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(Circulation. 1973;48:386.)
© 1973 American Heart Association, Inc.

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The Effects of Atrial Pacing on the Synergy and Hemodynamics of the Orthotopically Transplanted Canine Heart

SEVERI MATTILA M.D.¹; NEIL B. INGELS JR. PH.D.¹; GEORGE T. DAUGHTERS II M.S.¹; STEPHEN C. ADLER M.D.¹; LEWIS WEXLER M.D.¹; EUGENE DONG JR. M.D.¹

¹ From the Departments of Surgery and Radiology, Stanford University School of Medicine and the Palo Alto Medical Research Foundation, Palo Alto, California.

Instantaneous left ventricular dynamics were measured from cineradiographs utilizing implanted tantalum coils as myocardial site markers in the orthotopically transplanted canine heart. Four parameters of myocardial synergy were obtained: mean shortening, anisotropy of contraction, mean time to half shortening, and asynchrony of contraction. Estimates of end diastolic volume, end systolic volume, stroke volume, ejection fraction, and cardiac output were obtained. Heart rate was altered by pacing the left atrium of the donor heart. Of the nine parameters, only cardiac output was significantly changed by alterations in heart rate. The invariance of stroke volume with rate resulted in a proportional increase in cardiac output with cardioacceleration.

Key Words: Left ventricle • Stroke volume • Segmental shortening • Cardiac output • Time-to-half shortening • Asynchrony • Anisotropy

Submitted on July 13, 1972
Accepted on April 2, 1973