Implantable cardioverter defibrillator T wave oversensing caused by hyperglycemia

Care of the pacemaker/implantable cardioverter defibrillator patient in the ED

As the population ages and the prevalence of cardiovascular disease increases, patients with pacemakers and implantable cardioverter defibrillators (ICDs) more commonly present to the emergency department. These patients can have complex medical issues related to and independent of their pacemaker/ICD that require careful management by the emergency physician. This article will review the major diagnostic and therapeutic considerations in the emergency care of patients with pacemakers and ICDs.

[Progression of heart failure during cardiac resynchronization therapy: what is the cause?]

A 74 year old patient with cardiac resynchronization therapy (CRT) since 12 months presents with cardiac decompensation and dyspnea NYHA III-IV after improvement of cardiac symptoms for 9 months. Her history is remarkable for left ventricular hypertrophy, aortic valve replacement 14 years earlier, a left ventricular ejection fraction of 35-40%, and permanent third degree AV block. The 12 lead standard ECG reveals the cause of cardiac deterioration which is confirmed by telemetry. This case demonstrates the importance of optimized programming of CRT systems which differs from conventional programming of dual-chamber devices in some aspects.

[Avoidance of intermittent T-wave oversensing with device programming]

We report the case of a 35-year-old man who was suffering from severe heart failure due to cardiomyopathy. He underwent heart transplantation years ago and developed complex ventricular arrhythmias in the following months in combination with recurrent episodes of syncope due to hypertrophic non-obstructive cardiomyopathy in the transplanted heart, so a dual chamber ICD was implanted. Months later repetitive episodes of intermittent T-wave oversensing with consecutive activation of the ICD could be observed. Surgical revision of the electrode was performed and the patient was closely followed up. One year later, further episodes of T-wave oversensing led to multiple inappropriate IDC-shocks. A very short AV-conduction time was programmed to allow ventricular capture whenever possible, because T-wave oversense after ventricular capture would be annotated as single ventricular ectopy not resulting in antitachycardia pacing. As a consequence, the patient was free from inappropriate ICD-shocks, but showed several shorter episodes of T-wave oversensing. They were all initiated by atrial activity that was seen in the refractory period, thus leading to a loss of AV synchrony. Programming a very short post ventricular atrial refractory period (PVARP) in addition to a short AV-delay led to the complete disappearance of T-wave oversensing in this patient. During a 9-month follow-up, no further tachycardia episodes were detected by the device.

T-Wave Oversensing by an Implantable Cardioverter Defibrillator after Successful Ablation of Idiopathic Ventricular Fibrillation

Focal ablation of trigger premature ventricular complexes (PVCs) from the Purkinje system helped to suppress idiopathic ventricular fibrillation (VF) in an athlete who had suffered from frequent appropriate shock therapies. However, only a few days after successful ablation T-wave oversensing occurred during exercise and resulted in repetitive distressing defibrillator shocks. Despite lack of any changes on the surface ECG, the endocardially recorded electrogram revealed an unfavorable ratio of R-to-T-wave amplitude predisposing to double counting with accelerated heart rates. This case illustrates that T-wave oversensing may complicate the clinical course after successful ablation of malignant Purkinje ectopy.

Inappropriate ICD discharge due to T-wave oversensing in a patient with the brugada syndrome

Accurate sensing is an essential requirement for appropriate functioning of implantable cardioverter-defibrillator (ICD). T-wave oversensing remains as an annoying problem in currently available ICD. The Brugada syndrome with its inherent dynamic variations in electrophysiologic phenomena may complicate ICD therapy. We report a patient with diagnosis of Brugada syndrome who presented with frequent inappropriate therapy due to intermittent T-wave oversensing. This problem could not be eliminated by device reprogramming and necessitated implantation of a new sense/pace lead.