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1 Medicine, Cedars-Sinai Medical Center, Los Angeles, CA, USA; Medicine, David Geffen School of Medicine, UCLA, Los Angeles, CA, USA
* To whom correspondence should be addressed. E-mail: chenp{at}cshs.org.
Ibutilide can prolong refractory period and terminate reentry. Whether or not ibutilide has the same effects on the pulmonary vein (PV) focal discharge (FD) is unclear. We induced sustained atrial fibrillation (AF) in 7 dogs by rapid left atrial (LA) pacing for 74±46 days. Ibutilide was repeatedly infused until it terminated AF (0.02±0.01 mg/kg, N=5) or when a cumulative dose reached 0.04 mg/kg (N=2). High-resolution computerized epicardial mapping was performed. We found intermittent FD at the PVs (N=7) and reentry (N=4) at the PV-LA junction during AF. Ibutilide increased the cycle lengths (CLs) of consecutive reentry from 97±13 ms to 112±18 ms (p=0.03), and FD from 96±7 ms to 113±9 ms (p=0.02). In 4 dogs with both FD and reentry at the PVs, the incidence of reentry reduced from 3.5±1.9/sec at baseline to 2.2±1.8/sec after ibutilide administration (p=0.01252). However, the incidence of FD remained unchanged (4.1±1.1/sec at baseline and 4.2±0.9/s after ibutilide administration, p=NS). The conducted wavefronts between PV and LA were significantly reduced by ibutilide (10.4±2.0 /sec v.s. 8.0±1.6 /sec, p<0.001). The ibutilide dose needed to terminate AF correlated negatively with the baseline effective refractory period of PV (r=-0.89, p<0.001) and LA (r=-0.92, p<0.001). We conclude that ibutilide reduces reentrant wavefronts but not PV FD in a canine model of pacing-induced sustained AF. These findings suggest that the PV FD during AF is due to non-reentrant mechanisms. High dose of ibutilide may completely terminate all reentrant activity, converting AF to PV tachycardia prior to the resumption of sinus rhythm.
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