In this study, the spatial pattern of refractoriness and its effects on propagation of excitation during premature responses and tachycardia have been investigated using a computer model. The model simulated propagation, cycle length-dependent refractoriness, and slow propagation during the relative refractory period. Findings showed slow propagation near the origin of premature responses resulting in longer cycle lengths distal to the slowing. The nonuniform cycle lengths terminated by a premature response also represented the onset of the subsequent cycle, so the pattern of refractoriness was altered after both the premature and following cycle. This occurred even though cycle length affected only the immediately following refractory period in the model. The effect of nonuniform cycle lengths during a premature response on refractory periods after the subsequent response occurred with all cycle lengths of the later response. When the cycle length of that and further responses was sufficiently shortened to result in slowed propagation, changing spatial patterns of refractoriness and propagation occurred. The findings are evidence that responses with slow propagation during incomplete recovery of excitability can affect conduction velocity and refractoriness during multiple subsequent cycles. These effects are likely to occur in the heart but are modified by features such as sustained effects of cycle length on refractoriness, anisotropy, and electrotonic interactions.
