ICDs
T-wave oversensing and inappropriate shocks: a case report
Mayo Clinic Arizona—Mayo Clinic Hospital, Cardiovascular Diseases, 5777 East Mayo Boulevard, Phoenix, AZ 85054, USA
Manuscript submitted 21 January 2008. Accepted after revision 18 March 2008.
* Corresponding author. Tel: +1 480 342 0239; fax: +1 480 342 1606. E-mail address: altemose.gregory{at}mayo.edu
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Abstract |
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A 27-year-old male with congenital long QT syndrome, SCN5A mutation experienced recurrent inappropriate exercise-related implantable cardioverter defibrillator (ICD) shocks. This device showed T-wave oversensing with double, which lead to these device discharges. Dynamic T-wave oversensing was reproducibly provoked at exercise treadmill testing and was confirmed as the mechanism leading to double counting. The insertion of a new pacing and sensing lead with increased R-wave amplitude did not solve the problem. Exchanging the existing ICD generator with one capable of automatic sensitivity control (Biotronik, Lexos DR, Biotronik, Berlin, Germany) completely eliminated T-wave oversensing and inappropriate shocks.
Key Words: Long QT syndrome, T-wave oversensing, Inappropriate shocks
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Case report |
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A 27-year-old male with congenital long QT syndrome (LQTS), SCN5A mutation, was examined for recurrent implantable cardioverter defibrillator (ICD) (five shocks in 3 months) shocks. His most recent shock (Figure 1A) occurred during the final stages of vigorous exercise on a treadmill. The device revealed T-wave oversensing during sinus tachycardia with resultant double counting, which met the rate threshold criteria for ventricular fibrillation (VF), leading to an ensuing shock.
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He had previously undergone implantation of a dual chamber ICD (Medtronic GEM III, Medtronik, Inc., Minneapolis, MN, USA), 1 year prior, for the primary prevention of sudden cardiac death (SCD). Prior to considering ICD therapy, he underwent a thorough evaluation including genetic screening as a part of risk assessment due to a high incidence of SCD in (21 SCD between the ages of 1 and 35) family members. His QTc interval at the baseline was 478 ms, and an SCN5A genetic mutation was identified. Cardiac structure and function were normal by echocardiography. Although he had a history of paroxysmal atrial fibrillation (AF) noted over the past 7 years, the patient never received a shock for either AF or a ventricular tachyarrhythmia. His medical regimen included only 180 mg of verapamil once daily, as was recommended by a genetic electrophysiologist. At initial ICD implantation, R-wave amplitude was measured (10.3 mV) with a ventricular pacing threshold of 0.8 V at 0.5 ms. The atrial threshold was 0.7 V at 0.5 ms. The ventricular tachyarrhythmia detections were programmed as follows: VF 240 bpm and ventricular tachycardia 214 bpm. Therapies in both zones included shocks at 30 J. At the time of his most recent device interrogation, the R-wave amplitude had diminished to 4.5 mV and the T-wave amplitude measured 3.4 mV. The refractory period was non-programmable at 120 ms, and the R-wave sensitivity was reduced to 1.2 mV. Despite these alterations in device programming, a subsequent supervised exercise treadmill test with therapies temporarily disabled (Figure 1B) revealed continued T-wave oversensing with resultant inappropriate double counting.
The patient was then taken to the electrophysiology laboratory for implantation of a new right ventricular pacing and sensing lead in an attempt to obtain improved R-wave amplitude, possibly resolving inappropriate counting that triggered prior shocks. The new lead was placed at multiple (six different) locations, revealing a maximum R-wave amplitude of 4.5 mV and a T-wave amplitude of 2.8 mV. The peak amplitude of the T-wave occurred at 135 ms. Atrial pacing, through the existing generator, at 120 bpm led to T-wave oversensing and met the nominal rate threshold for VF detection. Owing to failure to adequately rectify the problem, a decision was made to replace the existing ICD generator. The newly implanted Biotronik ICD generator showed an R-wave amplitude of 11.1 mV and a T-wave amplitude of 6.8 mV when connected to the newly implanted pacing and sensing lead. (The newly implanted lead sensed a larger R-wave when compared with the chronic ICD lead and was thus retained and utilized.) Automatic sensitivity control (ASC) with enhanced T-wave suppression was programmed as follows: upper threshold (UT) for the detection of 75% of peak amplitude, lower threshold (LT) above 25%, and minimum threshold at 0.8 mV. The UT is active through the T-wave discrimination period of 350 ms (includes 100 ms refractory period). Atrial pacing up to 160 bpm did not result in T-wave oversensing. Repeat exercise treadmill testing with the new device showed no further T-wave oversensing (Figure 2). After a follow-up period of 18 months post-revision, the patient had not sustained any further shocks.
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Discussion |
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Ventricular oversensing is more likely to occur in integrated than dedicated bipolar leads,1
,2 and T-wave oversensing has been reported as high as 8%.3 Possible causes for T-wave oversensing include diminution of R-wave amplitude and relative or dynamic gain in the T-wave amplitude,4 progressive cardiomyopathy,1 electrolyte abnormalities such as hyperglycaemia and hyperkalaemia,5 medications such as histamine-2 receptor blockers,6 injury current-related increase in the T-wave voltage,7 and changes in the sympathetic tone. This patient had a device with true bipolar sensing. The diminution of the R-wave amplitude and an increase in the T-wave amplitude were observed in this patient. A potential solution to this problem included implantation of a new pacing and sensing lead, which did not lead to adequate resolution of this issue. There was no evidence of ongoing disease of the myocardium that could explain the alterations of R-wave and T-wave amplitudes as cardiac biomarkers, and echocardiographic assessment of ventricular size and function was normal. No metabolic abnormalities were present and no drugs were felt to be responsible for T-wave oversensing in this case. The device has been in situ for more than a year, and thus an injury current-related increase in the T-wave voltage is not an issue in this case. The filters used in this Medtronic device did not provide a larger absolute difference between the R-wave amplitude and T-wave amplitude. Moreover, a programmed reduction in the ventricular sensitivity with this device did not eliminate the problem, and the refractory period is non-programmable. The Biotronik filtering system resulted in larger R-waves and T-waves, even though the ratio remained the same.
To date, multiple algorithms have been proposed to reduce T-wave oversensing, including electrogram width criterion8 and three-fold programmable parameters with post-sense refractory period, decay delay, and linear decay. The ASC with enhanced T-wave suppression was utilized in this patient (Biotronik). This feature has programmable UT and LT, and high-pass filtering is enhanced to reduce the T-wave amplitude. The UT is active through the T-wave discrimination period of 350 ms (includes 100 ms refractory period).
This report shows that T-wave oversensing leads to inappropriate therapy in this patient with congenital LQTS. Alterations in programmed parameters of the existing device including the addition of a new right ventricular pacing and sensing lead did not resolve the problem. Ultimately, replacement of the ICD generator with a Biotronik device utilizing the ASC algorithm resulted in successful suppression of T-wave oversensing. Subsequent elimination of inappropriate shocks resulted in a vast improvement in this patient's quality of life.
Conflict of interest: none declared.
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References |
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[1] Weretka S, Michaelsen J, Becker R, Karle CA, Voss F, Hilbel T, et al. Ventricular oversensing: a study of 101 patients implanted with dual chamber defibrillators and two different lead systems. Pacing Clin Electrophysiol (2003) 26:65–70.[CrossRef][Medline]
[2] Schimpf R, Wolpert C, Bianchi F, Giustetto C, Gaita F, Bauersfeld U, et al. Congenital short QT syndrome and implantable cardioverter defibrillator treatment: inherent risk for inappropriate shock delivery. J Cardiovasc Electrophysiol (2003) 14:1273–77.[CrossRef][Web of Science][Medline]
[3] Singer I, de Borde R, Veltri EP, Siddoway LA, Levine JH, Griffith LS, et al. The automatic implantable cardioverter defibrillator: T wave sensing in the newest generation. Pacing Clin Electrophysiol (1988) 11:1584–91.[CrossRef][Medline]
[4] 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]
[5] Krishen A, Shepard RK, Leffler JA, Wood MA, Ellenbogen KA. Implantable cardioverter defibrillator T wave oversensing caused by hyperglycemia. Pacing Clin Electrophysiol (2001) 24:1701–3.[CrossRef][Medline]
[6] Perry GY, Kosar EM. Problems in managing patients with long QT syndrome and implantable cardioverter defibrillators: a report of two cases. Pacing Clin Electrophysiol (1996) 19:863–7.[CrossRef][Medline]
[7] Yokoyama M, Wada J, Barold SS. Transient early T wave sensing by implanted programmable demand pulse generator. Pacing Clin Electrophysiol (1981) 4:68–74.[CrossRef][Medline]
[8] Duru F, Bauersfeld U, Candinas R. Avoiding inappropriate ventricular tachycardia detection due to T-wave oversensing in an implantable cardioverter defibrillator: a novel application of the electrogram width criterion. Europace (2001) 3:80–4.
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