Derivation of orthogonal leads from the 12-lead ECG. Accuracy of a single transform for the derivation of atrial and ventricular waves

Vectorcardiograms are not usually recorded in clinical practice and must be derived from the conventional 12-lead ECG, for example by making use of Dower's transform. However, its accuracy for the derivation of the P wave is questionable. We tested the accuracy of Dower's transform on the P-wave and compared with a P-wave optimized transform in a database of 123 simultaneous recordings of ECGs and VCGs. This new transform achieved a lower error when we compared derived vs. true measured P-waves (12.2 ± 7.96 μVRMS) than Dower's transform (14.4 ± 9.5 μVRMS) and higher correlation values (Rx=0.93 ± 0.12, Ry= 0.90 ± 0.27, Rz=0.91 ± 0.18 vs. Dower's: Rx=0.88 ± 0.15, Ry=0.91 ± 0.26 , Rz=0.85 ± 0.23). We concluded that derivation of P-waves and QRS complexes VCGs were optimized by the use of different transform matrices for each wave in this database.