Differential Effects of Left Ventricular Pacing Sites on Regional Contraction Patterns and Global Performance.
OBJECTIVE
To 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.


METHODS
The 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.


METHODS
University large animal research laboratory.


METHODS
Ten acutely anesthetized and instrumented open-chested purpose-bred dogs.


METHODS
RV 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.


RESULTS
Two 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.


CONCLUSIONS
LV functional analysis from only a cross-sectional plane may be insufficient to characterize improved LV contraction synchrony during multisite CRT.
Cardiopulmonary Research Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA. Electronic address: pinskymr@upmc.edu.
Michael R
MR
Pinsky
Cardiopulmonary Research Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA.
Hyung Kook
HK
Kim
Cardiopulmonary Research Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA; Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany.
Sven
S
Zenker
Cardiovascular Systems Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA.
Lauren
L
Johnson
Cardiovascular Systems Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA.
Sanjeev
S
Shroff
D000818:Animals; D002302:Cardiac Output; D002304:Cardiac Pacing, Artificial; D058406:Cardiac Resynchronization Therapy; D004285:Dogs; D009200:Myocardial Contraction; D016277:Ventricular Function, Left
LV performance; canine model; cardiac resynchronization therapy; dyssynchrony; segmental shortening