1007-21 Effects of Changes in Atrioventricular Gradient and Isovolumic Relaxation Rates on Radionuclide Diastolic Filling in Man

Abstract

The relative influences of the left atrioventricular gradient (AVG) and the time constant of isovolumic relaxation (TAU) on diastolic filling parameters by radionuclide angiography (RNA) in man are unknown. Therefore, 8 atrially paced patients without coronary artery disease underwent simultaneous RNA with micromanometer measurements of left atrial (LA) pressure, left ventricular (LV) pressure and TAU during baseline and steady-state infusions of nitroprusside (NIP), dobutamine (DOB), and phenylephrine (PHEN). RNA was acquired in 32 frames and Fourier fitted to obtain peak filling rate (PFR) and non-normalized PFR (NNPFR). Results below are % change (Δ%) from baseline ( ± SD). NIP (Δ%) DOB (Δ%) PHEN (Δ%) TAU 4 ± 11 –18 ± 7 * 11 ± 12 * LA pressure –25 ± 13 * –12 ± 11 * 52 ± 35 * AVG –27 ± 18 * –12 ± 29 82 ± 63 * PFR –8 ± 7 * –14 ± 12 * 6 ± 11 NNPFR –28 ± 9 * –21 ± 19 * 29 ± 29 * * p < 005 Despite an augmented active relaxation with DOB, peak filling rate decreased significantly in response to decreased LA pressure. We conclude the RNA diastolic filling indices are critically dependent on the LA component of the AVG.