Vulnerability during short-term memory induced response in canine ventricle.

Cardiac short-term memory is an intrinsic property which can make the action potential duration produce a transient response after a sudden change in heart rate. The change of vulnerability was investigated by using computer simulation method during the transient period which was created by abruptly shortening the cycle length from 800ms to 300ms. The study was performed on a heterogeneous fiber consisting of endo-, mid-, and epi-cardiac canine myocytes. An OpenMP parallel algorithm was used to accelerate the calculation. The study shows that the vulnerable window (VW) relied on both pacing times and locations. At the cycle length of 300ms, compared with the situation of 500th beat, there was a large transmural dispersion of repolarization (TDR) at the 30th beat. For most of the sites along the fiber, VW consistently demonstrated widely at the beginning of the transient period. Generally, with sustained pacing, VW tended to become small. The results suggested that during a memory-induced transient response, the probability of an occurrence of reentrant wave increased immediately after an abrupt change in pacing rate because of the relatively large TDR and VW within this period. Therefore, avoidance of a sudden heart rate variation was indicated to be helpful for the suppression of reentrant arrhythmias.