Relation between radionuclide angiographic regional ejection fraction and left ventricular regional ischemia in awake dogs

Relation between myocardial perfusion and left ventricular function following acute coronary occlusion: disproportionate effects of anterior vs. inferior ischemia

This study examined the relation between left ventricular (LV) function and the severity of acute myocardial ischemia in a conscious dog model. The LV ejection fraction (EF) was measured by multigated equilibrium radionuclide angiography, and regional myocardial blood flow was measured with radioactive microspheres before and 10 minutes after distal and then proximal occlusion of the left anterior descending (LAD, 13 dogs) or left circumflex (LC, 13 dogs) coronary artery. Two methods were used to evaluate the extent of ischemia. The first method determined the mass of myocardium that was ischemic based on different degrees of reduced blood flow. The second method estimated the severity of ischemia expressed as blood flow deficit resulting from each coronary occlusion. Global LV function was very sensitive to ischemia, and the relation between change in function and the degree of ischemia were described best by linear functions. The best linear correlation between mass of ischemic myocardium and percent reduction in EF resulted from the ischemic region defined as all tissue with 25% or greater reduction in blood flow, r = 0.84 for LAD (Y = 0.96X + 1.8) and r = 0.75 for LC (Y = 0.53X + 2.0) occlusions. Defining ischemic mass by more severe reduction in blood flow resulted in exclusion of ischemic myocardium that affected function. The myocardial blood flow deficit also correlated linearly with percent reduction in EF, r = 0.89 for LAD (Y = 1.31X + 2.7) and r = 0.81 for LC (Y = 0.83X - 0.1) occlusions. The slope of the regression lines using both analyses of ischemia were significantly greater (p less than 0.01) for LAD than LC occlusions, indicating that for comparable degrees of ischemia LAD as compared to LC occlusion decreased EF to a greater extent. Calculation of EF from attenuated corrected volumes resulted in small changes in LAD, but not LC, EF and did not account for the disproportionate effects of LAD and LC ischemia. In a separate group of studies (n = 18) EF measured by radionuclide angiography after LAD or LC occlusions correlated well with biplane contrast angiography r = 0.93, SEE 5.1. These data suggest that disproportionately greater effects of LAD compared to LC ischemia on global EF in the dog are due primarily to different pathophysiologic responses to ischemia.

Value and limitation of biplane rest and exercise radionuclide angiography for assessing individual bypass grafts: a prospective study

This prospective study evaluated the ability of serial biplane rest and exercise radionuclide angiography to predict the status of individual coronary bypass grafts in 20 patients 2 to 6 months after surgery. The preoperative coronary angiogram was used to assign vessels to 10 regions of distribution on the radionuclide angiogram. Predictions of graft adequacy for individual vessels were based on a detailed assessment of rest and exercise wall motion in their regions of supply. Of 59 grafts, 38 were judged adequate (patent with less than 75% stenosis) and 21 inadequate by postoperative catheterization. Radionuclide prediction of graft status was possible for 32 of the 59 grafts, including 19 of 24 left anterior descending, 7 of 19 circumflex and 6 of 16 right coronary artery grafts. The status of the remaining 27 grafts could not be assessed because of normal wall motion in their region of supply both pre- and postoperatively (22 vessels) or because a region of supply was not represented on the biplane radionuclide angiogram (5 vessels). Of the 32 predictions made, 25 (78%) were correct, including 13 (93%) of 14 predictions of graft adequacy and 12 (67%) of 18 predictions of graft inadequacy. The single incorrect prediction of graft adequacy resulted from improved exercise wall motion in a region supplied by a graft judged as having a 75% anastomotic stenosis. Most incorrect predictions of graft inadequacy were due to new septal or other rest wall motion abnormalities postoperatively. The comparison of pre- and postoperative studies was essential to maintain the predictive ability of the test. Thus, a detailed analysis of regional wall motion by rest and exercise radionuclide angiography can be used to predict the status of individual coronary artery bypass grafts. Reliable predictions can be made for most successful anterior descending grafts, and may permit cardiac catheterization to be deferred in certain cases. However, the method is limited by the need to perform preoperative exercise studies, by the low number of right and circumflex coronary artery grafts that can be evaluated and by the poor specificity of predictions of graft failure.

Rate of left ventricular functional recovery by radionuclide angiography after exercise in coronary artery disease

To characterize determinants of the rate of recovery of left ventricular (LV) function after exercise-induced ischemia, sequential postexercise radionuclide angiography was performed prospectively in 38 consecutive patients with documented coronary artery disease (CAD). In each patient new or increased regional asynergy developed or absolute ejection fraction decreased at least 4% during exercise. Twenty patients showed immediate recovery of LV function after exercise (group 1) and 18 showed delayed recovery (group 2). Ejection fraction in the first postexercise period was significantly greater in group 1 (65 +/- 12%) than in group 2 (55 +/- 11%) (p less than 0.01). The mean number of coronary arteries with at least 70% diameter narrowing was greater in group 2 (2.7 +/- 0.5) than in group 1 (2.0 +/- 0.9) (p = 0.026); CAD score was also greater in group 2 than in group 1 (p = 0.005). The increase in LV end-diastolic volume from rest to end exercise was greater in group 2 than in group 1 (p = 0.005); neither the change in LV volume nor the change in heart rate or blood pressure after exercise separated the groups. The only independent predictor of the rate of functional recovery was the degree of exercise-induced regional myocardial asynergy (p less than 0.001). Thus, exercise radionuclide angiography in patients with CAD provides a model for evaluating postischemic myocardial function. Delayed functional recovery is associated with extensive exercise-induced regional asynergy as a result of severe CAD and is not primarily influenced by hemodynamic changes.

Left ventricular ejection fraction after acute coronary occlusion in conscious dogs: relation to the extent and site of myocardial infarction

The change in left ventricular radionuclide ejection fraction after acute occlusion of the left anterior descending (LAD) or circumflex (LC) coronary artery was compared with the ultimate histologic extent of myocardial infarction in conscious dogs. The acute change in ejection fraction correlated with size of infarction in 14 dogs with occlusions of the LAD coronary artery (r = .89, y = 1.12x + 14.2) and in 27 dogs with occlusions of the LC coronary artery (r = .71, y = 0.73x + 7.9); the slope of the regression equation was greater (p less than .05) for those with LAD than for those with LC occlusions. Multivariate analysis revealed no independent contribution of left ventricular weight, the subendocardial extent of infarction, or change in heart rate to the acute change in ejection fraction. These data indicate that the decrease in ejection fraction after coronary occlusion is determined primarily by the size of the ischemic area, which also determines size of infarction. In dogs instrumented over a long term, infarcts in the LAD myocardial distribution result in greater decreases in ejection fraction than infarcts of comparable size in the LC distribution.

Relation between left ventricular global and regional function and extent of myocardial ischemia in the canine heart

To develop a quantitative relation between the overall severity of acute ischemia and left ventricular global and regional function, two minor axis internal diameters and myocardial wall thickness were determined using ultrasonic crystals in 10 open chest dogs with carotid-left anterior descending artery cannulation. The overall extent of ischemia produced by graded stenosis of the cannulation system was estimated by total myocardial blood flow deficit, calculated using radioactive microspheres and a balloon-reservoir perfusion technique permitting precise separation of ischemic from nonischemic tissue. Although cardiac output and left ventricular stroke work were maintained through chamber enlargement until total myocardial blood flow deficit was about 10%, ejection indexes of left ventricular function decreased progressively with increasing ischemia and correlated inversely with total myocardial blood flow deficit (r = -0.55 to -0.73). Ejection indexes of left ventricular global function correlated directly with regional function in the ischemic zone (r = 0.67 to 0.83), although global function decreased at a far slower rate than regional contraction during progressive coronary stenosis with an ischemic region comprising about 25% of total left ventricular weight. During myocardial ischemia, regional dysfunction resulted in progressive global contractile dysfunction; left ventricular hemodynamic status was maintained until ischemia was severe.