QRS Duration
Sixty-five percent of patients in this study had documented QRS durations before and after implantation. The average increase in QRS was 37.48 ms with a standard deviation of 38.00 ms. The greatest increase in QRS duration was 103 ms. The greatest decrease in QRS duration was 38 ms, which may be explained by conduction system pacing. The data did not implicate an implantation location that was associated with significantly less QRS duration lengthening. The pre-implantation and post-implantation QRS duration correlation coefficient for the entire dataset regardless of implantation location was 0.02, and correlation coefficients were similar when individual implantation location groups were assessed. This demonstrates that, although there is typically an increase in QRS duration after pacing is initiated, it is not possible to predict prior to implantation which patients will have significant increases in QRS duration.