Cardiac CT
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Print“Recent advances in CT technology have transformed Cardiac CT from an interesting new technology into a “game-changing” technology that will revolutionize the care of patients with chest pain and change the way we practice medicine.” – Christopher Wolfram, MD, FACC - Cardiology Associates of Green Bay
CORONARY CALCIUM SCORING vs. CARDIAC CT ANGIOGRAPHY
Coronary Calcium Scoring: A simple test without contrast that even older generations of CT scanners can perform. Hard plaque in the wall of arteries contains calcium. Normal arteries have no calcium. The amount of calcium can be quanitified and is predictive of the total plaque burden. Coronary calcium scoring has been validated as a strong predictor of coronary heart disease events and provides predictive information beyond that provided by standard risk factors. This has been validated in multiple studies including the Multi-Ethnic Study of Atherosclerosis (MESA) reported in the New England Journal of Medicine in March 2008 which included over 6,700 patients.
Cardiac CT angiography: This is a comprehensive exam of the heart using contrast that can detect both soft and hard plaque in coronary arteries and determine the % stenosis. A tremendous amount of other information can also be obtained related to cardiac anatomy and function.
In conjunction with the Emergency Department, Bellin will be installing a New Toshiba Aquilion One 320 slice CT scanner in January 2010.
LIMITATIONS TO PRIOR GENERATIONS OF CT SCANNERS:
● Artifact: due to movement, arrhthymia, & need to overlap multiple CT rotations to reconstruct the heart.
● Need for low heart rate (<60 bpm) for good imaging quality, usually requiring beta blockers.
● Obese patients weighing over 250lbs often had poor quality scans due to imaging noise and artifact.
● Radiation exposure: 64 slice CT scanners expose patients to about 10-15mSv of radiation with a full Cardiac CT study. This was higher with the previous generation of scanners. Compare this to: Nuclear stress testing = 8-12 mSv. Worldwide ave. background radiation dose for humans is 2.4mSv/yr.
ADVANTAGES:
● Able to scan entire heart with one rotation. (Total scan time = fraction of a second or <1 heart beat)
● Eliminates most artifact due to patient movement, arrhythmia & previous need to reconstruct multiple CT rotations. This leads to a marked improvement in the resolution and overall quality of the scan.
● No need for heart rate control (beta blockers). Cardiac arrhythmias do not exclude patients.
● Obese patients can often have very good quality images due to decreases in artifact.
● Markedly reduces radiation dose: 2-4mSv (full Cardiac CT) vs 8-12 mSv (nuclear stress test)
● Able to perform a triple rule out scan (r/o PE, aortic dissection and coronary obstruction) with 7-14mSv.
● Because of shorter scan time, the amount of contrast dye required is also decreased.
This is the most accurate, comprehensive, low risk noninvasive cardiac test that we have ever had access to.
LIMITATIONS:
● The best spatial resolution achievable by 320 slice Toshiba Aquilion CT scanner is 0.35mm. This is impressive, but does not equal the 0.1 mm spatial resolution of conventional coronary angiography.
● Although myocardial perfusion imaging is now possible with this scanner, this form of imaging is not yet well validated and is not yet ready to replace nuclear stress testing to determine whether coronary stenosis are truly limiting blood flow.
● Patients with moderate stenosis, estimated at 40-70%, may still need further testing to determine the
functional significance of the stenosis.
● Contrast exposure is still a concern in patients with kidney disease.
PRACTICAL CONSIDERATIONS:
● Coronary Calcium Scoring is not covered by health insurance. Bellin Health offers coronary calcium scoring at a low $50 cost. This has been popular leading to a 3-4 month waiting list. If health providers order the test they will be given a priority & the test will typically be performed within 1-2 weeks.
● Cardiac CT Angiography has assigned billing codes and is reimbursed by Medicare/Medicaid & many private insurers, but only for certain strictly defined indications. When ordering this study for clinic patients,we typically get pre-approval, which is often a cumbersome, tedious process that can take weeks.
● The Bellin Emergency Room has been using a protocol for chest pain patients since the winter of 2008 that includes a pathway for some patients to have Cardiac CT. We have some wonderful examples of how this has improved diagnostic accuracy and led to better patient management. The current Cardiac CT chest pain pathway is limited by multiple exclusion criteria. Many of those exclusion criteria will be eliminated with the new 320 slice scanner.
FUTURE DIRECTIONS AND CONCLUSIONS
● This is a very exciting advance in technology that will truly change how we practice medicine. However, before the revolution reaches it’s full potential, results from further outcome studies will be needed in order to gain widespread acceptance for reimbursement by third-party payers in the US.
● Future advances such as plaque characterization (recognition of vulnerable plaque) and determining myocardial viability and perfusion will further expand the clinical utility of Cardiac CT in the future.
Authors:
Christopher Wolfram, MD, FACC and James Rider, MD, FACC
Cardiology Associates of Green Bay.
