Effect of Cardiac Fiber Orientation on Electrical Dyssynchrony in Ventricular Ectopy
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Background
Widened QRS complex confers worse prognosis in both pacing and premature ventricular contraction (PVC), and may predispose to heart failure. In healthy adult patients, cardiac fiber orientation is highly variable. While traversing the myocardial wall from epicardium to endocardium, helix angles are known to range between -90° and 90°. It is currently not well understood how the location of ectopy and variable epicardial and endocardial helix angle configurations interact to impact the underlying QRS duration of ectopic beats. Methods for identifying regions of favorable pacing accounting for individualized fiber orientation and cardiac geometry are currently lacking. In this work, we hypothesize that fiber orientation will impact QRS duration for pacing locations along the right ventricular (RV) septum. Computational modeling provided an efficient platform in which to systematically study these effects in a controlled manner.
Methods
Five fiber phenotypes with endocardial and epicardial helix angles ranging from 40° to 80° and -80° to -40° were studied, respectively. Three control pacing conditions were considered, using a fractal tree-generated Purkinje network, and a model of right and left bundle branch block (RBBB, LBBB). Five pacing locations along the inferior RV septum were considered. The monodomain equation coupled with the ten Tusscher Panfilov ionic model was used in finite element simulations of electrical propagation. Anisotropic and isotropic conduction velocities were 0.49 m/s and 0.21 m/s, respectively. Electrocardiograms (EKGs) were generated for each condition, and the QRS duration was measured as the variable of interest.
Results
Variable fiber phenotype prolonged the QRS duration by 1.88, 4.49, and 7.48 ms (3.92, 2.35, and 4.70%) in the Purkinje, RBBB, and LBBB conditions. In five pacing locations along the inferior RV septum, QRS duration prolonged by between 14.33 and 27.00 ms (6.72 and 13.02%). In addition, the site associated with the shortest and longest QRS duration differed depending on the fiber phenotype.
Conclusions
We introduce a pipeline to study individualized impacts of cardiac geometry and fiber orientation on QRS duration for variable pacing conditions. Our findings implicate fiber orientation as a risk factor for development of cardiomyopathy and suggest a possible role of preoperative fiber orientation characterization prior to pacemaker placement.
