Irreversible injury in myocardium occurs at ?
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
2 minutes
30 minutes
2 hours
5 hours