Some disease processes have been discretely boiled down to a single affirmative or exclusive test. The positive or negative likelihood ratios associated with these tests can be applied to specific diagnoses almost absent any clinical context.
Acute heart failure is not one of these diagnoses.
This systematic review of clinical and laboratory features associated with a diagnosis of acute heart failure in the Emergency Department reveals the cupboard is mostly barren. Most folks suggest a +LR >10 or a -LR <0.1 is a reasonable threshold for judging the informational value of a test. These authors – in order to generate anything like a positive reflection of the evidence – were charitable enough to include anything with a +LR >4 or -LR of <0.25 as meaningful.
And, even that didn’t generate much:
- An S3 on cardiac auscultation (+LR ~4.0).
- Chest x-ray sigs of fluid overload (+LR ~4.8-6.5)
- BNPs <100 or NT-proBNP <300 (-LR ~0.1)
- BNPs >500 ranged in +LR from ~4-9, while NT-proBNP never exceeded a +LR of ~3.3.
- Lung ultrasound probably had the best combination of LRs, with B-line scan having +LR ~7.4 and -LR ~0.16.
- Specific findings on bedside echocardiography seem potentially valuable, but very few patients were included in these studies.
The short answer: acute heart failure remains a multifactorial evaluation, and it would be erroneous to routinely rely on any single test.
“Diagnosing Acute Heart Failure in the Emergency Department: A Systematic Review and Meta-analysis”
http://onlinelibrary.wiley.com/doi/10.1111/acem.12878/full
I've always been an advocate for less radiation. I believe in reducing the excessive number of CTPAs for low-mod pretest probability VTE patients. Would I dare consider a CT for an undifferentiated dyspneic patient in whom I've actually ruled out PE?
Not until recently. Because of my aversion to excessive testing, and hell, PE is off the table, what do you mean CT?
But what I'm suggesting is to consider a SOB CT. For the sick patient, at risk for significant morbidity/mortality. Is it safe to continue admitting with a CXR, a diagnosis of multifactorial dyspnea, and a plan for fluids or diuretics or fluids? Or maybe antibiotics or nebs and steroids or anticoagulation?
Excessive imaging risks radiation, high costs, and incidentalomas. But if your threshold for getting a SOB CT is as high as mine used to be, we're only considering it for the sick undifferentiated patient. CT is certainly not perfect, interstitial findings may not parse out pneumonia vs fluid overload, but most of the time your diagnostic uncertainty will be relieved. Ah, an evident pneumonia, maybe distinct consolidation, maybe patchy opacities, maybe findings consistent with heart failure, maybe malignancy, and sometimes even PE when you thought not. For the sick undifferentiated dyspneic patient stop futzing around and realize you have a pretty reliable simple test at your disposal.
Try ultrasound first…
I agree, in general, with your line of reasoning regarding the diagnostic process and utility of ultrasound. FWIW, however, the studies evaluating the utility of U/S were quite small – and can they be generalized to the typical ED practitioner? Would an inexperienced practitioner, paradoxically, find additional false-positive findings on exam leading to additional CTs?
More likely, however, most departments are ultrasound averse due to lack of a good QA review process, lack of reliable equipment, lack of expertise, and lack of time. It's much faster and easier to place an order for a CT (without any of the skill uncertainty) than try and squeeze an ultrasound examination into a cramped room ….
Yeah, my ultrasound comment was an unnecessary parenthetical.