Purpose: the purpose of our study was to create a model of persistent
atrial fibrillation (AF) in the conscious, normal living sheep by
intermittent endocardial high rate (HR) right atrial pacing (P).
Method: surgical procedures were done in general anaesthesia, in the
intubated aduk sheep, body weight > 50 kg. In 13 sheep an experimental
pacemaker (PM) (Chorus ELA) was placed in the lateral neck and an
endocardial active fixation lead was inserted via the jugular vein and
fixed under fluoroscopic guidance at the right lateral atrium. Atrial
high rate pacing was programmed as follows: burst duration 5.2 sec,
pause after each burst 2.5-3.13 sec, interstimuli interval 78 to 109 ms,
pacing at 5 V, pulse duration 0.5 ms. After recovery from the procedure,
all sheep returned to the farm and had regular follow-up visits at our
animal facility. PM function and ECG were assessed. When persistent
AF occurred, the PM was turned off and rhythm control were continued
over weeks to months.
Results: 3 sheep died unexpectedly, 1 had Pm dysfunction. In the
remaining, AF occurred after a mean time of 4.74-3.44 months, range
1-13 months. Once in AF, AF persisted. All animals were ukimately
sacrificed. Three sheep had developed a cardiomegaly, heart weight
520-545 g.
Conclusions: our model provides experimental evidence that an atrial
focus firing intermittently at high rate may provoke chronic AF and
cardiac dysfunction.