CT Angiography: The Plaque Screening Test with Lots of Potential

Arnold fainted while fishing with his 14-year-old son. He consulted 3 doctors before I met him. He was 63 years old at that time.

The ER doc worked him up completely for potential stroke or heart attack and prescribed a statin. Arnold didn’t like the idea of taking statins, but he also didn’t like not knowing why he fainted. 

He went to another doctor, an internist who found nothing wrong but also recommended a statin. Arnold also went to a cardiologist who put him through a stress test. He passed. He got no recommendations other than a statin. 

Then Arnold came to see me. Based on a few tests, I suspected he has early insulin resistance. He also had an LDL of 98 mg/dL, perhaps the reason the previous 3 doctors recommended statin. Arnold and I discussed other tests, and eventually, we settled on getting a CT angiography (CTA).

Here’s the result: there’s a plaque in Arnold’s LAD (left anterior descending artery). The report stated that the plaque was “not occlusive,” though I explained that plaque just needed to be soft and form a clot to cause a heart attack. The discovery convinced Arnold to take a low-dose statin, not to lower LDL but to arrest inflammation in his arteries. 

Four years later, thanks to CTA and Arnold working hard to improve his health, Arnold’s plaque is stable, and his future risk of cardiovascular (CV) events is lower.  

What is CTA (CT Angiography)?

CTA is short for CT angiography or computed tomography angiography. 

CTA comes from two root terms: “angiography” (angiogram or arteriogram, a procedure that outlines blood vessels), and “CT” (combining X-rays and computers to create cross-sectional images of the body). So CTA will produce detailed images of the heart and blood vessels.   

In CTA, the CT scanner is typically a large, box-like machine with a hole or tunnel in the center. The patient lies on a narrow table that slides in and out of the box. There is a ring called a gantry, with X-ray tubes and X-ray detectors on the opposite sides of the ring. The gantry rotates around the patient. There is a computer workstation with the technologist nearby (and able to speak with the patient) in the room. 

Computerized X-ray imaging is combined with a special iodine-containing dye that’s injected into the vein. X-ray doesn’t pass through iodine, which makes the dye an excellent contrast material. The images are reformatted to create 3D images that may be viewed on a monitor, printed on film or by a 3D printer, or transferred to electronic media.

 

CT Angiography vs. Other CT scans

The big differences between coronary CTA and other CT scans are the speed of the CT scanner and the use of a heart monitor. The special challenge of coronary CTA is scanning the arteries—with each beat of the heart, blood vessels may move 5 or 6 times the distances of their radius (Budoff, 2006).

CT Angiography vs. Standard Coronary Angiography

A CT angiogram is a minimally invasive test as compared to the standard coronary angiogram. The standard angiogram is percutaneous—it uses a catheter (a thin tube) that is inserted through an artery in the arm or groin up to the area being examined.

 

CT Angiography vs. Stress Tests

One similarity between nuclear stress tests (a type of stress test) and CTA is that both use imaging and dye. However, instead of directly visualizing the arteries, a nuclear stress test measures blood flow as the patient walks on a treadmill. Any reduced blood flow is interpreted as a narrowed or blocked artery. 

Also, there’s exposure to radiation in both nuclear stress tests and CTA, though newer CT scans have significantly lower doses of radiation. CTA and nuclear stress tests also have the same cost (Johns Hopkins, 2015).

Why You Might Need a CT Angiography

According to Michigan Medicine (2019), you might need to undergo CTA to look for:

• A narrowing or blockage in arteries due to atherosclerosis (buildup of plaque that may restrict blood flow);
• Heart problems, like pericarditis (a buildup of fluid around the heart);
• Aneurysm (a blood vessel that bulges and in danger of rupturing);
• A tear in the aorta (the main artery that carries blood away from your heart);
• Pulmonary embolism (blood clot in the lungs);
• Abnormal blood vessel patterns (which may be a sign of a tumor).

Is CT Angiography Safe?

Johns Hopkins Medicine (2020) listed down several risks associated with CTA. The most commonly cited is the risk of repeated X-ray exposure, though the amount of radiation is considered minimal. Furthermore, no radiation remains in the body after a CT scan.

The patient may also feel a brief pain from the needle that will inject the dye. The patient may experience flushing, a headache, or a metallic taste in the mouth. There are reports too of allergic reactions to the dye, though such reactions are uncommon. Patients with diabetes or kidney problems may experience kidney failure, though this is rare.

Is CT Angiography Accurate?

For many doctors, the standard angiography (the one that uses dye, X-ray, and catheter) remains the standard for detecting blocked arteries. Stress tests, though, are increasingly becoming popular as the go-to technique for measuring plaque, as they are simpler, cheaper, and non-invasive. 

But in terms of accuracy, the minimally invasive CTA should give non-invasive stress tests and invasive angiography a stiff competition. 

In an article titled “CT angiography, underuse, overuse, or appropriate use?,” CTA accurately identified 85% of the patients who had significant stenosis (narrowing) and 90% of the patients without coronary artery disease. Moreover, CTA was almost as accurate as the standard angiography (van der Wall, 2009).

According to Johns Hopkins Medicine (2015):

…non-invasive CT scans of the heart’s vessels are far better at spotting clogged arteries that can trigger a heart attack than the commonly prescribed exercise stress that most patients with chest pain undergo.

In a study comparing CTA and SPECT-MPI (a type of nuclear stress test), CTA identified blockages in 9 out of 10 people, while the stress test picked up blockages in 6 out of 10 (Arbab-Zadeh, 2015). 

Recent studies also indicate CTA could add additional clarity to the popular stress testing. There has been a rapid “learning curve” encouraging the use of CTA and the latest equipment to avoid radiation exposure.

Much data in support of the diagnostic accuracy and prognostic value of non-invasive coronary angiography by computed tomography have emerged within the last few years. These data challenge the role of stress testing as the initial imaging modality in patients with suspected coronary artery disease. (Arbab-Zadeh, 2012)

Unfortunately, while CTA’s reliability has already been demonstrated, uncertainty persists because of the small number of people involved in comparative studies. Not to mention the current guidelines of the American Heart Association and the American College of Cardiology, which recommend stress testing, with CTA being reserved for patients with borderline stress test results. 

Is CT Angiography Effective?

We can’t end the discussion on CTA without mentioning the 2 landmark studies of PROMISE & SCOT-HEART.

The PROMISE Trial 

PROMISE (Prospective Multicenter Imaging Study for Evaluation of Chest Pain) was a multicenter trial. It was the first big study showing the potential of CTA.

Coronary CTA, by identifying patients at risk because of nonobstructive CAD, provides better prognostic information than functional testing in contemporary patients who have stable chest pain with a low burden of obstructive CAD, myocardial ischemia, and events. (Hoffmann, 2017)

In this study, patients with stable angina (chest pain) were randomized to get either a CTA or a “functional testing.” The term “functional” is used because these tests include assessment of vascular function following some form of exercise. Here, the 3 functional tests are stress EKG, nuclear stress, and stress echo. 

Patients were followed for 26.1 months. Endpoints were death, myocardial infarction (heart attack), or unstable angina hospitalizations. The result: Investigators found that the ability of CTA to predict CV events was significantly better than any of the functional tests in the study.

The PROMISE trial was also a “non-inferiority” trial. What does “non-inferiority” mean? It is a term that medical researchers use to show that the test or treatment studied is “at least as good as” the standard test or procedure. Again, the PROMISE trial showed CTA performed at least as well as any of the 3 stress tests at managing patients with angina.  

PROMISE made a case that CTA is better. Of course, more evidence is needed. And that is just what the SCOT-HEART Trial has provided.

THE SCOT-HEART TRIAL 

SCOT-HEART (Scottish Computed Tomography of the Heart) is a vital step in the science concerning CTA. 

In this trial, one group received “standard” evaluation while the other group had the “standard” plus CTA. “Standard” here refers to any of the 3 stress tests the physician wanted to do at the time of the clinical workup (The SCOT-HEART Investigators, 2015). 

The result: CTA found increased numbers and severity of lesions. This led to increased treatment and long-term improved outcomes. 

Notice that CTA led to “increased treatment.” Does that mean CTA just aggravated the situation? Now, this is where care should be used in interpreting what “increased treatment” means.

First, the standard group did receive fewer bypass procedures after year 1. This should be good, right? Well, not necessarily. 

Second, the patients who received “CTA+standard” testing did get more treatments—stents, bypasses, AND preventive treatments—during year 1. However, their treatments became less frequent in years 2 to 5, and they lived longer. This shows that patients who got a CTA are more likely to make life-saving changes in their habits.

Here’s the deal. We know CTA provides actual images of plaques, images that could help a person visualize his own risk for heart attack and stroke. That image can motivate the person more to adhere to the prescribed intervention. So, patients drop their carbs, lose pounds, get off the couch, get proper sleep, develop habits that will extend their lives.

Overall, the SCOT-HEART trial made a strong statement in favor of CTA.

 If you found this article helpful and want to start taking steps toward reversing your chronic disease, Dr. Brewer and the PrevMed staff are ready to serve you no matter where you’re located.

To find out more, schedule a consult here: prevmedhealth.com 

References 

Arbab-Zadeh A, Di Carli MF, Cerci R, George RT, et al. Accuracy of Computed Tomographic Angiography and Single-Photon Emission Computed Tomography-Acquired Myocardial Perfusion Imaging for the Diagnosis of Coronary Artery Disease. Circ Cardiovasc Imaging. 2015 Oct;8(10):e003533. doi: 10.1161/CIRCIMAGING.115.003533. 

Arbab-Zadeh A. Stress testing and non-invasive coronary angiography in patients with suspected coronary artery disease: time for a new paradigm. Heart Int. 2012 Feb 3;7(1):e2. doi: 10.4081/hi.2012.e2.  

Achenbach S, Narula J. Coronary CT Angiography: From Sensitivity to Specificity. J Am Coll Cardiol Cardiovasc Imaging. 2011;4(11):1227-1229. 

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Hoffmann U, Ferencik M, Udelson JE, Picard MH, et al. Prognostic Value of Noninvasive Cardiovascular Testing in Patients With Stable Chest Pain: Insights From the PROMISE Trial (Prospective Multicenter Imaging Study for Evaluation of Chest Pain). Circulation. 2017 Jun 13;135(24):2320-2332. doi: 10.1161/CIRCULATIONAHA.116.024360.

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Johns Hopkins Medicine. Heart CT Scans Outperform Stress Tests in Spotting Clogged Arteries. Johns Hopkins Medicine website. https://www.hopkinsmedicine.org/news/media/releases/heart_ct_scans_outperform_stress_tests_in_spotting_clogged_arteries. October 26, 2015. Accessed November 18, 2020.

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