Value of Posterior Leads (V7-V9) in Diagnosis of Posterior Wall ST Segment ElevationMyocardial Infarction

Background- The standard 12-lead electrocardiogram (ECG) has relatively low sensitivity for the diagnosis of posterior wall acute myocardial infarction (AMI). The prevalence of posterior wall myocardial infarction (MI) has been studied in a few studies. We evaluated ST-segment elevation (STE) prevalence in posterior leads in patients with acute coronary syndrome (ACS) in order to determine the prevalence of posterior wall MI and the value of posterior ECG leads in diagnosing it. Methods- Patients who were admitted with ACS during a 12-month period to our department were included in the study. Posterior electrocardiogram (V7-V9) was obtained in addition to the standard 12-lead electrocardiogram in the emergency room (ER) and also in the cardiac care unit (CCU). All ECGs were reviewed by a cardiologist for the presence of STE of at least 0.5 mm in two or more leads of V7-V9. Results- In total, 230 patients were diagnosed with AMI based on the World Health Organization criteria, out of 506 patients who were admitted with ACS. In addition, 146 patients (63.47%) had criteria of STE MI in 12-lead standard ECG and 84 patients (36.52%) had non-STE myocardial infarction on standard ECG. Five patients (6%, 95% CI; 2-13.3%) had STE in posterior leads without STE in the standard 12-lead ECG and initially were diagnosed as non- STE myocardial infarction. Overall, 31 patients (13.5%, 95% CI; 9.3-18.6%) had posterior STE myocardial infarction in 15-lead ECG, of which 18 cases (58.1%, 95% CI; 39.1-75.5%) were accompanied with inferior MI, 3 cases (9.7%, 95% CI; 2-25.8%) with anterior MI and 5 cases (16.1%, 95% CI; 5.5-33.7%) with anteroseptal MI in the standard ECG. Conclusion- The diagnosis of isolated posterior MI or posterior MI in the presence of other myocardial wall infarction is a challenging diagnosis. These patients may have normal standard ECGs. Obtaining posterior leads will lead to the diagnosis of posterior wall STE MI in a significant number of patients (Iranian Heart Journal 2007; 8 (4): 24-28).