Towards prevention of re-entrant arrhythmias: Injectable hydrogel electrodes enable direct capture of previously inaccessible cardiac tissue

Re-entrant arrhythmias—the leading cause of sudden cardiac death—are caused by diseased myocardial tissue and consequent delayed myocardial conduction. Access to the coronary veins that cross the “culprit” scar regions where re-entry originates can provide improved pacing to these delayed regions, offering a novel opportunity to prevent ventricular arrhythmias and circumvent the need for painful defibrillation, risky cardiac ablation, or toxic and often ineffective antiarrhythmic medications. However, there are no pacing electrodes which are small or focal enough to navigate these tributaries. To address this need, we have developed an injectable conductive hydrogel that can fill the epicardial coronary veins and their mid-myocardial tributaries. When connected to a standard pacing lead, these injected hydrogels can be converted into flexible electrodes that directly pace the previously inaccessible mid-myocardial tissue. In our two-component system, hydrogel precursor solutions can be injected through a dual lumen catheter in a minimally invasive deployment strategy to provide direct access to the diseased regions with precision and ease. Mixing of the two solutions upon injection into the vein activates redox-initiated crosslinking of the gel for rapid in situ cure without an external stimulus. An ex vivo porcine model was used to identify the requisite viscosity and cure rate for gel retention and homogeneity. Ionic species added to the hydrogel precursor solutions conferred conductivity above target myocardium values that was retained after implantation. Successful in vivo deployment demonstrated that the hydrogel electrode filled the anterior interventricular vein with extension into the septal (mid-myocardial) venous tributaries to depths far more distal and refined than any current technologies allow. In addition to successful capture and pacing of the heart, analysis of surface ECG tracings revealed a novel pacing observation highly specific for and suggestive of capture of extensive swaths of septal myocardial tissue. This is the first report of an injectable electrode used to successfully pace the mid-myocardium and mimic physiologic conduction. Furthermore, in vivo cardiac electroanatomical mapping studies in an ablation scar model showed uniform capture along the hydrogel in the vessels as well as increased capture area compared to point pacing. Collectively, these findings demonstrate that this injectable hydrogel electrode can be deployed to scarred regions of the heart to provide a reliable pacing modality that most closely resembles native conduction with the potential to eliminate delayed myocardial conduction and associated re-entry. ![Figure][1] One Sentence Summary Injectable hydrogel electrodes achieve pacing that mimics physiologic conduction by capturing midmyocardial tissue ### Competing Interest Statement The authors have filed a provisional patent titled: Electrically conductive hydrogels usable as pacemaker lead extensions, apparatus for delivery of a hydrogel into the venous system, and methods of treating ventricular arrhythmia with electrically conductive hydrogels injected in the venous system. MR, AP, ECH are involved in Rhythio Medical which seeks to commercialize the hydrogel electrodes. [1]: pending:yes