The mechanical cost of decreasing conduction velocity: A mathematical model of pacing-induced lower strain

Purpose : To simulate the effect of decreasing conduction velocity (Cvel) on average segmental myocardial strain using mathematical modeling. Method: The simulation was run using MatLab version 7.4 (The MathWorks, Inc. Natick, Massachusetts). A normal strain-time curve pattern was sampled from a normal human echo study using the 2D strain imaging software (GE Healthcare, Milwaukee, Wisconsin). Contraction was simulated from simultaneous segmental activation (Cvel=∞) through normal activation (Cvel=400cm/sec) to pacing Cvel (100 to 10cm/sec). The simulation generated average segmental strain-time waveforms for each velocity and peak strain as a function of Cvel and time to peak strain as a function of Cvel curves. Result: With decreasing Cvel, average peak segmental strain was found to be decreased and delayed. The following correlation equation represents the correlation between peak strain and Cvel : Strain= -20.12+27.65 x e (-0.29 x Cvel). At the highest pacing Cvel (100cm/sec) average peak segmental strain dropped by 10%, at 50cm/sec by 30% and at the lowest pacing Cvel (10cm/sec) peak strain dropped by >90%. Time to peak segmental strain was minimally longer with decreasing Cvel down to 70cm/sec (pacing velocity range). Further decreased velocity dramatically increased time to peak strain of the simulated segment. Conclusion: The simulation yielded a predictive correlation between slower conduction velocities and decreased and delayed segmental strain.