運動負荷心電図のST下降に関する検討：Treadmill Exercise Scoreの再評価とV5誘導の診断的価値について

Studies on ST depression in exercise stress ECG:Re-evaluation of the treadmill exercise score and diagnostic usefulness of the V5 lead

　運動負荷試験におけるECGの評価は，近年多段階負荷法が用いられるようになって大きく変ってきた。従来のMasterの二階段法においては，負荷後のECG，特にST下降について診断の基準が定められているが，運動中のECGモニターの重要性については古くから指摘されており，従って今日行なわれる多段階負荷法においては，ルーチンに運動中と運動後のECGが連続して記録される。運動中のECGには基線の動揺，ノイズ，筋電図などのアーチファクトが混入して詳細な分析は困難であったが，今日では経時加算の方式によってアーチファクトが効果的に除かれ，安定したECG曲線が得られるようになり，自動解析が可能となった^1,2）。

　運動負荷ECGはQRS群，ST，そして不整脈が評価の対象となるが，それぞれについて議論が多い^3）。特にST下降は古くから論じられており，冠動脈障害との関連からsensitivityとspecificityについて数多くの報告がなされているが^4〜8），ST下降のとらえ方に関しても種々の問題があり，運動中，および運動後の下降度とその勾配の予後的な意義もさることながら^9），その他に，有意なST下降の発現する時間の要素も重視されている^10,11）。

Clinical usefulness of treadmill exercise score (TES) after Hollenberg and others was re-evaluated on 56 patients with angiographically documented coronary artery lesions. The subjects consisted of 37 cases of myocardial infarction and 19 cases of stable angina pectoris. Symptom limited multiphasic treadmill stress testing was adopted for the study and continuously recorded ECG signals obtained from V5 and aVf from the beginning of exercise and to the end of the test were automatically proc-essed for a detailed analysis with CASE (Mar-quette). The all area factor AF-all is defined as a total area derived from four trendgrams of ST-depression and slope from two leads each and is measured with an automatic, digitized planimetry (Planix, error range±0.2%). The TES is obtained from the following formula ; TES= (FA-all)/(TMT x %HRmax), where TMT is treadmill time and %HRmax is percent of the age predicted maximal heart rate.

Statistically significant differences between single vessel and multivessel diseases were observed in the following parameters including not only TES, but also AF-all and AF-V5, and the time to reach 1mm ST depression in V5 and aVf. On the other hand, the magnitude of maximal ST depression in V5 and aVf were not useful to differentiate the severity of coronary lesions. Thus, these more simple parameters than TES were proved to be also useful and beside that, not AF-aVf, but AF-V5 could differentiate the severity of coronary lesions (χ2= 12.663, p 0.01). Sublingual nitroglycerin (0. 3 mg) altered all these parameters except for AF-aVf,and no parameters except for time factors reaching 1mm ST depression in V5 and aVf could specify the effect of exercise training in patients with coro-nary heart disease.

In conclusion, although the clinical usefulness ofTES was reconfirmed, parameters derived from V5 including AF and the time factor for 1mm ST depression in V5 were also reliable to differentiate the severity of coronary lesions and evaluate the effects of various clinical interventional procedures.