It is well known that taking a good history and physical, getting a non-ischemic EKG, and serial cardiac biomarkers, results in a risk of death/AMI of <5% in 30 days. Patients, in whom you still suspect have CAD, should undergo provocative testing within the next 72 hours based on the AHA/ACC guidelines. Their guidelines deem provocative testing as including:
- Exercise treadmill stress test,
- Myocardial perfusion scan,
- Stress echocardiography, and/or
- Coronary CT angiography (CCTA).
Myocardial perfusion scans and stress echos have a sensitivity of 85–90% and specificity of 75–80%. In contrast, CCTA’s have been shown to have a sensitivity of 93-97% and specificity of 80-90%.
ACRIN-PA Trial [1]
- Non-inferiority study
- 5 Pennsylvania EDs
- 1,370 patients, Age > 30 years
- Inclusion criteria: TIMI score of 0–2, EKG without ischemic changes, and negative first set of Cardiac Biomarkers
- Randomized 2 patients to CCTA arm (908 patients) for every 1 patient to Standard Stress arm (462 patients)
Primary Outcome:
- MI or Death from CAD at 30 days
Secondary Outcomes:
- Rate of discharge from ED
- Length of stay (LOS) in ED
- Rate of detection of CAD
- Resource utilization
What they found:
- 640/908 pts (70.5%) who underwent CCTA had coronary stenosis of <50% and none had MI or death due to CAD at 30 days
- Discharge from ED 49.6% with CCTA vs 22.7% with standard stress arm
- ED LOS 18 hr in CCTA arm vs 24.8 hr in standard stress arm
Conclusion: CCTA allows early discharge of low to intermediate risk patients presenting to the ED with possible ACS.
ROMICAT II Trial [2]
- Randomized controlled trial
- 9 EDs in the US
- 1,000 patients with acute chest pain with ages 40–74 years
- CCTA (501 patients) versus Standard Evaluation (499 patients)
Primary Outcome:
- Hospital length of stay
Secondary Outcomes:
- Cardiovascular events at 28 days
- Rate of discharge from ED
- Time to diagnosis
- Cost
- Utilization of resources
What they found:
- Hospital LOS decreased by 7.6 hr in CCTA group
- Rate of discharge from ED 47% in CCTA arm vs 12% in Standard Evaluation Arm
- No difference in cardiovascular events at 28 days
- Cost was similar between two groups $4,289 CCTA vs $4,060 in Standard arm
Conclusion: CCTA decreases length of stay without an increase in rate of cardiovascular events.
DISCUSSIONS POINTS
- CCTA with 0 lesions is NEGATIVE: These patients can certainly be discharged home with primary care follow up with a nearly 100% NPV for ACS/AMI.
- CCTA with <50% lesion is NOT NEGATIVE: This patient has CAD. It may not be clinically significant, but we can see plaques. 2/3 of AMIs occur from plaques that have <50% stenosis. Certainly we can start risk factor modification with beta blockers, ASA, and statins, but there are no studies looking at how this group of patients will do long term.
- CCTAs are anatomic studies and not functional studies. Identified lesions will lead to more diagnostic tests, which is one of the big arguments against CCTA. CCTA identifies CAD more often than standard stress modalities, which leads to more heart catheterizations and PCIs.
- As the number of CT slice increases, radiation dose decreases:
- A 64 slice CT = 10 – 15 mSv of radiation
- A 128 slice CT = 5 – 10 mSv of radiation
- A 256 slice CT = 1 – 5 mSv of radiation
- In contrast, a single-view CXR = 0.02 mSV of radiation
- There is currently an ongoing National Heart, Lung, and Blood Institute-funded trial called the PROMISE (Prospective Multi-center Imaging Study for Evaluation of Chest Pain) Study with 10,000 patients. Patients with symptoms suggestive of CAD will be randomized to a CCTA vs usual care with a functional test. What’s interesting about this study is it is being performed in the offices of primary care physicians and cardiologists rather than EDs. The study authors hypothesize that medically optimizing patients identified, as having non-obstructive CAD will yield improved long-term outcomes.
FINAL THOUGHTS
It is well known that in low risk patients, doing a good H&P, having a negative EKG (no ischemic changes), and negative serial cardiac biomarkers gives us about 99% NPV & 99% sensitivity for ACS/AMI. This is even without additional testing, such as CCTAs.
So are CCTAs worth the cost and potential harms in this low-risk group to add another 1% to the 99% NPV and 99% sensitivity rates? In my opinion, that answer is NO.
References:
- Litt HI et al. CT Angiography for Safe Discharge of Patients with Possible Acute Coronary Syndromes. NEJM 2012. PMID: 22449295
- Hoffmann U et al. Coronary CT Angiography Versus Standard Evaluation in Acute Chest Pain. NEJM 2012. PMID: 22830462
