Comparison of Body Surface Potential and Laplacian Mapping with Epicardial Mapping for Detection of Cardiac Ischemia in Pigs

The standard electrocardiogram (ECG) and the body surface potential map (BSPM) are only moderately sensitive for the detection of ischemia and cannot accurately localize ischemic regions within the heart. We have previously demonstrated that the body surface Laplacian map (BSLM) does provide the capability to localize electrical activity within the heart. The objective of this study was to compare the abilities of BSLM and BSPM to detect and localize ischemic regions within the heart with reference to direct epicardial potential measurements. Ischemia was induced in six anesthetized Yorkshire swine by occluding the distal left anterior descending (LAD) coronary artery, or a diagonal branch of the LAD and the obtuse marginal coronary artery. Atrial pacing was used to incrementally increase the degree of ischemia. BSPM, BSLM, and epicardial recordings were simultaneously obtained after occlusion of each coronary artery and subsequently during atrial pacing. We used a normalized measure of ischemia (shift in the ratio: ST segment height divided by QR amplitude) measured at each electrode and created corresponding maps of the spatial distribution of this measure for the BSPM, BSLM, and epicardial potential maps. The BSLM was more sensitive than the BSPM in identifying ischemia and was capable of localizing and resolving one or more ischemic areas while the BSPM was not. The BSLM also distinguished between different levels of ischemia associated with atrial pacing at different rates. Due to its better spatial resolution and sensitivity, the BSLM promises to provide an improved means for noninvasive localization of myocardial ischemia.