The Role of Atrial Contraction in Mitral Valve Closure
Tomasz Timek MD, Paul Dagum MD, David T. Lai FRACS, G. Randall Green MD, Julie R. Glasson MD, George T. Daughters MS, Neil B. Ingels, Jr. PhD, D. Craig Miller MD

To evaluate mitral valve closure and annular dynamics during ventricular pacing, eight sheep were implanted with radio-opaque markers on the left ventricle, mitral annulus, and mitral leaflets. Animals were studied after a 7-10 day recovery with biplane videofluoroscopy under baseline conditions and during ventricular (V) and atrioventricular (AV) pacing. V-pacing was associated with delayed leaflet coaptation, increased end-diastolic septal-lateral annular diameter, and increased regurgitant volume during isovolumic contraction. These variables were unchanged during AV-pacing relative to baseline. Properly timed atrial contraction is important for effective mitral valve closure.