6 The Journal of Invasive Cardiology Original Contribution Effect of Changes in Contractility on Pressure Drop Coefficient and Fractional Flow Reserve in a Porcine Model

AbstRACt: Objectives and background. Decisions based on invasive functional diagnostic measurements are often made in the set-ting of fluctuating hemodynamic variables that may alter resting or hyperemic measurements. The purpose of this investigation is to ana-lyze the effect of myocardial contractility (CY) on invasive functional parameters. We hypothesize that the pressure drop coefficient (CDP e ratio of pressure drop to distal dynamic pressure) and fractional flow reserve (FFR; ratio of average pressures distal and proximal to a steno-sis) are not affected by fluctuations in CY and can distinguish between different severities of epicardial stenosis. Methods. Simultaneous measurements of distal coronary-arterial pressure and velocity were performed in 10 pigs using a dual-sensor tipped guidewire for heart rate (HR) <110 bpm and HR>110 bpm, in the presence of coronary lesions of <50 % area stenosis (AS) and>50 % AS. Variations in myo-cardial function and vascular resistance were induced by atrial pacing, papaverine and balloon obstruction, respectively. The maximum rate of rise of left ventricular pressure ([dp/dt] max) was the index of contrac-tility. The contractile function of the heart was empirically defined a