64 Slice CT Coronary Angiogram – A Promising Advance In Cardiac Imaging

As India’s economy flourishes, there appears to be a rise in the coronary artery diseases (CAD) especially the affluent class. It is now evident to the medical community that in majority of cases it is not the tight narrowing of the coronary artery, which supplies the muscular walls of the heart, that cause sudden heart attacks but soft deposits of cholesterol called “plaques” along the inner walls of the arteries which rupture suddenly causing clotting within the artery. This results in sudden shut down of the blood supply to a part of the heart wall causing its death and resulting in a reduction in the heart’s pumping ability. The end result would be a significantly weakened heart.

Heart attacks may be the first symptom of an underlying serious coronary artery disease hence no chest pain should be ignored. On the other hand we know that 20 to 40% of patients who undergo invasive coronary angiogram for chest pain have no coronary artery disease and would have benefited from a non-invasive test. Advances in hardware and speed of the CT scanners have achieved a breakthrough in the form of the 64-slice CT scanner. This super fast CT scanner is capable of displaying exquisite 3D images of the heart, its walls and the chambers and the coronary arteries supplying it. Unlike the catheter angiogram it is a non – invasive procedure.

The scanner acquires thin cross sectional images of the entire chest, which are then stack piled on top of each other with the help of a high end computer and a special software to produce a 3D model of the heart . Superficial portions of the heart are then removed by the radiologist in a meticulously performed “virtual surgery” to reveal the underlying coronary arterial tree, from its origin to its fine tapering branching networks enveloping the surface of the heart. Each of the coronary arteries is then laid open to demonstrate plaques deposited on the inside. The consistency of these plaques, their length and thickness, the percentage of vessel lumen compromise by them and their distribution along the course of coronary arteries are then mapped, studied and displayed.

In contrast with the conventional catheter angiogram, where a dye is injected into the lumen of the coronary artery and hence only the inner contour of the artery can be mapped, the 64 slice CT scanner is able to demonstrate not only the lumen but also the wall of the coronary artery as well as the heart itself on which the arteries rest.

At times, though there is a large cholesterol plaque deposit on the wall of the artery, the artery remodels its lumen and becomes wider. This is called positive remodeling. These plaques may not be picked up on the catheter angiogram, as there is no reduction in the vessel caliber. However, these plaques may also be vulnerable to acute rupture resulting in heart attacks. The 64-slice CT scanner is able to demonstrate these plaques with ease.

Abnormal courses of the coronary arteries are well demonstrated by the 3D model of the heart on the 64-slice CT. It may be tedious and difficult to demonstrate such abnormal arteries by the conventional catheter angiogram.

The 64-slice CT scanner beautifully images coronary artery bypass grafts. Their course, anastomosis as well as flow of dye past them into the native artery are well seen . Stents placed within the native arteries or the grafts can be also imaged for their patency.

The myocardium or the muscular wall of the heart appears brighter as it is perfused by the dye that is injected during the 64-slice CT study. The parts of the muscle, which have a reduced blood supply, show up on the scan as dull or darker areas suggesting ischaemic changes. A demonstration of the upstream arterial narrowing and downstream myocardial ischaemic area on the 64-slice CT establishes a useful “cause and effect” disease pattern.

At times the coronary arteries have deposits of thick calcified plaques. Looking past these plaques into the lumen of the artery may be difficult on the 64-slice CT scanner.

However, research across the globe indicates that the 64 slice CT can pick up coronary artery disease in 99% of cases and should the scan be normal there is little chance of having any significant disease in the coronary arteries (Excellent negative predictive value)

Chest pain can be caused by several other conditions besides a heart attack, for example aortic dissection, thrombosis in the pulmonary arteries and lung conditions. The 64-slice CT rules out coronary artery disease and demonstrates the true cause of the chest pain in the same sitting by crisp pictures of the other organs inside the chest. This is an advantage over the catheter angiogram.
 

The 64 Slice CT Scanning of the Heart is proving to be a highly valuable non-invasive diagnostic tool in the detection of coronary artery disease especially at its early stage, in bypass graft evaluation and stent patency and in excluding coronary artery disease in patients with atypical chest pain.