Use of coronary CT Angiography in the evaluation of low-risk CP
For starters, important to remember that the discussion is restricted to low-risk CP patients (our typical CPEP). Tests will always have different performance characteristics in different patient populations. Also, as discussed by CK, our goal was to emphasize the prognostic/clinical strength of the test (how will these patients do once they are discharged from the ED?, can we pick up the 3-5% “missed ACS” cases?) rather than simply the diagnostic efficacy of the test (do the number of 50% blocked lesions match the number of lesions seen on invasive angiography?). This is important, as EK mentioned in passing, because there is a whole other discussion out there about whether or not lesions seen on invasive angiography should be stented. The COURAGE trial (April 12, 2007 NEJM) took patients with “stable” CP and documented 70% blockages on angiography or abnormal stress tests, and showed that mortality/MI rates were the same with maximal medical management or stenting. So, our articles:
1. Goldstein J, et al: A Randomized Controlled Trial of Multi-Slice Coronary Computed Tomography for Evaluation of Acute Chest Pain. JACC 2007; 49(8):863-8712.
197 low-risk patients, really compared 2 protocols; either 0/4 hour ECG/CIP then CTA, or 0/4/8 hour ECG/CIP then nuclear med (SPECT) stress testing. No test complications in the CT group, and no major adverse cardiac events at 6 months in any of the patients sent home from either group. Ultimately, accuracy was equivalent for the two approaches. Twenty-four % of the CTA group had intermediate disease on CTA or nondiagnostic CTA; these patients all required a second test (SPECT). There were also 11% false positive CTAs. The article emphasized the shorter ED length of stay for the CTA patients, but this was largely because of the additional time built into the SPECT protocol (a shorter rule-out time would have cut out much of the difference), and there was a several hundred dollar difference in “cost of care”, and as SA and CM pointed out, “cost of care” determinations are pretty much hand-waving. Also, only a 4% rate of disease in the whole group- in this small study of only 200 patients, safety conclusions will have wide confidence intervals.
2. Hollander J et al: Coronary Computed Tomographic Angiography for Rapid Discharge of Low-Risk Patients With Potential Acute Coronary Syndromes. Annals of Emergency Medicine, In Press.
568 patients evaluated with coronary CTA, low TIMI score, either receiving CTA without serial CIP (some received one set) or CTA after observation period (if they came to the ED at night). Everybody did great (except for the guy who died in a car crash). No major adverse cardiac events at 30 days (0%, 95% CI 0% to 0.8%). Again, a very low risk population (6 patients out of 568 received stents). Conclusion that CTA can be used to safely send home low risk patients (<1% risk of MI/death at 30 days). One large issue with the study-patients were enrolled in part because emergency physicians had decided to order a coronary CTA on them, introducing a significant selection bias.
3. Takakuwa K, Halpern E: Evaluation of a “Triple Rule-Out” Coronary CT Angiography Protocol: Use of 64-Section CT in Low-to-Moderate Risk ED Patients Suspected of Having Acute Coronary Syndrome. Radiology 2008;248(2):438-446.
This study had the same primary outcome of adverse clinical outcomes at 30 days, 197 low risk patients, but used the “Triple Rule-out” protocol, which involves higher radiation but evaluates the rest of the thorax. Negative predictive value for CTA 99.4%, but small study, low risk population, so CI 96.9%-100%. They did find other stuff; PEs, dissections, pancreatic and pulmonary masses, among others. Unfortunately, no clinically information was reported about the patients, so impossible to say if clinicians were already worried about these other diseases or not (serendipitous finds vs. clinically suspected). AN made the excellent point that in his case, a MRI (like a CT would have) diagnosed his constrictive pericarditis and gave him a new lease on life. As a counterpoint, CK related how a CT with a ?tumor finding led to her unnecessary surgery. Always a balance.
Other things to remember about coronary CTA:
-Static rather than Functional (stress test) study.
-For now, you need to be in normal sinus rhythm, and usually need betablockers/NTG to slow the HR and max. open the vessels to get good pictures. Stents and high calcium scores muck up the pictures.
-Think about the potential complications/patient exclusions. The radiation dose is substantial (10-20 mSv), which is estimated to increased overall cancer risk by 1 in 200 to 1 in several thousand. Doesn’t mean not to do it, but easily ordered technologies tend to be overused-just something to think about. Along the same line, what happens when the patient returns the next year with similar pain? Another CT and more radiation? How long are they “good for”? Unknown.
-In these studies, no renal issues from the dye load, but they (and all studies so far) have been small-no more than several hundred patients.
Can I wrap it up already? The room was pretty evenly split at the end of the night on whether they would advocate for this test in the vignette patient. I think the potential speed of the test (at least compared to our current CPEP) was appealing to some. To others, the potential to find other disease/explanations for the pain is an important selling point (“triple rule-out). Remember, in these low risk patients, there is such a small chance of a poor outcome that you could just send them all home without any testing and be right 90-95% of the time, so we really need much larger studies in this low risk group to be happy about safety (CIs for adverse cardiac outcomes are just too wide in studies 1 and 3. Study 2 with <1% risk of adverse event at 30 days but significant selection bias). For now, based on available data, coronary CTA is probably safe in low risk CP patients (similar performance to stress echo or nuclear stress/SPECT), and if you are trying to get more “bang for your buck” (thinking cardiac vs. PE, or cardiac vs. dissection), this might be the way to go. SA also brought up the excellent point that depending on where you practice, if it’s a small hospital, this test can be tele-radiologied to someone to read even if you don’t have a CTA radiologist on-site, and you might not have a cardiologist available to do stress echoes. So it comes down to patient selection (is CTA safe for your patient, and how clear is their clinical presentation) and what are the available resources/alternative strategies at your institution.