Effects of dichloroacetate on hemodynamic responses to dynamic exercise in dogs

Lactate release during reperfusion predicts low cardiac output syndrome after coronary bypass surgery

BACKGROUND

Cardioplegic arrest induces anaerobic myocardial metabolism with a net production of lactate from glycolysis. However, persistent lactate release during reperfusion suggests a delayed recovery of normal aerobic metabolism and may lead to depressed myocardial function necessitating inotropic or intraaortic balloon pump support (low output syndrome [LOS]). We examined the relation between perioperative myocardial metabolism and postoperative clinical outcomes in patients undergoing isolated coronary artery bypass surgery (CABG).

METHODS

We reviewed 623 patients who were enrolled in clinical studies evaluating perioperative myocardial metabolism between 1983 and 1996. Arterial and coronary sinus blood samples were obtained intraoperatively to assess myocardial metabolism. Clinical data regarding patient demographics and postoperative outcomes were prospectively collected and entered into our institutional database.

RESULTS

Low output syndrome developed in 36 patients (5.8%). Myocardial lactate release was higher in these patients compared with those who did not develop postoperative LOS. Advanced age and poor preoperative left ventricular function were independent predictors of lactate release during reperfusion. Persistent lactate release after 5 minutes of reperfusion was the only independent predictor of postoperative LOS in this low-risk population.

CONCLUSIONS

Persistent lactate release during reperfusion occurs in a significant proportion of low-risk patients undergoing isolated CABG and is an independent predictor of postoperative low cardiac output syndrome. Persistent lactate release during reperfusion suggests a delayed recovery of aerobic myocardial metabolism and may be related to intraoperative misadventure or inadequate myocardial protection. Myocardial lactate release may be useful as an alternative end-point in clinical trials evaluating perioperative myocardial protection.

Dichloroacetate as metabolic therapy for myocardial ischemia and failure

This article critically reviews the pharmacologic effects of the investigational drug dichloroacetate (DCA), which activates the mitochondrial pyruvate dehydrogenase enzyme complex in cardiac tissue and thus preferentially facilitates aerobic oxidation of carbohydrate over fatty acids. The pharmacologic effects of DCA are compared with other interventions, such as glucose plus insulin, inhibitors of long chain fatty acid oxidation and adenosine, that are also thought to exert their therapeutic effects by altering myocardial energy metabolism. Short-term clinical and laboratory experiments demonstrate that intravenous DCA rapidly stimulates pyruvate dehydrogenase enzyme complex activity and, therefore, aerobic glucose oxidation in myocardial cells. Typically these effects are associated with suppression of myocardial long chain fatty acid metabolism and increased left ventricular stroke work and cardiac output without changes in coronary blood flow or myocardial oxygen consumption. Although long-term studies are lacking, short-term parenteral administration of DCA appears to be safe and capable of significantly improving myocardial function in conditions of limited oxygen availability by increasing the efficient conversion of myocardial substrate fuels into energy.

Metabolic control of the circulation: implications for congestive heart failure

The role of metabolic processes in the control of the normal circulation will be discussed with particular emphasis on how metabolic events, particularly those that occur with the performance of exercise, result in production of vasoactive substances and sympathetic activation. Heart failure patients will have altered metabolism, particularly in skeletal muscle, that may result in a lesser degree of peripheral vasodilation and will also have an abnormal response to sympathetic stimuli, with less cardiac stimulation but preserved peripheral vasoconstriction. The consequences of these abnormalities on the hemodynamics and metabolic processes that occur with exercise in the heart failure patient will be discussed in detail. The effect of therapeutic interventions such as drug therapy and exercise training will be reviewed.