Value of a bipolar modified inferior lead in detection of inferior myocardial ischaemia.

Only bipolar leads are normally available for ambulatory monitoring. Bipolar precordial leads are reliable for detecting left coronary artery insufficiency, but may not detect changes caused by right coronary artery insufficiency. The magnitude and polarity of ST segment changes in a bipolar modified inferior lead and in CM5 were compared with those in standard electrocardiographic leads in 10 consecutive patients with acute myocardial infarction (eight inferior and two anteroseptal). The polarity of the ST segment in the modified orthogonal y lead was the same as that in aVF in all eight patients with inferior myocardial infarction and in six the size of the ST segment shift was identical in the two leads as well. In two patients the ST segment shift was larger in the modified orthogonal y lead than in aVF. In one of the two patients with anteroseptal myocardial infarction the polarity of the ST segment shift was the same in the modified orthogonal y lead and aVF. In the other patient it was slightly different. The CM5 lead did not reliably detect inferior myocardial ischaemia. A modified orthogonal y lead is suitable for the detection of inferior myocardial ischaemia.