Study objectives: To assess sensitivity, specificity, and odds ratios of ECG findings on leads V4R, V8, and V9 for acute myocardial infarction.
Design: Prospective, two-stage cohort study.
Setting: A 660-bed university-affiliated community hospital.
Type of participants: One hundred forty-nine admitted patients with suspected myocardial infarction or unstable angina.
Interventions: Standard 12-lead ECG followed immediately by V4R, V8, and V9.
Measurements: Initial ECG findings of ST-segment displacement, Q waves, T-wave inversion, and eligibility for thrombolytic therapy.
Results: Major abnormalities (ST-segment deviation, T-wave inversion, Q waves) were found on the extra three leads in 28.9% (43 of 149) of patients. Sensitivity of ST-segment elevation for acute myocardial infarction on 12 versus 15 leads increased from 47.1% to 58.8%, respectively, with no decrease in specificity. McNemar's pair-matched analysis for ST-segment elevation on myocardial infarction subgroup showed an association of ST elevation with the 15-lead ECG (P < .05). An eightfold increase in the odds of detecting ST elevation was found (90% confidence interval, 1.42 to 14.58); 22% of patients negative for ST elevation on 12 leads were positive on 15 leads. Analysis of ECG criteria for thrombolytic therapy presenting uniquely on extra leads showed an increased sensitivity from 35.3% to 44.1% on 12 versus 15 leads, respectively; there was a sixfold increase in the odds of meeting ECG thrombolytic therapy criteria (90% confidence interval, 0.34 to 11.66); 13.5% of patients not meeting criteria on 12 leads did so on 15 leads.
Conclusion: The 15-lead ECG provides increased sensitivity and odds of detecting ST-segment elevation in acute myocardial infarction patients with no loss of specificity; its use may expand the selection of thrombolytic therapy candidates and provide a fuller ECG description of the extent of myocardial injury and necrosis.