Inappropriate Shocks due to Chattering of the Leads from Cardiac Contractility Modulation Device and a Defibrillation Lead

Aim: Optimizer is an investigational device based on the concept of Cardiac contractility modulation (CCM). It sends strong electrical signals during the absolute refractory period. These non-excitatory electric signals increase the influx of calcium ions into the cardiomyocytes resulting in enhanced cardiac contractility. It is designed to work in parallel with all cardiac devices. We would like to present a patient who suffered inappropriate implantable cardioverter defibrillators (ICD) shocks due to lead chattering between the Optimizer leads and an ICD lead.

Methods and Results: 72-year-old male with ischemic cardiomyopathy status-post ICD and Optimizer device was evaluated as a routine follow-up. His Optimizer device had three leads--one lead in right atrium and two leads in right ventricle. Single-coil defibrillator lead in right ventricle showed high impedance and alert warning. The ICD lead was exchanged successfully. All the device parameters were within normal limit before patient was discharged home.
Two weeks later, the patient presented with multiple ICD shocks. Interrogation of the ICD showed intermittent, repetitive noises which were sensed as ventricular fibrillation and treated. The noise signals were not high frequency repetition as in electromagnetic interference. Lead failure was unlikely since all parameters including lead impedance of the ICD lead were normal.
Fluoroscopic evaluation confirmed the leads were intermittently chattering inside the right ventricle. This was considered to be the cause of inappropriate sensing of the ICD lead. After much discussion, the Optimizer system including all the leads was removed. There was no more noise signal detected by ICD and no more inappropriate defibrillations.

Conclusions: Most common causes of abnormal sensing and inappropriate therapy in cardiac implantable devices are electromagnetic interference and lead failure. However, we should be aware that mechanical interactions including intra-cardiac lead chattering can cause considerable interference leading to inappropriate therapies.