Anteroposterior vs Anterolateral Shock Vectors for Atrial Fibrillation Cardioversion: Design and Rationale of the SHOCK-VECTOR Trial

Atrial fibrillation (AF) is increasing in prevalence and is associated with a burden of morbidity, mortality, and resource use. Maintaining sinus rhythm is associated with better survival and quality of life. Guidelines recommend electrical cardioversion to restore sinus rhythm, but evidence regarding electrode position and addition of manual pressure is inconclusive. A total of 1750 patients undergoing cardioversion of AF are to be randomised to anterolateral (AL) vs anteroposterior (AP) electrode placement, and to addition of manual pressure vs none on a second shock if the first is unsuccessful. All shocks are administered with biphasic maximal (≥ 200 J) energy. A third shock is allowed using any technique at the discretion of treating clinicians. The primary outcome is first shock success for AL vs AP. Secondary outcomes include success for manual pressure vs none and cumulative success for AL vs AP. Key subgroup analyses are based on sex, obesity, and left atrial size. Exploratory biophysical data, including electrical impedance, current and actual energy delivery, are collected. SHOCK-VECTOR is registered at clinicaltrials.gov (Anteroposterior vs Anterolateral Electrode Position for Electrical Cardioversion of Atrial Fibrillation; NCT05511389). Enrollment began in February 2023; 390 patients completed the study during the pilot phase. Expansion to other centres in Canada is ongoing. We have shown the feasibility of enrolling patients in a randomised trial to test electrode placement and manual pressure in patients with AF undergoing electrical cardioversion. This will be the first adequately powered study of this topic, permitting meaningful subgroup analyses.