The Journal of Thoracic and Cardiovascular Surgery, Vol 82, 447-456, Copyright © 1981 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Effects of selectively produced changes in cardiac rhythm or conduction upon flow in the superior vena cava
F Urthaler, HC Coghlan and TN James
The effects of changes in cardiac rhythm or conduction on the rate of
volume flow in the superior vena cava (SVC) were studied in 25 dogs
anesthetized with sodium pentobarbital. Slowing of sinus rate from 145 +/-
16 to 114 +/- 12 beats/min was achieved by selective perfusion of Ringer's
solution into the sinus node artery. During sinus slowing there was a
continuous change in the systolic-diastolic flow ratio measured in the SVC.
At control sinus rate (net), total forward flow as 6.3 ml/beat with a
systolic volume of 6.5 ml and a diastolic volume of - 0.2 ml. At the
slowest bradycardia, total forward flow had increased by 25%. Since there
was no significant change in the systolic volume, the entire 25% increase
in forward flow occurred during ventricular diastole. During
atrioventricular (AV) block (second-degree or complete), achieved by
selective perfusion of eserine into the AV node artery, unimpaired
acceleration of flow was readily demonstrable in the SVC even in the
absence of ventricular contraction. Thus systolic ventricular suction (vis
a fronte) has little or no effect on right atrial filling. During
high-degree AV block, the normal atrial contraction readily opened the
tricuspid valve, and when both atrium and ventricle were filled to or near
maximum capacity, atrial contraction was consistently vigorous enough to
propel blood into the pulmonary artery. Given appropriate hemodynamic
circumstances, these results confirm the remarkable effectiveness of right
atrial contractile performance.
