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.