Background & Objective: Patients with ischemic heart disease classified to two major groups: patients with stable angina and patients with Acute Coronary Syndrome (ACS). Previous studies showed that posterior segment of left ventricle is a silent segment on ECG, and routine 12 leads electrocardiogram (ECG) is not sensitive for evaluation of posterior infarction. This study designed for evaluation of ST segment deviation on posterior leads of ECG in patients with ACS at Beheshti hospital in 2002.
Materials & Methods: This is a descriptive-analytical and prospective study. In 347 patients with diagnosis of ACS who were admitted in the emergency department, 12 leads ECG with additional three leads (V7-V8-V9) was carried out. For statistical analysis, calculation of percentages for sensitivity, odds ratios, and %95 confidence intervals was performed.
Results: Major abnormalities (ST elevation 1mm and ST depression  1mm) were found on the extra three leads in %21.6 (75 out of 347). Sensitivity of ST segment elevation for acute myocardial infarction on 12 versus 15 leads increased from %68.5 to %90.7 (P=0.0005). Sensitivity of ST segment depression for acute myocardial infarction on 12 versus 15 leads increased from %31.5 to %40.7 (p=0.157). Sensitivity of ST segment elevation for unstable angina (239 cases) on 12 versus 15 leads from zero to %5 and sensitivity of ST segment depression for unstable angina on 12 versus 15 leads increased from %31.8 to %36.8 (P=0.25 ).
Conclusion: The 15-leads ECG provides increased sensitivity of detecting ST–segment deviation in acute myocardial infarction and unstable angina.