EBM – July 2, 2010
Alexis Ponder
ARTICLE: “Rapid Measurement of B-Type Natriuretic Peptide in the Emergency
Diagnosis of Heart Failure” Maisel et al. NEJM 2002: 347(3) 161-167
SCENARIO:
40yo M with PMH of CHF - EF 30% and COPD presents to the ED with chief complaint
of acute shortness of breath. He is afebrile and vital signs are stable, O2 sat 93% on 2L.
On exam, you note crackles and wheezing, mild lower extremity edema. You are told that
patient’s cardiac enzymes are negative, WBC is 11. BNP ordered comes back – 50pg/ml.
How would you treat him?
METHODS:
- Prospective study of 1586 patients who came to ED with acute dyspnea as
presenting symptom at 7 sites (5 US, 1 France, 1 Norway)
o April 1999-December 2000
- BNP measured with bedside assay
- Exclusion criteria: under age 18, dyspnea was clearly not secondary to congestive
heart failure, acute MI, renal failure (Cr 1.2), or unstable angina unless
predominant symptom at presentation was dyspnea
- Gold standard in this case: Clinical diagnosis of CHF was adjudicated by two
independent cardiologists, who were blinded to the results of the assay
o Reviewed medical records – asked to agree on severity according to
NYHA classification in all cases
o Note: study does not reveal how well the 2 observers agreed
RESULTS:
- Diagnosis of dyspnea assigned to categories:
o Due to CHF = 744 (47%)
o Due to non-cardiac cause with hx of LV dysfxn = 72 (5%)
o Not due to CHF = 770 (49%)
- BNP values associated with these assigned groups obtained
o Due to CHF = 675 ± 450
o Due to non-cardiac cause with hx of LV dysfxn = 346 ± 390
o Not due to CHF = 110 ± 225
- Primary outcome: dyspnea due to CHF
BNP
SENSITIVITY SPECIFICITY POSITIVE LR NEGATIVE LR
(pg/ml)
(%)
(%)
Sens/(1-Spec)
(1-Sens)/Spec
97
62
2.5
.05
50
85
83
5.0
.18
150
Example: BNP = 50
- LR+ = 97/(1-62) = 97 / 38 = 2.5
- LR- = (1-97)/62 = 3 / 62 = .05
LIKELIHOOD RATIO NOMOGRAM:
Example:
In the patient with BNP of 50, propose the
pre-test probability is 20%
-
LR+ = 2.5, post-test probability = ~40%
-
LR - = 0.5, post-test probability = ~1%
CONSIDERATIONS:
- Does this test truly measure heart failure? No, but the goal is to find how closely
this test can approximate shortness of breath due to heart failure v. other noncardiac causes
o BNP is a more useful diagnostic test at extremely low levels in specific
populations, identifying those patient’s whose dyspnea is not due to CHF
o As the BNP value increases, it becomes increasingly more difficult to
utilize this value to differentiate dyspnea due to CHF v. other causes
-
SCNENARIO: What about the patient above? Does this BNP value help
influence your clinical impression? In this case, the value is low enough to help
exclude CHF as the primary cause of his dyspnea