Biventricular Paced QRS Area Predicts Acute Hemodynamic CRT Response Better Than QRS Duration or QRS Amplitudes

Vectorcardiographic (VCG) QRS area of left bundle branch block (LBBB) predicts acute hemodynamic response in cardiac resynchronization therapy (CRT) patients. We hypothesized that changes in QRS area occurring with biventricular pacing (BV) might predict acute hemodynamic CRT response (AHR).

VCGs of 624 BV paced electrocardiograms (25 LBBB patients with 35 different pacing configurations) were calculated according to Frank's orthogonal lead system. Maximum QRS vector amplitudes (X_Ampl , Y_Ampl , Z_Ampl , and 3D_Amp ) and QRS areas (X_Area , Y_Area , Z_Area , and 3D_Area ) in the orthogonal leads (X, Y, and Z) and in 3-dimensional projection were measured. Volume of the 3D vector loop and global QRS duration (QRSD) on the surface electrocardiogram were assessed. Differences (Δ) in VCG parameters between BV paced and LBBB QRS complexes were calculated. An increase of 10% in dP/dt max was considered as AHR. LBBB conduction is characterized by a large Z_Area (109 microVs, interquartile range [IQR]:75;135), significantly larger than X_Area (22 microVs, IQR:10;57) and Y_Area (44 microVs, IQR:32;62, P < 0.001). Overall, QRS duration, amplitudes, and areas decrease significantly with BV pacing (P < 0.001). Of all VCG parameters, 3D_Ampl , Δ3D_Ampl , Z_Area, ΔZ_Area , Δ3D_Area , and ΔQRSD differentiate AHR response from nonresponse (P < 0.05). ΔZ_Area predicted best positive AHR (area under the curve = 0.813) and outperformed any other VCG parameter or QRSD measurement.

Of all VCG parameters, reduction in QRS area, calculated in Frank's Z lead, predicts acute hemodynamic response best. This method might be an easy, noninvasive tool to guide CRT implantation and optimization.