Usefulness of st depression in ventricular premature complexes to predict myocardial ischemia

Abstract

Patients with coronary artery disease (CAD) frequently have ventricular premature complexes (VPCs) both at rest and during exercise. These ectopic beats may arise from almost any location in the ventricle and unless they are frequent enough to produce ventricular tachycardia, they are considered by most physicians to have little clinical significance. VPCs are more common (10% to 40%) in patients with CAD than in those without CAD.1 The voltage and configuration of these ectopic beats vary a good deal and ST-segment depression in these complexes have not been correlated with the presence or absence of ischemia. We have recently noted, during treadmill stress testing, that the VPCs occurring at rest usually have minimal ST-segment deviations. As in subjects with left bundle branch block, the complexes in nonischemic subjects have ST deviation no >10% of the R-wave amplitude. There is evidence that when an acute myocardial infarction is suspected in a patient with left bundle branch block, significant ST deviation is indicative of an acute ischemic process.2 An unpublished observational study performed in 2000 by Ronald H. Selvester, MD, at Long Beach Memorial Heart Institute suggests that nonischemic patients with left bundle branch block have ST deviation no >10% of the QRS amplitude. In these nonischemic subjects with left bundle branch block, he showed that plotting ST deviation (scaled at 10% of the peak QRS) against the peak QRS gave a 45° slope. All but 2 of 135 measurements fell within a 10% boundary on each side of the slope (Figure 1). We have noted that patients with significant CAD undergoing increased exercise appear to become more ischemic and the VPCs may have more ST-segment depression. Incorporating Selvester’s 10% rule, we hypothesize that ST depression of VPCs >10% of the R-wave amplitude may identify significant ischemia. If changes in the ST segment of VPCs were a consistent finding during ischemia, this would provide one more marker that would be useful when doing exercise testing.