Review Question - QID 100618

The woman in question is having an ST-elevation myocardial infarction (STEMI) resulting from reduced blood flow to cardiomyocytes. After 30 minutes of ischemia, injury to cardiomyocytes is irreversible.

Cardiomyocytes cease to contract within 60 seconds after onset of total ischemia. If ischemia lasts less than 30 minutes, restoration of blood flow leads to reversible contractile dysfunction (stunning), and contractility gradually returns to normal over the course of hours to days. However, after 30 minutes of ischemia as is likely based on this patient's history, the injury is irreversible and the process of coagulative necrosis begins during the first 24 hours.

Achar et al. review the acute coronary syndromes, which include unstable angina and non-ST-segment elevation MI as well as STEMI. They recommend patients with chest pain at rest for greater than 20 minutes and syncopal symptoms should be seen in the emergency department. Diagnosis of acute MI is confirmed with at least two of the following: ischemic symptoms, diagnostic EKG changes, or elevations in serum cardiac markers like troponin.

Buja describes the immediate sequelae of occlusion of coronary circulation, including loss of contractile function, potential for ventricular fibrillation and sudden cardiac death. He reports that the subendocardium of the left ventricle is most vulnerable to reductions in blood flow and that irreversible injury begins here and spreads outward through to the subepicardium.

Figure A is an EKG with ST elevation in V2-V5 consistent with an anterior MI.
Illustration A is a diagram relating degree and duration of coronary obstruction to potential contractile recovery of cardiomyocytes.

Incorrect Answers:
Answer 1-3: Up until 30 minutes, ischemic effects on cardiomyocytes are reversible.
Answer 5: Damage to cardiomyocytes is irreversible after thirty minutes.