Contractile reserve and left ventricular function in regional myocardial ischemia in the dog.

Abstract

SUMMARY Contractile activity remaining in a region made ischemic by acute occlusion of the left anterior descending coronary artery (LAD) was assessed in dogs relative to its role in maintaining left ventricular (LV) function. Compensatory increases in contractility of normal myocardium were eliminated by treating all dogs with reserpine (3 mg/kg) to deplete their catecholamine stores. LV function was determined by measuring stroke volume while increasing the LV filling pressure with a shunt from the aorta to left atrium. Heart rate and mean aortic pressure were kept constant. LV function was studied after occlusion of the LAD alone and after the selective infusion of potassium chloride (1 mEq/ml) into the LAD to raise the regiotal extracellular potassium concentration to 30 mEq/mi. The reduction in LV function induced by LAD ligation was less than the reduction caused by abolishing contraction in the entire zone supplied by the LAD with infusion of potassium. The WHEN a coronary artery is occluded abruptly, loss of segmental shortening in the region of myocardium fed by this artery is generally observed. However, some collateral coronary blood flow remains and residual contractile function may remain in the region. The role of such contractile activity remaining in a region made ischemic by occlusion of a coronary artery on the overall function of the left ventricle has not been defined. Further, the relation between the size of the ischemic area and the extent of reduction in overall left ventricular (LV) function has not been precisely determined. When regional myocardial ischemia is induced, LV function is affected by the lateral dimensions of the ischemic region, the distribution of contractile activity transmurally in this region as determined by the remaining collateral coronary blood flow, the compliance of the ischemic zone, and compensatory increases in contractility in nonischemic zones of myocardium resulting from augmented sympathetic tone. This may explain the marked variation in the reported observations on this subject. '-9 We studied the effects of regional myocardial ischemia and total cardioplegia. The effects of involving varying amounts of the ventricle on overall LV function were also examined. stores.'0 This was done to abolish the compensatory increase in contractility that may occur in the nonischemic myocardium after coronary artery ligation.Dogs were anesthetized with sodium pentobarbital (30 mg/kg i.v.). Additional pentobarbital was administered as required to maintain anesthesia. After intubation with a cuffed endotracheal tube, dogs were ventilated with an intermittent positive pressure respiratory with 100% oxygen. A thoracotomy was performed in the fifth intercostal space and the heart was exposed by incising the pericardium. The left anterior descending coronary artery (LAD) was isolated and ligated 3-20 mm from its origin to vary the size of the ischemic region.After ligation of the LAD, a cannula was inserted distal to the occlusion and perfusion was continued through a pol...

Effect of Pericardium on Regional Myocardial Systolic Function in Acute Ischemia.

“…Furthermore, the endsystolic volume or diameter of the left ventricle is regulated by the corresponding pressure and contractile state of the ventricle (Mehler et al 1975 ; Kass and Maughan 1988 ;Sagawa et al 1988). Therefore, considering the facts that the ischemic myocardium of the ventricle still has a residual contractile force during an early phase of coronary occlusion (Hood et al 1969 ;Yoran et al 1982), lengthening of the end-systolic segment in ischemic and non-ischemic regions with no change in corresponding pressure after the removal of pericardium might be due to the attenuation of the effects of the right ventricular contraction on the left ventricle. We proposed the above two possible explanations for the further increase in both end-systolic segment lengths after pericardiectomy.…”

The effect of coronary arterial pressure on myocardial distensibility. Absence of a “garden hose” effect during in-vivo conditions

“…Although KCI can produce primary vasoconstriction, ischemia is unlikely. In contrast to ischemia, discontinuation of the regional KCI infusion results in complete restoration of function (11,14).…”

“…In three dogs, potassium chloride (KCI) at a concentration of 1.0 mEq/ml was infused into the LAD perfusion line at a rate of 0.34 or 0.68 ml/min in order to abolish regional myocardial contraction (11,14). After 10 min of regional cardioplegia the segment length was recorded.…”