VENTRICULAR PERFORMANCE Quantification of the contractile response to injury : assessment of the work - length relationship in the intact heart

We used a sonomicrometric determination of ventricular dimension to examine the effect of ischemia and reperfusion on the work-length relationship in the intact heart to develop a useful and precise variable of ventricular contractile response to injury. Twenty anesthetized dogs were instrumented with epicardial ultrasonic dimension transducers to record right ventricular free wall chord length and left ventricular minor-axis length, micromanometers to record ventricular pressures, and an electromagnetic probe to record pulmonary arterial (n = 8) or aortic (n = 7) flow. Dogs were subjected to either 20 min (n = 7) or 30 min (n = 13) of global cardiac ischemia supported by cardiopulmonary bypass. Data were acquired over a range of end-diastolic volumes produced by transient (5 to 10 sec) vena caval occlusion before and after ischemia. In both ventricles, systolic epicardial dimensional shortening correlated with flow probe-measured stroke volume (mean r = .969) and regional stroke work calculated as the integral of instantaneous ventricular pressure and epicardial dimension correlated with measured global stroke work (mean r = .960), confirming the validity of dimensional measurements. Regression analysis demonstrated a highly linear relationship between calculated regional stroke work and end-diastolic length in the right ventricle (mean r = .973) and left ventricle (mean r = .967), quantifiable by a slope (Mw) and x intercept (Lw). Change in afterload produced by pulmonary arterial or aortic constriction resulted in no significant changes in Mw or Lw in either ventricle. Ischemia and reperfusion decreased Mw and shifted Lw to the right in both ventricles. The decrease in MW with 30 min ischemia exceeded the decrease with 20 min ischemia by 29% in the right ventricle and by 32% in the left (p < .04) with up to 1 hr of reperfusion. Changes in Lw were not related to severity of injury. After ischemia, infusion of calcium increased Mw by 177% in the right ventricle and by 67% in the left (p < .03) without significant changes in Lw. Independent of load conditions, the slope, Mw, of the linear stroke work vs end-diastolic length relationship is a valid and precise index of right and left ventricular contractile response to global ischemia in the intact circulation. This variable may be useful in evaluating therapies designed to limit myocardial injury and enhance ventricular functional performance. Circulation 76, No. 3, 717-727, 1987. AN IMPORTANT GOAL of both cardiovascular research and clinical practice is to minimize myocardial damage during periods of arrested coronary perfusion and to aid recovery of depressed myocardial performance after reperfusion. Biochemical variables may serve as precise indicators of acute myocardial cell injury, but the development of sensitive functional variables of injury and recovery is important, since From the Department of Surgery, Duke University Medical Center, Durham, NC. Supported by NIH grant HL26302 and by a grant from the American Heart Association, North Carolina Affiliate. Address for correspondence: James J. Morris III, M.D., Box 31223, Duke University Medical Center, Durham, NC 27710. Received Sept. 8, 1986; revision accepted May 28, 1987. Vol. 76, No. 3, September 1987 ventricular contractile performance ultimately determines survival. The ability to quantify numerically intrinsic right and left ventricular performance after ischemic injury would permit more rigorous experimental evaluation of interventions designed to limit myocardial ischemic damage and lead to a better understanding of the pathophysiology of acute ventricular dysfunction. One of the most widely used characterizations of ventricular contractile performance is that first proposed by Frank' and Patterson and Starling2 relating the amount of mechanical energy generated by the ventricle during each cardiac cycle to initial muscle fiber length. Numerical quantification of ventricular performance via this relationship has been difficult because 717 by gest on N ovem er 8, 2017 http://ciajournals.org/ D ow nladed from