Electrocardiographic Comparison of Dobutamine and Bruce Cardiac Stress Testing With High Resolution Mapping in Experimental Models

Brian Zenger1, Wilson Good2, Rob MacLeod1
1University of Utah, 2The SCI Institute


Abstract

Introduction: Myocardial ischemia occurs when the demand for nutrients and perfusion by the heart outweighs the available supply. Clinical tests to detect acute myocardial ischemia induce transient cardiac stress by means of exercise or pharmaceutical stimulation and measure electrical changes of the heart on the body surface via an electrocardiogram (ECG). Such tests assume that both mechanisms induce identical—or at least similar—forms of ischemia. However, no definitive experiments have been performed to assess the electrical differences produced during different stressing mechanisms. To improve ECG detection of myocardial ischemia, we must study how varied stressing agents (pharmacological or paced stressors) change ECG signatures.

Methods: Electrical recordings within the myocardium, on the epicardial surface, and on the body surface of a porcine model of acute, controlled ischemia were measured during ischemic episodes. These episodes were induced with constant hydraulic occlusion of the left anterior descending coronary artery at 10% of normal flow rates . Heart stress was modulated either via pacing with clinical standard BRUCE test protocol heart rates, or by clinical standard continuous dobutamine infusions. Each episode lasted 15 minutes with stepwise increase in pacing rate or pharmacological infusion rate every 3 minutes.

Results: Preliminary qualitative results suggest significant differences in the recorded electrical signal between pacing and pharmacological stress mechanisms. Differences include the location and volume of ischemia and its temporal progression measured within the heart . The remote signals recorded on the epicardial and body surface measurements also showed morphological differences.

Discussion: These results, although preliminary, show that significant differences occur in the electrical signatures of myocardial ischemia depending on the type of stress placed on the heart. Such results suggest that, despite previous theory, different stresses on the heart require unique diagnostic criteria to detect and monitor myocardial ischemia.