Evaluation of baseline contractile reserve vs dyssynchrony as a predictor of functional improvement and long term outcome after resynchronization pacing therapy: A radionuclide stress study

Abstract

To assess the predictive value of baseline ventricular dyssynchrony and myocardial contractile reserve (mCR) in identifying responders to cardiac resynchronization therapy (CRT). We prospectively studied 57 patients selected for CRT according to current recommendations. Regional dyssynchrony was evaluated by parametric phase imaging of ecg-gated equilibrium radionuclide angiography (ERNA). The mean inter-ventricular phase delay and the standard deviation to mean left ventricular (LV) phase angle were used as a measure of inter- and intra-ventricular dyssynchrony, respectively. Change in LV ejection fraction (LVEF) during low-dose dobutamine (LDD) was measured to assess mCR. ERNA was repeated at 6months to evaluate changes in LVEF after CRT. Combined end-points of re-hospitalization for heart failure, heart transplantation, and cardiac death were assessed over a period of 76months (mean 43±31). Baseline dyssynchrony was present in most patients (85%). After CRT only one half of patients showed a reduction in intra-ventricular dyssynchrony and 33% an increase in LVEF by >5%. Improvement of LVEF was not predicted by baseline LVEF, clinical presentation, dyssynchrony parameters or QRS duration. There was a significant relationship between changes in LVEF during LDD testing and after CRT (r=0.65; P<.0001). Logistic regression analysis identified mCR as independent predictor of improvement in LVEF (P=.039; OR=3.84; CI 95%=1.06-13.9), resynchronization (P=.046; OR=4.20; CI 95%=1.03-17.2), and event-free survival (P=.002; OR=0.10; CI 95%=0.02-0.43). In patients with left ventricular dysfunction and baseline dyssynchrony as assessed by ERNA, evaluation of mCR during LDD may help predicting functional improvement and selecting potential responders to CRT.