6. 低心機能合併症例の周術期管理

Perioperative Management of Cardiac Surgery in Patients with Preoperative Heart Failure

日本循環器学会/日本心不全学会が定めた『急性・慢性心不全診療ガイドライン（2017年改訂版）』1）によると，心不全とは「なんらかの心臓機能障害，すなわち，心臓に器質的および/あるいは機能的異常が生じて心ポンプ機能の代償機転が破綻した結果，呼吸困難・倦怠感や浮腫が出現し，それに伴い運動耐容能が低下する臨床症候群」と定義されている．さらに，心不全（HF）は左室駆出率（LVEF）によっても分類され，40％未満（HF with reduced EF：HFrEF），50％以上（HF with preserved EF：HFpEF），40％以上50％未満（HF with mid-range EF：HFmEF），治療によってLVEFが40％以上に改善した場合（HFpEF improved）に分類されている2）．本稿では，外科的治療が前提となる後天的心臓構造異常（弁膜疾患，虚血性心疾患など）を有し，それらの疾患自体または高血圧や心筋症の併存に起因するHFrEFを主徴とする患者の周術期管理を述べる．

The lower preoperative left ventricular ejection fraction （LVEF）, the more postoperative death. The perioperative management for cardiovascular patients with heart failure （LVEF＜40％） is of great importance in cardiac surgery. The failing heart is characterized by intracellular Ca2＋ handling abnormalities during excitation/contraction coupling （i.e., less amount of cytosolic Ca2＋ recruitment in systole and insufficient cytosolic Ca2＋ extrusion in diastole）, which are caused by increased reverse-mode Na＋/Ca2＋ exchange activity and abnormal sarcoplasmic reticular Ca2＋ channels （ryanodine receptors） and Ca2＋ pumps （adenosine triphosphatase：ATPases）. Myocardial ischemia/reperfusion （I/R） damage is characterized by intracellular acidosis followed by Ca2＋ overload during I/R. The failing/hypertrophied myocardium has a low coronary vascular density, leading to low oxygen supply to the cardiomyocyte, and is vulnerable to Ca2＋ load during I/R. Based on those abnormalities, hypothermic cardioplegia is recommended to suppress myocardial oxygen demand in open heart surgery for patients with heart failure （low LVEF）. Optimal medical managements using adrenergic stimulators, vasodilators, antiarrhythmics, cardiac pacing, NO inhalation, or myocardial Ca2＋ sensitizers under preload adjustment may be essential for hemodynamic improvement of postoperative low cardiac output syndrome. On a case-by-case basis, mechanical circulatory support systems should be utilized before the development of multiple organ failure.