Changes in QRS segments during exercise in relation to scintigraphic myocardial perfusion defects: a multivariate analysis.

Background: The relation between QRS changes during exercise and ischemic heart disease is controversial. The present investigation addressed whether exercise QRS changes are related 1) to myocardial ischemia or necrosis, 2) to possibly confounding factors such as baseline QRS size and changes in heart rate and ST magnitude during exercise, and 3) to the location of scintigraphic defects.
Methods: Advanced computerized vectorcardiography (MIDA1000, Ortivus Medical AB, Sweden) was recorded in 71 consecutive patients referred for 201TI exercise myocardial scintigraphy. Maximal exercise tests were performed in the sitting position on a bicycle ergometer. Planar scintigraphic images were obtained immediately after exercise and 4 hours later in three projections, and were evaluated blindly.
Results: Exercise QRS changes correlated to baseline QRS size (X, Y, and Z leads; P < 0.005), change in heart rate (X and Y leads; P < 0.01), and ST change at J + 20 ms (X, Y, and Z leads; P < 0.0001). Increased QRS magnitudes in the Y and Z leads correlated to late perfusion defects (P < 0.0001). These correlations remained after correction for baseline QRS size and changes in heart rate and ST magnitude at J+20 ms during exercise (P < 0.0001). No consistent relationships were observed between the location of myocardial perfusion defects and the stress-induced alterations in QRS.
Conclusions: Baseline QRS size and changes in heart rate and ST magnitude may have important confounding effects on the QRS response to exercise. However, even after consideration of these factors, the QRS response to exercise was related to late (4 h) scintigraphic myocardial perfusion defects. The findings suggest that the presence of myocardial infarctions or long-lasting ischemia after exercise is associated with increased QRS magnitudes during exercise.