Infarcts and Ischemia ECG 8
- Normal sinus rhythm
- Posterior myocardial infarction
The posterior wall demonstrates ECG changes the opposite of other myocardial segments due to the location; thus, instead of ST segment elevation, a posterior myocardial infarction is characterized by ST segment depression in lead V1 and frequently V2. The R wave is large in lead V1. Turn the ECG upside down, and you will see ST segment elevation in V1 and a large Q wave — normal findings of a myocardial infarction.
Note that the causes of the R wave being larger than the S wave in lead V1 include a posterior myocardial infarction, right bundle branch block, Wolff-Parkinson-White Syndrome Type A, right ventricular hypertrophy, ventricular tachycardia with a right bundle branch block pattern and isolated posterior wall hypertrophy (can occur with Duchenne’s muscular dystrophy).