Cardiac arrhythmias

In 25 cases at open heart surgery, atrial and ventricular close bipolar electrograms, an atrial unipolar electrogram, and a lead-IL electrocardiogram were simultaneously monitored throughout each procedure. In six cases the ventricles or atria, or both, were paced by electrical stimulation. Although atrial activity could frequently not be clearly delineated on the lead II electrocardiogram, the time relationship between atrial and ventricular depolarization could at all times be determined from the electrograms. During ventricular premature beats and ventricular rhythms, retrograde A-V con-duction and retrograde activation of the atria were common, and unidirectional retro-grade A-V block was infrequent. In spontaneous and induced cardiac arrhythmias the fastest pacemaker of the heart, atrial, His bundle, or ventricular, usually activated the entire heart. ADDITIONAL INDEXING WORDS: Electrograms, atrial and ventricular Ventricular rhythms Atrioventricular conduction THAT the fastest pacemaker of the heart will activate the entire heart is an axiom in cardiac physiology. Yet, in the literature, there is a controversy as to the incidence of ventriculo-atrial conduction during ventricu-lar rhythms in man.'-" Most observations on cardiac arrhythmias have been made from the standard lead elec-trocardiogram. During arrhythmias, it is often difficult or impossible to delineate the relation-ship between atrial and ventricular depolariz-ation from standard lead electrocardiographic tracings. In order to depict clearly atrial and ventricular depolarization during spontaneous and induced arrhythmias, electrograms from the atria and ventricles of the human hear