of Dexamethasone and Multiple-Dose Methylprednisolone on Infarct Size in Experimental Infarction
LYLE D. JOYCE, M.D., DEAN J. MACCARTER, PHD., CLAYTON H. SHATNEY, M.D., AND RICHARD C. LILLEHEI, M.D., PH.D. University
A brief review of the recent literature indicates the search being made for a pharmacologic agent which has minimal side effects and can effectively reduce the size of acute myocardial infarctions. The traditional impression that the fate of the ischemic zone around the border of an infarct was predetermined regardless of the type of therapy has now been discarded. The task now is to find the agent that can salvage the greatest amount of tissue with the least risk. Such an agent would have a major impact on the morbidity and mortality of patients suffering myocardial infarctions. Several investigators [IO, 19, 20, 231 have found that glucocorticoids can decrease infarct size. We previously reported a 21% reduction in infarct size in dogs with methylprednisolone sodium succinate (MPSS), 30 mg/kg, given intravenously at 15 min following ligation of the distal left anterior descending coronary artery, a 57% reduction if the drug was given 1 hr after ligation, a 28% reduction if given at 2 hr, and a 39% reduction if given at 3 hr postligation ; thus, it is apparent that temporal factors of treatment are of great importance in determining the ultimate infarct size. These findings stimulated our interest in designing the present experiment to evaluate the effects of another steroid, dexamethasone sodium phosphate (DMSP), and also to assess the possible additive effects that multiple-dose MPSS might give. 0022-4804/78/0243-02
Copyright 0 1978 by Academic Ress, Inc. All rights of reproduction in any form reserved.
Adult mongrel dogs weighing 17.5 to 26 kg were used in this study. All animals were anesthetized with an intravenous dose of sodium pentabarbitol(30 mg/kg), intubated, and ventilated with room air on a Harvard positive pressure pump. A coronary sinus catheter was introduced via the right jugular vein and positioned fluoroscopically. The second catheter was introduced into the aortic root by a carotid artery for constant aortic pressure monitoring using a Statham P23Db pressure transducer. A left thoracotomy was then performed through the fifth intercostal space, and the pericardium was opened for exposure of the left side of the heart. The left anterior descending coronary artery (LAD) was examined and only dogs exhibiting a similar anatomical distribution of this vessel and its apical branch were used in the experiment. In those dogs that met this criteria, a left atrial catheter was placed, and control baseline readings of the aortic blood pressure, left atria1 pressure (LAP), cardiac output, and heart rate were measured. Control blood samples were drawn from the aortic root and the coronary sinus. At this time the distal third of the left anterior descending coronary artery and its apical branch were each ligated with No. 4-O silk (Fig. 1). The physician then left the experiment and the technician randomly
JOYCE ET AL.: EXPERIMENTAL
FIG. 1. Myocardial infarction model. Ligatures are placed around the distal third of the left anterior descending artery and its apical branch.
treated the animals as outlined below. Fifteen animals received no treatment and comprised the control group, 15 animals received DMSP, 6 mg/kg body weight intravenously, 1 hr after coronary artery ligation, 15 animals after 2 hr, and 15 animals after 3 hr. A fifth group was made up of 15 animals receiving MPSS, 30 mg/kg intravenously, at 1, 2, and 3 hr, and a sixth group received MPSS at 1 hr only. Hourly hemodynamic data were recorded and bloods were collected every 2 hr for evaluation of metabolic parameters. After 6 hr of coronary artery occlusion, the animals were sacrificed and the heart was removed and rinsed with water to remove all blood from the chambers of the heart. The left ventricle was then dissected from the rest of the heart, weighed, and sliced transversely into l-cm sections. Ligatures were carefully reexamined at this point for tightness. These sections were then incubated in a nitro-blue tetrazolium bath for I5 min as previously described . After incubation, the slices were removed and washed and the unstained (infarcted) myocardium was carefully dissected from the stained (normal) muscle. The infarcted portion was weighed and divided by the left ventricular weight to obtain the percentage infarct. Serial blood samples were analyzed for the following: (1) coronary sinus: pH, POZ, PCOp, hematocrit, oxygen saturation,
oxygen content, lactate, and creatine phosphokinase (CPK) activity, and (2) systemic (aortic root): pH, POZ, PCOZ, oxygen saturation, and oxygen content. The serum concentration of lactate was determined by the method of Barker and Solmerson [ 11. Serum concentration of CPK was determined by the Sigma method . With standard formulas, several derived functions were calculated from the measurable hemodynamic and metabolic indices. Student’s t test was used to statistically analyze all results. Since the tissue treatments are so widely varied among the groups, comparison of the hemodynamic and metabolic parameters was made between values at the time that the treatment was given and the remainder of the experimental period. Thus, each group is compared to its own control as well as to the control group of animals that received no treatment. RESULTS
The summary of the dog weights, left ventricular weights, and infarct size is shown in Table 1. The infarct size is calculated as a percentage of the total left ventricular weight. The average animal weights are similar and range from 20.7 to 21.9 kg. The controls constitute the lightest group, but TABLE
there is no statistical significance between any of the groups. On the other hand, left ventricular weights ranged from 87.9 to 105.5 g. The three DMSP groups demonstrated statistically significant increases in left ventricular weights when compared with any of the other groups. The average infarct size in the control group was 16% of the left ventricular weight. The administration of DMSP, 6 mg/kg, at 1 hr after coronary artery ligation resulted in an infarct size of 11.5% with a 28% reduction compared to the controls (P < 0.05). When DMSP was given 2 hr postligation, infarct size was 11.8% with a 26% reduction (P < 0.05). Administration at 3 hr demonstrated a 14.5% infarct which was not significantly reduced compared to the controls. When we gave MPSS, 30 mg/kg, after 1 hr of coronary artery occlusion, the infarct volume was 10.1% which is a 37% reduction from the controls (P < 0.025). Multiple dose MPSS (30 mg/kg at 1, 2, and 3 hr) gave a 26% reduction in infarct size (P < 0.05). Thus, multiple-dose demonstrated no advantage over single-dose therapy. Hemodynamic
Following ligation of the left anterior descending coronary artery and its apical branch, all the treated dogs showed an immediate reduction in cardiac index. Control dogs also had a drop in index and it continued to deteriorate. The cardiac index in controls was significantly less than the baseline value by the second hour (P < 0.005) and remained so throughout the rest of the experiment (P < 0.0025-0.025). In the treated dogs, only the DMSP 1-hr group showed a significant reduction in index after the drug was administered. This was significant by the second hour (P < 0.005) and remained significantly lower throughout the rest of the experiment (P < 0.005-0.01). The mean systemic arterial blood pressure decreased in all groups. The control group demonstrated a significant depression in pressure by the end of the first hour (P
VOL. 24, NO. 3, MARCH