Predictors of Transthoracic Impedance in Patients Who Underwent Elective Electrical Cardioversion

Abstract

Successful synchronized direct current cardioversion (DCCV) requires adequate current delivery to the heart. However, adequate current for successful DCCV is not yet established. Trans-myocardial current depends on two factors: input energy and transthoracic impedance (TTI). While factors affecting TTI have been studied in animal models, factors affecting TTI in humans have not been well established. Here we explored the potential factors that affect TTI in humans. Retrospective review of patients undergoing DCCV at a large quaternary medical center between October 2019 and August 2021 was conducted. Pertinent clinical information, including demographics, echocardiography findings, laboratory findings and body characteristics were collected. Cardioversion details including joules delivered and TTI were recorded by the defibrillator for each patient's first shock. Predictors of thoracic impedance were assessed using regression analysis. A total of 220 patients (29% female) were included in the analysis. 143 (65%) of the patients underwent DCCV for atrial fibrillation, 77 (35%) underwent DCCV for atrial flutter. Mean impedance in our population was 73 ± 18 ohms. In a regression model with high impedance defined as the upper quartile of our cohort, BMI, female sex, obstructive sleep apnea and chronic kidney disease (All p values <0.05) were significantly associated with high impedance. According to an ROC analysis, BMI has a high predictive value for high impedance, with an AUC of 0.76. In conclusion, our study reveals that elevated BMI, female sex, sleep apnea and chronic kidney disease were predictors of higher TTI. These factors may help in determining the appropriate initial shocking energy in patients undergoing DCCV for atrial fibrillation and flutter.