May 18, 2010Open Access
Hemodynamic Improvement in Cardiac Resynchronization Does Not Require Improvement in Left Ventricular Rotation Mechanics
Key Result
Cardiac resynchronization therapy acutely improved hemodynamic parameters without significantly changing left ventricular rotation mechanics in an experimental model of 7 dogs with heart failure.
Structured PICO
Does cardiac resynchronization therapy improve LV rotation mechanics in dogs with left bundle branch block and pacing-induced heart failure?
P
Population
Dogs with left bundle branch block and pacing-induced heart failure (n=7)
I
Intervention
Cardiac resynchronization therapy (CRT)
C
Comparator
Baseline (left bundle branch block with pacing-induced heart failure)
O
Outcome
Left ventricular (LV) rotation mechanics (LV rotation, rotation rate, LV torsion, LV torsion rate) measured by 3-dimensional tagged magnetic resonance imagingsurrogate
CRT acutely improves hemodynamic parameters without improving LV rotation mechanics, indicating that LV rotation mechanics is a specific but insensitive index of acute hemodynamic response to CRT.
Abstract
BACKGROUND: Earlier studies have yielded conflicting evidence on whether or not cardiac resynchronization therapy (CRT) improves left ventricular (LV) rotation mechanics. METHODS AND RESULTS: In dogs with left bundle branch block and pacing-induced heart failure (n=7), we studied the effects of CRT on LV rotation mechanics in vivo by 3-dimensional tagged magnetic resonance imaging with a temporal resolution of 14 ms. CRT significantly improved hemodynamic parameters but did not significantly change the LV rotation or rotation rate. LV torsion, defined as LV rotation of each slice with respect to that of the most basal slice, was not significantly changed by CRT. CRT did not significantly change the LV torsion rate. There was no significant circumferential regional heterogeneity (anterior, lateral, inferior, and septal) in LV rotation mechanics in either left bundle branch block with pacing-induced heart failure or CRT, but there was significant apex-to-base regional heterogeneity. CONCLUSIONS: CRT acutely improves hemodynamic parameters without improving LV rotation mechanics. There is no significant circumferential regional heterogeneity of LV rotation mechanics in the mechanically dyssynchronous heart. These results suggest that LV rotation mechanics is an index of global LV function, which requires coordination of all regions of the left ventricle, and improvement in LV rotation mechanics appears to be a specific but insensitive index of acute hemodynamic response to CRT.