In an elderly patient with history of CHF & COPD who presents to the ER with shortness of breath, how can I differentiate the underlying etiology?
- submitted by Elena Shagisultanova
The problem with experts is that they do not know what they do not know. NNT.
In a study of 259 primary care patients:
symptoms
Dyspnea on exertion: 100% sens / 17% spec / +LR 1.2 / (-)LR 0
Orthopnea: 22% sens / 74% spec / +LR 0.84 / (-)LR 1.05
PND: 39% sens / 80% spec / +LR 1.95 / (-)LR 0.76
Peripheral edema: sens 49% / spec 47% / +LR 0.92 / (-)LR 1.08
history
HTN: 20% sens / 65% spec / +LR 0.57 / (-)LR 1.23
MI: 59% sens / 86% spec / PPV 44% / NPV 92% / +LR 4.21 / (-)LR 0.48
DM: 12% sens / 98% spec / PPV 56% / NPV 86% / +LR 6 / (-)LR 0.90
tobacco: 73% sens / 41% spec / +LR 1.23 / (-)LR 0.66
signs
tachycardia: 22% sens / 92% spec / +LR 2.75 / (-)LR 0.85
JVD: 17% sens / 98% spec / +LR 8.5 / (-)LR 0.85
Gallop/Canter: 24% sens / 99% spec / +LR 24 / (-)LR 0.77
Crackles/Rales: 29% sens / 77% spec / +LR 1.26 / (-)LR 0.92
Wheezes: 12% sens / 82% spec / +LR 0.67 / (-) LR 1.1
The gold standard in this paper is left ventricular systolic function impairment determined if fractional shortening was less than 25%. Re: Davie. QJM 1997; 90: 335.
Diagnostic Tests
BNP: in the Breathing Not Properly study, using CXR and/or echo as the gold standard, a BNP > 100 pg/mL had 90% sens / 76% spec / +LR 3.91 / (-)LR 0.13. In this study only 3% of patients with HF had BNP levels less than 50 pg/mL (re: NEJM 2002; 347(2))
In patients with AF, BNP > 100 pg/mL had 94.5% sens / 39.7% spec / PPV 82.5 / NPV 70.7 / +LR 1.6 / (-)LR 0.1. A BNP less than 50 had a (-)LR 0.07. A BNP > 400 had a +LR 4.7, > 800 had a +LR 5.2. (re: Knudsen. JACC 2005; 46: 838).
The N-terminal pro-BNP has a sensitivity of 90%, specificity of 84% when using the cutoffs for patients less than 50y, 50-75y, and >75y, of 450, 900, and 1800 pg/mL respectively. That's a +LR 5.6 and a (-)LR of 0.12. A NT-proBNP level less than 300 pg/mL had a NPV 98%. (re: Eur Heart J 2006; 27: 330).
If you compare to the above information, a history of MI or DM, and either JVD or an S3 have higher positive likelihood ratios for CHF than a BNP > 100 pg/mL.
CXR: a cardiothoracic ratio greater than 0.50 has a sensitivity of 51% and specificity of 79% to diagnose decreased ejection fraction. (+LR 2.4 / (-)LR 0.62). (re: J Gen Intern Med 1996; 11: 625)