THE EFFECT OF MIDAZOLAM ON LEFT-VENTRICULAR PUMP PERFORMANCE AND CONTRACTILITY IN ANESTHETIZED PATIENTS WITH CORONARY-ARTERY DISEASE - EFFECT OF PREOPERATIVE EJECTION FRACTION

Forty patients undergoing coronary artery bypass grafting were studied , of whom 24 had depressed global left ventricular (LV) function at pr eoperative catheterization, to evaluate the effects of midazolam on LV pump performance and contractility. Transesophageal echocardiography and simultaneous hemodynamic measurements were used to assess LV prelo ad, afterload, and systolic performance during inhalation of 100% O-2 and after 0.1 mg/kg of midazolam. Systolic function indices were expre ssed as a percent of the predicted value for observed end-systolic str ess to estimate LV contractility. In the entire study population, mida zolam did not affect cardiac index. Heart rate and mean arterial press ure were reduced (63 +/- 13 to 59 +/- 12 bm; P < 0.0006 and 89 +/- 15 to 76 +/- 16 mm Hg; P < 0.0001) as were pulmonary capillary wedge pres sure, central venous pressure, and systemic and pulmonary vascular res istance. Afterload, as measured by end-systolic stress, was reduced (5 5 +/- 33 to 48 +/- 26 kdyne/cm(2); P = 0.007) with no change in fracti onal shortening or percent area change. As a result, systolic function decreased in relation to observed end-systolic stress, providing evid ence of reduced LV contractility. Thus, midazolam administration (0.1 mg/kg) caused no change in cardiac pump performance but decreased LV c ontractility in the entire population. Myocardial contractility was lo wer at baseline and after the administration of midazolam in the depre ssed ejection fraction group, but the decrease in contractility was no t exaggerated in the depressed ejection fraction group. Thus, mild adv erse myocardial effects of midazolam appear to be offset by induced re duction of afterload, and are not more severe in high-risk patients wi th depressed preoperative left ventricular ejection fraction.