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Difficulty: MediumCardiovascular System

A 71-year-old man is transported to the hospital by emergency medical services due to the abrupt onset of severe difficulty breathing. Three days ago, the patient experienced a prolonged episode of substernal discomfort and diaphoresis but declined to seek medical care, assuming it was severe heartburn. His medical history includes hypertension, hyperlipidemia, and a 45-pack-year history of smoking.

On arrival, his blood pressure is 88/54 mm Hg, heart rate is 118/min, and respiratory rate is 26/min. Oxygen saturation is 86% on room air. The patient is diaphoretic and unable to speak in full sentences. Neck veins are distended. Lung auscultation reveals diffuse bilateral crackles and prominent expiratory wheezing. Cardiac examination demonstrates a rapid regular rhythm with a loud, blowing holosystolic murmur that is most prominent at the cardiac apex and radiates to the left axilla.

An electrocardiogram displays normal sinus rhythm with prominent Q waves and inverted T waves in leads II, III, and aVF.

Based on the clinical presentation, which of the following is the most likely etiology of this patient's acute respiratory distress?

  1. A
    Acute bronchospasm due to an exacerbation of chronic obstructive pulmonary disease
  2. B
    Necrotic rupture of the interventricular septum
  3. Ischemic rupture of the posteromedial papillary muscleAnswer
  4. D
    Rapid accumulation of blood in the pericardial space
  5. E
    Exudative alveolar filling from a community-acquired bacterial infection

Answer

The most likely etiology is ischemic rupture of the posteromedial papillary muscle, leading to acute severe mitral regurgitation and subsequent cardiogenic pulmonary edema.
The correct answer is ischemic rupture of the posteromedial papillary muscle. This patient presents with acute cardiogenic shock and severe pulmonary edema 3 days after an unmanaged inferior myocardial infarction (evidenced by Q waves in leads II, III, and aVF). The posteromedial papillary muscle is particularly vulnerable to ischemia because it receives a single blood supply from the posterior descending artery (typically a branch of the right coronary artery). Rupture of this muscle leads to acute, severe mitral regurgitation, producing a classic harsh holosystolic murmur at the apex that radiates to the axilla. The sudden regurgitant volume rapidly increases left atrial pressure, leading to acute cardiogenic pulmonary edema. This edema fluid in the airways can cause bronchospasm and wheezing, often referred to as 'cardiac asthma'.

Step-by-Step Solution

1
Analyze the patient's history and electrocardiogram findings.
The patient had prolonged chest pain 3 days ago, and the ECG shows Q waves in leads II, III, and aVF, indicating a recent inferior myocardial infarction.
Identifying the timing and location of the myocardial infarction is critical for predicting specific post-infarction mechanical complications.
2
Evaluate the new physical examination findings.
The patient presents with cardiogenic shock (hypotension, tachycardia) and a new, loud holosystolic murmur at the apex radiating to the axilla, which is classic for mitral regurgitation.
Different mechanical complications of MI produce distinct murmurs and hemodynamic profiles.
3
Synthesize the findings to determine the primary cause of the respiratory distress.
An inferior MI often involves the right coronary artery, which provides the sole blood supply to the posteromedial papillary muscle. Rupture of this muscle causes acute severe mitral regurgitation, rapid left atrial volume overload, and subsequent acute pulmonary edema (manifesting as crackles and wheezing, or 'cardiac asthma').
Connecting the inferior MI to its most common structural complication explains all the patient's symptoms, including the pulmonary findings.

Key Concept

Post-myocardial infarction mechanical complications: Posteromedial papillary muscle rupture.
Estimated Time:1m 30s
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Topics

Cardiovascular System

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