Post #25: Diagnostic testing for Coronary Artery Disease – Coronary CTA

Although CT angiography (CTA) has been available since the 1970s, it was not until ultra-fast CT scanning enabled radiologists to image the beating heart with clearer resolution (around 1998) that performing CTA of the heart became a practical imaging study.  CCTA does carry significant radiation exposure, but it is a safer procedure than traditional coronary arteriography and in some cases can even replace the more invasive arteriography.   

A few words on Coronary Artery Calcium scores

CT scan of the heart, also called Cardiac electron-beam tomography is performed without contrast and findings are reported as coronary artery calcium (CAC), now as a calcium score measuring pixels of calcium.  CAC is considered by some cardiologists to be a useful predictive test for early detection of coronary artery disease, but insurance companies and Medicare have resisted covering the study.   Because of this, calcium scores are mostly marketed as a direct-to-patient imaging study, and paid for by the patient.  Radiology benefit management companies rarely authorize coronary artery calcium scores.  Nevertheless, calcium scores are considered a risk factor, and high values (>100) alone may even be a criterion for authorization for MPI or stress ECHO.  (see post #22)

The role of Cardiac CT angiography is also controversial as a non-invasive diagnostic tests for coronary artery disease (CAD).  Current guidelines continue to favor functional testing for myocardial ischemia (ETT, stress ECHO, MPI) reserving anatomic testing (with CCTA) for those without known CAD but with equivocal functional testing, or for patients unable to perform functional testing.  Many cardiologists disagree with this limitation.  In the US the test is often used as an alternative to invasive coronary angiography in patients with low pre-test probability of having CAD. 

Since 2016, many articles have discussed the pro ( and con ( of CCTA.  This blog will detail the most up-to-date guidelines that determine prior authorization of the study in the U.S. 

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CCTA is indicated and can be approved for the following criteria: 
•    Patients with a low or intermediate pre-test probability of CAD with persistent symptoms after a negative or          equivocal stress test. 
•    To replace coronary arteriography in patients with low pre-test probability of CAD scheduled for high or                moderate risk surgery who cannot perform a stress test or have had an abnormal stress test. 
•    For symptomatic patients to assess post CABG graft integrity when only graft patency is the concern and not       the status of native coronary arteries (e.g. early graft failure)
•    For symptomatic patients after unsuccessful conventional coronary arteriography. 
•    Prior to a CABG re-do to determine if the bypass grafts are directly beneath the sternum so as to plan                   alternative access to enter the chest. 
•    To assess unexplained new onset of congestive heart failure or cardiomyopathy with no prior history of CAD        and low or intermediate pre-test probability of CAD (as long as no conventional coronary arteriogram has            been done since onset of CHF symptoms). 
•    Prior equivocal anatomy on conventional coronary arteriography
•    Ventricular tachycardia if CCTA would replace conventional arteriography
•    Pre-op evaluation before surgery for aortic dissection, AAA or other vascular surgery if CCTA would replace       conventional arteriography.
•    To assess suspected coronary artery anomalies (use code 75574) or suspected congenital heart disease (as        alternative to chest CTA)
•    For suspected Vasculitis, Kawasaki’s or Takayasu’s disease
•    Cardiac trauma: to detect injury to aorta or coronary artery or myocardial or pericardial injury
•    Resuscitated sudden death and unable to have conventional coronary angiography or if a sibling had                   sudden death syndrome < 30 and anomalous coronary artery. 
•    Suspected anomalous coronary arteries in patient < 40 with persistent exertional chest pain and normal               stress test. 

CCTA has many contraindications and should not be performed in cases of
1.    Routine follow-up of stable or asymptomatic patients with known CAD
2.    Arrhythmias such as atrial fibrillation or flutter, frequent PVCs, PACs, or high-grade heart block. 
3.    Multifocal atrial tachycardia
4.    Inability to lie flat
5.    BMI greater than 40
6.    Inability to hold breath for at least 10 seconds
7.    Inability to obtain a heart rate less than 65 bpm after beta blockers.
8.    Renal insufficiency
9.    Coronary calcification score greater than 1000
10.    High pre-test probability for CAD (these patients should have conventional coronary                                                arteriography, especially if PCI is anticipated). 
11.    Pre-operative assessment in anticipation of non-cardiac nonvascular surgery.
12.    Evaluation of coronary arteries post heart transplant
13.    Identification of plaque composition and morphology
14.    Evaluation of coronary stent patency 

This list incorporates guidelines from 3 major Radiology Benefits Managers. 

Lesson #25: CCTA can be a very useful imaging study for avoiding more invasive conventional coronary angiography in low to intermediate pre-test probability patients with equivocal stress testing. Its value in patients with high pre-test probability of CAD is less clear.  

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