Intramural multisite recording of transmembrane potential in the heart

Heart surface optical mapping of transmembrane potentials has been widely u sed in studies of normal and pathological heart rhythms and defibrillation. In these studies, three-dimensional spatio-temporal events can only be inf erred from two-dimensional surface potential maps. We present a novel optic al system that enables high fidelity transmural recording of transmembrane potentials. A probe constructed from optical fibers Is used to deliver exci tation light and collect fluorescence from seven positions, each 1 mm apart , through the left ventricle wall of the rabbit heart. Excitation Is provid ed by the 488-nm line of a water-cooled argon-ion laser. The fluorescence o f the voltage-sensitive dye di-4-ANEPPS from each tissue site is split at 6 00 nm and imaged onto separate photodiodes for later signal ratioing. The o ptics and electronics are easily expandable to accommodate multiple optical probes. The system is used to record the first simultaneous measurements o f transmembrane potential at a number of sites through the intact heart wal l.