The Effect of Ventricular Activation Sequence on Cardiac Performance During Pacing

The aim of this study was to evaluate the importance of a normal ventricular activation pattern for cardiac performance. In nine mongrel clogs, atrial pacing was compared to AV synchronous pacing at three different A V delays (150, 100, and 60 nis). In six dogs, proximal septal AV synchronous pacing was compared to apical A V synchronous pacing at three different A V delays. AV synchronous pacing was performed after RF induced complete heart block. Hemodynarnics were evaluated by assessment of positive and negative dP/dt, cardiac output, and left ventricular and pulmonary pressures. Atrial pacing was superior to AV synchronous pacing with respect to positive and negative dP/dt and cardiac output. This difference was present at all AV delays. Proximal septal pacing was associated with a higher positive and negative dP/dl compared to apical pacing at all AV delays. Left ventricular activation time was significantly shorter during proximal septal pacing than during apical pacing (88 ± 4 vs 115 ± 4 ms, P < 0.001). We conclude that atrial and proximal septal pacing improves cardiac function and shortens the ventricular activation time compared to apical AV synchronous pacing independent of the AV interval.