Effects of arbutamine stress testing compared to treadmill exercise stress testing on electrocardiographic responses of ischemia and myocardial oxygen demand

Abstract

The purpose of the study was to compare certain hemodynamic and electrocardiographic effects of incremental doses of arbutamine(ESA), a new beta-agonist pharmacologic stress agent, with exercise(ETT). Ten volunteers, mean age 66 years, with known or suspected coronary artery disease completed a symptom-limited ESA and ETT(modified Naughton protocol) to 85% of their age predicted maximum heart rate (APMHR) in a randomized cross-over study design. The ESA delivery system controlled infusion via an intravenous line to increase the subject's heart rate by 8 bt*min⁻¹. Heart rate(HR), systolic blood pressure(SBP), diastolic blood pressure (DBP), rate pressure product (RPP), and both an average of 3 independent observers visual ST segment shifts at J₆₀(VAVEST60) and computer ST segment shifts at J₆₀(CST60) were analyzed from the electrocardiogram(ECG) at baseline(0%TT), 25%TT, 50%TT, 75%TT, and at peak stress(100%TT). The occurrence and character of any dysrhythmias also were noted. Two-way repeated measures analysis of variance for each cardiovascular and electrocardiographic variable demonstrated no difference(p<0.05) by treatment effect alone. All variables, HR, SBP, DBP, RPP, VAVEST60, and CST60, showed a Significant (p<0.05) time effect while only SBP and RPP showed a significant (p≤0.01) time*treatment interaction effect. The following ectopic occurrences were noted during the ESA: PAC (n=4), PVC(n=3), couplet(n=2), and VT(n=5). The ETT produced a PAC(n=1), PVC's(n=3), and a couplet(n=1). The ESA produced a similar ST shift pattern in the ECG responses as did the ETT, however, it did this at a lower myocardial demand with a greater tendency for arrhythmias. These findings suggest a possible difference in receptor stimulation. The Similarities to exercise in the response variables measured in this study offer arbutamine as an alternative mode of stressing the heart for patient populations with multiple health limitations who could not perform an adequate exercise test.