring for Arrhythmias

• Extended ambulatory monitoring is reasonable to screen for atrial fibrillation (AF) in HCM patients with risk factors such as left atrial dilation, advanced age, and NYHA class III-IV heart failure 1
• Extended monitoring may also be considered in adult HCM patients without AF risk factors to assess for asymptomatic paroxysmal AF 1
• Longer periods of monitoring may detect more episodes of NSVT, though the optimal monitoring duration remains to be established 1