Vectorcardiographic and Electrocardiographic Diagnosis of Diaphragmatic Myocardial Infarction in Patients With Left Bundle Branch Block

In this study, an attempt was made to determine if the electrocardiogram (ECG) or vectorcardiogram (VCG) might show previously unrecognized evidence of myocardial infarction, particularly diaphragmatic infarction, in the presence of complete left bundle branch lock (LBBB). ECGs and VCGs of 12 patients with LBBB and diaphragmatic infarction were compared to ECGs and VCGs of 10 patients with LBBB and no infarction. Diaphragmatic infarction was diagnosed on the basis of a typical history and inferior surface perfusion defect on Thallium-201 imaging. The presence of a qR complex in II, III, or aVF irrespective of the size of the q wave, appeared specific for infarction, but identified only 5 of 12 (42%). In contradistinction, a QS complex was nonspecific. Since we found q waves in II, III, or aVF not in 5 patients with left axis deviation but in 5 of 7 patients without it, we would like to suggest the possibility that the presence of left axis deviation is a factor which causes the q waves in the inferior leads to be unnoticeable. A diminished maximum spatial vector of 1.59 mv or less identified infarction (not necessarily diaphragmatic only) also in 5 of 12 (42%). In the frontal plane, a 0.04 sec QRS vector ⩽ 0.4 mv identified diaphragmatic infarction in 6 of 12 (50%), and in the left sagittal plane, a ratio of the magnitude of the ST vector to the magnitude of the maximum T vector 0.35 indentified a diaphragmatic infarction in 8 of 12 (67%).