WASHINGTON — Whether to use a cardiac-focused CT protocol or a triple rule-out approach for assessing acute chest pain in the emergency department depends to some degree on what your clinical suspicions are, said Dr. Charles S. White at the annual meeting of the Society of Cardiovascular Computed Tomography.
“The question here is: Do you want to focus just on the coronaries, or do you want to expand the search and look for those 85% of other causes … that we might be able to detect with the triple rule out?” said Dr. White, chief of thoracic radiology at the University of Maryland Medical Center in Baltimore.
In the cardiac-focused CT approach, the field of view is limited to the area of the coronary arteries and therefore offers better spatial resolution of these vessels than the triple rule-out approach. This approach takes about 8 seconds on average and uses less radiation and contrast. The scanning direction is craniocaudal.
With the triple rule-out approach, the intent is to image the entire thorax, allowing visualization not only of the coronary arteries but the aorta and the pulmonary arteries. This approach allows evaluation for coronary artery disease, pulmonary embolism, and aortic dissection—earning it the triple rule-out moniker.
The trade-off for this expanded field of view is decreased spatial resolution, compared with the cardiac-focused approach. This approach involves a longer scan time (15 seconds) and involves greater radiation doses and more contrast than the cardiac-focused approach does. To minimize the chance of motion defects associated with a longer scan time, the scan is performed caudocranially. Motion is not as great a concern in the upper thorax, which is imaged last.
“The bottom line, I think, in terms of protocol between cardiac and triple rule out is that it depends on your level or suspicion that the cause of chest pain might be pulmonary embolism,” said Dr. White. “When you have some level of suspicion of a pulmonary embolism, a triple rule-out study may be appropriate. If you don't, then a dedicated CT [angiography] would be the way to go.”
In the University of Maryland Medical Center's ED, “We are generally still doing triple rule-out protocols,” said Dr. White. Cardiac-only studies can be ordered by emergency physicians as well. However, in their experience, most triple rule-out patients (75%) have calcium scores of zero or close to it. Roughly 15% have significant stenosis.
There are a number of challenges associated with using the triple rule-out protocol. Getting patient cooperation can be difficult. When using 64-slice CT, however, it's not crucial to get the heart rate down below 90 beats per minute. “As long as it's a stable heart rate, a 64-slice scanner will generally get you fairly good images,” said Dr. White.
Cost also is an issue with the triple rule-out approach, as is the greater radiation dose. The amount of technical labor required also is a concern. The ideal option is to have an in-house service to read the images on a 24-hour, 7-day a week basis.
However, industry is increasingly offering options to allow for off-hour coverage, such as the ability of radiologists and cardiologists to do preliminary reviews of images wherever they are.
“The bottom line is that about 50% of studies are negative. Off-hours, those patients are fairly easy to read … and you can probably send them home,” said Dr. White. The images of the remaining patients are evaluated further the next morning.
Dr. White disclosed that he has received research support from Phillips Medical Systems.