Origin of the Giant R Wave in Acute Transmural Myocardial Infarction in the Pig

An increase in R wave amplitude and a diminution of S wave amplitude, together with ST segment elevation, have been described as very early electrocardiographic changes during clinical and experimental acute myocardial infarction. The genesis of these QRS changes remains unclear. We assessed the quantitative relationship between the local conduction delay and the formation of the giant R wave, using multiple epicardial, intramural unipolar, and bipolar electrodes in 30 open-chest pigs with acute transmural myocardial ischemia. Blood pressure, heart rate, serum electrolytes, hematocrit, and left ventricular size remained constant, or varied insignificantly throughout the experiments. In nonischemic pigs, transmural left ventricular activation occurred nearly simultaneously, and the activation time was not correlated with the net QRS potential. During acute ischemia, a giant R wave developed at all of the electrodes located within the ischemia region; R wave amplitude began to increase 1min after coronary artery ligation (p