Mechanism of Synchronization in Isorhythmic Dissociation: I. EXPERIMENTS ON DOGS

Third degree heart block was produced in anesthetized dogs by injecting 95% ethanol into the region of the A-V node. When the ventricles were paced artificially at a constant rate near the spontaneous rate of the S-A node, then the atria and ventricles became synchronized. During synchronization, th...

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Bibliographic Details
Published in:Circulation research 1970-09, Vol.27 (3), p.429-443
Main Authors: LEVY, MATTHEW N, ZIESKE, HARRISON
Format: Article
Language:English
Subjects:
Animals
Arteries
Autonomic Nervous System - physiopathology
Blood Pressure
Computers, Analog
Dogs
Heart Atria - physiopathology
Heart Block - physiopathology
Heart Conduction System - physiopathology
Heart Ventricles - physiopathology
Muscle Contraction
Pressoreceptors - physiopathology
Reflex
Sinoatrial Node - physiopathology
Vagus Nerve - physiopathology
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Summary:Third degree heart block was produced in anesthetized dogs by injecting 95% ethanol into the region of the A-V node. When the ventricles were paced artificially at a constant rate near the spontaneous rate of the S-A node, then the atria and ventricles became synchronized. During synchronization, the P wave oscillated rhythmically around the QRS. When the P preceded the QRS, the arterial blood pressure increased, whereas when the P wave followed the QRS, the blood pressure fell. Synchronization depended on such rhythmical fluctuations in blood pressure because (1) when the blood pressure changes were severely attenuated, synchronization ceased, and (2) simulation of the blood pressure changes by means of a servo-controlled pump also produced synchronization. A biological control system operates in such a way that (1) the P-R interval affects blood pressure by virtue of changes in the atrial contribution to ventricular filling; (2) the blood pressure has an inverse effect on atrial frequency through the baroreceptor reflex, and perhaps other mechanisms; and (3) changes in atrial frequency alter the P-R interval, to complete the control loop.
ISSN:0009-7330
1524-4571
DOI:10.1161/01.RES.27.3.429