Comparative Left Ventricular Function Following Atrial, Septal, and Apical Single Chamber Heart Pacing in the Young PETER P. KARPAWICH and SEEMA MITAL From the Section of Pediatric Cardiology, Children's Hospital of Michigan, Wayne State University School of Medicine, Detroit, Michigan KARPAWICH, P.P. ET AL.: Comparitive Left Ventricular Atrial, Septal, and Apical Single Chamber Func- tion Following Heart Pacing in the Young. Ventricular pacing, typically initiated from a RV apical elec- trode, inherently causes abnormal biventricular activation, decreases LVfunction, and causes histopatbo- logical changes. Since pacing initiated in childhood can he expected to have a more protracted course compared with the adult, the consequences of this alteration in LV hemodynamics gain added signifi- cance among the young pacemaker recipient. The purpose of this study was to evaluate the potential of improving paced LV function by a septal electrode implant site. Acute alterations in cardiac index, LV pressure, and contraction indices, including dP/dt, Vmax. and Vpm, were compared among 22 patients (median age 10 years) with normal cardiac anatomy during intracardiac electrophysiological studies. LV hemodynamics were measured during intrinsic rhythms and following 15 minutes of atrial, HV apical, and septal pacing at an appropriate exercise rate for age of 150 ppm. Results showed a significant de- crease in LV dP/dt, Vmax, and Vpm, and increase in LV end-diastolic pressure only with apical pacing. Septal pacing, in spite of loss of any atrial contribution to ventricular filling, maintained comparable in- dices with intrinsic and atrial paced rhythms. This study demonstrates that normalized LV function is maintained by septal and deteriorates with apical pacing acutely among young, nonischemic hearts. Con- tinued evaluation of appropriate pacing electrode designs to permit septal implant is needed to ensure op- timal chronically paced LV function. (PACE 1997; 20[Pt. I]:1983-1988) pacing, septum, ventricular function, hemodynamics Introduction In the normal heart, optinial ventricular func- tion is maintained by nearly simultaneous biven- tricular activation sequences utilizing the special- ized septal conduction system. The paced ventricle, with or without the addition of any atrial contribution to filling, inherently may exhibit less than optimal function compared with normal. An- imal studies have shown that a normal ventricular contraction pattern is a prerequisite for preserva- tion of optimal systolic and diastolic function.^ Ventricular pacemakers in current use typically use the right ventricular (RV) apex for pacing electrode Address for reprints: Peter P. Karpawich, M.D., Section of Car- diology, Children's Hospital of Michigan, 3901 Beaubien Blvd., Detroit, MI 48201. Fax: (313) 993-0894. Received Novemher 14, 1995; revised March 4, 1996; accepted May 14, 1996. attachment. Pacing from this site causes an abnor- mal activation sequence and asynchronous ventric- ular contraction which results in abnormal wall motion,^-^ diminished left ventricular (LV) func- tion, and decrease in the stroke volume of ejecting hearts.^-^ In addition, histopathological alterations in the form of myofibrillar rearrangements, dys- trophic myocardial calcifications, prominent Purk- iuje cells, and mitocbondrial disorganization have been demonstrated in mature and immature human and canine hearts with prolonged ventricu- lar pacing.^^ These changes may play a contribu- tory role in causing adverse bemodynamics and predispose to dysrhythmias. The present study was designed to compare indices of LV contractility following single cham- ber right heart pacing from various locations— atrial, septal. and apical, in the young, nonis- chemic heart—in order to potentially improve paced ventricular function. PACE, Vol. 20 August 1997, Part I 1983