THE EFFECTS OF CYANOSIS ON MYOCARDIAL BLOOD-FLOW, OXYGEN UTILIZATION,AND LACTATE PRODUCTION IN DOGS

To elucidate differences in myocardial blood flow and metabolism betwe en cyanotic and normal hearts, a model of chronic cyanosis was created in five adult mongrel dogs by anastomosing the inferior vena cava to the left atrium. After 6 to 9 months, myocardial blood flow, the ratio of subendocardial to subepicardial flow, oxygen consumption, oxygen e xtraction ratio, and lactate consumption in these cyanotic dogs and fi ve control dogs were determined under baseline conditions and during p harmacologic stress with isoproterenol (0.2 mu g/kg/min). Radioactive microspheres were used to determine left and right ventricular blood f low rates, and arterial and coronary sinus differences in oxygen and l actate levels were measured. At baseline and during stress, oxygen con sumption and oxygen extraction ratios were identical in control and cy anotic hearts. Total myocardial blood flow was increased with stress a nd did not differ between cyanotic and control hearts. Left ventricula r muscle from cyanotic hearts did exhibit lower endocardial/epicardial blood flow ratios than those of control hearts at rest, and the relat ive subendocardial flow decreased further with stress. During isoprote renol infusion, myocardial lactate production, indicative of anaerobic metabolism, was evident in two of five cyanotic animals and none of t he control dogs. The relative subendocardial ischemia and its further aggravation by stress in cyanotic hearts may contribute to the pathoph ysiologic basis of myocardial dysfunction in cyanotic heart disease.