Computed Tomography Ct Angiography - Diagnosing Heart Disease: Heart Disease

Content provided by the Faculty of the Harvard Medical School

Computed tomography (CT) angiography

Traditional computed tomography (CT) devices are doughnut-shaped machines that house rotating x-ray tubes that take pictures of thin "slices" of your anatomy. A computer assembles these images into a three-dimensional picture. One drawback of standard CT scans of the heart is that the machines aren't fast enough to capture the beating heart. Since the heart is constantly contracting and expanding, the movement blurs the images of the arteries on most scans. It's like trying to take a photograph of a speeding car with a slow shutter speed.

Two developments now make it possible to get images sharp enough to actually see blockages inside the coronary arteries. First, beta blockers, such as atenolol (Tenormin) and metoprolol (Lopressor, Toprol XL), can slow down the heart rate. This reduces the "speeding car" effect so that doctors can get a better look at the heart.

Second, the technology has improved, providing the equivalent of much faster film to photograph that speeding car. Traditional CT devices typically have four internal scanners. In 2004, devices with as many as 64 scanners became available. This represents a significant advance in terms of imaging: The greater the number of scanners, the better the resulting image. These newer CT devices can take dozens of snapshots from different angles. These simultaneous snapshots are then used to reconstruct a complete image of what is going on inside the arteries.

The advantage of the newer technology is that it can show whether someone has coronary artery blockages without subjecting them to a coronary angiogram. (That's why these scans are now referred to as "CT angiograms.") Although coronary angiograms are generally safe, they carry a low but real risk for complications such as stroke, heart attack, kidney problems, and even death.

Even so, there are several issues to consider before undergoing a CT angiogram. First, not all CT scanners are created equal. If you opt for a CT angiogram, make sure the device is the latest generation. Second, although the scans are noninvasive, they do carry risks. There is considerable radiation exposure associated with a CT scan, which may increase the risk for cancer. Perhaps the most significant issue, though, is that the scans may reveal partial blockages that might not otherwise have been visible. While this may seem like a good thing, it's not clear that it is. Some people will want to "fix" these with angioplasty and coronary artery bypass surgery rather than try lifestyle changes and medications. This can lead to greater expense and greater risk for complications, and studies show that going after these narrowings in people who have no symptoms does not help them avoid heart attacks or live longer. It is not clear yet whether using CT scans in place of angiograms will improve health outcomes — ultimately the most important consideration.

Last updated:	May 03, 2007