A 62-year-old woman with no significant medical history is brought to the emergency department due to fatigue and substernal chest pain that began 6 hours ago. On arrival, ECG is consistent with ST-segment elevation myocardial infarction. Coronary angiography shows right-dominant coronary circulation and a thrombotic occlusion of the proximal right coronary artery, which supplies blood to the patient's right ventricle and the inferior and posterior portions of the left ventricle. A drug-eluting stent is placed, and she is discharged 2 days later without complication. After 6 weeks, the patient follows up in the clinic and undergoes echocardiography that shows left ventricular contractile dysfunction with normal right ventricular function. Which of the following characteristics of the right ventricle compared to the left ventricle best explains these echocardiography findings?

Question

A 62-year-old woman with no significant medical history is brought to the emergency department due to fatigue and substernal chest pain that began 6 hours ago.  On arrival, ECG is consistent with ST-segment elevation myocardial infarction.  Coronary angiography shows right-dominant coronary circulation and a thrombotic occlusion of the proximal right coronary artery, which supplies blood to the patient's right ventricle and the inferior and posterior portions of the left ventricle.  A drug-eluting stent is placed, and she is discharged 2 days later without complication.  After 6 weeks, the patient follows up in the clinic and undergoes echocardiography that shows left ventricular contractile dysfunction with normal right ventricular function.  Which of the following characteristics of the right ventricle compared to the left ventricle best explains these echocardiography findings?

Quizplus · Accepted Answer

11ec160b_3a97_c99d_9249_abdabc816715_MD0001_00 Myocardial infarction (MI) involving the left ventricle (LV) commonly leads to scarring and a sustained reduction in contractile function; however, contractile function of the right ventricle (RV) almost always returns to normal following MI. Some of the reasons for protection of the RV from infarction include: The relatively small muscle mass and afterload of the RV create less oxygen demand and necessitate lower oxygen extraction at rest. This allows for a large capacity to increase oxygen extraction during periods of ischemia. The relatively low systolic pressure of the RV (eg, ≤25 mm Hg) allows for coronary perfusion throughout the cardiac cycle; during MI, this enables the RV to pull blood flow from collateral vessels during both systole and diastole. In contrast, the high systolic pressure of the LV (eg, 120 mm Hg) blocks coronary blood flow of the LV walls during systole, allowing for perfusion during diastole only. These factors likely contribute to the typical clinical course of MI involving the RV, which is acute RV contractile dysfunction often leading to profound hypotension and hemodynamic instability; acute mortality risk is high, but there is minimal long-term RV dysfunction for those who survive. (Choice A) The large muscle mass of the LV necessitates higher oxygen extraction at rest, with relatively little capacity to increase oxygen extraction during periods of ischemia. (Choice B) The most robust collateral flow occurs from the left to the right coronary arteries, suggesting the RV has a more developed collateral circulation and may be more dependent on collateral flow than the LV. (Choice C) Ischemic preconditioning refers to the myocardium being repeatedly exposed to mildly ischemic states (eg, during periods of exercise), which stimulates adjustments (eg, collateral circulation development, cellular improvements in oxygen utilization) that allow future ischemic states to be better tolerated. The RV is thought to experience heightened ischemic preconditioning compared to the LV, contributing to protection of the RV from infarction. (Choice D) Fibroblast proliferation is more prominent in the muscular LV, where repair of a larger mass of tissue is needed. Educational objective: The right ventricle (RV) is relatively protected from myocardial infarction (MI), and contractile function of the RV usually returns to normal following MI. Factors contributing to this protection include relatively small muscle mass with high capacity to increase oxygen extraction, perfusion throughout the cardiac cycle, and heightened ischemic preconditioning.

A 62-Year-Old Woman with No Significant Medical History Is Brought