A new fabrication technique for directly coupled transmural cardiac electrodes

Many current attempts at electrophysiological elucidation of cardiac arrhythmia mechanisms have centered around activation sequence mapping. This is most commonly performed with polarized unipolar or bipolar metal electrodes, which, because of unstable direct current (DC) base-line potentials, necessitate alternating current (AC)-coupled amplification. An ideal nonpolarizable unipolar electrode offers unhindered exchange of charge allowing for stable DC recordings of biological electrical activity. In addition to activation information, DC unipolar recordings enable quantitation of systolic and diastolic potentials, other low-frequency phenomena of interest such as repolarization, as well as rapid recovery from such rapid extreme potential shifts such as defibrillation. Previous attempts to apply nonpolarizable electrodes to transmural cardiac investigations required complex wick electrode techniques to prevent mechanical movement of the fluid-metal interface when chlorided silver wire was used. We have developed a technique to fabricate miniature sintered Ag-AgCl electrodes that are mounted at various locations on a 20-gauge stainless steel needle permitting stable transmural DC unipolar electrogram recordings in vivo. The electrodes are low noise, rugged, sterilizable, and reusable and should prove useful in three-dimensional electrophysiological characterization of the heart.