Acute Effects of Pacing at Different Ventricular Sites on Left Ventricular Rotational Mechanics in a Porcine Model

Objective: The purpose of this study was to examine the acute effects of pacing at different ventricular sites on hemodynamics and left ventricular (LV) rotational mechanics using speckle-tracking echocardiography (STE) in a porcine model. Design: A prospective laboratory investigation. Setting: University research laboratory. Participants: Yorkshire pigs. Interventions: In 9 pigs, after midline sternotomy, epicardial pacing was performed from the right ventricular outflow tract (RVOT), right ventricular apex (RVA), and LV free wall. Measurements and Main Results: Two-dimensional STE and conductance catheter-derived LV pressure-volume measurements were made to determine the impact of pacing from various sites on LV rotational parameters (twist/untwist) and hemodynamics. RVOT pacing caused the least decrease in end-systolic pressure from baseline (-9.5%), when compared with RVA (-19.1%) and LV (-23.4%). Systolic and diastolic parameters (Emax, Tau) also were different among RVOT (4.7 +/- 0.8 mmHg/mL, 32 +/- 4 ms), RVA (3.9 +/- 0.7 mmHg/mL, 37 +/- 6 ms), and LV sites (3.6 +/- 0.8 mmHg/mL, 42 +/- 7 ms). Similar to the effects of pacing on hemodynamics, RVOT pacing better preserved LV twist (11.1 +/- 1.8 v8.6 +/- 1.7, 5.9 +/- 0.7 degrees) and untwisting rate (64.6 +/- 8.5 v 56.2 +/- 5.3, 48.2 +/- 8.5 degrees/s) when compared with RV apical pacing and LV pacing. Furthermore, prolongation of conduction from LV lateral to anteroseptal at LV base (26.5 +/- 3.8 v 13.8 +/- 3.3 ms, p < 0.05) and LV midpapillary muscle level (35.6 +/- 5.6 v 14.1 +/- 2.4 ms, p < 0.05) was observed with LV pacing compared with RVOT pacing. Conclusions: The present data showed that the LV twist/untwist and cardiac systolic and diastolic function were least affected by RVOT pacing. This finding may be explained by the proximity of this location to the native ventricular conduction system. (C) 2015 Elsevier Inc. All rights reserved.