Quantitative assessment of myocardial ischemia by electrocardiographic and scintigraphic imaging

Abstract

We calculated distributions of epicardial potentials from body-surface electrocardiograms (ECGs) recorded during controlled myocardial ischemia and compared them with scintigraphic estimates of ischemia’s extent/severity>. The study population consisted of patients suffering from single-vessel coronary artery disease, referred for elective percutaneous transluminal coronary angioplasty of either the left anterior descending ( n = 7), the right coronary ( n = 9), or the left circumflex ( n = 2) artery. After the target vessel had been dilated, a 1960s “study” inflation was performed with a non-perfusion-type balloon catheter; at its commencement, technetium-99m sestamibi was injected via a femoral-vein catheter, and ECGs were recorded throughout the inflation from 120 leads. Single photon emission computed tomographic imaging was performed one hour after the injection of radionuclide to obtain an “occlusion image”, and again one hour after a repeat injection 24 hours later to obtain a “control image”; the latter image was subtracted from the former, to derive a scintigraphic difference map (Δ map). The ECGs were signal-averaged over a 10-s window at preinflation and peak-inflation states, the preinflation averaged complexes were subtracted from the peak-inflation ones to produce body-surface Δ maps, and the corresponding Δ maps of epicardial potentials were calculated by applying the electrocardiographic inverse solution; this procedure is referred to as electrocardiographic imaging. The ECG-derived epicardial Δ maps related spatially to the scintigraphic Δ maps in all patients. The percent areas and surface integrals of positive values in ECG-derived Δ maps were found to be very good single-variable predictors of the extent ( r = 0.73; p = 0.0006) and severity ( r = 0.72; p = 0.0008) of the scintigraphically-estimated perfusion defect; a regression equation using two ECG-derived predictors further improved the agreement with scintigraphic estimates ( r = 0.81; p = 0.0004 for estimates of severity). These findings suggest that noninvasive electrocardiographic imaging might provide quantitative estimates of the extent/ severity of myocardial ischemia that agree closely with those provided by scintigraphic techniques.