Inappropriate shocks diagnosed by stored electrograms of implantable cardioverter defibrillators--two case reports

Fracture of the Subcutaneous Patch Electrode in a Patient With an Implanted Cardioverter-Defibrillator

There are more than 20 years of experience with implantation of defibrillator devices in humans and the procedure is an important therapeutic option for patients at high risk of life-threatening ventricular arrhythmias. The incidence of new defibrillator implantation has gradually increased, being used even in children, (1) although pediatric use is associated with several complications, especially with epicardial systems,(2) including fracture of the subcutaneous patch,(3-5) mainly because of growth.(3) We present a case of subcutaneous patch electrode fracture in the left axillary pectoral region of a patient who needed the patch for effective defibrillation, and we discuss the methods of treatment.

New-generation lithotripters for treatment of patients with implantable cardioverter defibrillator: experimental approach and review of literature

PURPOSE

The influence of shockwaves applied during extracorporeal shockwave lithotripsy on the function of implantable cardioverter defibrillators was evaluated. Mechanical influences as well as proper electrical function were tested in an experimental approach.

MATERIALS AND METHODS

Two implantable defibrillators (Ventak Mini 1743 and AVII 1821) were exposed to the shockwaves of a new-generation lithotripter. Each of the antidysrhythmic devices was tested at several distances from and within the focus of the lithotripter. All studies were performed with maximum energy and the number of shockwaves used for stone treatment. The devices were connected to an ECG simulator, and continuous recording of a surface ECG, a shock ECG, and marker channel was performed.

RESULTS

No macroscopic and microscopic mechanical damage was observed. The detection function of the implantable defibrillators was not altered by any electromagnetic artifacts even when brought into the focus of the shockwaves. All induced ventricular dysrhythmias were terminated properly regarding artifact sensing. However, after defibrillation, the pacing function of the Ventak Mini cardioverter defibrillator, which was programmed into the demand mode, failed. In this case, there was no post-shock pacing in the period of post-defibrillation asystole. The failure was caused by artifact oversensing.

CONCLUSION

In patients with implanted cardiac devices undergoing treatment with a new-generation lithotripter, deactivation of the defibrillator is not mandatory. For safety reasons, continuous ECG recording is recommended. To avoid pacing failure by artifact oversensing, the shockwaves should be applied in a R-wave synchronous mode.