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Color segment of heart scan done with the 64-slice Toshiba Aquilion scanner showing track of coronary artery in green where area of blockage was identified.

In March 2007, Consumer Reports on Health published an article on new studies in the treatment of heart disease, and leading the list of key recommendations for heart patients was that they needn’t bother with 64-slice CT angiography.

Pretty amazing, if you believe their advice, especially if your facility bought the expensive equipment to do the scans.

With the 64-slice GE Lightspeed VCT that The Southern Heart Center, a division of The Hattiesburg Clinic, acquired for $1.5 million and put into operation on October 17, 2005, the coronary arteries can now be non-invasively studied and for the first time, the early stages of atherosclerosis can be investigated. They also use it to evaluate atypical chest pain.

The machine itself is a large donut shape with an x-ray component inside that rotates around a table that slides into the center where the patient lies. After dye is injected into the arm, which illuminates the areas to be studied, computerized cross-sections of the heart, or “slices,” are obtained. Radiation is controlled by using thinner slices of approx .625 mm, not visualizing the entire chest, and synchronizing the EKG that coordinates with the x-ray to only activate during the resting phase, i.e. between heart beats of the cardiac cycle. Thus, radiation levels are no greater than that of a nuclear stress test.

This process produces two images: one shows the heart in color and 3-dimensional; it is more “eye-candy” than of the greatest diagnostic value.  The black and white “slices” are where the real diagnosing comes into play.

“With 64-slice CT, we can see calcium, a component of hardened plaque in the wall of the artery, which shows up as a bright white area, which is a marker really for the problem, rather than the stoppage or narrowing itself,” said Dr. Arthur C. Martin, a board-certified internist and cardiologist with The Southern Heart Center, and director of CT imaging. “Plaque actively irritates and inflames the arteries, and calcium being nature’s anti-oxidant and an anti-inflammatory, goes to that spot. We also see ‘soft’ plaque, which shows up as a dark smudge.  We can’t tell yet whether that will be the ‘vulnerable’ plaque that will rupture the wall of the artery, spilling out into the bloodstream and causing clots to occur, which are the actual blockage itself, but the ability to discern that will be coming in the future. Heart catheterization, however, is still needed at this time to show the percent of blockage.”

What is visualized will dictate whether or not treatment will be mild with medicine-like statins (Lipitor, Vytorin, Zetia and the like) for cholesterol control along with lifestyle changes in stress, exercise and diet, or whether more aggressive treatment is needed and cardiologists and cardiac surgeons will proceed with traditional angiography, angioplasty, coronary artery bypass and so forth.
Along with visualization of the heart and coronary arteries, they can also study the valves, chambers, heart function, tumors, and other abnormalities of the heart. Even chest and lung tumors, as well as esophageal acid reflux disease indicators might be picked up.
“And 2,500 scans later since I was there to put the CT into operation, the main beauty of it remains the non-invasive detection of coronary disease, and the visualization of plaque in the walls of the arteries for the first time,” said Martin.

CT angiography, combining the use of x-rays with computer capabilities, is not new and has been around for sometime but in a slower form, only taking 8 or 16 re-assembled computer slices. The beating heart with its tiny arteries was just too fast to be captured clearly at those speeds. But with the new 64-slice generation of CT, and the heartbeat slowed down to 60 beats/minute with beta blockers, startlingly clear color images of the heart, as well as black and white slices are produced. It is especially good at discerning the presence of calcium, a component of plaque, that has built up in artery walls.

CT’s non invasive characteristics and short examination time are very enticing to the ears and ‘hearts’ of the general public. Unlike conventional angiography, which is performed by threading a catheter up thru the groin into the heart, CT only requires the injection of dye into an arm.  CT is also very fast with the entire procedure taking less than a half hour to complete, something else patients really like. 
Dr. Alan Covin, a board-certified cardiologist with HeartSouth, regularly uses the cardiac CTA in his practice.  “I can see a new patient, perform the cardiac CTA with a calcium score, give them the results and get them back to work or on the appropriate therapy all in the same day,” said Covin.

High radiation in CT angiography is another problem the Consumer Reports article mentions, and has been documented in more than one study. However, according to several experts, and mentioned by Martin, reduction in radiation can be achieved by timing the x-rays to the heartbeat cycle only during the resting phases, thus reducing exposure to that of no more than other intensive heart studies.  Also, some companies such as Phillips tout themselves as “low-dose” or “dose-conscious” in that area. 

Covin believes, “Proper use of the cardiac CTA should decrease the radiation exposure to the population at large, if not to the individual patient since it will decrease the number of nuclear stress tests and diagnostic heart catheterizations performed.  As our confidence in the findings increase, we should be able to limit the exposure to radiation in the cath lab by focusing on the diseased artery identified by the cardiac CTA.


June 2007

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