CT angiography provides added advantage to children with great artery anomalies

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Researchers in France found that 64-slice CT coronary angiography performs as well as invasive angiography to detect significant coronary lesions in children who have undergone the arterial switch procedure for transposition of the great arteries. They also found that CT provides information on the underlying mechanism of coronary luminal narrowing.

Phalla Ou, MD, and colleagues from University Rene Descartes in Paris evaluated 130 consecutive children with contrast-enhanced MDCT performed within 24 hours before or after catheter angiography was performed. CTA was successfully performed in 97 percent of the 5 and 6 year olds (J Am Coll Cardiol Img 2008;1;331-339).

All CT exams were performed with a 64-slice LightSpeed VCT scanner (GE Healthcare).

Researchers reported that CTA detected all 12 patients with significant coronary stenoses identified by catheter angiography. Furthermore, they said that CTA also has the ability to elucidate the underlying mechanism of coronary artery narrowing, for example, through stretching, compression, and/or kinking caused by the surrounding great arteries.

“CT may in fact be able to show mild coronary pathology that is not detectable in invasive angiography, but these observations lack validation and their clinical relevance is unclear,” the authors wrote.

Investigators concluded that coronary CTA can be performed in a shorter time, has a lower rate of complications and will most likely be associated with a lower cost than conventional invasive angiography.

“It is our opinion that CT angiography can be adopted as the follow-up method of choice for examining the coronary circulation in children after arterial switch procedure for transposition of the great arteries,” they said.

In an accompanying commentary, Lawrence M. Boxt, MD, director of cardiac MRI and CT at North Shore University Hospital in Manhasset, N.Y., said that although the CTA exams were performed without complication, the children might have been exposed to an unknown, but greater future risk posed by the exposure of radiation.

“Thus, in all patients undergoing angiography or MDCT (and especially in children), we are faced with the conundrum of weighing a small chance of low-risk, short-term complications of angiography (i.e., hematoma or contrast reaction) against an unknown risk of more severe, later complications (i.e., leukemia or lymphoma),” Boxt said.

The average radiation dose for the CTA studies was 4.5 mSv, which was significantly greater than that for catheter angiography: 3.1 mSv (p < 0.001).

The investigators used a standard CT acquisition protocol, scanning in a continuous, low dose (70 kV, 20 mA) fluoroscopy mode over the ascending aorta. Once they measured maximum aortic opacification, they used a low kilovolt dose reduction algorithm (80 kV, range 150 to 350 mA, based upon patient body weight).

Boxt concluded by saying if the radiation dose is similar for both modalities, than the risk of radiation-related complication is probably nearly the same. The significant problem, however, may lie in an increasing number of CT exams performed in children, he said.

“Thus, if our choice of angiography versus CT is reduced to an assessment of the risk of short-term complication, then the choice of CT becomes more attractive,” he said.

Technical Characteristics of CT Versus Coronary Catheter Angiography
  CT CCA p Value
Duration of the procedure (min +/- SD) 20 +/- 6 45 +/- 23 <0.001
Radiation dose (mSv +/- SD)
[median, minimum - maximum]
 4.5 +/- 0.5
[4.6, 3.9 - 7]
 3.1 +/- 1.6
[3.4, 2 - 6.5]
<0.001
Contrast volume (ml +/- SD)  30 +/- 7 37 +/- 25 0.6
Sedation (n patients) 0 119  <0.0001
Complications (n complications) 0 6  <0.0001
The choice to use CT or catheter angiography in children undergoing arterial switch procedure comes down to radiation dose versus complications.