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Europace 2005 7(6):560-568; doi:10.1016/j.eupc.2005.06.008
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© 2005 The European Society of Cardiology. Published by Elsevier Ltd. All rights reserved.

The effects of 5-HT4 receptor blockade and stimulation, during six hours of atrial fibrillation

Dionyssios I. Leftheriotis*, George N. Theodorakis, Dimitrios Poulis, Panagiota G. Flevari, Efthimios G. Livanis, Efstathios K. Iliodromitis, Apostolos Papalois and Dimitrios Th. Kremastinos

2nd Department of Cardiology, Onassis Cardiac Surgery Center 356 Syngrou Avenue, 17674 Athens, Greece

AIMS: Stimulation of atrial 5-HT4 receptors is associated with arrhythmias. Their blockade prolongs atrial effective refractory period (ERP), following short runs of atrial fibrillation (AF). The role of 5-HT4 receptors during longer periods of AF is unknown. In this study, we investigated the effects of the selective 5-HT4 receptor stimulation and blockade on porcine atria, during 6 h of AF.

METHODS: Atrial ERP, monophasic action potential (MAP) duration, time to sinus rhythm restoration (TSRR) and ERP/MAP ratio were assessed in 27 pigs, at baseline and every hour, during 6 h of AF, induced by rapid atrial pacing. Ten animals were used as controls, 10 were administered the selective 5-HT4 antagonist SB203186 and seven were administered the selective 5-HT4 agonist RS67333.

RESULTS: During the first few hours of fibrillation, ERP, MAP and TSRR were preserved in SB203186-treated pigs, while they were shortened in controls and RS67333-treated animals. After 6 h of arrhythmia, ERP and MAP were shortened in all three groups, but the decrease was less in SB203186-treated pigs. ERP/MAP ratio increased in controls and RS67333-treated animals, while it remained unchanged in SB203186-treated pigs. Towards the end of the AF period, four of the SB203186-treated pigs developed sustained atrial tachycardia.

CONCLUSION: Following short periods of AF, 5-HT4 receptors' blockade protects the porcine atria against ERP and MAP shortening, while their stimulation has the opposite result. This beneficial effect, though, is gradually diminished following longer periods of AF and atrial tachycardia may develop.

Key Words: atrial fibrillation, serotonin (5-HT)

*Corresponding author. Tel.: +30 210 9493372/3000, +30 6944785025 (mobile); fax: +30 10 9493 373. dionle1{at}otenet.gr


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