X線CT法によるACバイパスグラフト開存状況の把握

Evaluation of aortocoronary bypass graft patency by X-ray computed tomography

　近年，虚血性心疾患に対する外科的治療法として大動脈—冠状動脈（AC）バイパス術が一般化しつつあり，欠くべからざる治療法の一つとなっている^1）。ACバイパス術ではグラフト内血流が十分保たれるところに意義があり，そのため術後のグラフト開存状況の把握は患者の管理上重要な意味を持つ。従来よりグラフト開存状況の非観血的検査法として，運動負荷検査法^2〜5），RI法^6,7），色素希釈法^8），パルスドップラー法^9）などが研究されているが，それぞれに長短があり，現在のところグラフト開存状況の正確な評価は観血的検査法である選択的バイパスグラフィ（SBG）によらざるをえない。

　本報ではACバイパス術施行後の症例に対しX線CT法を施行し，SBG所見との対比によりX線CT法のACバイパスグラフト開存性把握における有用性を検討，評価する。

The patency of aortocoronary (AC) bypass grafts was evaluated by X-ray computed tomography (CT) in 25 patients and the results were compared with the findings of selective bypassgraphy (SBG).

Cardiac CT images were taken from aortic arch to cardiac apex with scanning time of 9 seconds and slice width of 5 or 10 mm. For contrast enhance-ment (CE), 220 ml of 30% meglumine iothalamate was administered with intravenous drip infusion : 110 ml as an initial loading dose and 110 ml as a subsequent maintenance dose, before and during the scanning respectively. The interpretation of the CT images was made without knowledge of the SBG results. When the increment of the CT numbers within the graft with CE was identicalwith that within the aorta or cardiac chambers (back ground), the graft was defined to be patent by CT, otherwise to be occluded.

Forty-four of 48 grafts (91.7%) could be detected by CT and their patency assessed with CE was coincident with the SBG diagnoses (42 patent, 2 occluded). Four grafts (8.3%) could not be detected by CT : two grafts were patent and another two were occluded by SBG. In one patient, that had received an AC bypass graft on his left anterior descending artery two years before and had begunto have exertional angina again, the increment of the CT number within the graft was about half of that within the back ground ; suggesting a significant bypass flow reduction.

In conclusion, CT proved to be a promising noninvasive method for the recognition of AC bypass grafts and for the evaluation of their patency. The possibility of this procedure for the quantitative detection of the bypass flow was also suggested.