Presentations to the ED with acute dyspnoea are a bit of challenge. History, examination and tests are used to decide if people have heart failure, pneumonia, COPD, or something else. I think diagnosing heart failure in the ED is a particular challenge, as commonly used ED strategies aren’t particularly good tests for LVF.
In a pretty robust study of patients with no cardiovascular disease, normal hearts on ECHO, and normal BNP measurements in 2007 the incidence of bibasal creps in the 80-95 age group was 70%. (CI 58-92% p<0.001). Incidence increases with age with 11% in 45-64, 34% in 65-79. The auscultator was the same senior cardiologist who was blinded to patient diagnoses, so someone who is better than your or I at listening with a steth.
Right okay. So I should get a CXR then right?
Well…. a meta-analysis in 1997 looked at this and pooled data from 29 studies.
|Venous Redistribution||65% (95 % CI 55-75%)||67% (95% CI 53-79%)|
|Cardiomegaly||51% (95% CI 43 – 60%)||79%(95% CI 71-85%)|
So it’s not an excellent test to rule in or rule out heart failure, however I couldn’t get at the full text for this one, so I don’t know how they were defining a true positive diagnosis of left ventricular failure.
In a subsequent retrospective analysis of the Acute Decompensated Heart Failure National Registry (85 376 patients), 15 937 had CXRs with no signs of congestion on the initial ED XR. That’s a negative rate of 18.7% (CI 18.4-18.9%). So nearly 1 in 5 heart failure patients don’t have obvious CXR signs.
Right. So is there any collection of tests or investigations that have a high sensitivity and specificity for diagnosing say interstitial oedema versus consolidation?
Yup. Well…maybe…Lung USS.
Comet tail artifact (aka B-lines) on USS appear in heart failure but not generally in COPD. In 66 consecutive patients with dyspnoea and 80 patients without. B-lines appeared in all 40 patients with pulmonary oedema. That gives a sensitivity of 100% and a specificity of 92%. (1 normal patient had them, and 2 COPD patients had ‘em).
However the gold standard test they were using to diagnose LVF or COPD was a CXR (blinded). This means that they were not really using a great test to compare the new test to. Also we’ve not got large trials of lung USS compared to any other tests, so the best I can say with any integrity is that it’s promising.
Really promising; The ETUDES study published in january 2009, compared B-lines and N-type BNP (blood test ‘for heart failure). They did a prospective blinded, observational study for a convenience sample of patients (bias alert) presenting to the ED with dypsnoea. They did an 8 zone lung USS, if all 8 zones were positive for B-lines the positive LR ratio for pulmonary oedema was infinite (diagnostic). Scanners were USS happy ED physicians or medical students who had had 2.5 hrs training . USS performed better than BNP, but this was a single centre study, with inherent bias, and a small sample size.
So in summary –
Use the quiet time listening to the back of an old persons’ chest to think about what you are going to do. The bases will be crackly.
You don’t need a CXR to diagnose LVF as 20% of the time your CXR is going to be clear.
Lung USS is promising.
Liteplo, Andrew S., et al. “Emergency Thoracic Ultrasound in the Differentiation of the Etiology of Shortness of Breath (ETUDES): Sonographic B‐lines and N‐terminal Pro‐brain‐type Natriuretic Peptide in Diagnosing Congestive Heart Failure.” Academic Emergency Medicine 16.3 (2009): 201-210.