Cardiophile MD Archive

Coronary reserve is reduced in all of the following conditions except:

A. Tachycardia

B. Decrease in preload

C. Systolic hypertension

D. Anemia

Answer: B. Decrease in preload

Maximum possible perfusion and coronary reserve are reduced when the diastolic period (time available for subendocardial perfusion) is decreased as in tachycardia. It is also reduced when diastolic perfusion is impaired due to increased preload. Coronary reserve is also diminished by factors that increase resting flow, like those that increases oxygen consumption (systolic pressure, heart rate, and contractility). Anemia and hypoxia decrease the arterial oxygen supply and hence trigger increase in resting flow.

Transmural infarction is completed within —- hours of coronary occlusion in experimental infarction.

A. 1-2 hours

B. 2-3 hours

C. 4-6 hours

D. 3-4 hours

Answer: C. 4-6 hours

Irreversible injury to subendocardium occurs within 1 hour as the region is most vulnerable to ischemia. Transmural infarction is largely completed with 4-6 hours.

Acute preconditioning can occur with all of the following except:

A. Adenosine A1 receptor blockade

B. Stimulation of protein kinase C

C. Opening K+ATP channels

D. Preceding angina

Answer: A. Adenosine A1 receptor blockade

Acute preconditioning occurs naturally with angina preceding infarction. It can be induced pharmacologically by adenosine A1 receptor stimulation, protein kinase C stimulating agents and agents which open K+ATP channnels.

All of the following are involved in coronary vasodilation by acetyl choline except:

A. Nitric oxide

B. Guanyl cyclase

C. Cyclic GMP

D. Cyclic AMP

Answer: D. Cyclic AMP

Acetylcholine normally dilates arteries via the  endothelium-dependent relaxing factor [nitric oxide (NO)]. Nitric oxide to guanylyl cyclase and increases cyclic guanosine monophosphate (cGMP), which causes vascular smooth muscle relaxation. When the endothelium is removed, the dilation to acetylcholine is converted to vasoconstriction because of the muscarinic vascular smooth muscle contraction.

All of the following factors accelerate the progression of irreversible myocardial injury after coronary occlusion except:

A. Tachycardia

B. Anemia

C. Arterial hypotension

D. Prior repetitive reversible ischemia

Answer: D. Prior repetitive reversible ischemia

Tachycardia increases myocardial oxygen consumption while anemia and arterial hypotension reduce oxygen delivery, all accelerating the progression of irreversible injury. Repetitive reversible ischemia or angina prior to the coronary occlusion reduces injury by ischemic preconditioning.