Authors

• Vedran Velagić — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0001-5425-5840
• Richard Matasić — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0003-1289-1704
• Mislav Puljević — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0003-1477-2581
• Borka Pezo-Nikolić — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0002-0504-5238
• Martina Lovrić Benčić — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0001-8446-6120
• Davor Puljević — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0003-3603-2242
• Davor Miličić — University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia — ORCID: 0000-0001-9101-1570

Keywords

implantable cardioverter defibrillator, ventricular tachycardia, inadequate shock

DOI

Full Text

**Introduction**: T wave “oversensing” is a relatively common phenomenon that can lead to inappropriate shocks in cardioverter-defibrillator (ICD) carriers. The most common cause of this phenomenon is the low R wave sensing amplitude, but hyperglycemia, hyperkalemia, Brugada syndrome, etc. could also be the culprit (1-3). Here, we present a case where the T wave oversensing occurred exclusively during monomorphic ventricular tachycardia. **Case report:** 53-years-old patient was admitted into the emergency room because of the ICD shock. The underlying condition was ischemic cardiomyopathy due to inferior myocardial infarction. Echocardiography revealed aneurysmal parts of inferior and posterior wall and moderately reduced systolic function of the left ventricle. Later on, during the disease course, the Holter monitoring detected sustained, monomorphic, hemodynamically stable ventricular tachycardia (VT) with the heart rate of 180/min. Therefore, single chamber ICD was implanted. The ICD follow-up revealed the same VT-s that were repeatedly successfully terminated by a single overdrive. All parameters of the ICD function were within normal limits. Patient received optimal medical therapy for heart failure and was in good functional status (NYHA class I-II). Antiarrhythmic therapy consisted of amiodarone and bisoprolol. Interrogation of the device revealed monomorphic VT, cycle length of 330-350 ms, which was adequately diagnosed in VT zone 1. Soon, T wave oversensing occurred, which produced a very short RR intervals of 120-180 ms. These intervals belong to the ventricular fibrillation zone that was too short for the anti-tachycardia pacing delivery which was previously always effective. In awake patient, DC shock delivery occurred, which successfully terminated the arrhythmia. In order to avoid further inappropriate shocks, sensing vector was changed in the ICD programming. In further follow-up there were no more inappropriate shocks. **Conclusion:** Monomorphic ventricular tachycardia can be interpreted as ventricular fibrillation by the ICD due to T wave oversensing which may be the cause of inadequate shock. This can be avoided by programming different sensing vector of the device. To our knowledge, this cause of inadequate ICD therapy has not been previously described.

Literature

1. Francis J. T Wave Oversensing. Indian Pacing Electrophysiol J. 2010;10(6):236–8. https://pubmed.ncbi.nlm.nih.gov/20552058/
2. Krishen A, Shepard RK, Leffler JA, Wood MA, Ellenbogen KA. Implantable cardioverter defibrillator T wave oversensing caused by hyperglycemia. Pacing Clin Electrophysiol. 2001;24(11):1701–3. https://doi.org/10.1046/j.1460-9592.2001.01701.x
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