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Difficulty: EasyCardiovascular System

A 68-year-old man presents to the urgent care clinic with a 2-day history of progressively worsening shortness of breath and cough. He states that he is having to work much harder to breathe than usual. His past medical history is significant for a myocardial infarction 3 years ago and chronic obstructive pulmonary disease (COPD) managed with an inhaled long-acting bronchodilator. He has a 40-pack-year smoking history. Temperature is 37.0°C (98.6°F), blood pressure is 152/90 mmHg, pulse is 108/min, and respiratory rate is 26/min. Oxygen saturation is 89% on room air. Lung auscultation reveals diffuse expiratory wheezes and scattered basilar crackles. Cardiac examination is difficult to hear clearly due to loud breath sounds, and the neck veins are not easily visible due to his body habitus. Which of the following is the most appropriate next diagnostic test to determine whether his symptoms are primarily due to acute decompensated heart failure rather than a COPD exacerbation?

  1. Serum B-type natriuretic peptideAnswer
  2. B
    Arterial blood gas analysis
  3. C
    Pulmonary function testing
  4. D
    Sputum Gram stain and culture
  5. E
    D-dimer assay

Answer

Serum B-type natriuretic peptide
The correct answer is serum B-type natriuretic peptide (BNP). This patient presents with acute dyspnea and wheezing in the setting of both a smoking history (COPD) and coronary artery disease (prior myocardial infarction). Wheezing can be a classic sign of a COPD exacerbation, but it can also occur in acute decompensated heart failure ('cardiac asthma') due to peribronchial fluid accumulation. Because his physical exam is non-diagnostic for volume overload (obscured JVP, no clear S3), a serum BNP level is the most useful next step. BNP is released from ventricular myocytes in response to increased wall tension. A normal BNP has a very high negative predictive value for ruling out heart failure, whereas a significantly elevated level supports a cardiac etiology for the dyspnea.

Step-by-Step Solution

1
Identify the patient's overlapping clinical features and risk factors.
The patient has dyspnea, wheezing, and hypoxemia with a history of both structural heart disease (prior myocardial infarction) and chronic lung disease (COPD).
Recognizing that 'cardiac asthma' (wheezing due to heart failure) mimics a COPD exacerbation is essential for determining the diagnostic approach.
2
Determine the limitation of the physical examination.
The physical exam cannot definitively confirm fluid overload (JVP is obscured) or rule out heart failure due to loud respiratory sounds.
When clinical signs are ambiguous, an objective biomarker is needed to differentiate the two conditions.
3
Select the most specific diagnostic test to distinguish heart failure from pulmonary disease.
Serum B-type natriuretic peptide (BNP) is selected.
BNP is released by ventricular myocytes under stretch; normal levels highly rule out acute decompensated heart failure, pointing toward COPD, while significantly elevated levels point toward heart failure.

Key Concept

B-type natriuretic peptide (BNP) is the most helpful laboratory test for differentiating between acute decompensated heart failure and a COPD exacerbation in patients presenting with undifferentiated dyspnea and wheezing.
Estimated Time:1m 0s
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Topics

Cardiovascular System

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