低冠灌流状態における高心拍数の血行動態におよぼす影響

Effects on Hemodynamics of High Heart Rate under Fixed Low Coronary Flow State

緒言

　冠状動脈硬化症や，急性心筋硬塞にともなう房室ブロックや，徐脈の治療に心拍数増加の目的で心臓ペースメーカやカテコールアミンが使用される。これらの疾患において心拍の増加が血行動態におよぼす効果は，冠循環に異常のない場合とくらべて異なったものがあるのではないかと考えられる。いわゆる冠不全においては冠血流量が少なく，また心筋の酸素要求に対して冠血流量の増加が制限されている状態と理解することができる。最近ICUなどで急性心筋硬塞や心臓性ショックに合併した徐脈が治療の対象となる機会が増加する傾向にあるのにかんがみて，本実験においては冠不全をsimulateした実験標本を用いて心拍増加が心血行動態におよほす効果を検討した。

This study was undertaken to determine the effects of high heart rate on hemodynamics under fixed low coronary flow state. Experi-ments were carried out on mongrel dog. Arterial blood was conducted from the left subclavian artery, through an occulsive coro-nary perfusion pump to the left coronary artery by means of a coronary catheter, the tip of which was secured with a rumell tour-niquet placed around the origin of the left main coronary artery. The coronary pump was adjusted to deliver low coronary flow, ranging from two third to one half of expect-ed normal coronary flow. The heart was paced with a battery operated cardiac pacemaker and epicardial electrodes at the ventricular rate of 60, 90, 120, 150 and 180 per minute, while stimulating concurrently the right vagus to eliminate arrhythmias. Aortic pressure, left ventricular end-diastolic pressure (LVEDP), cardiac output, left ventricular oxygen con-sumption, left ventricular work and cardiac efficiency were determined during each obser-vation. Control observations were made on the dogs with normal coronary circulation.

The fall of aortic pressure, left ventricular work and cardiac efficiency, and the rise of LVEDP was observed frequently at higher ventricular rates in the dogs with fixed low coronary flow. These hemodynamical values remained relatively unchanged both at slow and higher rates in the dog with nomal coro-nary circulation. However, hemodynamical deteriorations at higher heart rates in the dogs with low coronary flow were not related directly to the amount of reduced coronary flow, but rather to initially high values of LVEDP.

Extraction ratio of myocardial oxygen in the dogs with high LVEDP were found significa-ntly lowered, whereas those of the dogs with normal values of LVEDP were elevated. Con-sequently, it seemed relevant to state that the impairment of myocardial oxygen utilization should take place in acute heart failure, fre-quently encountered under the situation of restricted coronary flow, and that it might play some roles in the hemodynamical deterio-rations at higher ventricular rates.