Abstract 9437: A Novel Index of Left Ventricular Contractility Loss Due to Mechanical Dyssynchrony, “Strain Rate Dispersion Index”, Predicts Responders to Cardiac Resynchronization Therapy

Abstract

Background: Echocardiographic time-delay indices of left ventricular (LV) mechanical dyssynchrony cannot accurately predict responders to cardiac resynchronization therapy (CRT). It may be due to the limitation that they cannot reflect LV contractility wasted by dyssynchrony. We thus determined whether a novel index of LV contractility loss caused by dyssynchrony, “strain rate dispersion index (SRDI)”, measured by using speckle tracking method could better predict the response to CRT than time-delay indices. Methods: We studied 27 patients with NYHA class III or IV heart failure (HF) and low LV ejection fraction (<35%) before and 6 months after CRT. In the apical 4-chamber view and mid-ventricular short-axis view, the standard deviation of time to segmental peak strain (St) among 6 segments (St-SD) was calculated as a time-delay index. SRDI was calculated as the average of segmental peak systolic strain rate (SR) minus global peak systolic SR, indicating the estimated global LV contractility loss caused by dyssynchrony. Longitudinal and circumferential indices were measured (L-St-SD and C-St-SD, L-SRDI and C-SRDI, respectively). Responder to CRT was defined as decrease of LV end-diastolic volume (ESV) >15% or improvement of HF symptom (NYH A class≥1). Results: ESV decreased from 164±108 to 137±99 ml (p<0.05) 6 months after CRT. Seventeen patients were identified as responders (63%). Although QRS duration and C-St-SD at baseline were comparable between responders and nonresponders, L-St-SD, L-SRDI, and C-SRDI were significantly higher in responders (L-St-SD: 153±61 vs 86±41 ms, p<0.01; L-SRDI: 0.21±0.07 vs 0.11±0.06 s - 1 , p<0.01; C-SRDI: 0.19±0.11 vs 0.10±0.05 s - 1 , p<0.05). QRS duration did not correlate with the changes in ESV (ΔΕSV) whereas L-St-SD (r=-0.50), C-St-SD (r=-0.53), L-SRDI (r=-0.45), and C-SRDI (r=-0.53) significantly correlated with ΔESV. By multivariate analysis, C-SRDI was the single independent predictor of ΔESV (β=-0.53, p<0.01). During the follow up, adverse events occurred in 8 out of 9 nonresponders; death in 2 patients and readmission due to worsening HF in 6 patients. In contrast, no such events occurred in the responders. Conclusions: SRDI could predict the response to CRT better than time-delay indices.