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EXPERIMENTAL STUDIES

Determination of refractory periods and conduction velocity during atrial fibrillation using atrial capture in dogs

Direct assessment of the wavelength and its modulation by a sodium channel blocker, pilsicainide

^a Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine, Tokyo, Japan

Manuscript received January 15, 1999; revised manuscript received August 11, 1999, accepted September 10, 1999.

Reprint requests and correspondence: Dr. Hideo Mitamura, Cardiopulmonary Division, Department of Medicine, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
mitamura{at}med.keio.ac.jp

OBJECTIVES

The purposes of this study were to measure the atrial refractory period and the conduction velocity (CV) during atrial fibrillation (AF) and to explore the antiarrhythmic mechanism of a sodium channel blocker, pilsicainide, during AF.

BACKGROUND

Sodium channel blockers not only decrease the CV, but also prolong the atrial refractory period, particularly during rapid excitation. Because these effects on the wavelength are counteractive and rate dependent, it is critical to measure these parameters during AF.

METHODS

In eight dogs, after AF was induced under vagal stimulation, a single extra-stimulus was repeatedly introduced from the left atrium and its capture was statistically determined for each coupling interval. The local CV was also measured during constant capture of the fibrillating atrium by rapid pacing. The same procedure was repeated after pilsicainide administration.

RESULTS

Pilsicainide significantly increased the mode of AF intervals from 81 ± 10 to 107 ± 16 ms (p < 0.01). While the CV was decreased from 0.9 ± 0.1 to 0.7 ± 0.1 m/s (p < 0.02), the effective refractory period during AF was increased from 69 ± 11 ms to 99 ± 17 ms (p < 0.01). As a result, the wavelength was significantly increased by pilsicainide from 6.6 ± 0.9 to 7.6 ± 1.2 cm (p < 0.05).

CONCLUSIONS

During AF, whereas the sodium channel blocker pilsicainide decreases CV, it lengthens the wavelength by increasing the refractory period, an action that is likely to contribute to the drug’s ability to terminate the arrhythmia. The direct measurement of refractoriness and CV during AF may provide new insights into the determinations of the arrhythmia and antiarrhythmic drug action.

Abbreviations and Acronyms   AF = atrial fibrillation   Avg FF = average of 100 atrial activation (FF) intervals   CI = coupling interval   CV = conduction velocity   ERPAF = effective refractory period during atrial fibrillation   FRPAF = functional refractory period during atrial fibrillation   Mode FF = mode of 100 FF intervals

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