The electromotive force of the ventricular free wall and papillary muscle preparations.

The electromotive force of the ventricular tissues with different anatomy and activation patterns was studied. The left ventricular wall was perfused with Tyrode's solution from the circumflex branch of the left coronary artery and was stimulated first at an epicardial and then endocardial site to induce ectopic beats. The early QRS voltage was compared with the activated area at the same instant. In other experiments, the whole heart was perfused from the aorta, and the anterior papillary muscle of the right ventricle was introduced into a small separate chamber. Different locations were stimulated to induce longitudinal and transverse activation, and the remote potential was measured with leads in both directions. By means of a calibration system with artificial dipoles, the strength of the double layer was expressed in terms of mA X cm per unit area of the activation wave front. The results indicated that epicardial stimulation of the left ventricular wall produced voltage proportional to the activated area; the average moment was found to be 0.11 mA X cm per unit area. The potential curve produced by endocardial stimulation of the same preparation was characterized by an initial low-voltage phase, followed by a sharp upstroke. The right ventricular papillary muscle produced a larger double layer moment during activation in the longitudinal direction, but voltage due to transverse activation was several times smaller.