Fig. 3: Schematic of injectable hydrogel system to transform coronary veins into flexible electrodes that capture inaccessible cardiac tissue.

A Hydrogel precursors solutions are delivered using a dual lumen catheter to fill coronary veins and tributaries that span the myocardium near the scarred tissue. Upon mixing of the two hydrogel solutions in the coronary veins, redox-initiated crosslinking results in rapid cure of the ionic hydrogel. B Subsequent connection to a pacemaker lead to the ionic hydrogel electrode provides increased tissue contact across the myocardium. C Wavefront activation of the myocardium along the hydrogel electrode reduces the energy required for defibrillation. D Lead I of surface ECG showing electrical activation at baseline (sinus rhythm) and when paced. Peak of the baseline QRS morphology was matched with the peak of QRS morphology obtained from pacing with hydrogel in AIV (Top, left to right) Baseline: Activation during sinus rhythm starts from the sinoatrial node and travels through the atrioventricular node into the Purkinje fibers in the ventricles. Pacing the myocardium directly causes the QRS morphology to invert indicative of deviation from normal conduction. Point pacing with metal electrode and hydrogel point creates a dog-bone shaped activation that radiates outward from the source of the electrical stimulus. Hydrogel line pacing also created an inverted QRS morphology which indicates direct myocardial activation. Pacing from hydrogel in the AIV displayed clear capture with a QRS morphology existing after every pacing spike. No observed inversion of the QRS morphology and a short isoelectric window before initial activation indicates possible capture of the deep septal bundle branches and Purkinje fibers (inset). Source data are provided as a Source Data file.