Synchronous rhythms in coronary heart disease: an hypothesis concerning the anomalous nature of some common ventricular arrhythmias - investigation with an electronic analogue

Abstract

Various temporal aspects of arrhythmias containing frequent, single ventricular ectopic complexes are investi¬ gated using 24 hour tape recordings of ECGs, High-speed electronic analysis of records containing such complexes reveal characteristics difficult to reconcile with existing theories of the origin of these beats. A general hypothesis (posed by Vellani and Neilson) is investigated in order to explain these arrhythmias. The general hypothesis assumes that a ventricular parasystolic pacemaker, although protected by entrance block, is not totally impervious to sinus excitation of the surrounding ventricular myocardium. The action of sinus excitation on the ectopic focus is graded with respect to its time of arrival in the ectopic pacemaker cycle and this may cause synchronization between the otherwise separate sinus and ectopic rhythms. Divers experimental evidence and various reported arrhythmias are cited in support of the general hypothesis. Four particular hypotheses, whereby the action of sinus excitation affects the ectopic rhythm, are formulated on the basis of existing knowledge of cardiac electrophysiology. These are simulated on purpose-built electronic analogues in order to investigate their arrhythmic properties which are compared to the characteristics seen earlier in ECGs. It is concluded that two of these particular hypotheses contain the most likely explanation of the ECGs investigated, and that these hypotheses may account for many arrhythmias containing single ventricular ectopic complexes. It is pointed out that much of cardiac electrical activity, both normal and abnormal, may be viewed in terms of coupled relaxation oscillations, and that the proposed hypotheses emanate naturally from such thinking.