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.
| Sign | Sensitivity | Specificity |
| 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.
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