Irreversible injury in myocardium occurs at ?: (A) 2 minutes, (B) 30 minutes, (C) 2 hours, (D) 5 hours
Answer is B. Ans. is 'b' i.e., 30 minutes The metabolic rate of the hea is high, and its stores of substrate are low. So, hea is critically dependent on a continuous supply of oxygen and nutrients. Ischemia of myocardium induces profound functional, biochemical and morphological consequences. Myocardial function is more sensitive to isc_hemia (loss of contractility occurs within 60 seconds) than myocardial structure (irreversible injury occurs in 20-40 minutes, thus myocardial necrosis begins at approximately 30 minutes after coronary occlusion. Key events in ischemic cardiac myocytes Feature Time Onset of ATP depletion Seconds Loss of contractility < 2 minutes ATP reduced to 50% 10 minutes ATP reduced to 10% 40 minutes Irrversible injury 2040 min Microvascular injury > 1 hr