Large Q and S waves in lead III on the electrocardiogram distinguish patients with hypertrophic cardiomyopathy from athletes.

OBJECTIVE: To identify electrocardiographic findings, especially deep Q and S waves in lead III, that differentiate athletes from patients with hypertrophic cardiomyopathy (HCM).

METHODS: Digital ECGs of athletes and patients with HCM followed at the Stanford Center for Inherited Cardiovascular Disease were studied retrospectively. All patients with HCM had an echocardiogram performed. A multivariable logistic regression model was used to calculate ORs for various demographic and ECG characteristics. Linear regression was used to correlate ECG characteristics with echocardiogram findings.

RESULTS: We studied 1124 athletes and 240 patients with HCM. The average Q+S wave amplitude in lead III (IIIQ+S) was significantly higher in patients with HCM compared with athletes (0.71±0.69 mV vs 0.21±0.17 mV, p<0.001). In patients with HCM, IIIQ+S directly correlated with interventricular septal (IVS) thickness on echocardiography (ρ=0.45, p<0.001). In a multivariable analysis adjusted for demographic and ECG characteristics, higher IIIQ+S values remained independently associated with HCM compared with athletes (OR=4.2 per 0.5 mV, p<0.001). In subgroup analyses of young patients, African-American subjects and subjects without left axis deviation (LAD), IIIQ+S remained associated with HCM. The addition of IIIQ+S>1.0 mV as an abnormal finding to the International Criteria for athletic ECG interpretation improved sensitivity from 64.2% to 70.4%, with a minimal decrease in specificity.

CONCLUSION: Large Q and S waves in lead III distinguished athletes from patients with HCM, independent of axis and well-known ECG markers associated with HCM. The correlation between IVS thickness in patients with HCM and IIIQ+S suggests a partial explanation for this association.