Partition of Coronary Flow and Cardiac Oxygen Extraction Between Coronary Sinus and Other Coronary Drainage Channels

Abstract

The open-chest anesthetized dog was prepared to permit the partition of coronary outflow into the coronary sinus and the extracoronary sinus venous channels. The effects of increased resistance-load of the left ventricle, of augmented effort of the right ventricle, and of induced acceleration of the heart rate were analyzed. In several animals, the effect of l -epinephrine exhibition was also determined. The effect of spontaneous tachycardia which developed in two dogs was also analyzed. A balloon inserted into the right ventricular cavity was used to augment its effort under isovolumic conditions. Overall, the coronary sinus was found to drain approximately 60 per cent of the total coronary flow. Notable deviations from this mean were encountered in all experiments. The most marked occurred during spontaneous tachycardia and l -epinephrine exhibition, Significant changes also were observed when heart rate changes were induced. Increasing right ventricular effort had no apparent effect on the amount of blood drained via the coronary sinus. Augmenting left ventricular effort increased both coronary sinus and extra-coronary- sinus drainage more or less proportionately on the whole. Myocardial oxygen consumption was measured as the sum of the oxygen consumption calculated from the coronary sinus and from the extra-coronary-sinus channels. In each case, this measurement was the product of flow in the drainage system and the arteriovenous oxygen difference found in that system. The venous oxygen content in the two drainage systems differed significantly and altered to varying degrees when conditions changed. Augmentation of left ventricular effort primarily increased the oxygen usage measured from the coronary sinus, while increased effort of the right ventricle primarily augmented that measured from the extra-coronary-sinus channels. These observations lend support to the hypothesis that the coronary sinus represents blood draining primarily from the left ventricle and the extra-coronary-sinus channels primarily that from the right ventricle. However, the extra-coronary-sinus channels also drain the left ventricle, and the percentage distribution between them and the coronary sinus can vary significantly as far as cardiac oxygen consumption is concerned, especially when l -epinephrine is exhibited or when the heart changes its rate spontaneously or with an artificial pacemaker. It is concluded that while the coronary sinus catheterization method is the best available to compute the oxygen usage of the left ventricle in the closed-chest animal or in man, it has limits of accuracy as a completely reliable method for assessing the oxygen consumed by the whole heart or the left ventricle. This limitation applies especially (1) during stress when the heart speeds up, (2) in hearts that are abnormal or diseased, and (3) when the effects of inotropic agents are being examined.