Low-Dose Computed Tomography Coronary Angiography With Prospective Electrocardiogram Triggering: Feasibility in a Large Population
What is the feasibility of prospective electrocardiogram (ECG) triggering for low-dose computed tomographic coronary angiography (CTCA)?
CTCA using a 64-slice scanner and prospective ECG triggering was attempted in 612 consecutive patients. Intravenous metoprolol (2-30 mg) was utilized to achieve a target heart rate of ≤65 bpm. The coronary arteries were analyzed on a 16-segment model in all segments with a diameter >1.5 mm. Image quality was subjectively graded as 1, excellent; 2, good; 3, adequate; and 4, nonevaluable.
CTCA was not feasible in 46 patients (7.5%) due to inadequate heart rate control or irregular rhythm in the majority. The mean effective radiation dose was 1.8 ± 0.6 mSv. In the 566 evaluable patients, a total of 2,264 vessels and 7,814 segments were scored, of which 7,516 (96.2%) were of diagnostic image quality (score 1-3), including 53.5% with excellent image quality. Image quality was considered diagnostic in 96.2% of segments. Each coronary segment was of diagnostic image quality in 547 patients (89%); a single nondiagnostic segment was found in 32%; two nondiagnostic segments in 18; and three or more were found in the remaining patients. Factors related to image quality included coronary artery calcium score and body mass index. There was a strong correlation between heart rate and the incidence of nondiagnostic segments (r = 0.809, p < 0.001). Receiver operator curve analysis identified a heart rate <62 bpm as being associated with a low (1.2%) incidence of nondiagnostic segments compared to 8.4% with heart rate above 62 bpm (p < 0.001).
CTCA with ECG triggering results in low radiation exposure in a high percentage of patients with a diagnostic quality study in a relatively unselected population.
Coronary CT angiography has been established as an accurate means for evaluating coronary anatomy. Its greatest strength lies in the negative predictive value for subsequent identification of obstructive disease when an entirely normal study is encountered. Limitations of the technique include relatively high contrast load required, limited image quality in the presence of calcium and large body habitus, and the need to control heart rate to avoid motion artifact. One of the major other concerns has been the relatively high radiation exposure associated with CTCA. Earlier generation scanners and imaging protocols often resulted in radiation exposure of 10-15 mSv. Subsequent to the initial studies, multiple advances have been made in imaging protocol such as those presented here, which have reduced the radiation exposure dramatically, as assessed by the average radiation exposure of 1.8 ± 0.06 mSv in this study. Many initial attempts at producing radiation exposure resulted in image degradation in lower likelihood of diagnostic studies. The technique presented in this paper, among other techniques, simultaneously results in lower radiation exposure and preservation of high diagnostic studies. The technique presented here is adaptable to a wide range of currently existing CT platforms and, as such, may see wider acceptance than several other proposed methodologies, which rely on platform-specific imaging.
Keywords: Coronary Angiography, Tomography, Cardiology, Electrocardiography, Heart Rate, Radiation Dosage
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