Friday, December 7, 2012

More About ABIs Than You Ever Needed


These American Heart Association scientific statements are really quite lovely.  Although much of the scientific discussion in this article pertains to the diagnosis of chronic vascular disease in the outpatient setting, measuring the ankle-brachial index has a place the the Emergency Department as well.

While most of the studies included in their mini-systematic review report AUCs for chronic peripheral vascular disease, the same principles apply for determination of acute peripheral vascular disease – relevant after lower-extremity penetrating trauma or fracture.  And, if you're going to use a test, sometimes it's fun to know all the gritty details underpinning the evidence, how the cut-offs were determined, the difference between doppler and oscillometric devices, how discrepancies between legs should be handled, etc.

In any event, an interesting piece of literature to skim and save as a reference.

"Measurement and Interpretation of the Ankle-Brachial Index : A Scientific Statement From the American Heart Association"

Wednesday, December 5, 2012

Send Your PE Patient to MRI!

Well, not exactly...but this is at least a "proof of concept" for cardiovascular magnetic resonance and the diagnosis of pulmonary embolism.

Obviously, helical CT has become the standard diagnostic modality for pulmonary embolism due to its rapid acquisition time and high sensitivity.  Unfortunately, contrast-enhanced scans through the thorax carry with them short- and long-term health risks.  So, what about MRI?

This small case series of twelve PE+ patients and twelve healthy controls undergoing CMR showed fair discriminatory power for pulmonary embolism.  On a per-patient basis, sensitivity was 100% – but to best evaluate a diagnostic test, it's probably important to consider a higher-resolution measure.  On a per-lobe basis, sensitivity was only 71% – with a kappa of only 0.69 for the reading radiologists.

And, then there's the minor issue that CMR is a 20-minute scan with 10 minutes of post-processing, so even when this is ready for prime-time, it's still going to have some practical limitations.

"Pulmonary Perfusion Imaging: New Insights Into Functional Consequences of Pulmonary Embolism Using a Multicomponent Cardiovascular Magnetic Resonance Imaging Protocol" 
www.ncbi.nlm.nih.gov/pubmed/23194944

Monday, December 3, 2012

Don't Put Away the LP Needles Yet

There's been a bit of a healthy debate regarding the sensitivity of a negative non-contrast head CT for the diagnosis of subarachnoid hemorrhage.  At least one prominent Emergency Physician educator used some time at ACEP this year to describe why it wasn't time to rely solely on imaging, while a second prominent EP used his lecture time to say essentially the opposite.

This publication, in Annals of Emergency Medicine, tries to address this question and determine just how frequently a negative CT misses a subarachnoid hemorrhage from occult aneurysmal leakage.  Over 11 years, in 21 Emergency Departments, they were able to identify 55 cases in which CT missed a subarachnoid hemorrhage – some of whom had negative CTs within six hours of headache onset.

This study suffers as studies tend to suffer from the retrospective nature of chart review, from missing and imputed data, and from a small sample size despite the extensive time frame reviewed.  Overall, though, I would score it as a point for the "still needs LP" crowd – clearly, you will miss some SAH by foregoing LP.  But, modern CT scanners may have better sensitivity than the ones included from the early part of this decade-long review – and the false-positives and harms from false-positive LPs grow ever-closer to the the false-negatives from CT.

Still not a perfect argument in either direction.

"Nontraumatic Subarachnoid Hemorrhage in the Setting of Negative Cranial Computed Tomography Results: External Validation of a Clinical and Imaging Prediction Rule"
www.ncbi.nlm.nih.gov/pubmed/23026788