本態性血小板血症を有する僧帽弁閉鎖不全症に対する開心術

Cardiac Surgery for Mitral Regurgitation Associated with Essential Thrombocythemia

本態性血小板血症（essential thrombocythemia）は血小板増多を特徴とする慢性骨髄増殖性疾患の一型で，血小板異常による出血傾向と血栓傾向の両方の側面を併せ持つ疾患である．開心術においては出血傾向による術中の止血や，血栓傾向による周術期の血栓弁やグラフト閉塞などの懸念が生じ，注意が必要な病態である1，2）．われわれは，本態性血小板血症を合併した僧帽弁閉鎖不全症の症例に対して開心術を行い，術中にheparin抵抗性が認められ体外循環管理に注意を要した症例を経験したため報告する．

An 80-year-old woman with essential thrombocythemia was diagnosed with severe mitral regurgitation and moderate tricuspid regurgitation. Preoperatively, she had been treated with hydroxycarbamide and low-dose aspirin since her platelet count was high （96.2×104/μl）. After the platelet count was reduced to 46.2×104/μl， she underwent mitral valve repair and tricuspid valve annuloplasty. Atypical heparin resistance was noted intraoperatively. After initial heparin infusion, the activated clotting time （ACT） increased as expected. However, it decreased after initiation of cardiopulmonary bypass, despite additional heparin infusion and heparin concentration maintenance. A correlation between platelet factor 4 and heparin resistance was suggested. On discharge, she had no complications. We should consider the possibility of heparin resistance in essential thrombocythemia even when platelet count is adequately controlled.