CT Coronary Angiography Test Characteristics & Cost Effectiveness to Exclude CAD
Search Strategy: Using PubMed “special queries” to investigate “Systematic Reviews” you enter “Coronary Computed Tomography.” [For future searches type: (coronary computed tomography) AND systematic[sb] in the pub med search line and the same links pop up]. A simpler pub med search with the query line ‘Acute Coronary Syndrome Diagnosis *Tomography’ reveals 14 articles:
As the summer of ’09 winds down you remember its simple pleasures; baseball, swimming pools, and town hall meetings on healthcare. As you approach your final patient for this Saturday, you’re pleased to hear she’s so up to date on her current events. She tells you she believes in “change” and the new administration’s emphasis on prevention led her to seek early intervention for her episode of chest pain tonight. Though she lacks a primary care physician or any kind of insurance plan, she harkens back to our last President’s assurances that everyone can get medical care in the USA—“just go the local ED.”
Tickled by the irony of it all, you obtain more history even though the charge nurse constantly reminds you of the week’s left without being seen numbers in an effort to make her shift report stand out among her peers. The patient’s chest pain is a heaviness that, on occasion, radiates to the shoulder. The episodic chest pain is substernal and severe with associated shortness of breath. A similar episode occurred 3 months before, but she decided not to act on it. After tonight’s 10-minute episode, her grandson convinced her that she might be having a heart attack.
Risk factors? She “used to smoke cigarettes,” never did drugs, and never had her cholesterol checked. Her father died at the age of 52 from “heart trouble.” Her mother has hypertension, but no diabetes. Though the first set of triage vitals indicate a BP of 220/110, her last few are in the range of 145-160 systolic/85-95 diastolic. Her pulse is a mere 88, respirations timed at 14 and her pulse ox is 99%. Her EKG looks pristine, one that you hope you’ll have when you go for your first next check up—the one your doctor friends recommended to you 5 years ago.
She looks great to you and her physical exam is entirely normal. All of her labs don’t prompt the ‘!’ on HMED—so they’re normal. A quick glance at some CDRs from previous Journal Club sessions on emed.wustl.edu draws your attention to the TIMI score and your quick informatics skills enable you to download an update done by Sanchis. You calculate her TIMI to be 0-1, depending on how much you trust your patient. A quick “obs stress” would get you out of thinking further until you realize…there’s no stress testing on Sunday! As you summon your inner Aubin/Wagner/Carpenter et. al and prepare to defend your decision of hospital admission to the Firm Cardiology team, an idea pops into your head—what about a coronary CT angiogram? After all, we CT everything else! Why not the heart? You find out Dr. Sanjeev Bhalla is on and you’re even happier. But how good is the CT? Will it give you ‘enough’ confidence to tell this lady she’s not having stuttering acute coronary syndrome?
Population: Low risk chest pain patients presenting to the ED
Intervention: Multidetector CT coronary angiography
Comparison: Routine risk stratification and coronary care
Outcome: Coronary artery disease diagnostic accuracy, ED length-of-stay, hospitalization rates and length-of-stay, radiation exposure, contrast reactions, short-term and long-term cardiac-mortality
Second years: Detection of non-ST-elevation myocardial infarction and unstable angina in the acute setting: meta-analysis of diagnostic performance of multi-detector computed tomographic angiography, BMC Cardiovasc Disord 2007; 7: 39 (http://pmid.us/18093295)
Third years: 64-Slice computed tomography angiography in the diagnosis and assessment of coronary artery disease: systematic review and meta-analysis, Heart 2008; 94: 1386-93 (http://pmid.us/18669550)
Fourth years: Sixty-four–slice Computed Tomography of the Coronary Arteries: Cost–Effectiveness Analysis of Patients Presenting to the Emergency Department with Low-risk Chest Pain, Acad Emerg Med 2008; 15: 623-32 (http://pmid.us/19086322)
Article 1: A randomized controlled trial of multi-slice coronary computed tomography for evaluation of acute chest pain, J Am Coll Cardiol 2007; 49: 863-871.
Article 2: Detection of non-ST-elevation myocardial infarction and unstable angina in the acute setting: meta-analysis of diagnostic performance of multi-detector computed tomographic angiography, BMC Cardiovasc Disord 2007; 7: 39
Article 3: 64-Slice computed tomography angiography in the diagnosis and assessment of coronary artery disease: systematic review and meta-analysis, Heart 2008; 94: 1386-93
Article 4: Sixty-four–slice Computed Tomography of the Coronary Arteries: Cost– Effectiveness Analysis of Patients Presenting to the Emergency Department with Low-risk Chest Pain, Acad Emerg Med 2008; 15: 623-32
The (Not So) Succinct Answer
Chest pain is a the second most common (5.4% of all visits in 2006!) ED complaint among U.S. patients. Although the majority of these patients receive extensive ED or inpatient evaluations, 2-4% are still sent home with an undiagnosed acute coronary syndrome. Fear of an acute coronary event permeates our society for better and worse. Emergency department visits continue to climb and chest pain evaluations contribute a large part to waiting and boarding times. Multi-Detector Coronary Computed Tomography Angiograpy (MDCTA) offers a glimpse of hope to many emergency physicians who, if they could, would rule out a medical emergency in a matter of a few hours as opposed to a matter of days. However engrossed society becomes with new technology and however receptive emergency physicians are to advances that make them more efficient, adopting medical breakthrough’s requires caution especially when risks to patients will become more apparent in a time frame of 10-15 years and the current diagnostic strategies offer decent discriminative power. One recent Harvard retrospective review of ED patients with ≥ 3 CT scans over one year by Griffey et. al. (EM Abstracts mp3 attached) demonstrated a mean number of CT scans of 13 (maximum 70 CT scans) over a mean of 7.7-years with over half of these studies representing repeat images. If EM were to incorporate MDCTA into routine clinical practice, we risk adding chest pain imaging to this radiographic slippery slope.
In the only RCT conducted among emergency department patients at low risk for heart disease, MDCTA performed equally well to current standard strategies and resulted in time and cost-savings to the institution. This came at the expense of additional testing in the MDCTA arm and hence additional exposure to harm from medical diagnostic tests. The diagnostic properties of MDCTA in a cohort of low risk patients appeared satisfactory according to our meta-analysis. However the numbers remain relatively small to justify an immediate change in practice. Finally, since MDCTA offers similar benefit as traditional testing, cost-savings that benefit the institution are likely to vary based on resources.
That brings the argument for MDCTA in emergency departments back to the issue of resources. Ideally, MDCTA would be interpreted by any radiologist in a matter of minutes in several settings. The technique would require little preparation and the diagnostic capabilities would be superior to current tests. However, none of this is true currently. MDCTAs require special equipment and man-power to be done accurately. In the best circumstances about 1 of every 5 is non-diagnostic and patients require significant preparation in order to maximize the diagnostic efficacy of the test. Current testing compares favorably to MDCTA without added radiation exposure.
While much of our infrastructure is likely to change or undergo significant modification in the future, our current health care system seeks to ‘bend’ costs away from more resource utilization to less. Of note, in the RCT and in recent ED research examining this very question, none of the patients identified went on to have a coronary event at 6 months to one year! Perhaps the question we should ask is how “bad” are we at risk stratifying our patients now? What improvements to clinical operations (CDRs ? Risk-stratification networks ? Better point-of-care biomarkers ?) can we develop to make the prevalence of undiagnosed cardiac events shrink from 3% to less than 1%? Legendary EM researcher Jeff Kline has actually started a business called PREtest Consult to enhance clinical decision making using statistical models based upon attribute matching from similar cohorts.
For now MDCTA remains a potential diagnostic strategy that will require further investment in infrastructure, further comparative-effectiveness analysis, and a discussion among emergency physicians to determine at what cost does the search for new methods to increase efficiency outweigh the benefits we provide to our patients in the current system.