Europace Advance Access originally published online on May 3, 2007
Europace 2007 9(8):694-696; doi:10.1093/europace/eum056
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ICD AND MONITORING
An unusual mechanism causing inappropriate implantable cardioverter defibrillator shocks: transient reduction in R-wave amplitude
Arrhythmia Service, McMaster University, Hamilton Health Sciences Corporation, Hamilton, Ontario, Canada
Manuscript submitted 5 December 2006. Accepted after revision 8 March 2007.
* Corresponding author: Cardiac Electrophysiology and Pacing, Kingston General Hospital, Queen's University, 861 Apple Down Dr, Kingston, Ontario, Canada K7L 2V7. Tel: +1 613 549 6666/ext 3801; fax: +1 613 548 1387. E-mail address: barancha{at}kgh.kari.net
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Abstract |
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Inappropriate shocks delivered by the implantable cardioverter defibrillator (ICD) are an increasingly recognized complication. The most frequent cause is related to supraventricular rhythms associated with fast conduction to the ventricles that are incorrectly detected as ventricular tachycardia leading to inappropriate antitachycardia pacing and/or shocks. Oversensing is a frequent cause of inappropriate shocks usually due to increased amplitude of the T-wave secondary to ischaemia or electrolyte disorders that lead to T-wave double counting.We describe an unusual case of T-wave double counting during sinus rhythm caused by transient reduction in R-wave amplitude with no changes in T-wave amplitude resulting in inappropriate shocks.
Key Words: ICD-inappropriate shocks, Transient reduction in R-wave amplitude
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Introduction |
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TopAbstractIntroductionCase reportDiscussionConclusionReferences |
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Inappropriate shocks delivered by the implantable cardioverter defibrillator (ICD) are an increasingly recognized complication. The most frequent cause is related to supraventricular rhythms associated with fast conduction to the ventricles that are incorrectly detected as ventricular tachycardia leading to inappropriate antitachycardia pacing and/or shocks. Oversensing is a frequent cause of inappropriate shocks usually due to increased amplitude of the T-wave secondary to ischaemia or electrolyte disorders that lead to T-wave double counting.1
–3 We describe an unusual case of T-wave double counting during sinus rhythm caused by transient reduction in R-wave amplitude with no changes in T-wave amplitude resulting in inappropriate shocks.
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Case report |
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The patient was a 69-year-old male with idiopathic dilated cardiomyopathy (ejection fraction 28%) who had an ICD implanted on in February 2002 due to syncope and monomorphic ventricular tachycardia (VT). He also had previous history of paroxysmal atrial fibrillation.
The device implanted was a dual chamber V-232 Photon micro DR model (St Jude Medical). The atrial lead inserted was a 1488TC Tendril SDX (St Jude Medical), and the ventricular lead was a steroid eluting active fixation 1559 TVL-ADX (St Jude Medical).
The ventricular lead implant measurements were: R-wave 8 mV, pacing threshold 0.5 V at 0.5 ms, impedance 520 Ohms, high voltage lead impedance 80 Ohms. The atrial lead had satisfactory measurements at implant as well. The device was tested in the operating room twice successfully with the least sensitive settings. Shocks at 20 and 15 J successfully converted VF into normal sinus rhythm. Therapies were programmed in two zones: VF zone from 222 bpm, delivering shocks (29 J) up to six times, and the VT zone was programmed from 176 bpm with two sequences of ATP (91–84%) followed by shocks at 29 J x 6. Atrial and ventricular sensitivity was programmed to be automatic; A/V post-sensed threshold was set at 50/50% and A/V post-sensed decay delay at 0/0 ms.
During a 2-year follow-up, the patient had one inappropriate shock due to atrial fibrillation with rapid ventricular response. Antiarrhythmic drugs were adjusted and the cutoff for VT was increased.
On April 2004, the patient presented to the ICD outpatient follow-up clinic after having five consecutive shocks at rest.
Interrogation of the device demonstrated an interesting phenomenon. All therapies had been delivered during sinus rhythm at 150 bpm. The R-wave amplitude showed beat-to-beat changes in amplitude from an initial value of 10.2 mV to a minimal value of <1 mV (Figure 1). This device uses the automatic sensitivity feature which produces an automatic adjustment of sensitivity in order to detect the R-wave. The device automatically increases sensitivity in the presence of a reduced R-wave amplitude allowing detection of the T-wave triggering double counting. This automatic sensitivity feature leaded to double counting above the VT/VF cutoff zone leading to the delivery of inappropriate shocks (Figure 2).
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The R-wave amplitude ranged between 10–14 mV during follow-up since implant.
Reprogramming the A/V post-sensed decay delay from 0 to 221 ms, incorporating the T-wave into the refractory period of the sensed event to prevent double counting, overcame the oversensing problem. Non-invasive programmed electrical stimulation was performed to ensure appropriate sensing of VF and defibrillation threshold after reprogramming. Signal amplitude, thresholds, and impedance were 11.5 mV, 0.5 V at 0.5 ms, and 399 Ohms, respectively. Defibrillation threshold was 16 J. Isoproterenol was used to increase the heart rate over 150 bpm to try to reproduce the phenomenon, but the signal amplitude remained constant ranging between 10.5–12.1 mV.
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Discussion |
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This case is, to the best of our knowledge, the first report of ICD inappropriate shocks due to transient reduction in R-wave amplitude without changes in T-wave amplitude during sinus rhythm. Inappropriate shocks were triggered by T-wave double counting in a device with auto sensitivity control.
Inappropriate ICD therapy is a well-recognized complication and proper recognition of the different causes is essential to ensure patient well being.4,5 Most of the previous reports regarding inappropriate ICD therapies due to oversensing, describe double counting related to T-wave oversensing during tachycardia.6 Washizuka et al.7 described two similar cases but careful analysis revealed T-wave oversensing related to an increase in the amplitude of the T-wave rather than to a reduction in the R-wave amplitude.
Reduced R-wave amplitude during VT has been previously described as a cause of undersensing, and different explanations have been proposed:8 (1) fusion of two wave fronts, (2) alternating conduction delay or block, and (3) alternating ventricular volumes. This phenomenon was reproducible and required lead repositioning with a different sensing electrode.
We defined a transient reduction in the R-wave amplitude as a difference in the amplitude size in three consecutive sensed signals in the ventricular channel of more than 25%. Once a minimum value has been reached, the R-wave amplitude has to increase to return to baseline values.
Our case presented a diagnostic challenge, as there was no evidence of lead fracture, insulation defects, respiratory or positional changes, or far field sensing. Oversensing always occurred when the amplitude of the R-wave signal was below 1 mV, almost the same amplitude of the baseline T-wave that remained unchanged. The patient received inappropriate therapies when double counting reached the VT/VF cutoff level. We ruled out other potential explanations for transient reduction of R-wave amplitude; however, the mechanism of the reported finding remains unclear.
This phenomenon was not reproducible during non-invasive programmed electrical stimulation.
This particular ICD (V-232 Photon micro DR; St Jude Medical), has automatic sensitivity control which allows sensitivity changes on a beat-to-beat basis, thus increasing or decreasing according to the signal amplitude detected by the lead. Similarly, a special sensitivity enhancement feature called A/V post-sensed decay delay is also a characteristic of this device. This feature allows a sensing refractory period after the signal that is detected to prevent the T-wave from being sensed, thus preventing double counting. The A/V post-sensed decay delay was programmed from 0 to 221 ms, allowing the sensed refractory period to include the T-wave, thereby preventing oversensing.
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Conclusion |
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Transient reduction in the R-wave amplitude during sinus rhythm is defined as a change in amplitude size in three consecutive sensed signals in the ventricular channel of more than 25% without changes in the T-wave amplitude. This may lead to inappropriate therapies in ICDs with automatic adjustment of sensitivity strictly related to the change in amplitude of the R-wave but not in T-wave amplitude. The underlying mechanism of transient reduction in the R-wave amplitude remains unclear, but given the irreproducibility of this condition, micro-dislodgement is possible. Appropriate recognition of this condition is relevant and can be easily managed by reprogramming specific features preventing further episodes of inappropriate shocks and potentially unnecessary lead repositioning.
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References |
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[1] Swerdlow CD, Zhang. Implantable cardioverter defibrillator shocks. A troubleshooting guide. Rev Cardiovasc Med (2001) 2:61–72.[CrossRef][Medline]
[2] Swerdlow CD, Friedman PA. Advanced ICD troubleshooting: part I. Pacing Clin Electrophysiol (2005) 28:1322–46.[CrossRef][Medline]
[3] Washizuka T, Chinushi M, Tagawa M, Kasai H, Watanabe H, Hosaka H, et al. Inappropriate discharges from fourth generation implantable cardioverter defibrillators in patients with ventricular arrhythmias. Jpn Circ J (2001) 65:927–30.[CrossRef][Medline]
[4] Dorwarth U, Frey B, Dugas M, Matis T, Fiek M, Schmoeckel M, et al. Transvenous defibrillation leads: high incidence of failure during long-term follow-up. J Cardiovasc Electrophysiol (2003) 14:38–43.[CrossRef][Web of Science][Medline]
[5] Scher DL. Troubleshooting pacemakers and implantable cardioverter-defibrillators. Curr Opin Cardiol (2004) 19:36–46.[CrossRef][Web of Science][Medline]
[6] Saeed M, Jin A, Pontone G, Higgins S, Gold M, Harari D, et al. Prevalence of sensing abnormalities in dual chamber implantable cardioverter defibrillators. Ann Noninvasive Electrocardiol (2003) 8:219–26.[CrossRef][Web of Science][Medline]
[7] Washizuka T, Chinushi M, Kasai H, Watanabe H, Tagawa M, Hosaka Y, et al. Inappropriate discharges from an intravenous implantable cardioverter defibrillator due to T-wave oversensing. Jpn Circ J (2001) 65:685–7.[CrossRef][Medline]
[8] Jongnarangsin K, Mela T. Implantable cardioverter defibrillator sensing failure due to endocardial R-wave electrical alternans. J Cardiovasc Electrophysiol (2002) 13:702–4.[CrossRef][Web of Science][Medline]
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