Effects of inspiration, expiration, and apnea upon pacemaking and block in atrial fibrillation

The effects of inspiration, expiration, and apnea on A-V transmission system block and on A-V junctional and idioventricular pacemakers were studied in 53 examinations on 29 patients with atrial fibrillation. The severity of block and the location, prevalence, and firing frequency of subsidiary pacemakers were measured separately in each phase of respiration and compared by quantitative methods. In most patients, apnea increased the severity of A-V block, the prevalence of A-V junctional escape and ventricular automaticity but reduced the prevalence of A-V junctional tachycardia. The firing frequency of the subsidiary pacemakers was not affected. Occasionally apnea shortened the coupling interval of premature ventricular contractions. Cheyne-Stokes respiration markedly accentuated the effects of apnea and often produced bursts of ventricular tachycardia in patients who had only isolated ventricular ectopic beats during regular respiration. The data indicate that intermittent respiration has deleterious effects upon cardiac activity and should be corrected whenever possible.

His bundle recordings in patients with reciprocating tachycardias and Wolff-Parkinson-White syndrome

The mechanisms of reciprocating tachycardias were studied in three patients with WPW syndrome using the catheter technic of His bundle recordings. In the first case it could not be determined with certainty whether the tachycardias involved two anatomically independent fascicles or a single longitudinally dissociated pathway. They were terminated by carotid sinus pressure, which caused A-V nodal block, or by properly timed atrial stimuli, which interrupted the circuit. Short-lived paroxysms of atrial fibrillation in cases 1 and 2 were most probably related to atrial vulnerability. In case 3 there were three types of QRS complexes in lead II representing (a) exclusive His bundle conduction, (b) simultaneous His and Kent bundle conduction, and (c) coexisting His and infra-nodal preferential (Mahaim fiber[?]) conduction. This patient also had three types of reciprocating tachycardias-two of ventricular, and one of atrial origin. The reciprocating circuit probably involved the three pathways.

Electrophysiological effects of direct current countershock before and after ouabain sensitization and after diphenylhydantoin desensitization in the dog

The effects of synchronized direct current countershock on ventricular automaticity, intraventricular conduction, and atrioventricular conduction were studied before and after ouabain administration and after diphenylhydantoin. At the level of electrical energy that induced ventricular arrhythmias, averaging 159 watt-seconds, countershock transiently increased ventricular automaticity and prolonged both intraventricular and atrioventricular conduction time. Immediately after ouabain-induced ventricular tachycardia returned to regular sinus rhythm, underlying ventricular automaticity and intraventricular and atrioventricular conduction times were increased. An average of 23 watt-seconds produced overt and persistent ventricular tachycardias due to enhanced automaticity or re-entry. Atrioventricular and intraventricular conduction times were also prolonged, and transient complete heart block occurred in two experiments. Diphenylhydantoin administration at this time depressed ventricular automaticity, caused a speeding of atrioventricular and intraventricular conduction times and increased the electrical energy necessary to produce ventricular tachycardia to 355 watt-seconds.