Septal Q wave in exercise testing: angiographic correlation.

A study of septal Q wave response in lead CM5 was carried out to evaluate its usefulness in predicting coronary artery disease. Q wave amplitude was measured in 50 patients with coronary artery disease and 50 normal subjects before and immediately after exercise. In the 100 patients evaluated with coronary angiography, the septal Q wave in lead, CM5 was smaller in patients with coronary artery disease than in normal subjects at rest (probability [p] less than 0.001) and immediately after exercise (p less than 0.001). An embryonic (0.5 mm) or absent Q wave in lead CM5 was significantly more frequent in patients with coronary artery disease than in normal subjects both at rest (76 versus 48 percent) and after exercise (82 versus 16 percent). The sensitivity for S-T depression was 52 percent, the specificity 74 percent and the predictive value 70 percent. The respective values for Q wave were 82, 88 and 87 percent. These differences were not significant (p less than 0.05). When either a positive S-T or Q wave response was used, the sensitivity increased to 92 percent (p less than 0.05), and the specificity and predictive values remained unchanged (p less than 0.01). An increase in Q wave amplitude with exercise identified a false positive S-T segment response to stress in 75 percent of cases. Absence of the Q wave in lead CM5 with S-T depression after identified a true positive response in 100 percent of cases. These findings suggest that low Q wave voltage and it failure to increase after exercise imply abnormal septal activation, reflecting loss of contraction associated with ischemia. This finding may be a useful marker for ischemia; the increase in the septal Q wave with exercise may be of value in identifying a false positive S-T segment response.