Practice News / Events

THE “NEXT BIG THING”:
CT Angiography
By Dr. Andrew G. Kumpuris

Everyone is always looking for the “next big thing”.  Cardiologists are no different. Perhaps the first “big thing” occurred quite by accident. In October 1958, Dr. F. Mason Sones, while injecting
dye into a 27 year old rheumatic patient, was horrified to see his catheter whiplash and inadvertently power inject contrast into the right coronary artery. He watched in horror, anticipating a calamity. When it did not happen, Sones was wise enough to realize that perhaps he was on to something. The era of coronary angiography was born. What has followed has been nothing short of revolutionary. Coronary angiography, or cardiac catheterization as it is often called, has become the foundation technology, without which there would be no cardiac surgery, angioplasty, or stent insertion. The importance of making a definitive diagnosis cannot be overstated. However, cardiac catheterization has its limitations. It does have risks, it is expensive, and it is invasive. Physicians are still faced with the dilemma of trying to diagnose coronary disease before it becomes clinically manifested. To put the problem in the proper context, it is estimated that less than half of the individuals with coronary disease even know they have the disease and more than half of the individuals with the disease have as their initial presenting symptom death orinfarction. Better tests with easier application are clearly needed.

What is CT Angiography (CTA)? Noninvasive imaging of the heart has been a challenge because of the heart’s constant motion. EKG-synchronized computed tomography (CT) has solved many of the problems and allowed for exquisite imaging of cardiac anatomy and pathology with unparalleled spatial (space) and temporal (time) resolution. Current generation scanners have multi-row detectors capable of generating numerous images with each rotation of the gantry (tube).The scan can be done in a prospective manner by activating the X-ray for only the time needed to acquire the image or in a retrospective manner by scanning several cardiac cycles and using the EKG to reconstruct the images based on the timing interval from the R wave. Computer generated cardiac images may include the overall cardiac anatomy, coronary anatomy, coronary lumen, atrial appendage, calcifications, and hard or soft plaque. Because of the differences in the absorption of X-ray by various types of tissue, CTA can distinguish different tissue types (histology) and define plaque characteristics with remarkable accuracy.

Who is a Candidate for CTA? Proper diagnosis leads to proper treatment. Daily, clinicians face the challenge of making an accurate diagnosis. If one considers the spectrum of patients presenting to physicians with chest pain or related symptoms, about 25% are easily addressed with a history and physical and simple diagnostic tests. At the other end of the spectrum, 25% are deemed high risk for disease due to a combination of symptoms, physical findings, or risk factors. It is the middle 50% that CTA is best suited. Those patients with somewhat atypical clinical histories, confusing stress studies, multiple risk factors, or worrisome family histories make up an appropriate population of ideal candidates.

Comparing CTA with Cardiac Catheterization
These technologies are complimentary, but considerable overlap does exist. First, cardiac catheterization defines the lumen of the vessel with significantly better spatial resolution (0.125 square mm). However, it does not “see” the vessel wall nor does it do well with linear disease (as opposed to obstructive disease). Cardiac catheterization yields little information about the nature of the obstructing lesion. CTA, in contrast, does not have the spatial resolution of catheterization
(0.625 square mm.), but it is considerably better in defining soft plaque, calcified plaque, and
extent of disease. Presently, clinicians are well aware that a considerable number of cardiac
events are caused by soft plaques of less that 50%. In an era of increasing knowledge of plaque vulnerability and worrisome plaque characteristics, the histologic information provided by CTA will undoubtedly become more and more important. Both technologies require the administration of contrast dye. The volume of dye required is comparable for the two techniques. As all cardiologists know, cardiac catheterization is an arterial injection of dye. This rarely produces symptoms, even in patients with well documented dye allergies. In contrast, CTA is a venous injection based technology. Allergic reactions and dye-related nausea and vomiting are much more common. Radiation is also an issue to be considered. CTA exposes the patient to about one-half times as much as Cath and about 2.5 as much as a cardiolite scan. Clearly, multiple radiation-requiring tests over a brief time span should be avoided. As CTA works its way into the mainstream of diagnostic studies it is inevitable that new strategies for evaluating patients
will evolve.

Contraindications to CTA Valuable information can frequently be obtained even from CTAs of marginal quality. There are few absolute contraindications to performing a CTA but there are clinical conditions when either the quality of the study may be in question or the potential for complications may be excessive. Below is a list of clinical conditions where a clinician should question if CTA is the appropriate diagnostic test. 1. Excessive heart rate unresponsive to the administration of oral or IV beta blockers 2. Renal insufficiency where the creatinine is more than 1.9 3. Frequent premature ventricular or atrial contractions (unresponsive to therapy) 4.Atrial fibrillation 5. Presence of a coronary stent, especially if it is less than 3.0 mm 6. Iodine dye allergy 7. Profound obesity 8. Excessive coronary calcification 9. Recent diagnostic studies requiring radiation exposure (especially women)

Conclusion Time will tell if the new “next big thing” is the “real thing”. The need for a simple low risk diagnostic test to detect the many patients with clinically quiescent disease remains an enormous challenge. It is very reasonable to hope that CTA will fill the void in our current capabilities. Not only can the current technology aid in both diagnosis and prognosis, but future advances likely will allow this test to be used with greater accuracy in designing therapeutic interventions and monitoring their effects. The future has never looked brighter.