Optical measurements of intramural action potentials in isolated porcine hearts using optrodes

BACKGROUND Measurements of intramural membrane potential (V-m) would greatly increase knowledge of cardiac arrhythmias and defibrillation. Optrodes offer the possibility for three-dimensional V-m mapping, but their signal quality has been inadequate. OBJECTIVE The purpose of this work was to improve optrode signal quality and use optrodes to measure intramural distribution of action potentials and shock-induced V-m changes in porcine hearts. METHODS Optrodes were made from seven optical fibers 225 or 325 mu m in diameter. Fiber ends were polished at a 45 degrees angle, which improved Light collection and allowed their insertion without a needle. Fluorescent measurements were performed in isolated porcine hearts perfused with Tyrode's solution or blood using V-m-sensitive dye RH-237 and a 200-W Hg/Xe Lamp. RESULTS The signal-to-noise ratio for 325-mu m fibers was 44 +/- 23 in blood-perfused hearts (n = 5) and 106 +/- 45 in Tyrode's-perfused hearts (n = 3), which represents an approximately four-fold improvement over previously reported data. There was close correspondence between optical and electrical measuremerits of activation times and action potential duration (APD). No significant intramural APD gradients were observed at cycle Lengths up to 4 s and in the presence of dofetilide or d-sotalol. Application of shocks (5-50 V/cm) produced large intramural V. changes (up to approximate to 200% action potential amplitude), possibly reflecting a combined effect of tissue discontinuities and optrode geometry. CONCLUSIONS A substantial improvement of optrode signal quality was achieved. Optical measurements of APD and activation times matched electrical measurements. Optrode measurements revealed no significant intramural APD gradients. Application of shocks caused Large intramural V-m changes that could be influenced by the optrode geometry.