Detection of myocardial ischaemia by transthoracic leads in ambulatory electrocardiographic monitoring.

OBJECTIVE To determine the best sites for ambulatory monitoring leads to detect myocardial ischaemia. PATIENTS 50 consecutive patients recovering from myocardial infarction. Six patients were excluded because of unsatisfactory recordings or baseline electrocardiographic abnormalities that influenced the diagnostic accuracy of ST segment depression. In 38 patients important ST segment changes were seen before the study recordings. MAIN OUTCOME MEASURE Reproducibility of detecting the electrocardiographic ST segment changes with 12 bipolar leads alone or in combination. RESULTS The highest reproducibility rate was found in infarcts involving both the anterior and inferior left ventricular walls (80%). The reproducibility decreased as the extent of ventricular wall involvement decreased and was lowest in inferior infarcts (31%) (p < 0.001). For large infarcts the detection rate was almost equal for the 12 study leads, whereas disparity between leads increased as the infarct size decreased. The highest overall reproducibility was found in a transthoracic lead (V2, V9R) (76%). This lead was significantly better (p = 0.03) than lead CM5 (50%). When the transthoracic lead was combined with an inferior lead, the reproducibility increased (82%) and was significantly better than the combination of CM5 and an inferior lead (58%) (p = 0.02). CONCLUSIONS Extensive ischaemic electrocardiographic changes are better detected than smaller ones and anterior infarcts better than inferior. A transthoracic lead (V2, V9R) was significantly better than CM5 both alone and when CM5 and the transthoracic lead were combined with an inferior lead.