LOAD INDEPENDENCE OF RADIONUCLIDE DIASTOLIC FILLING MEASUREMENTS IN ACUTE CORONARY-OCCLUSION

Background. An accurate noninvasive method for measuring the effects o f pharmacologic agents on active relaxation of the left ventricle woul d provide a valuable tool for monitoring the treatment of diastolic he art failure related to coronary artery disease. Methods and Results. T he time constant of isovolumic relaxation (T) and the left atrioventri cular gradient were measured with micromanometer catheters and diastol ic left ventricular filling variables were measured with radionuclide ventriculography in nine anesthetized, open-chest dogs with an acute c oronary artery occlusion. Infusion of the positive inotropic drug dobu tamine hydrochloride (5 to 10 mu g/kg/min) resulted in a 35% shortenin g of T and a 37% increase in the radionuclide first-half filling fract ion (both p < 0.05), but no change in the left atrioventricular gradie nt, Conversely, infusion of the alpha-adrenergic vasoconstrictor pheny lephrine hydrochloride (20 to 40 mu g/min) augmented left ventricular load, increasing the atrioventricular gradient by 45%, but had no sign ificant effect on T or the first-half filling fraction, Infusion of th e direct-acting vasodilator, sodium nitroprusside (80 to 120 mu g/min) , was accompanied by a 14% lengthening of T with a corresponding 28% d ecrease in the first-half filling fraction (both p < 0.05). Conclusion , In an anesthetized, open-chest canine model of acute myocardial isch emia, the radionuclide first-half filling fraction reflects pharmacolo gically induced changes in the lusitropic state of the left ventricle with relative independence of loading conditions.