CASE REPORT

Inappropriate ICD discharges due to “triple counting”during normal sinus rhythm

Ejaz Khan & Apostolos Voudouris &

Stephen R. Shorofsky & Robert W. Peters

Received: 19 July 2006 /Accepted: 22 November 2006 /Published online: 23 February 2007# Springer Science + Business Media, LLC 2007

AbstractObjective To describe the clinical course of a patient withmultiple ICD shocks in the setting of advanced renal failureand hyperkalemia.Methods The patient was brought to the ElectrophysiologyLaboratory where the ICD was interrogated.Results The patient was found to be hyperkalemic (serumpotassium 7.6 mg/dl). Analysis of stored intracardiacelectrograms from the ICD revealed “triple counting”(twice during his QRS complex and once during the Twave) and multiple inappropriate shocks. Correction of hiselectrolyte abnormality normalized his electrogram and nofurther ICD activations were observed.Conclusion Electrolyte abnormalities can distort the intra-cardiac electrogram in patients with ICD’s and thesechanges can lead to multiple inappropriate shocks.

Keywords Implantable cardioverter defibrillator (ICD) .

Hyperkalemia . Oversensing . Ventricular tachycardia .

Renal insufficiency

AbbreviationsICD implantable cardioverter defibrillator

1 Introduction

Implantable cardioverter defibrillators (ICD) have beendemonstrated to reduce mortality in patients with severe leftventricular dysfunction (MUSTT, MADIT 1, SC-HFT,etc.). However, not all ICD discharges are the result ofpotentially lethal ventricular arrhythmias. We describeherein an individual with hyperkalemia who experiencedrecurrent ICD shocks due to “triple counting” of a widenedQRS complex and prominent T waves.

2 Case report

A 61-year old man with a history of complex congenitalheart disease and severe congestive heart failure had asingle lead ICD (St. Jude V-199) implanted in 2003because of sustained monomorphic ventricular tachycardia.The amplitude of the endocardial ventricular electrogramsrecorded at the time of implantation was 8.8 mV duringnormal sinus rhythm. Subsequent follow-up was uneventfuluntil May of 2005 when he experienced sudden worseningof his heart failure. His dosage of lisinopril and furosemidewere increased and spironolactone was added to hismedical regimen. Several weeks later, he was admitted tothe hospital with repeated ICD shocks. The electrocardio-gram showed atrial fibrillation with a ventricular responseof 96 beats/min and a wide QRS complex with peaked Twaves (Fig. 1). Recordings from his ICD revealed 60shocks over a 3-h period associated with “triple counting”(twice during his QRS complex and once during the T wave(Fig. 2a). The ICD had been programmed as a two zonedevice with a ventricular tachycardia zone set at 375 msand a ventricular fibrillation zone set at 300 ms. Sensitivitywas programmed to 0.3 mV. His serum potassium was

J Interv Card Electrophysiol (2006) 17:153–155DOI 10.1007/s10840-006-9062-0

E. Khan :A. Voudouris : S. R. Shorofsky : R. W. PetersDivision of Cardiology, Department of Medicine,The University of Maryland School of Medicine,Baltimore, MD, USA

R. W. Peters (*)Division of Cardiology, 4D 129A,Department of Veterans Affairs Medical Center,10 North Greene Street, Baltimore, MD 21201, USAe-mail: robert.peters2@va.gov

7.6 meq/l and his serum creatinine was 7.6 mg/dl. Withemergent treatment of his hyperkalemia and improvementof his renal failure, his QRS complex and T wavesnormalized (Fig. 2b) and no further inappropriate ICDactivations were observed.

3 Discussion

Despite recent technological advances, inappropriate ICDdischarges remain a vexing problem which may occur in upto 25% of patients with ICD’s [1]. The potential etiologiesof inappropriate discharges are multiple and includemechanical problems (e.g. lead and/or insulation disrup-tion), sensing of extraneous “noise” such as electromagnet-ic interference or myopotentials, supraventriculararrhythmias, and double sensing of widened QRS com-plexes or prominent T waves [2].

As the indications for ICDs expand, and medical therapyof heart failure evolves, the population of patients withICD’s has gradually become older and sicker and presents awide array of complex medical problems. Hyperkalemiafrequently complicates heart failure in the setting of renalinsufficiency, especially with the concomitant use of ACEinhibitors and aldosterone antagonists [3]. Elevated potas-sium levels are a particular challenge in patients with ICDsbecause of the presence of QRS widening and prominent Twaves [4]. In the present report, we describe a situationin which ICD “triple counting” occurred. In this case,“triple counting” was due to double sensing of a widened

Fig. 2 Intracardiac electrogram recorded from the ICD duringhyperkalemia (panel a) and 3 days later following resolution of thehyperkalemia (panel b). In both panels, the toptrace is the rate sensingelectrogram whereas the bottomtrace is from RV coil to can. Notetriple counting (twice during the widened QRS complex and onceduring the T wave) during the hyperkalemia. Panel a was recorded bythe device during a “detected” event. R=ventricularly sensed event, F=fib interval, S=sinus interval and “Trigger” indicates a tachyarrhyth-mia was detected and charging begun. X indicates that the recordedelectrogram did not match a stored template. At the time panel b wasrecorded, the template had not yet been updated. In panel b, far field pwaves are denoted by the arrows indicating that the patient was insinus rhythm during this recording

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Fig. 1 A 12 lead electrocardio-gram recorded when the serumpotassium was 7.6 meq/l.Note the widened QRScomplex and peaked Twaves

154 J Interv Card Electrophysiol (2006) 17:153–155

QRS complex and subsequent sensing of prominent Twaves, leading to multiple inappropriate shocks. Prompttherapy was successful in lowering the patient’s serumpotassium concentration, precluding further inappropriateICD therapies.

A couple of other aspects regarding the ICD in ourpatient are deserving of comment. Starting with a sensed Rwave, the V-199 ICD has a sensitivity control feature(called “decay delay”) designed to prevent oversensing.This feature automatically decreases sensitivity by 3 mV/suntil the next R wave is sensed. An alternative approach toeliminate oversensing in our patient would have been toreprogram the ICD to a later onset of sensitivity decay thatsloped more gradually, allowing the T wave to fall belowthe sensing threshold. Decreasing sensitivity could con-ceivably cause undersensing, however, so that appropriatesensing during induced ventricular fibrillation would needto be verified.

When activated by a rapid ventricular arrhythmia, mostICD’s deliver a series of five or six shocks, after which theybecome quiescent, even if the arrhythmia does notterminate. If normal sinus rhythm is detected, the deviceresets and will deliver another shock or series of shocks ifventricular tachycardia is re-initiated. In our patient,distortion of the post-shock electrograms temporarily

eliminated oversensing, allowing the ICD to reset. Thedevice was then able to administer additional shocks as theelectrograms reverted to their pre-shock state with accom-panying oversensing. This same scenario was repeatedmultiple times, so our patient received a total of 60 shocks.

In summary, our case illustrates how the intracardiacelectrogram can be distorted by electrolyte abnormalitiesand how these alterations can lead to inappropriate ICDdischarges.

References

1. Weretka, S., Michaelson, J., Becker, R., Karle, C. A., Voss, F.,Hilbel, T., et al. (2003). Ventricular oversensing: A study of 101patients implanted with dual chamber defibrillators and twodifferent lead systems. PACE, 26, 65–70.

2. Washizuka, T., Chinushi, M., Kasai, H., Watanabe, H., Tagawa, M.,Hosaka, Y., et al. (2001). Inappropriate discharges from anintravenous implantable cardioverter defibrillator due to T-waveoversensing. Japanese Circulation Journal, 65, 685–687.

3. Kimmel, P. L. (2006). Update in nephrology and hypertension.Annals of Internal Medicine, 144, 281–285.

4. Koul, A. K., Keller, S., Clancy, J. F., Lampert, R., Batsford, W. P.,& Rosenfeld, L. E. (2004). Hyperkalemia induced T waveoversensing leading to loss of biventricular pacing and inappropri-ate ICD shocks. PACE, 27, 681–683.

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