Inter-catheter impedance variation during internal atrial defibrillation

Abstract

Introduction: According to the European Society of Cardiology, atrial fibrillation (AF) has a prevalence of 1–2% in the general population, rising to over 5.5% in individuals over 55 years of age and accounts for in excess of 30% of all arrhythmia related hospital admissions. For chronic AF sufferers (where all other therapies have proved ineffective), restoration of sinus rhythm through electrical shock remains the treatment of choice. Internal atrial defibrillation thresholds as low as 1.27 joules have been reported. However, at low energies, complex electro-mechanical interac- tions at the catheter-tissue interface have long been suspected as a major source of variation in the amount of electrical energy required to terminate this arrhythmia. The objective of this work was to characterise the variation of inter-catheter impedance during internal atrial defibrillation.Methods: For this study, a custom low-power programmable impedance spectrometer was built to deliver a sinusoidal current of ± 200 μA in magnitude from 1–100 kHz in frequency. Using this system, the complex impedance between a pair of defibrillation electrode poles (placed in the distal coronary sinus and wall of the right atrium) was recorded between successive atrial defibrillation attempts.Results: A total of ten porcine models were investigated. Measurements detected inter-catheter impedance variations ranging from 15.5% to 28.9%. Subsequent data analysis revealed a mean inter-catheter impedance of 43.9 Ω with a variance of approximately 20.1% recorded.Conclusions: Complex electro-mechanical interactions at the catheter-tissue interface have been identified as a cause of significant variation in inter-catheter impedance; which alters the associated cardioversion threshold during internal atrial defibrillation. Further research will be required to fully understand and mitigate adverse effects of the physical mechanisms involved.