INHIBITION OF THE PACEMAKER CURRENT - A BRADYCARDIAC THERAPY FOR OFF-PUMP CORONARY OPERATIONS

Background. The accurate performance of coronary anastomoses on the be ating heart requires some form of myocardial immobilization that can b e achieved pharmacologically. Different classes of drugs can be used t o induce bradycardia, but the most effective in this setting of off-pu mp operation has not yet been determined. Methods. Fifty-six isolated buffer-perfused rabbit hearts were divided into seven equal groups, Co ntrol hearts were continuously perfused throughout the experimental ti me course. A second,group of hearts underwent 60 minutes of potassium arrest (at 37 degrees C) followed by 1 hour of reperfusion. The follow ing pharmacologic approaches were tested in the remaining five groups: short-acting beta-blockade (esmolol, 6 x 10(-3) mol/L and 3 x 10(-4) mol/L), opening of adenosine triphosphate-dependent potassium channels (nicorandil, 10(-3) mol/L and 10(-5) mol/L), and inhibition of the pa cemaker current, which largely accounts for the diastolic depolarizati on of sinoatrial node cells (S 16257-2, 3 x 10(-6) mol/L). Each drug w as infused at a constant rate for 60 minutes, after which hearts were perfused for 1 additional hour with drug-free buffer. Heart rate and i sovolumic measurements of function and coronary flow were serially tak en during and after drug infusion. Results. The worst recovery of syst olic and, moreover, diastolic function was yielded by potassium arrest . Neither esmolol nor nicorandil was able to induce a significant brad ycardia. However, nicorandil did not impair function which, conversely , was markedly depressed after esmolol therapy. Significant bradycardi a (p < 0.0001 versus corresponding baseline values and versus all othe r groups) was only achieved with pacemaker current inhibition, which w as otherwise associated with an excellent preservation of contractilit y, diastolic function, and coronary now. Conclusions. Inhibition of th e pacemaker current seems to be an effective approach for inducing int raoperative bradycardia without compromising left ventricular function or flow. (Ann Thorac Surg 1998;66:148-52) (C) 1998 by The Society of Thoracic Surgeons.