Characteristic ECG Findings in Hypertrophic Obstructive Cardiomyopathy (HOCM)
The 12-lead ECG is abnormal in 75-95% of patients with phenotypic hypertrophic cardiomyopathy (HCM), with characteristic findings including left ventricular hypertrophy (LVH), abnormal Q waves, repolarization abnormalities, and conduction disturbances. 1
Primary ECG Abnormalities in HOCM
Left Ventricular Hypertrophy
- LVH by voltage criteria is common but not universal
- Unlike hypertensive heart disease where isolated voltage criteria may be seen, HCM typically shows more extensive ECG abnormalities 1
- Voltage criteria alone are insufficient for diagnosis, as they correlate poorly with the severity or pattern of hypertrophy 1
Q Waves
- Pathological Q waves (≥40 ms duration and/or ≥25% of R wave depth and/or ≥3 mm depth in at least two contiguous leads) 2
- Often present in inferolateral leads (II, III, aVF) or anteroseptal leads (V1-V4)
- Q waves in HCM typically occur with positive T waves, helping distinguish them from myocardial infarction patterns 2
- Represent areas of myocardial fibrosis and asymmetrical distribution of LVH 2
Repolarization Abnormalities
- ST-segment depression and T-wave inversions, particularly in lateral and inferior leads
- Deep, widespread T-wave inversions may be seen, especially in apical variants
- Marked repolarization abnormalities help distinguish HCM from hypertensive heart disease 1
Conduction Abnormalities
- Left axis deviation
- Left anterior fascicular block
- Intraventricular conduction delays
- Prolonged PR interval
Additional ECG Features
Atrial Abnormalities
- Left atrial enlargement (P-mitrale)
- Increased risk of atrial fibrillation (present in up to 50% of patients) 1
Ventricular Arrhythmias
- Premature ventricular complexes
- Non-sustained ventricular tachycardia (NSVT) may be detected on ambulatory monitoring in approximately 20% of adults with HCM 1
- NSVT is an important risk marker for sudden cardiac death 1
Diagnostic Value and Clinical Implications
Differential Diagnosis
- ECG abnormalities help distinguish HCM from:
Early Detection
- ECG abnormalities may precede development of echocardiographic LVH
- Q waves and repolarization abnormalities are highly specific (98% specificity) markers for sarcomere mutation carriers without LVH 4
- ECG screening is recommended as part of the initial evaluation and follow-up of patients with HCM and their first-degree relatives 1
Risk Stratification
- Non-sustained ventricular tachycardia on ambulatory monitoring is associated with increased risk of sudden cardiac death 1
- Annual 12-lead ECGs are reasonable in stable HCM patients to evaluate for asymptomatic changes in conduction or rhythm 1
Monitoring Recommendations
- 12-lead ECG is recommended in the initial evaluation and periodic follow-up (every 1-2 years) 1
- 24-48 hour ambulatory ECG monitoring is recommended in initial evaluation and follow-up to identify ventricular arrhythmias 1
- Extended monitoring is reasonable in patients with risk factors for atrial fibrillation 1
Pitfalls and Caveats
- ECG abnormalities do not reliably correlate with the severity or pattern of hypertrophy 1
- Normal ECG does not exclude HCM (5-25% of patients may have normal ECGs)
- ECG voltage criteria alone have limited sensitivity and specificity
- Q waves in HCM may mimic myocardial infarction patterns, requiring careful clinical correlation
- Ethnicity affects ECG patterns - black patients may have more pronounced voltage criteria even with hypertension 1
Understanding these characteristic ECG findings is essential for early detection, differential diagnosis, and risk stratification in patients with HOCM.