Acute hemodynamic effects of alternate and combined site pacing in patients after cardiac surgery

We hypothesized that pacing at sites other than the right ventricular (RV) apex or at two or more ventricular sites would activate the myocardium more rapidly and improve cardiac function in patients undergoing coronary revas cularization or aortic valve replacement. Epicardial electrodes were placed on the right atrium (A), RV paraseptal area close to the RV apex (B), RV o utflow tract (C), LV apex (D), in patients undergoing bypass surgery. At co nstant rate and AV delay, we measured CO during A pacing, DVI pacing at B, C, D, and various combinations of sites in random order in ten patients wit h EF > 50% and 27 patients with EF less than or equal to 50%. When pacing a t two sites, we made one electrode a cathode and one an anode and noted two distinct thresholds by careful observation of the 12-lead EGG. There were no significant differences in CO, systemic vascular resistance, systolic, o r mean arterial pressure. Significant differences were noted in QRS duratio n, which increased progressively going from AAI to 3-site, 2-site, and sing le site pacing (P < 0.05 each comparison). Thus: (1) QRS duration correlate d inversely with the number of ventricular sites paced; (2) despite this, C O did not improve irrespective of baseline EF; (3) multi-site pacing produc ed multiple distinct thresholds which appeared to be related to the number of sites paced, and (4) unique ECG patterns confirmed multisite pacing.