Optimal phase analysis of electrocardiogram-gated computed tomography angiography in patients with Stanford type A acute aortic dissection

Abstract

Objective: To determine the phase that facilitates flap observation of the ascending aorta in Stanford type A acute aortic dissection with perfused false lumen.

Methods: We reconstructed retrospective Electrocardiogram-gated Computed Tomography Angiography images of the ascending aorta of all 20 patients to 20 phases of curved-multiplanar reconstruction in 5% increment. One radiologist created and randomized 10 cross-sectional images of each phase for every patient and two radiologists scored these images on a 5-point scale depending on the degree of flap stoppage. We calculated the average score for each phase of each case and compared them among the three groups.

Results: Image scores were significantly better in the 65 %-100 % R-R interval group than those in the 5%-30 % (p < 2e-16) and 35 %-60 % R-R interval groups(p = 7.2e-10). Similar scores were observed in the Heart Rate > 70 group (p = 0.00039, 2.2e-14). Moreover a similar tendency was observed in the arrhythmia group (p = 0.0035, 0.294). No difference was found in the degree of flap stoppage in the 65 %-100 % R-R interval group between the Heart Rate > 70 and Heart Rate ≤ 70 groups (p = 0.466) and between the arrhythmia and non-arrhythmia groups (p = 0.1240).

Conclusion: In observing the ascending aorta, We obtained a good image at 65 %-100 % R-R interval and similar tendency was observed in the patients with arrhythmia.

Keywords: AAD, acute aortic dissection; AC, atrial contraction phase; AEC, automatic exposure control; AR, Aortic Regurgitation; Aorta thoracic; CTA, computed tomography angiography; Computed tomography angiography; D, diastolic phase; DLP, dose-length-product; Dissecting; E, effective dose; ECG, electrocardiogram; Electrocardiography; HR, heart rate; IVR, isovolumetric relaxation phase; MPR, multiplanar reconstruction; RF, rapid filling phase; RR, R-R interval; Radiation dose; S, systolic phase; SF, slow filling phase; bpm, beats per minute.

Fig. 1

A) The ascending aorta was reconstructed using Curved-MPR and from the lower end of the left and right coronary artery origins to the right brachiocephalic artery origin, which was divided into 10 equal parts. In each series, cross-sectional images of 10 cross sections at a height including the coronary artery side were created. (B) Sample images corresponding to each score. Cross-sectional images of the ascending aorta of a 92-year-old woman with the image scores of 5, 4, 3, 2, and 1 in.(A) 75 %, (B) 95 %, (C) 10 %, (D) 15 %, and (E) 20 % R–R interval, respectively. The higher the score, the easier it is to observe the flap.

Fig. 2

(A) Changes in the pressure curve of the left heart system, electrocardiogram, and pressure–volume curve with heartbeat. (B) The predicted phase of each cardiac cycle. Approximately 5 %–30 % R–R interval is in the early S phase, 35 %–60 % in the late S and late D phases, and 65 %–100 % in the middle and late D phases. S (systolic phase), D (diastolic phase), IVR (isovolumetric relaxation phase), RF (rapid filling phase), SF (slow filling phase), AC (atrial contraction phase), Ao (aorta), LV(left ventricle), LA(left atrium), and ECG(electrocardiogram).

Fig. 3

(A) Among the 20 patients, the average image score for each phase was calculated, and the transition was graphed. In most cases, a high score (>4) was recorded in the 65 %–100 % R-R interval, and no such trend was noted in the 5%–60 % R-R interval. (B) The average image score for each phase of the 20 patients was calculated, and the transition was graphed. In the 5 %–60 % R-R interval, the average image scores were <4.5, whereas in the 65 %–100 % R-R interval range they scored >4.5. (C) The obtained image scores were divided into three groups, and the Friedman test and Bonferroni correction were performed. Significant differences were observed among the three groups, and the image score in the 65 %–100 % R-R interval group was better than that in the other two groups.

Fig. 4

(A) The image scores for the heart rate > 70 group were categorized into three groups, for which the Friedman test and Bonferroni correction were performed. Significant differences were noted among the three groups, and the image score in the 65 %–100 % R-R interval group was better than that in the 5%–30 % R-R interval group. (B) The Mann–Whitney test showed no significant difference in the average image score in the 65 %–100 % R-R interval between the heart rate > 70 and heart rate ≤ 70 groups. It seems that the difference in heart rate does not affect the readability of flap.

Fig. 5

(A) The image scores obtained in the three R-R interval groups in the heart rate > 70 group were assessed using the Friedman test and Bonferroni correction. We found variations among the three groups and a better image score in the 65 %–100 % R-R interval group than that in the 5 %–30 % R-R interval group. (B) Mann–Whitney test revealed no significant different in the average image score of the 65–100 % R-R interval group in the arrhythmia and non-arrhythmia groups. It seems that the presence or absence of arrhythmia may not affect the readability of flap.