A computer-based model of parasystolic activity modulated by ventricular activation in the open-chest dog.

The modulated parasystole hypothesis proposed by Moe has been suggested as a common mechanism of a wide variety of arrhythmias. To represent the arrhythmic patterns defined by the model as an actual ECG trace, a "hybrid" experimental system was devised. The system consisted of the intact canine heart connected to a microcomputer that operated as the modulated parasystolic pacemaker. An intrinsic cycle length of the "ectopic" pacemaker was modulated by the phase-dependent effect of the activity of the intact heart in situ. Discharges in the "ectopic" pacemaker were transmitted to the right ventricle. The result was that the theoretically defined patterns of the ectopic activity were represented as real ECG traces. Some published examples of intermittent parasystole that had been attributed to other complex mechanisms were accurately reproduced when the estimated phase response curves were set in the "ectopic" pacemaker. A wide variety of clinical eCG tracings of ventricular arrhythmias may be reproduced by this hybrid experimental model.