Different methods of 3D QRS area calculation from vectorcardiographic X, Y, and Z Leads.

3DQRSarea is a strong marker for cardiac resynchronization therapy and can be obtained by taking the (i) summation or the (ii) difference of the areas subtended by positive and negative deflections in X, Y, Z vectorcardiographic electrocardiogram (ECG) leads. We correlated both methods with the instantaneous-absolute-3D-voltage-time-integral (VTI QRS-3D ). 3DQRSarea consistently underestimated the VTI QRS -3D , but the summation method was a closer and more reliable approximation. The dissimilarity was less apparent in left bundle branch block (r 2 summation .996 vs. difference .972) and biventricular paced ECGs (r 2  .996 vs. .957) but was more apparent in normal ECGs (r 2  .988 vs. .653).