Effect of QRS area reduction and myocardial scar on the hemodynamic response to cardiac resynchronization therapy

Background Vectorcardiographic QRS area (QRS area) predicts clinical outcomes after cardiac resynchronization therapy (CRT). Myocardial scar adversely affects clinical outcomes after CRT. Objective To determine whether, in patients with an ideally deployed quadripolar left ventricular (LV) lead (QUAD), reducing QRS area leads to an acute hemodynamic response (AHR); and, whether scar affects this interaction. Methods Patients (n=26, aged 69.2 ± 9.12 years [mean ± SD]) underwent assessment of the maximum rate of change of LV pressure (ΔLV dP/dt max) during CRT using various LV pacing locations (LVPLs). A cardiac magnetic resonance (CMR) scan was used to localize LV myocardial scar. Results Interindividually, ΔQRS area (area under the receiver-operating characteristic curve AUC]: 0.81, p<0.001) and change in QRS duration (ΔQRSd) (AUC: 0.76, p<0.001) predicted ΔLV dP/dt max after CRT. Scar burden correlated with ΔQRS area (r=0.35, p=0.003), ΔQRS area (r=0.35, p=0.003) and ΔQRSd (r=0.46, p<0.001). A reduction in QRS area was observed with LVPLs remote from scar (-3.28 ± 38.1μVs) or in LVPLs in patients with no scar at all (-43.8 ± 36.8 μVs), whereas LVPLs over scar increased QRS area (22.2 ± 58.4 μVs) (p<0.001 for all comparisons). LVPLs within 1 scarred LV segment were associated with a lower ΔLV dP/dt max (-2.21 ± 11.5%) than LVPLs remote from scar (5.23 ± 10.3%, p<0.001) or LVPLs in patients with no scar at all (10.2 ± 7.75%) (both p<0.001). Conclusion Reducing QRS area improves the AHR to CRT. Myocardial scar adversely affects ΔQRS area and the AHR. These findings may support the use of ΔQRS area and CMR in optimizing CRT using QUAD.