Emergency medical services bring a 65-year-old male to the resuscitation bay following the… — USMLE Step 2 CK

Emergency medical services bring a 65-year-old male to the resuscitation bay following the sudden onset of profound shortness of breath and altered mentation. The patient's wife states these symptoms began abruptly one hour ago while he was watching television. His medical history is notable for severe chronic obstructive pulmonary disease (COPD) managed with home oxygen therapy. Four days ago, he suffered an inferior ST-segment elevation myocardial infarction and was treated with percutaneous coronary intervention of the right coronary artery.

Vital signs are:

Parameter	Value
Blood pressure	$82/52$ mm Hg
Heart rate	$122$ /min
Respiratory rate	$28$ /min
Oxygen saturation	$84\%$ on high-flow oxygen

On physical examination, the patient is obtunded, diaphoretic, and using accessory muscles of respiration. Jugular venous pulsations are visible up to 11 cm $\text{H}_2\text{O}$ . Auscultation of the chest reveals widespread coarse crackles and prolonged expiratory wheezing. Cardiac auscultation is significant for a hyperdynamic precordium and a new, loud, grade 4/6 holosystolic murmur heard loudest at the apex that radiates to the left axilla.

Arterial blood gas analysis and laboratory studies demonstrate:

Test	Result	Reference Range
pH	$7.20$	$7.35-7.45$
PaCO $_2$	$60$ mm Hg	$35-45$ mm Hg
PaO $_2$	$50$ mm Hg	$75-105$ mm Hg
HCO $_3^-$	$23$ mEq/L	$22-28$ mEq/L
TSH	$4.2 \ \mu\text{U/mL}$	$0.5-5.0 \ \mu\text{U/mL}$
Free T4	$1.1$ ng/dL	$0.9-2.4$ ng/dL

Which of the following is the most appropriate next step in the management of this patient?

Endotracheal intubation and initiation of intravenous dobutamineAnswer
B
Administration of nebulized albuterol and intravenous methylprednisolone
C
Transport the patient for immediate computed tomography pulmonary angiography
D
Administration of intravenous sodium bicarbonate infusion
E
Initiation of intravenous levothyroxine

Answer

Endotracheal intubation and initiation of intravenous dobutamine

The correct answer is endotracheal intubation and initiation of intravenous dobutamine. This patient has acute mitral regurgitation secondary to posteromedial papillary muscle rupture, a classic mechanical complication occurring 3-5 days after an inferior myocardial infarction. The profound hemodynamic instability and respiratory failure (pH 7.20, PaCO2 60 mm Hg) with altered mentation require immediate airway protection via intubation. Concurrently, intravenous dobutamine provides essential inotropic support and mild afterload reduction, which increases forward cardiac output and decreases the regurgitant fraction into the left atrium, stabilizing the patient as a bridge to emergency surgical intervention.

Step-by-Step Solution

Analyze the patient's presentation and recent medical history.

The patient had an inferior MI 4 days ago and now presents with sudden shock, flash pulmonary edema (crackles, hypoxemia), and a new holosystolic murmur at the apex radiating to the axilla.

Identifying the timeline and the new physical exam findings is critical to recognizing mechanical complications of a myocardial infarction.

Synthesize the findings to establish a diagnosis.

The clinical picture strongly indicates acute mitral regurgitation secondary to posteromedial papillary muscle rupture.

The posteromedial papillary muscle has a single blood supply (usually the posterior descending artery) making it highly susceptible to ischemic rupture 3-5 days after an inferior MI.

Determine the necessary acute management.

The patient requires endotracheal intubation and intravenous dobutamine.

Severe respiratory acidosis (pH 7.20, PaCO2 60) and altered mentation mandate immediate airway protection. Dobutamine provides inotropy and mild vasodilation, increasing forward cardiac output and reducing regurgitant flow into the left atrium, serving as a bridge to emergency surgical repair.

Key Concept

Acute mitral regurgitation from papillary muscle rupture is a mechanical complication of inferior myocardial infarction (3-5 days post-MI) presenting with sudden cardiogenic shock and a new holosystolic murmur. Management requires afterload reduction/inotropy (e.g., dobutamine, intra-aortic balloon pump) and definitive surgical repair.

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