Photoplethysmogram-derived pulse arrival time for interventricular dyssynchrony evaluation in cardiac resynchronization therapy

Background Interventricular (VV) dyssynchrony impairs the hemodynamic benefit of cardiac resynchronization therapy (CRT), while conventional electrocardiographic assessment reflects electrical rather than mechanical activation. Pulse arrival time (PAT), measured as the interval from QRS onset to peripheral pulse detection, may provide a simple, noninvasive surrogate of electromechanical timing. Purpose To determine whether PAT reflects changes in VV synchrony across different pacing modes and programmed VV delays in CRT patients. Methods Thirty-one heart failure patients with left bundle branch block who underwent routine 6-month CRT follow-up were enrolled. A photoplethysmogram (PPG) sensor was placed on the left earlobe, and a single-lead electrocardiogram was recorded concurrently. Measurements were obtained during AAI pacing, right ventricular pacing (RVP), left ventricular pacing (LVP), biventricular simultaneous pacing (BivP), and BivP with varying VV paced delays. PAT was measured from the QRS onset on electrocardiogram to the upstroke on PPG and averaged over 10 beats. Results Mean PAT differed significantly across pacing modes. BivP (215 ± 25 ms) produced the shortest PAT, significantly shorter than during LVP (230 ± 30 ms), AAI (234 ± 26 ms), and RVP (243 ± 28 ms; all P < 0.001; Figure 1, Left panel). PAT was also longer during RVP than AAI (P = 0.02), whereas AAI and LVP did not differ (P = 0.41). When varying the VV delay, PAT was minimal during simultaneous BivP and increased in a graded manner with both RV-first and LV-first preactivation (Figure 1, Right panel). Relative to simultaneous activation, PAT rose by 9 ± 7, 17 ± 9, and 22 ± 10 ms at RV preactivation of 20, 40, and 60 ms, and by 7 ± 5, 15 ± 6, and 17 ± 8 ms at LV preactivation of 20, 40, and 60 ms, respectively (all P < 0.001), demonstrating symmetric and sensitive responsiveness to imposed VV dyssynchrony. Conclusion PAT decreased consistently with improved VV synchrony and showed a graded, bidirectional sensitivity to preactivation delays. PPG-derived PAT therefore represents a practical, fully noninvasive marker of VV electromechanical timing and may support individualized optimization during CRT programming.