Abstract 11637: Optimization in Cardiac Resynchronization Therapy: Fusion or Filling?
Introduction: The benefit of atrioventricular (AV) and int¬¬erventricular (VV) optimization to Cardiac Resynchronization Therapy (CRT) is thought to be caused by improving ventricular filling as well as resynchronization due to fusion of the electrical wavefronts originating from the left (LV) and right ventricular (RV) pacing electrodes and from the right bundle branch (intrinsic conduction). We investigated the importance of these factors by comparing CRT optimization in dogs without (AV block, AVB) and with possible fusion with intrinsic conduction (left bundle branch block, LBBB).
Methods: CRT was performed in anaesthetized dogs with chronic LBBB (n=6) or AVB (n=6) by sequential atrial (A) and biventricular pacing of RV apex and LV posterolateral wall. A-LV and A-RV delays varied from 70 to 230 ms in random 20 ms steps. LV contractility was assessed as LV dP/dtmax. Arrays of data were subjected to quadratic fitting to account for measurement variability. Electrical mapping was performed using ≈100 endo- and epicardial electrodes.
Results: Combined AV-VV optimization in the AV block group resulted in a maximal LV dP/dtmax increase of 15±7%. Highest response was typically seen during a large range of AV-delays with fixed RV-LV timing difference (LV pre-excitation, see AVB example in figure). In the LBBB group, a similar maximal increase in LV dP/dtmax (18±4%) was obtained using optimization. These optima occurred also at fixed RV-LV timing differences at short AV-delays, but at longer AV-delays, optimal function was achieved at constant A-LV delay (see LBBB example in figure). Electrical mapping confirmed the presence of fusion with intrinsic conduction during the latter circumstances.
Conclusions: In CRT, optimal hemodynamic function is achieved by a fixed timing difference of RV and LV activation, which can be achieved by combined RV and LV pacing (AVB and LBBB) or fusion of LV pacing and intrinsic conduction (LBBB), whereas filling is not an important factor.
- © 2011 by American Heart Association, Inc.