Letters
Cardiovascular diseases
Volume 196 - Issue 10

Inappropriate defibrillator shocks caused by oversensing of T-wave in hyperkalaemia

Authors:  Bo Xu, Howard Connor and Robert Ziffer

Med J Aust 2012; 196 (10): 626. || doi: 10.5694/mja12.10165
Published online: 4 June 2012
To the Editor: A 62-year-old woman was admitted on 10 January 2012 for cardiac monitoring after her implantable cardioverter-defibrillator (ICD) discharged four times over a few hours. She had a history of ventricular tachycardia due to ischaemic cardiomyopathy, and had had an ICD (D284DRG Maximo II DR, Medtronic, Minneapolis, Minn, USA) inserted 6 years earlier. Her ICD had ...
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To the Editor: A 62-year-old woman was admitted on 10 January 2012 for cardiac monitoring after her implantable cardioverter–defibrillator (ICD) discharged four times over a few hours. She had a history of ventricular tachycardia due to ischaemic cardiomyopathy, and had had an ICD (D284DRG Maximo II DR, Medtronic, Minneapolis, Minn, USA) inserted 6 years earlier. Her ICD had not previously discharged since insertion. Her medical history included hypertension and emphysema. Interrogation of the device revealed that during the defibrillator shocks, the patient was in sinus rhythm, and the ICD was double counting tall T-waves as R-waves (Box). She did not have ventricular tachycardia or fibrillation. The T-waves suggested underlying hyperkalaemia, and her serum potassium level was 6.2 mmol/L (reference interval, 3.5–5.0 mmol/L). It was discovered that, 1 month before presenting at our hospital, she had been started on potassium replacement therapy to treat a serum potassium level of 3.7 mmol/L, and had not undergone follow-up blood tests. We discontinued the patient’s potassium replacement therapy and treated her hyperkalaemia with oral potassium-binding resin. After correction of the hyperkalaemia, the patient’s T-wave morphology normalised, and there were no further inappropriate shocks.

We believe this is the first Australian report of inappropriate defibrillator shock caused by oversensing of T-wave in hyperkalaemia. There are only three other similar published cases in the literature.-3 As in this case, the oversensing of T-wave in the other cases was corrected by addressing the underlying cause of hyperkalaemia. Fortunately, the inappropriate shocks in our patient led to the discovery of hyperkalaemia. This case highlights the importance of regular monitoring of blood tests when starting a new medication. Use of an apparently innocent medicine such as oral potassium can lead to defibrillator shocks and serious complications. Patients’ medications should be reviewed and monitored regularly in this context.

Implantable cardioverter–defibrillator electrogram recordings demonstrating appropriate sensing of QRS-complexes and inappropriate double counting of tall T-waves in a patient with hyperkalaemia

FVT = fast ventricular tachycardia. CD = cardioversion delivered. Black arrows = QRS-complexes. Red arrows = tall T-waves. First dotted black arrow (recording A) = first treatment, when antitachycardia pacing was done. Second dotted black arrow (recording B) = second treatment, when CD occurred. Time scale: each square represents 0.2 seconds. Inappropriate double counting of tall T-waves in hyperkalaemia led to the ventricular rate being perceived as double the actual rate, leading to initial treatment of the perceived FVT with antitachycardia pacing. Inappropriate double counting of tall T-waves continued despite antitachycardia pacing, resulting in the treatment of the perceived FVT with CD.

Authors

  • Bo Xu1
  • Howard Connor2
  • Robert Ziffer2
  • 1. Cardiac Investigation Unit, St. Vincent’s Hospital, Melbourne, VIC.
  • 2. Central Gippsland Health Service, Sale, VIC.

Correspondence: bo.xu@svhm.org.au

Competing interests

No relevant disclosures.

References

View this article on Wiley Online Library

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