RT-49
|
Predictors of atrial
fibrillation during rapid atrial pacing in dogs
|
|
|
Andreas Goette, J. Christoph
Geller, Joerg Mittag, Wolfgang M. Hartung, Jonathan J. Langberg*, Helmut U. Klein.
University Hospital Magdeburg, Department of Internal Medicine, Division of Cardiology,
Magdeburg, Germany, *Emory University Hospital, Division of Cardiology, Atlanta, USA
|
|
Method
|
|
Nine mongrel dogs (weight 25 ± 1 kg) were used in the
study. The animals were anesthetized with morphine (4 mg/kg) followed by methohexital (70
mg/kg) intravenously. Thereafter, the anesthesia was maintained with isoflurane. The
surface electrocardiogram, right atrial pressure, and blood pressure were continuously
monitored. A bipolar active-fixation permanent pacing lead (CPI model 4269) was introduced
into the right internal jugular vein and placed in the right atrial appendage. Thereafter,
hemostatic sheaths were inserted into the femoral vein and two quadripolar electrode
catheters (Bard Electrophysiology, Billerica, MA, 5 mm interelectrode spacing) were
advanced into the right atrial appendage and the lateral right atrium, respectively.
Autonomic blockade induced using an initial bolus of atropine and propranolol (0.04 mg/kg
and 0.2 mg/kg) followed by maintenance infusion for the duration of the experiment
(atropine: 0.007 mg/kg/hr and propranolol: 0.04 mg/kg/hr). After infusion of atropine and
propranolol, high-frequency atrial pacing was initiated and was maintained for the
following seven hours. Bipolar pacing of the electrode catheter positioned in the right
atrial appendage was performed at a rate of 800 beats per minute. The atrial ERP was
determined just before initiation of high-frequency pacing. Rapid pacing was briefly
interrupted every 30 minutes for the following two hours, and thereafter once an hour for
the duration of rapid pacing to allow repeated assessment of the ERP. All refractory
period measurements were made using the permanent pacing lead. A drive train of 8 stimuli
(S1, 350 msec cycle length, 2 msec pulse duration) was delivered via the permanent pacing
lead. An extra stimulus (S2) was added early in atrial diastole and the interval between
S1 and S2 was incremented in 2-msec steps until a propagated atrial response was produced.
A pulse amplitude of twice diastolic threshold was used to determine the ERP. The episodes
of atrial fibrillation after rapid pacing had been discontinued to measure the ERP were
recorded on photographic paper at a speed of 100 mm/sec (Electronics for Medicine). The
cycle length of induced atrial fibrillation was determined manually by measuring all
intervals from the recorded bipolar electrograms in the right atrial appendage.
|
