Are the sites of endocardial origin of the left ventricular papillary muscles primary determinants of the morphology of the normal QRS complex?

There is extensive variation in the appearance of the QRS complex of a standard 12 lead ECG of normal subjects. This study tests the hypothesis that a primary determinant of the morphology of the normal QRS complex of the left ventricle is papillary muscles origin. Magnetic resonance imaging was used to determine the site of endocardial insertion of the papillary muscles. The papillary muscle data was then inputted into a schematic, which was used to guide a simulation of the left ventricular activation. A simulated ECG and vector-cardiogram (VCG) were produced. The 10 subjects used were healthy with no history of cardiac disease. The simulated and original ECGs were compared for each subject; the frontal electrical axis was calculated and compared. VCGs produced for each individual were analyzed and the effect of the papillary muscle position on VCG morphology analyzed. It was found that the simulated and original ECGs for each subject had similar QRS waveforms that showed normal morphologies. The frontal axis had a good correlation but no concordance and the VCG showed the closer the papillary muscle origins to the septum the wider the VCG spread