The case for modulated parasystole.

Several recently published tracings of parasystolic rhythms with unusual features were studied to determine whether the biphasic response curve characteristic of modulated parasystole could be extracted from the patterns of arrhythmia. Even in cases in which the possibility of modulation had been rejected, the phase response curves could be derived by inverse analysis of the ectopic intervals. When the derived curves were inserted into the program of the computer model, almost exact matches for the clinical patterns were recorded. In one case, in which the right atrium was driven at increasing rates, the patterns of manifest ectopic ventricular responses appeared to be re-entrant rather than parasystolic. In this case, similar patterns as a function of heart rate were recorded from a mathematical model of reflection.