Modeling vectorcardiograms based on left ventricle papillary muscle position

Background: Vectorcardiographic QRS loops illustrate the electrical activation of the left ventricle (LV) in 3-dimensional space; however, the individual variability in these loops is not well understood. The left bundle-branch fan distributes the initial activation to the LV and has been shown to distribute its fascicles between the LV papillary muscles. Computer models of LV activation using papillary muscle as the initial electrical activation points accurately predict QRS duration and frontal plane axis.

Methods: Twelve healthy adults received standard 12-lead electrocardiograms and 1.5-T cardiac magnetic resonance imaging. A software developed by ECG-TECH Corp (Huntington Station, NY) generated 3-dimensional QRS vector loops for each subject. Short- and long-axis papillary muscle positions were measured for each subject using cardiac magnetic resonance images. A theoretical plane equidistant from the endocardial origins of each papillary muscle was constructed. Vectors perpendicular to the QRS vector loop and the theoretical plane termed the plane identifier were used for comparison. Spearman rank correlation was used to compare the azimuth and elevation of the plane identifiers of the QRS vector loop and the theoretical plane.

Results: No correlation was found between the azimuth or elevation of the theoretical plane and the QRS vector loops with Spearman rank correlation coefficients of ρ = 0.11 (P = .71) and ρ = 0.22 (P = .49), respectively. Subgroup analysis by QRS vector loop morphology (planar vs nonplanar, narrow vs wide) also demonstrated no correlation.

Conclusions: Modeling the activation of the LV based on papillary muscle position alone may be overly simplistic. Better understanding of what other factors contribute to individual variation in LV activation will help develop a more useful theoretical model.