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and Bilchick KC (2022) Cardiac magnetic resonance defines mechanisms of sex-based differences in outcomes following cardiac resynchronization therapy.

Introduction: Simultaneous assessment of cardiac electrical activation and left ventricular (LV) function could identify optimal cardiac resynchronization therapy (CRT) pacing strategies, leading to improved CRT response and outcomes. Hypothesis: Changes in three-dimensional (3D) cardiac electrical activation timing correlate with LV function. Methods: 3D cardiac electrical activation maps from the CardioInsight 252-electrode mapping vest (Medtronic) and cardiac ultrasound images were acquired during and 6 months after CRT defibrillator implantation. Maps were acquired for intrinsic electrical activation and three CRT pacing configurations: synchronized LV pacing, right ventricular (RV) pacing, and biventricular (BIV) pacing. Three novel electrical activation parameters were calculated: LV80, RV80, and BIV80, defined as the time at which 80% of the LV, RV, or both ventricles, respectively, were electrically activated. Results: In 30 CRT patients (65.6 ± 11.3 years old, 36.7% female, 43.3% with LV scar, 57% with left bundle branch block [LBBB], and 43% with right bundle branch block [RBBB]), simultaneous measurements of electrical activation and LV function were obtained. Figure panels A and B show representative plots of the proportion of the LV and RV activated versus time within the QRS for a patient with LBBB. In this patient, BIV pacing improved the LV80 but worsened the RV80 compared with the intrinsic rhythm, consistent with a discordant effect on ventricular function. Panel C shows that synchronized LV pacing has a more unfavorable effect on RV activation than BIV pacing in this patient. In the entire cohort, the BIV80 was significantly associated with the change in LVESVI six months after CRT (p<0.05) (panel D). Conclusion: A novel measurement of 3D cardiac electrical activation demonstrates the effects of different CRT pacing strategies on LV and RV function and predicts LV functional improvement after CRT.

Introduction: Patients with cardiac resynchronization therapy (CRT) upgrades with right ventricular pacing (RVP) dependence may have a different prognosis after CRT and require a distinct implementation strategy. Hypothesis: Left ventricular (LV) size/function, optimal AHA segments for LV pacing, and survival post-CRT is different for patients with RV pacing undergoing CRT upgrade procedures. Methods: Cardiac magnetic resonance (CMR) with cine imaging, DENSE strain mechanical activation mapping, and scar imaging was performed prior to implants of CRT systems that were "de novo" (Group 1) or upgraded from pre-existing pacemakers or ICDs with RVP (Group 2) and without RVP (Group 3). Optimal LV pacing sites were identified based on latest activation. Patients were followed for clinical outcomes. Results: In 92 patients (23.5% female, 65.8 ± 10.7 years old), the baseline LVEDVI by CMR was significantly smaller in RVP upgrade (Group 2) patients (101.8 +/- 34.3 cc/m 2 ) compared with de novo (Group 1; 140.5 +/- 38.2 cc/m 2 ); p=0.001) and non-RVP upgrade patients (Group 3; 153.6 +/- 46.4 cc/m 2 ; p=0.001) (Figure 1). RVP upgrade patients also had the widest baseline QRS (178.2 +/- 26.6 ms v. 159.7 +/- 18.5 ms in Group 1 v. 154.5 +/- 20.1 ms in Group 3; p = 0.001) and were more likely to have latest mechanical activation in an anterior LV segment (50%) versus Group 1 (10%) and Group 3 (35%) patients (p = 0.0007). As shown in Figure 2, RVP upgrade patients had the worst survival (p = 0.007). Conclusion: Patients with RVP dependence undergoing CRT upgrades are more likely to have smaller baseline LV volumes by CMR, greater QRS durations, optimal pacing sites in anterior segments, and unfavorable survival.

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