ミトコンドリア脳筋症におけるペーシング負荷時の心筋代謝

Effects of Cardiac Pacing on Myocardial Metabolism in Mitochondrial Disease

　ミトコンドリア脳筋症は心筋疾患にも関与し，遺伝学的解析が進んでいるが，心筋代謝の検討は少ない．そこで，心筋代謝を検討する目的で，心臓ペーシング負荷時の冠静脈洞採血を施行し，乳酸とピルビン酸の代謝動態を検討した．対象はKearns-Sayre syndrome（KSS）の2例（47歳，64歳）である．ペーシング（140 bpm,5 min）前後で，血行動態測定とともに大動脈と冠静脈洞より採血した．ペーシングによりdouble productsは増加したが，冠静脈洞の乳酸とピルビン酸は増加せず，乳酸産生を認めなかった．KSSではミトコンドリア機能異常のために，運動負荷にて骨格筋の過剰な乳酸産生を認めるとされるが．心筋ではペーシングにて乳酸産生がなく，KSSの骨格筋と心筋代謝が異なる可能性があり，心筋がATP産生予備能を有することが示唆された．

Mitochondrial diseases have Mitochondrial DNA defects, which could cause myocardial dysfunction as well as myopathy. To evaluate the myocardial metabo-lism in Mitochondrial disease, we investigated the myocardial lactate extraction during cardiac pacing in two men with Kearns-Sayre syndrome (KSS).

The patients, aged 47 and 64 years, had typical clinical evidence of KSS. We measured lactate, pyruyate. O2 saturation in aorta and coronary sinus, and hemo-dynamic parameters before and after cardiac pacing (140 bpm, 5 minutes). Atrial pacing was made in one patient and AV sequential pacing in the other because of complete AV block.

Double products increased 63%and 92%during cardiac pacing. Following cardiac pacing, there was no marked increase in the concentration of lactate (aorta, 31.8, 6.3 to 31.8, 2.08; coronary sinus, 19.2, 3.7 to 19.1, 4.4 mg/ dl) and pyruvate (aorta, 3.46, 0.55 to 2.08, 0.51; coronary sinus. 0.97, 0.26 to 1.15. o.32 mg/dl). There was no myocardial lactate production.

It has been pointed out that the skeletal muscle in KSS produces excessive lactate on a exercise test because of mitochondrial dysfunction. These results suggest that there are metabolic differences between mvocardium and skeletal muscle in mitochondrial dis-ease. One particular intriguing hypothesis is that at least in some Mitochondrial diseases accumulation of the deleted mitochondrial DNA in patients with mitochon-drial disease differs among tissues.