Mitral annular dynamics during rapid atrial pacing.
BACKGROUND
Ovine mitral annular area (MAA) reduction predominantly occurs before ventricular systole. We used the myocardial marker methods to investigate left atrial and MAA dynamics during rapid atrial pacing.


METHODS
Seven sheep underwent implantation of 21 myocardial markers around the mitral annulus, the left ventricle and left atrium. After 7 to 10 days, animals were studied with biplane videofluoroscopy to determine 3-dimensional marker coordinates unpaced and during rapid atrial pacing at 140 minutes(-1). Left ventricle volume, left atrial volume (LAV), and MAA were calculated from marker coordinates. End diastole (ED) was defined at peak of the electrocardiogram R wave; times of minimum MAA and minimum LAV were expressed relative to ED (t = 0). Percent reduction in MAA and LAV were calculated from maximum and minimum values between diastole and early systole.


RESULTS
The time of minimum MAA occurred earlier relative to ED during rapid pacing compared with control (-48 +/- 21 vs 19 +/- 14 msec; P <.001), as did the time of minimum LAV (-47 +/- 18 vs 4 +/- 16 msec; P <.001). Minimum MAA and LAV were significantly smaller with rapid pacing (6. 8 +/- 0.6 vs 6.5 +/- 0.5 cm(2); P <.05, respectively; and 15.4 +/- 2. 4 vs 16.5 +/- 2.3 mL; P <.01, respectively), and a relatively greater fractional reduction in MAA and LAV was observed during presystole.


CONCLUSIONS
Rapid atrial pacing resulted in greater MAA and LAV reduction, both of which occurred entirely during diastole. This study supports the notion that MAA reduction is closely linked to LA dynamics.
Timek
T A
TA
Department of Cardiovascular and Thoracic Surgery, Stanford University School of Medicine, CA 94305-5247, USA.
Lai
D T
DT
Dagum
P
P
Green
G R
GR
Glasson
J R
JR
Daughters
G T
GT
Ingels
N B
NB
Miller
D C
DC
D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D003971:Diastole; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology*; D006439:Hemodynamics; D008943:Mitral Valve / Q000502:physiology / Q000503:physiopathology*; D012756:Sheep; D013599:Systole; D013997:Time Factors; D016277:Ventricular Function, Left