• Michael R Pinsky, Hyung Kook Kim, Sven Zenker, Lauren Johnson, and Sanjeev Shroff.
• Cardiopulmonary Research Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA. Electronic address: pinskymr@upmc.edu.
• J. Cardiothorac. Vasc. Anesth. 2016 Jun 1; 30 (3): 709715709-15.

ObjectiveTo define the differential effect of site-specific ventricular counterpacing efficacy during cardiac resynchronization therapy (CRT) to identify the most informative imaging views to quantify it. Cross-sectional and long-axis views commonly are used to assess left ventricular (LV) contractility.DesignThe effects of LV apical (LVa) and free-wall (LVfw) pacing during CRT on long- and short-axis contraction, cardiac output, and stroke work were assessed in an open-chested acute canine model to determine whether LVa and LVfw would induce earlier apical than basilar LV radial contraction and earlier free-wall than septal contraction, respectively. Apical (CRTa) and free-wall (CRTfw) using right ventricular (RV) pacing-induced dyssynchrony also were examined.SettingUniversity large animal research laboratory.ParticipantsTen acutely anesthetized and instrumented open-chested purpose-bred dogs.InterventionsRV pacing served as the model of cardiac dyssynchrony. Selective LVfw and LVa pacing alone or with RV (CRTfw and CRTa, respectively) were studied relative to right atrial pacing (RA) as the control.Measurements And Main ResultsTwo pairs of 3 ultrasonic crystals were place along the LV longitudinal axis-apex and mid-to-base pairs along septal and free wall lines. Conductance catheter-defined longitudinal LV segmental volumes and pressure-volume data were collected. RV decreased cardiac output and stroke work compared with RA (2.0±0.3 v 1.4±0.1 L/min; 137±22 v 60±14 mJ; p<0.05, respectively). LVfw but not LVa decreased stroke work (130±35 mJ), and CRTa but not CRTfw improved both (2.1±0.2 L/min; 113±13 mJ; p<0.01 v RV pacing). No difference in time to minimal length free wall-to-septal crystal was seen with pacing. Both LVa and CRTa displayed increased apical-to-basilar shortening delay compared with RA, RV, and LVfw (42±47, 9±105, and 1±46 msec, respectively; p<0.05). No matching regional LV volume changes were seen during LVa.ConclusionsLV functional analysis from only a cross-sectional plane may be insufficient to characterize improved LV contraction synchrony during multisite CRT.Copyright © 2016 Elsevier Inc. All rights reserved.

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