A 62-year-old man comes to the emergency department due to a 2-week history of shortness of breath and fatigue. The patient becomes out of breath easily when walking short distances and has had a dry nighttime cough, which he attributes to seasonal allergy. He has had no chest pain or pressure, palpitations, light-headedness, or syncope. The patient has not seen a physician in more than 10 years and has no diagnosed medical conditions. He has a 25-pack-year smoking history and drinks alcohol socially. The patient has no family history of heart disease. He worked in construction for most of his life. Blood pressure is 138/80 mm Hg and pulse is 94/min and regular. BMI is 24 kg/m2. Which of the following would be most useful for excluding heart failure as the cause of this patient's symptoms?
Clinical findings for heart failure | ||
Sensitivity | Specificity | |
Dyspnea | High | Low |
Serum BNP >100 pg/mL | High | Moderate |
Lower extremity edema | Moderate | Moderate |
Jugular venous distension | Moderate | Moderate |
Pulmonary crackles | Moderate | Moderate |
Orthopnea | Moderate | High |
Audible S3 | Low | High |
BNP = brain natriuretic peptide. | ||
The differential diagnosis for shortness of breath is broad and includes heart failure, coronary artery disease, and a variety of noncardiac conditions (eg, pneumonia, chronic obstructive pulmonary disease, pulmonary embolism, anemia). Heart failure is a clinical diagnosis based on an aggregation of signs and symptoms (eg, peripheral edema, jugular venous distension, dyspnea, orthopnea) related to vascular congestion, volume overload, and diminished cardiac output. Serologic tests, radiography, and echocardiography can further support the diagnosis.
Brain natriuretic peptide (BNP) is released from the ventricular myocardium in response to myocardial stretch caused by volume and pressure overload. A serum BNP level >100 pg/mL is highly sensitive for heart failure (ie, most patients with heart failure have an elevated serum BNP); therefore, a low serum BNP level (<100 pg/mL) is highly useful in ruling out heart failure. An important caveat is that the BNP level can be falsely low in patients with heart failure and obesity because BNP undergoes increased clearance by fat cells. The cutoff value for N-terminal pro-BNP (NT pro-BNP), used in some centers, is slightly different.
An elevated BNP has only moderate specificity for heart failure because a number of other conditions (eg, systemic hypertension, acute pulmonary embolism, renal failure) also cause myocardial stretch and elevated BNP.
(Choice A) An audible S3 is present in only a small fraction of patients with heart failure (low sensitivity); therefore, its absence is not useful in ruling out heart failure. Because of high specificity, the presence of an S3 is highly supportive of a diagnosis of heart failure.
(Choices B and E) Pulmonary crackles have only moderate sensitivity for heart failure, likely due to offloading of fluid by pulmonary lymphatics in early heart failure. Jugular venous distension also has only moderate sensitivity, possibly due to difficulties with accurate measurement. Therefore, the absence of either of these findings is only somewhat useful in ruling out heart failure.
(Choice D) A cardiothoracic ratio >0.5 (ie, heart width > half the width of the left thoracic cavity) on posterior-anterior chest x-ray is only moderately sensitive for heart failure, likely in large part because patients with heart failure with preserved ejection fraction do not have significant enlargement of the left ventricular cavity.
Educational objective:
Elevated serum brain natriuretic peptide (BNP) >100 pg/mL is highly sensitive for heart failure in patients without obesity. Therefore, a low serum BNP is highly useful in ruling out heart failure in patients with shortness of breath but without obesity.