Identification of septal ischemia during exercise by Q-wave analysis: correlation with coronary angiography.

Septal Q-wave amplitudes were studied in lead CM5 to evaluate its utility in predicting segmental coronary artery pathoanatomy. Q-wave amplitudes were measured in 41 patients with coronary artery disease (CAD) before and immediately after treadmill exercise. All patients studied had either significant single-vessel CAD (greater than 70% diameter reduction) or normal coronary anatomy; 13 had left anterior descending (LAD) CAD, 8 had right coronary occlusions, 8 had left circumflex (LC) CAD, and 12 had angiographically normal coronary arteries. Septal Q-wave amplitude measurements at rest and during peak exercise were recorded in 0.5 mm increments and classified as increasing in 20 patients, decreasing in 8, and no change in 13 with exercise. All 13 patients with isolated LAD narrowing had either no change (5 patients) or a decrease (8 patients) in the septal Q wave with exercise. Statistical analysis revealed 62% sensitivity and 100% specificity for single LAD narrowing if a decreasing Q wave was noted with exercise. Patients with isolated right or LC CAD or normal coronary anatomy had mixed septal Q-wave responses to exercise. Only patients with LAD narrowing had reductions in Q-wave amplitude with treadmill exercise. This finding suggests that low Q-wave voltage and its failure to increase after exercise imply abnormal septal activation, reflecting loss of contraction associated with ischemia from LAD narrowing.