Category: Radiology

Misleading Claims for Coronary CTA

The authors of this article make several discrete claims regarding the utility of coronary CT angiography – simply stated right in the title of the article:  “Routine coronary computed tomographic angiography reduces unnecessary hospital admissions, length of stay, recidivism rates, and invasive coronary angiography in the Emergency Department triage of chest pain”.  And, essentially all the assertions made in this observational, retrospective review are suspect.

Reduces unnecessary hospital admissions:
The article in no fashion addresses “unnecessary” hospital admissions.  After all, of their selected cohort of patients, a tiny fraction – 9 of 1,788 – ruled-in for acute MI.  A total of 42 underwent revascularization, but this is a measure reflecting only the aggressiveness of their local cardiology groups.  It would seem the real problem regarding “unnecessary” admissions is an inability to select patients with appropriate clinical probability for further evaluation.

Reduces length of stay:
There is a less than 1 hour reduction in length of stay only for discharged ED patients.  A true accounting of the LOS and congestion of chest pain patients ought to include admitted patients who depart the ED for their hospital observation bed soon after their initial biomarker result – but that would probably make their overall result contrary to their chosen narrative.  The reduction in length of stay is also influenced by the authors exclusion of patients who had ED LOS less than 3 hours – as the authors simply decide no adequate evaluation of low-risk chest pain patients could be performed in that timeframe.

Reduces recidivism rates:
The reduction in recidivism rates may have reached statistical significance, but the absolute difference was only 20 patients, most of whom were discharged from the Emergency Department.

Reduces invasive coronary angiography:
There is a reduction in coronary angiography – mostly, from what I can tell, in that the handful of patients with multi-vessel disease detected on CCTA were referred to CABG, and the use of invasive coronary angiography was obviated.  The absolute difference was only 19 angiography episodes – an avoidance of a handful of $2000-$3000 procedures at the cost of nearly a thousand $700-$1200 CCTAs.

Finally, their abstract conclusion claims it reduces healthcare resource utilization:
The authors never explicitly define this endpoint – which is probably for the best, as I count 960 non-invasive and 8 invasive tests in their CCTA cohort versus 368 non-invasive and 27 invasive tests in their “standard evaluation” cohort.  The admission rate, however, is more than halved from 40% to 14%.  A reduction in resource utilization would be contrary to general consensus from trials of CCTA versus standard care.

Most disturbingly, this article reports “Disclosures: none”.  However, a simple internet search reveals multiple authors having prior relationships with Siemens and GE Healthcare.  Perhaps by some narrowest definition this isn’t untruthful, but it is certainly misleading.

“Routine coronary computed tomographic angiography reduces unnecessary hospital admissions, length of stay, recidivism rates, and invasive coronary angiography in the Emergency Department triage of chest pain”
http://www.ncbi.nlm.nih.gov/pubmed/23684682

Negative CTs and Pediatric Abdominal Trauma

I am biased – I helped set the Pediatric Emergency Care Applied Research Network up back as a research assistant peon before medical school – so it always pleases me to report on PECARN’s newest outputs.

This is a preplanned sub-analysis of their massive observational pediatric blunt trauma study.  Their pediatric blunt trauma decision instrument, unfortunately, turned out to not be terribly useful.  This data on the outcomes of patients with negative abdominal CT scans, at least, ought to help us.

Of the 3,819 patients enrolled with normal abdominal CTs following blunt trauma, 6 went on to have clinically significant abdominal injuries requiring intervention.  They provide a lot of detail about the patient population, but their conclusion is pretty simple: don’t routinely admit these trauma patients for observation to try and catch that 0.02%.  If there’s no other indication for admission, they may be discharged with appropriate symptom return precautions.

“A Multicenter Study of the Risk of Intra-Abdominal Injury in Children After Normal Abdominal Computed Tomography Scan Results in the Emergency Department”
www.ncbi.nlm.nih.gov/pubmed/23622949

How I (Hardly Ever) Scan For Pulmonary Embolism

There’s probably no diagnosis in the Emergency Department that confounds residents more than the practice variation between attendings regarding the evaluation for pulmonary embolism.  Some folks send d-Dimers with reckless abandon on patients with near-zero pretest probability, others make emotional decisions to “take PE off the table” when faced with no other explanation, and then there’s a group that only very rarely pursues the diagnosis.

I rarely pursue the diagnosis – mostly because the epidemiological evidence suggests we’re only harming folks by making additional diagnoses of pulmonary embolism.  Therefore, in a patient who is otherwise physiologically intact, a diagnosis of pulmonary embolism is more likely to result in iatrogenic bleeding risk rather than treatment benefit.  And, then, there’s the backwards fashion in which I use d-Dimer: I order it at the same time as the CTA in an otherwise intermediate- or high-risk patient, and then cancel the CTA if the d-Dimer is normal.

I use this strategy based on this prospectively collected data from the Kaiser system, published obscurely in The Permanente Journal several years back.  These authors evaluated 744 patients over 16 months who underwent CTA for rule-out PE, 347 of which had latex agglutination d-Dimer levels less than 1.0 µg/mL.  In this cohort of 347, there were seven positive scans – six of which were ultimately found to be false positives.  A handful of patients were lost, but the remainder had zero events in the three-month follow-up period.

So – d-Dimer negative, cancel the CTA, regardless of the pretest probability.  So far, so good!

“Computed Tomography Angiography in Patients Evaluated for Acute Pulmonary Embolism with Low Serum D-dimer Levels: A Prospective Study”
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2911823/

Pooled CCTA Outcomes

The state of the art for coronary CT angiograms progressed a great deal in the past year.  Four recent studies, CT-STAT, ACRIN-PA, ROMICAT II, and a fourth by Goldstein et al., have added to our knowledge base regarding the performance characteristics of this test.

Overall, by pooling 3,266 patients from these four trials, a couple new features shake out as statistically significant.  Specifically, patients undergoing CCTA were significantly more likely (6.3% vs 8.4%) to undergo ICA, and then more likely to receive revascularization (2.6% vs. 4.6%).  This adds to what we already knew – CCTA shortens ED length of stay and reduces overall ED costs compared with “usual care”.

But, we still don’t really know if this test is improving important patient-oriented outcomes.  These intervention numbers are quite low – meaning a great number of patients simply received expensive diagnostic testing, without any sort of treatment.  Then, we don’t even know if these revascularizations are improving (or worsening!) outcomes.  Technology keeps blundering forward with its flawed disconnect from rationality – the costs go up and up, but we don’t hardly stop to measure whether we’re actually doing any good….

“Outcomes After Coronary Computed Tomography Angiography in the Emergency Department”
content.onlinejacc.org/article.aspx?articleID=1569168

Pouring Money Into Prehospital Stroke Thrombolysis

Staying consistent with the “brain attack!” slogan folks developed for stroke, the innovations in treatment continue to progress in their attempts to mimic myocardial infarction.  In myocardial infarction, a great deal of focus has been placed on rapid diagnosis and either thrombolysis or interventional catheterization.  This extends to the prehospital arena, with experimentation with ECG transmission, pre-hospital lytics, and pre-hospital cath lab activations.

For stroke, they’re still trying to replicate this pre-hospital diagnosis and treatment – made slightly more complex because the diagnostics involved requires CT scanning.  However, with enough funding from telehealth and imaging industry, “mobile stroke units” have been created for feasibility evaluations. 

And, these authors have certainly demonstrated that it is feasible, diagnosing 48 acute strokes in the prehospital setting and giving half of them thrombolysis.  One patient given rt-PA had sepsis rather than an acute stroke, which is of uncertain significance in an underpowered feasibility case series such as this.

However, there’s a difference between can and should.  I’m uncertain whether we should even be exploring the can portion in this pilot, considering should means a grossly excessive allocation of resources for a therapy of uncertain benefit.  Given the small absolute benefits seen in the handful of trials that even showed a benefit, I can’t possibly see how trials of pre-hospital lytics could favor anything but surrogate endpoints, rather than patient-oriented endpoints.  30 minutes faster to TPA?  At what cost, and did outcomes change?

I won’t fault the authors for their interesting experiment – as long as they don’t seriously propose it as The Future based on our current evidence.

“Prehospital thrombolysis in acute stroke : Results of the PHANTOM-S pilot study” 
www.ncbi.nlm.nih.gov/pubmed/23223534

More C-Spine “Doom and Gloom”

If you haven’t been paying attention to the literature, then you’re practicing completely unawares of an epidemic of missed spinal cord injuries.  From the literature that suggests CT isn’t adequately sensitive and the final common pathway for c-spine clearance should be MRI, to this new article that says all of those studies in summary aren’t enough – and patients might also need “erect cervical spine radiographs”.

This is a case series – the authors bill it as a retrospective review, but the methods are laughably absent, at best – of four patients the authors identified as having cervical spine instability missed through traditional diagnostic methods.  These patients, aged 61 through 87, received Emergency Department evaluation for cervical spine injury, were treated conservatively initially, and eventually needed operative intervention.  The ED work-up of these patients can probably best be described as “interesting” – e.g., a 61 year-old female thrown from horse whose initial work-up involved only three-view radiographs of the cervical spine.  Or, a seventy-five year old man with a cervical fracture on CT who was managed initially in a semi-rigid collar without other assessment for ligamentous injury.

Regardless, each of these patients had some combination of eventual CT or MRI that failed to adequately describe the extent of cervical spine instability, but a simple erect radiograph demonstrated subluxation.  Interestingly, this is a little bit of full circle back to the days of flexion/extension films.  While other studies have demonstrated MRI picks up signal abnormalities not detected on CT imaging, the clinical significance of this is debatable.  Conversely, these dynamic/load-bearing plain radiographs offer a true functional test without precisely describing the injury – akin to the difference between cardiac stress testing and coronary angiograms.

These injuries are quite rare, and not every patient needs an MRI or dynamic testing for cervical stability.  However, in the end, these tests have a role and should be utilized as necessary in the appropriate clinical situation.

“Erect Radiographs to Assess Clinical Instability in Patients with Blunt Cervical Spine Trauma”
jbjs.org/article.aspx?articleID=1392339

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

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

What To Do With The “Dizzy” Patient?

As the authors in this retrospective review state, “Vertigo/dizziness is a common and challenging problem faced by the ER physician.”  And, this is obviously true.  Is it dysequilibrium?  Is it true vertigo?  Is it central or peripheral?  And, finally, “now what”?

This is a clearly pro-MRI and con-CT study which, unfortunately, leads to a massive disconnect with reality.  For most institutions, CT might be feasible, but MRI comes to town once a week for scheduled studies only.  But, in this review of 448 head CTs for dizziness, the CT picked up essentially 10 interesting findings – but 16% of the subset of follow-up MRIs performed changed the initial diagnosis.  Mostly, the missed diagnoses on CT were posterior circulation strokes and intracranial masses.  

So, essentially what they observed was more false negatives than true positives for CT.  This implies – at least in a retrospective fashion – that if your pretest probability is high enough for an intracranial process causing dizziness, the intention ought to be to conclude your investigations only with a negative MRI.  I think most folks – given infinite resources – would agree.  Otherwise, you’ll need to base imaging (if any) on clinical findings and risk factors for cerebrovascular disease in an attempt to develop an estimate for their true probability.

“Utility of head CT in the evaluation of vertigo/dizziness in the emergency department”
www.ncbi.nlm.nih.gov/pubmed/22940762