We read with interest the paper of Guillon et al. reportingchanges of Tp-e (peak to end of T wave) and QTc intervals during caesareansection under spinal anaesthesia [1]. This study confirms the transientincrease in QTc after oxtytocin bolus injection, which has already beendescribed in patients presenting for surgical termination of pregnancy undergeneral anaesthesia [2]. The authors also report an increase in Tp-e afteroxytocin administration, and conclude that its use might lead to arrhythmias duringcaesarean section [2]. We agree that increased duration of the last part ofcardiac repolarisation (reflected by Tp-e lengthening on the surfaceelectrocardiogram) induced by drugs, is usually a marker of increased risk ofcardiac arrhythmia. However, an increase in the global duration ofrepolarisation (i.e. QTc) is generally associated with an increase in Tp-e.Conversely, for drugs increasing only QTc, without concomitant change of Tp-e,e.g. with sevoflurane, the arrhythmogenic potential is weak [3].

In the present study, the increased duration in QTc intervalwas significant only during the first minute after oxytocin adminstration, andthe increase in Tp-e lasted over 4 minutes after QTc duration had returned tonormal. Therefore, mathematically the authors mainly show a shortening of thefirst part of repolarisation (i.e. time between Q onset and T wave peak). Thisobservation appears somewhat unexpected and cannot be considered as a definiteproof of a direct arrhythmogenic potential of oxytocin. Moreover, in ourexperience, precise determination of the T-wave peak is particularly difficultwhen T-wave morphological changes occur; a very frequent condition afteroxytocin bolus administration [2].

It would thus be interesting to know if distorted T waveswere observed in the present study and if so, how this was addressed by theauthors to obtain precise calculation of repolarisation intervals.Additionally, Antzelevitch who introduced the concept of spatial dispersion ofrepolarisation, has suggested that Tp-e should be measured in precordial leads,and not bipolar limb leads, as performed in the present study. This allows anacceptable estimation of transmural dispersion of repolarisation [4].

Finally, we would like to emphasise that arrhythmic eventsafter oxytocin administration are extremely rare, and probably more related toindirect cardiovascular effects, such as poor haemodynamic function, ratherthan related to the direct cardiac effects of oxytocin.

B. Charbit
Hôpital la Pitié-Salpêtrière, Paris, France

F. J. Mercier
Hôpital Antoine Béclère, Clamart, France

Dan Benhamou
Hôpital Bicêtre, Le Kremlin-Bicêtre, France

E-mail : beny.charbit@psl.aphp.fr

No external funding and no competing interests declared

References

1       Guillon A,Leyre S, Remerand F, et al. Modification of Tp-e and QTc intervals duringcaesarean section under spinal anaesthesia. Anaesthesia; 65: 337-42.

2       Charbit B,Funck-Brentano C, Samain E, Jannier-Guillou V, Albaladejo P, Marty J. QT intervalprolongation after oxytocin bolus during surgical induced abortion. ClinicalPharmacology and Therapeutics 2004; 76: 359-64.

3       Whyte SD,Booker PD, Buckley DG. The effects of propofol and sevoflurane on the QTinterval and transmural dispersion of repolarization in children. Anesthesiaand Analgesia 2005; 100: 71-7.

4       AntzelevitchC. Drug-induced spatial dispersion of repolarization. Cardiology Journal 2008;15: 100-21.