Direct Measurement of Intracardiac Blood Flow in Dogs with Experimental Ventricular Septal Defects

Abstract

Experimental ventricular septal defects (VSD's) were produced in dogs under general anesthesia by excising a 9-mm core of tissue from the septum with a cylindrical cutting tool. A specially designed electromagnetic flow transducer was wedged into the defect compressing the septal tissue around it, thus causing all of the shunted blood to pass through the lumen. The sensing electrodes were in direct contact with the blood stream, allowing the transducer to be calibrated externally, and to be used as a primary standard of measurement. When left-to-right shunts were measured by the Fick technique, the average error was 57percnt; (2% to 154%). When pulmonary arterial oxygen saturation exceeded 85%, measurements using the Fick method showed errors greater than 30% (61% to 154%) in 9 of 11 animals. The VSD's were of moderate size and resulted in right ventricular systolic pressures between 1/4; and 1/2; of systemic. The flow pattern and the interventricular pressure difference were remarkably similar in contour. Delay in right ventricular activation occurred in most animals as a result of surgical disturbance of the conduction system. Diastolic shunting, which varied between 15% and 25% of the total, was noted in animals with or without changes in conduction pattern. The sequence of ventricular activation was an important factor in controlling systolic shunting and may be an important factor in the distribution of myocardial work.