Intramural Measurement of Transmembrane Potential in the Isolated Pig Heart: Validation of a Novel Technique

INTRODUCTION: Transmembrane potentials can be recorded at multiple intramural sites in the intact heart using fiber optic probes or optrodes. The technique has considerable potential utility for studies of arrhythmia and defibrillation, but has not been validated in large mammalian hearts. METHODS AND RESULTS: An optrode was used to acquire intramural transmembrane potentials in six isolated Langendorff-perfused pig hearts. Mechanical activity was suppressed with 2,3-butanedione monoxime (BDM). Excitation light (488 nm) was delivered to and fluorescence collected from six sites, each spaced 1.4 mm apart across the left ventricle (LV) free wall that was stained with di-4 ANEPPS. Intramural membrane potentials were compared with extracellular potentials recorded at adjacent locations in sinus rhythm, and during atrial and subepicardial ventricular pacing (1-3 Hz). In three hearts, epicardial intracellular potentials were also measured close to the optrode. Optical action potentials were reproducible, with no significant transmural variation in morphology. There was close correspondence between subepicardial optical and intracellular potentials (R2 = 0.948, n = 23). The onset of activation at and its progression across adjacent optical and extracellular recording sites were consistent, as was the variation of action potential duration (APD) with cycle length. However, there was greater variability in absolute APD estimated from optical and extracellular records (R2 = 0.773, n = 258). Comparison of extracellular potentials at the same intramural sites in vivo confirms that heart isolation and BDM slow electrical propagation and depress restitution relationships, but otherwise preserve intramural patterns of electrical activation. CONCLUSIONS: We have demonstrated that our optrode provides reliable intramural transmembrane potential recordings in the isolated pig heart preparation.