Estimation of myocardial ischemic injury during ventricular fibrillation with total circulatory arrest using high-energy phosphates and lactate as metabolic markers. STUDY OBJECTIVE: To define the time course of myocardial ischemic injury using high-energy phosphate (HEP) depletion and the cessation of lactate production as metabolic markers. SETTING: Data were collected in a laboratory animal model. TYPE OF PARTICIPANTS: Ten immature mixed breed swine weighing 23.2 +/- 3.5 kg. DESIGN: After thoracotomy, transmural myocardial biopsies were taken in vivo during normal sinus rhythm and at designated times during ventricular fibrillation with total circulatory arrest (VF-TCA). MEASUREMENTS AND MAIN RESULTS: Frozen tissue samples were analyzed for adenine nucleotides, by high-performance liquid chromatography, and lactate by enzymatic assay. At five minutes of VF-TCA, myocardial adenosine triphosphate averaged 50% of control. At 15 minutes of VF-TCA, 89% of animals had myocardial adenosine triphosphate levels above 20% of control and adenylate charge ratio above 0.60. With more than 30 minutes of VF-TCA, all animals had adenosine triphosphate levels below 10% of control and adenylate charge ratio below 0.30. In addition, myocardial lactate levels plateaued after 30 minutes of VF-TCA, indicating the cessation of lactate production. CONCLUSION: These results suggest that the myocardium can tolerate VF-TCA for as long as 15 minutes without irreversible injury; however, post-ischemic myocardial dysfunction may occur after as little as five minutes of VF-TCA. With more than 30 minutes of VF-TCA, myocardial injury is likely to be irreversible. 