Modulation of Cardiac Autonomic Nervous ActivityEarly after Cardioversion of Atrial Fibrillation byBiphasic WaveformJASMIN ORTAK, M.D., FRANZISKA KURTZ, M.S., ANN-SOPHIE KRENZIEN, M.D.,NINA JANCA, M.D., IRIS WILKE, M.D., MELANIE BARANTKE, M.D.,FRANK EBERHARDT, M.D., UWE K.H. WIEGAND, M.D., HERIBERT SCHUNKERT, M.D.,and HENDRIK BONNEMEIER, M.D.From the Medizinische Klinik II, Universitat zu Lubeck, Lubeck, Germany

Background: Imbalance of cardiac autonomic nervous modulation might prominently contribute toearly relapses of atrial fibrillation (AF) after cardioversion (CV). The biphasic (Bi) waveform is moreeffective than the monophasic (Mo) waveform in CV of AF. Whether these waveforms have different effectson autonomic modulation early after CV is unknown.

Methods: We investigated 171 consecutive patients after successful electrical CV (mean age 65.4 years,82% male, 80% structural heart disease). Bi waveform was used in 89, Mo waveform in 82. Heart ratevariability (HRV) was analyzed from 24-hour Holter recordings, started directly after CV.

Results: Mean delivered total energy was significantly lower in the Bi group (Bi 223 163 W, Mo 355 211 W, P < 0.001). Mean RR interval decreased within 5 hours after CV and increased again within theremaining hours, without significant differences between Bi and Mo groups. Time courses of time domainparameters of HRV revealed Bi profiles with the lowest levels 6 hours after CV in both groups. However,the hourly values of HRV were significantly higher in the Bi subgroup.

Conclusion: Our study indicates that waveform and total delivered energy significantly influence au-tonomic modulation of the sinus node in the early phase after CV of AF. In contrast to Bi CV, Mo CV ischaracterized by a significant decrease of cardiac vagal modulation, which may have an arrhythmic effectby increasing the degree of early electrical stunning after CV of AF. (PACE 2007; 30:S207S211)

atrial fibrillation, biphasic shock, cardioversion, heart rate variability

IntroductionDespite peri- and postinterventional antiar-

rhythmic drug therapy, atrial fibrillation (AF) re-curs often after electrical cardioversion (CV).1 Thebiphasic (Bi) waveform is more effective than themonophasic (Mo) waveform in CV of AF.2 Recentstudies demonstrating that Bi waveforms requireless energy for CV of AF than Mo waveforms, sug-gested a lesser amount of post-CV myocardial in-jury caused by the Bi waveform.3

Various factors have been evoked that mightidentify patients at risk of AF relapse after CV,including modulation of cardiac autonomic ner-vous activity.46 The majority of relapses after CVof AF occur within 2 weeks.7 Short-term record-ings of heart rate variability (HRV) before hospi-tal discharge have shown a prominent increasein sympathetic and decrease in vagal modulationafter CV in patients with early recurrence of AF(ERAF), which might be a major determinant of itsre-initiation.5 However, the relationship between

Address for reprints: Hendrik Bonnemeier, M.D., Medizinis-che Klinik II, Universitat zu Lubeck, Ratzeburger Allee160, 23538 Lubeck, Germany. Fax: +49-451-500-2363; e-mail:Bonnemei@medinf.mu-luebeck.de

CV waveform and electrical atrial stability and car-diac autonomic modulation has not been studied.We hypothesized that Bi waveforms and loweramounts of delivered energy mitigate post-CV elec-trical stunning and influence cardiac autonomicnervous modulation. Therefore, we analyzed car-diac autonomic activity immediately after Mo andBi CV of persistent AF.

MethodsPatient Population

We studied 200 consecutive patients who un-derwent successful, elective, external electrical CVof persistent AF. All patients underwent completephysical examination, 12-lead ECGs, and echocar-diography before the procedure, performed in aquiet environment, between 01:00 and 02:00 p.m.,under light sedation with midazolam 1.05.0 mg,and analgesia with fentanyl 0.050.1 mg. The pa-tients were randomly assigned to Bi delivered byPhysiocontrol LifePak12, versus Mo waveformsdelivered by Physiocontrol LifePak 9, external de-vices (Medtronic Inc., Minneapolis, MN, USA),and delivery of 50, 100, 200, 300, and 360 Wsteps of energy. After CV, all patients remainedat bedrest until the next morning, 18 of whomwere excluded because of insufficient ambulatory

C2007, The Authors. Journal compilation C2007, Blackwell Publishing, Inc.

PACE, Vol. 30 January 2007, Supplement 1 S207

ORTAK, ET AL.

Figure 1. AD: Mean hourly measurements of RR inter-val (A) and HRV indices (BD) after monophasic (Mo)versus biphasic (Bi) shocks delivery. *P < 0.05; P