Physiological relevance of quantifying segmental contraction synchrony

Background: Most current indices of synchrony quantify left ventricular (LV) contraction pattern in terms of a single, global (integrated) measure. We report the development and physiological relevance of a novel method to quantify LV segmental contraction synchrony. Methods: LV pressure-volume and echocardiographic data were collected in seven anesthetized, opened-chest dogs under several pacing modes: right atrial (RA) (control), right ventricular (RV) (dyssynchrony), and additional LV pacing at either apex (CRTa) or free wall (CRTf). Cross-correlation-based integrated (CCSI _int) and segmental (CCSI _seg) measures of synchrony were calculated from speckle-tracking derived radial strain, along with a commonly used index (maximum time delay). LV contractility was quantified using either E _es (ESPVR slope) or ESPVR _area (defined in the manuscript). Results: RV pacing decreased CCSI _int at LV base (0.95 ± 0.02 [RA] vs 0.64 ± 0.14 [RV]; P < 0.05) and only CRTa improved it (0.93 ± 0.03; P < 0.05 vs RV). The CCSI _seg analysis identified anteroseptal and septal segments as being responsible for the low CCSI _int during RV pacing and inferior segment for poor resynchronization with CRTf. Changes in ESPVR _area, and not in E _es, indicated depressed LV contractility with RV pacing, an observation consistent with significantly decreased global LV performance (stroke work [SW]: 252 ± 23 [RA] vs 151 ± 24 [RV] mJ; P < 0.05). Only CRTa improved SW and contractility (SW: 240 ± 19 mJ; ESPVR _area: 545 ± 175 mmHg•mL; both P < 0.01 vs RV). Only changes in CCSI _seg and global LV contractility were strongly correlated (R ²= 0.698, P = 0.005). Conclusion: CCSI _seg provided insights into the changes in LV integrated contraction pattern and a better link to global LV contractility changes.