A 53-year-old man comes to the emergency department due to squeezing chest pain that started 2 hours ago. He also has severe shortness of breath that is worse when lying down. He has never had pain like this before. He has no significant medical history and takes no medications. A routine health maintenance visit 2 weeks ago was normal. Blood pressure is 112/60 mm Hg, and pulse is 110/min and regular. Chest auscultation reveals a grade III/VI holosystolic murmur at the cardiac apex and bibasilar crackles in the lungs. ECG shows ST segment elevations in II, III, and aVF. Which of the following is most likely to be significantly increased in this patient?

Question

A 53-year-old man comes to the emergency department due to squeezing chest pain that started 2 hours ago.  He also has severe shortness of breath that is worse when lying down.  He has never had pain like this before.  He has no significant medical history and takes no medications.  A routine health maintenance visit 2 weeks ago was normal.  Blood pressure is 112/60 mm Hg, and pulse is 110/min and regular.  Chest auscultation reveals a grade III/VI holosystolic murmur at the cardiac apex and bibasilar crackles in the lungs.  ECG shows ST segment elevations in II, III, and aVF.  Which of the following is most likely to be significantly increased in this patient?

Quizplus · Accepted Answer

This patient's clinical presentation is consistent with inferior wall myocardial infarction (MI) (eg, sudden onset of chest pain, ST-segment elevation in leads II, III, and aVF) complicated by acute mitral regurgitation (MR) (eg, holosystolic murmur at apex) and pulmonary edema (eg, bibasilar crackles). Acute MR developing within hours of MI is most likely due to papillary muscle displacement as a result of hypokinesis of the underlying left ventricle (LV) wall (acute MR can also develop several days after MI due to papillary muscle rupture, rather than displacement). The posteromedial mitral papillary muscle is most commonly affected due to singular blood supply from the right coronary artery along the inferior myocardial wall. Acute MR leads to an excessive volume of blood leaking back into the left atrium. During diastole, there is rapid passive filling of the LV, which is further augmented by left atrial contraction at end diastole. Acute MR leads to excessive diastolic volume overload, which in turn causes elevated left ventricular end diastolic pressure (LVEDP). This elevated LV filling pressure is reflected back to the left atrium and pulmonary circulation and is responsible for the signs and symptoms of acute pulmonary edema and heart failure. (Choice A) Cardiac output, the volume of blood ejected from the LV into the aorta per minute (forward blood flow), is decreased in acute MR because a large portion of LV stroke volume is ejected back into the left atrium. (Choices B and C) Left atrial size and compliance are increased in patients with chronic MR as the left atrium dilates gradually over time to accommodate excessive left atrial volume and pressure. A normal left atrium is not compliant, and the sudden increase in left atrial volume with acute MR causes an abrupt increase in left atrial pressures without a significant increase in size (as the atrium has not yet dilated to accommodate the regurgitant volume), leading to acute pulmonary edema. (Choice D) LV compliance is increased in patients with chronic LV volume overload (chronic MR or aortic regurgitation) but does not change abruptly in patients with acute MR. Patients with acute MI can have decreased LV compliance due to stiffening of ischemic myocardium. Educational objective: Acute mitral regurgitation (MR) can occur due to papillary muscle displacement in patients with acute myocardial infarction. It leads to abrupt elevation of left atrial and ventricular filling pressures and consequent acute pulmonary edema. Unlike chronic MR, acute MR does not cause any significant change in left atrial or ventricular size or compliance. References: Acute valvular regurgitation. (http://www.ncbi.nlm.nih.gov/pubmed/19564568) Papillary muscle rupture. (http://www.ncbi.nlm.nih.gov/pubmed/29763151)

A 53-Year-Old Man Comes to the Emergency Department Due to Squeezing