The electrical substrate of vectorcardiographic QRS area in cardiac resynchronization therapy: insights from ECG-imaging

Abstract Background The QRS area shows promise as a vectorcardiographic (VCG) marker for electrical dyssynchrony in patient selection for cardiac resynchronization therapy (CRT). Nevertheless, little information is known about the underlying cardiac electrical substrate it may reflect. Purpose The aim of this study was to compare the VCG QRS area with measures of cardiac electrical dyssynchrony derived from electrocardiographic imaging (ECG-imaging). Methods QRS area from the synthesized VCG (Kors transformation matrix from the 12-lead ECG) was computed for 27 patients who underwent ECG-imaging (11 patients with no history of structural heart disease and 16 consecutive CRT patients). ECG-imaging measures for electrical dyssynchrony analyzed were: ventricular electrical uncoupling (VEU) computed as the difference between the average LV and RV activation times from ECG-imaging, standard deviation of activation times from the left ventricle (LV SDAT, and the maximal activation (Max AT). Pearson correlation analyses between VCG QRS area and ECG-imaging measures of dyssynchrony were carried out for the entire cohort and for patients with a wide-QRS only. Results ECG-imaging measures of dyssynchrony compared with QRS area in 11 patients with no structural heart disease with narrow-QRS (blue) and 16 candidates for CRT with heart failure (HF) and predominantly wide-QRS (LBBB [n=6], IVCD [n=8], RVpaced [n=1], and nQRS-HF [n=1]) are provided in Figure 1. QRS area were associated with all ECG-imaging measures of dyssynchrony. However, sub-analysis in only the wide-QRS patients revealed that QRS area exhibited the strongest association with VEU. Conclusion Vectorcardiographic QRS area is associated with cardiac electrical dyssynchrony on ECG-imaging, exhibiting a particularly strong association with ventricular electrical uncoupling.