Alterations in QRS during ischemia of the left ventricular free-wall in goats.

Summary X, Y , and Z axis electrocardiograms, spatial magnitude and spatial velocity electrocardiograms and QRS loops in three planes were recorded from goats before and during ischemia of the left ventricular free-wall produced by injection of ceramic microspheres into branches of the left circumflex coronary artery. Epicardial electrograms were recorded from ischemic and nonischemic regions of the left ventricle to determine time of arrival of depolarization at epicardial sites subjacent. Ischemia produced tardy and unopposed activation of the left ventricular free-wall and oriented major vectors caudad and dorsad, as opposed to their craniad and dorsad orientation in the control state. Peak magnitude of QRS portion of the spatial magnitude electrocardiogram increased markedly, and duration of QRS doubled. Epicardium in the ischemic zone depolarized tardily, whereas in the control state, epicardium from all areas on the left ventricle was activated early during QRS and nearly simultaneously.