title: Atrial fibrillation pacing decreases intravascular shear stress in a New Zealand white rabbit model: implications in endothelial function.
abstract: Atrial fibrillation (AF) is characterized by multiple rapid and irregular atrial depolarization, leading to rapid ventricular responses exceeding 100 beats per minute (bpm). We hypothesized that rapid and irregular pacing reduced intravascular shear stress (ISS) with implication to modulating endothelial responses. To simulate AF, we paced the left atrial appendage of New Zealand White rabbits (n = 4) at rapid and irregular intervals. Surface electrical cardiograms were recorded for atrial and ventricular rhythm, and intravascular convective heat transfer was measured by microthermal sensors, from which ISS was inferred. Rapid and irregular pacing decreased arterial systolic and diastolic pressures (baseline, 99/75 mmHg; rapid regular pacing, 92/73; rapid irregular pacing, 90/68; p < 0.001, n = 4), temporal gradients ([Formula: see text] from 1,275 ± 80 to 1,056 ± 180 dyne/cm(2) s), and reduced ISS (from baseline at 32.0 ± 2.4 to 22.7 ± 3.5 dyne/cm(2)). Computational fluid dynamics code demonstrated that experimentally inferred ISS provided a close approximation to the computed wall shear stress at a given catheter to vessel diameter ratio, shear stress range, and catheter position. In an in vitro flow system in which time-averaged shear stress was maintained at [Formula: see text] , we further demonstrated that rapid pulse rates at 150 bpm down-regulated endothelial nitric oxide, promoted superoxide (O 2 (.-) ) production, and increased monocyte binding to endothelial cells. These findings suggest that rapid pacing reduces ISS and [Formula: see text] , and rapid pulse rates modulate endothelial responses.
authors.affiliation: Department of Biomedical Engineering and Cardiovascular Medicine, School of Engineering and Medicine, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Nelson
authors.initials: N
authors.lastname: Jen
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.forename: Juhyun
authors.initials: J
authors.lastname: Lee
authors.forename: Steve
authors.initials: S
authors.lastname: Wasmund
authors.forename: Xiaohu
authors.initials: X
authors.lastname: Dai
authors.forename: Christina
authors.initials: C
authors.lastname: Chen
authors.forename: Pai
authors.initials: P
authors.lastname: Chawareeyawong
authors.forename: Yongmo
authors.initials: Y
authors.lastname: Yang
authors.forename: Rongsong
authors.initials: R
authors.lastname: Li
authors.forename: Mohamed H
authors.initials: MH
authors.lastname: Hamdan
authors.forename: Tzung K
authors.initials: TK
authors.lastname: Hsiai
mesh_terms: D000818:Animals; D001011:Aorta / Q000473:pathology; D001281:Atrial Fibrillation / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology; D002304:Cardiac Pacing, Artificial; D018481:Convection; D004195:Disease Models, Animal; D004562:Electrocardiography; D042783:Endothelial Cells / Q000473:pathology; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D011817:Rabbits; D013314:Stress, Mechanical; D014463:Ultrasonography