European Heart Journal Advance Access originally published online on September 25, 2006
European Heart Journal 2006 27(20):2482; doi:10.1093/eurheartj/ehl264
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Incidence of syncope after ICD implantation: low or high?: reply
La Paz University Hospital
Arrhythmia Unit
Castellana 261
Madrid
Spain
La Paz University Hospital
Arrhythmia Unit
Castellana 261
Madrid
Spain
E-mail address: jlmerino{at}secardiologia.es
We appreciate the comments and interest of Garcia Moran and Mont in our work. We agree with them that our results were obtained from a selected implantable cardioverter-defibrillator (ICD) recipient population with syncopal spontaneous ventricular tachycardia (VT) and, therefore, they should not be extrapolated to the general population of patients who presented syncope before ICD implantation.1–4 Syncope can originate from many different mechanisms, which can be related or not to VT. This was discussed in our original manuscript and was also admitted in the report of Garcia Moran et al.,2 who suggested that some patients with non-arrhythmic syncope were enrolled in their study because none of the syncopal recurrences had an arrhythmic mechanism following ICD implantation. Indeed, their population appears substantially different from ours, because none of their 38 patients presented with spontaneous monomorphic VT before ICD implantation and this was induced by programmed electrical stimulation in only 31 patients.2
Garcia Moran and Mont speculated that the high incidence of syncopal recurrence which was found in our patients was related to the use of low-energy shocks (LESs) because very LESs (<2 J) have been found to be proarrhythmic at ICD implantation.5 They also speculated that programming high energy shocks (HESs) in the VT zone instead may reduce the incidence of VT acceleration and syncope. LES requires less charging time and a shorter time from VT detection to termination which may protect against syncope. On the contrary, LES may also promote syncope by VT degeneration into a faster VT/VF, which, in turn, may increase the final time to arrhythmia termination. However, VT degeneration into VF by HES presented also in three out of seven syncopal recurrences in our patients.1 In addition, despite similar antitachycardia pacing and LES programming, only a single syncopal episode occurred at follow-up in our group of 50 patients presenting with non-syncopal VT before ICD implantation.1 This latter finding matches the low syncope occurrence that Garcia Moran et al.2 found by programming up to 16 antitachycardia pacing sequences which were followed by LES (‘low energy cardioversion was attempted by successive shocks of progressively increasing energy’). Therefore, any statement that is not supported by a controlled trial comparing LES and HES should be considered just a speculation.
We disagree with Garcia Moran and Mont about the existence of a controversy about the recurrence of syncope in ICD recipients, since a controversy exists when conflicting data from different sources are available. However, this is not the case for syncope because most reports3,4 establish its recurrence 
15% in the general population of ICD recipients presenting with syncope before implantation and 30% in the only one report1 studying the subpopulation of patients with syncopal VT before implantation.
In conclusion, syncope at spontaneous VT presentation identifies a subset of patients with high risk of syncope following ICD implantation, despite similar left ventricular ejection fraction, tachycardia cycle length, and device programming that patients presenting with no syncope at VT documentation. This risk cannot be extrapolated to other ICD populations.
References
- Abello M, Merino JL, Peinado R, Gnoatto M, Arias MA, Gonzalez-Vasserot M, Sobrino JA. (2006) Syncope following cardioverter defibrillator implantation in patients with spontaneous syncopal monomorphic ventricular tachycardia. Eur Heart J 27:89–95.
[Abstract/Free Full Text] - Garcia Moran E, Mont L, Cuesta A, Matas M, Brugada J. (2002) Low recurrence of syncope in patients with inducible sustained ventricular tachyarrhythmias treated with an implantable cardioverter-defibrillator. Eur Heart J 23:901–907.
[Abstract/Free Full Text] - Bansch D, Brunn J, Castrucci M, Weber M, Gietzen F, Borggrefe M, Breithardt G, Block M. (1998) Syncope in patients with an implantable cardioverter-defibrillator: incidence, prediction and implications for driving restrictions. J Am Coll Cardiol 31:608–615.
[Abstract/Free Full Text] - Kou WH, Calkins H, Lewis RR, Bolling SF, Kirsch MM, Langberg JJ, de Buitleir M, Sousa J, El-Atassi R, Morady F. (1991) Incidence of loss of consciousness during automatic implantable cardioverter-defibrillator shocks. Ann Intern Med 115:942–945.[ISI][Medline]
- Lauer MR, Young C, Liem LB, Ottoboni L, Peterson J, Goold P, Sung RJ. (1994) Ventricular fibrillation induced by low-energy shocks from programmable implantable cardioverter defibrillators in patients with coronary artery disease. Am J Cardiol 73:559–563.[CrossRef][ISI][Medline]
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