虚血性心疾患における運動時狭心痛と心筋虚血—201Tl心筋断層法による検討

The relation between angina and myocardial ischernia during exercise stress in coronary artery disease

　狭心痛は虚血性心疾患の主症状であるが，典型的な心筋梗塞の心電図変化を有しながら既往に胸痛のない症例や，運動負荷試験において心電図上明らかな虚血性変化を示すにもかかわらず狭心痛のない症例に遭遇する二とはまれではない。殊にホルター心電図による長時間心電図記録の発達は，全く胸痛のない一過性の心筋虚血，いわゆるsilent myocardial ischemiaがかなりの高頻度に存在することを示唆した^1〜3）。しかし，乙の狭心痛の出現には，局所での虚血刺激の他，その伝導や中枢における疼痛に対する閾値等複雑な問題がからみあっており十分理解されているとはいいがたい^4,5）。他方運動負荷²⁰¹Tl心筋断層法（single photon emission CT, SPECT）は，一過性心筋虚血の有用な診断法として広く臨床応用されている^6,7）。今回，我々は，冠動脈疾患（CAD）を対象に運動負荷（Ex）直後および3時間後の再分布（RD）時に²⁰¹Tlによる心筋SPECTを撮影，Exによる胸痛の発生と心筋虚血の関連を検討した。

To investigate the relation between angina and the extent or severity of myocardial ischemia during exercise stress (Ex), Ex myocardial single photon emi-ssion CTs (SPECT) with thallium-201 were perfor-med in 35 patients with coronary artery disease (CAD). Myocardial SPECTs were obtained both at immediately after Ex and 3 hours after Ex (redistri-bution, RD). By using short axis tomograms. myocar-dial Tl distribution was expressed into two-dimen-sional functional maps both at Ex and RD. Simila-rly, myocardial Tl washout (WO) rates of the entire left ventricles were expressed as a two dimensional polar map (Bull's-eye maps).

The myocardial segments which T1 WO rates fell below normal limits (less than 30%) were con-sidered as exercise induced ischemia. And the extent of ischemia was calculated as the percentage of ische-mic segments to entire left ventricle by using Bull's-eye WO rates maps. The severity of exercise induced s chemia was defined as minimal WO rate. To testwhether minimal WO rates represented severity of myocardial ischemia, we studied followings in 9 pati-ents with single vessel CAD (SVD) without previous history of myocardial infarction. By using Ex Tl di-stribution image, Tl uptake ratio of Tl activity of the myocardial segment which showed minimal WO rate (namely, lowest Tl activity in that image) to maximal Tl activity was calculated, and the relation between minimal WO rate and Tl uptake ratio was studied. In 9 patients with SVD, minimal WO rates correla-ted well with Tl uptake ratios (r=-0.87, p<0.01), and so it was considered that minimal WO rates re-presented the severity of myocardial ischemia.

In all patients with CAD, development of transient myocardial ischemia during Ex was indicated by myocardial SPECT, and they were divided into 2 groups whether angina developed during Ex or not. In 16 patients angina developed (symptomatic ische-mia), but in 19 patients angina did not develop (silent ischemia).

Age, sex, history of myocardial infarction, heart rate and the extent of ischemia by SPECT did not different between these 2 groups. But in patients with symptomatic ischemia, minimal T1 WO rates were significantly lower than those in patients with silent ischemia (-15±18% vs 3±11%, p<0.01).

We concluded that the severity of myocardial ische-mia is one of the important factors to relate with anginal chest pain during Ex in patients with CAD.