Effects of electrode-myocardial separation on cardiac stimulation in conductive solution

Electrode-Myocardial Separation. Introduction: Effects of a conductive bath and electrode-myocardial separation on cardiac stimulation have not been elucidated. These factors may play a role in endocardial catheter stimulation or defibrillation. Methods and Results: We studied effects of a bath and separation on transmembrane voltage changes during stimulation (Delta Vm) and excitation thresholds in rabbit hearts, cultured rat cardiac cell monolayers, and cardiac bidomain computer models. Similar to previous epicardial measurements with no bath, a dogbone pattern of Delta Vm during stimulation was found in bathed epicardium and right ventricular septal endocardium and in models of bathed anisotropic myocardium, Electrode-myocardial separation altered spatial distributions of Delta Vm, moved reversals of the sign of Delta Vm farther from the stimulation epicenter, and decreased aspect ratio of Delta Vm (i.e., length/width of dogbone contours of Delta Vm). The separation increased thresholds and reduced maximal Delta Vm, while Delta Vm at sites away from maxima increased or decreased, Anodal thresholds in models initially were larger than those in experiments and decreased when models were altered to include nonuniform cellular coupling. Existence of nonuniformity in monolayers was indicated by irregular excitation patterns, Conclusion: Electrode-myocardial separation alters spatial distributions of Delta Vm, which may impact on arrhythmia induction by altering distributions of states of Vm-sensitive ion channels. The results also indicate that excitation thresholds may depend on tissue nonuniformities.