Europace Advance Access published online on June 1, 2007
Europace, doi:10.1093/europace/eum106
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Atrial fibrillation reduces the atrial impedance amplitude during cardiac cycle: a novel detection algorithm to improve recognition of atrial fibrillation in pacemaker patients
1 Universitätsklinikum Freiburg, Medizinische Klinik III, Department of Cardiology and Angiology, Hugstetter Str. 55, D-79106 Freiburg, Germany; 2 Biotronik GmbH & Co. KG, Woermannkehre 1, D-12359 Berlin, Germany
Aims In carriers of dual chamber pacemakers and implantable cardioverter-defibrillators (ICD), detection of atrial fibrillation (AF) is crucial for adequate mode switch function and to avoid inappropriate shock delivery. Detection algorithms rely on the atrial rate and on the relationship of atrial to ventricular intracardiac electrograms, but the relative portion of misclassified AF episodes remains high. Although myocardial impedance is a reliable indicator of contraction, little is known about atrial impedance as a marker of atrial arrhythmias.
Methods During an electrophysiological study, we investigated the effect of induced AF on impedance at the right atrial free wall (RAFW) and right atrial appendage (RAA) in 20 patients. Using biphasic square-wave pulses (128 Hz, 200 µA/15 µs), impedance changes were recorded during sinus rhythm (SR-1), atrial pacing at 120 beats/min, AF induced by rapid atrial burst pacing, and after spontaneous AF termination (SR-2).
Results At the RAA, peak-to-peak impedance amplitude during cardiac cycle (
Z) dropped from 51.7 ± 35.3 
(SR-1) or 49.6 ± 30.6 (pacing) to 24.6 ± 22.0 (AF, P 
0.0005), and subsequently increased to 37.7 ± 24.7 (SR-2, P 0.0004 v. AF). At the RAFW, Z changed from 16.2 ± 15.5 (SR-1) or 13.5 ± 9.9 (pacing) to 5.9 ± 4.1 (AF, P 0.003), and to 11.4 ± 10.7 (SR-2, P 0.015). Given a discrimination threshold of 65%, the sensitivity and the specificity of Z to detect AF were 79 ± 18 and 89 ± 14%, respectively (95% confidence interval).
Conclusion AF causes Z drop in pacemaker and ICD recipients. This impedance based algorithm can be used as an alternative method of AF detection.
Key Words: Atrial fibrillation, Myocardial impedance, Mode switch, Cardiac pacing
* Corresponding author. E-mail address: Thomas.faber{at}uniklinik-freiburg.de
B.S. and S.A. contributed equally to the study and the manuscript.
Manuscript submitted 1 February 2007. Accepted after revision 24 March 2007.
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