Maps of optical action potentials and NADH fluorescence in intact working hearts

Abstract

Voltage-sensitive dyes were used to stain intact perfused hearts and to simultaneously measure optical action potentials (APs) from 124 sites on the epicardium. Patterns of electrical depolarization (activation) and repolarization (recovery) along the surface of the heart were determined from the upstrokes and repolarization phases of optical APs. Standard surface extracellular techniques can detect electrical activation but not the recovery or the duration of APs. The optical recordings were previously shown to be equivalent to intracellular electrode measurements (Salama and Morad, Science Wash. DC 191: 485-487, 1976) and now reveal that AP durations are heterogeneous throughout the epicardium, with durations increasing from the base to the apex of the ventricles. In hearts beating under normal sinus rhythm, the direction and conduction velocity of the activation waves could be altered by electrical stimulation. The normal heterogeneities in AP durations became more pronounced in the presence of the Ca2+-entry blocker, verapamil. The local metabolic state of the tissue was also monitored optically through its intrinsic NADH fluorescence measured from 124 separate regions on the heart. The time course and extent of metabolic injury caused by general anoxia or by a local ischemia induced by a coronary ligation was monitored through maps of NADH fluorescence. The present technique makes it possible to correlate changes in the metabolic state of the muscle with detailed changes in patterns of electrical activity and thus provides a powerful new tool to study fundamental aspects of normal and abnormal cardiac rhythm.

The Future of Optical Mapping is Bright

“…Optical imaging of voltage and calcium in the heart, which we pioneered 2 decades ago, [1][2][3] is indeed an important and increasingly more valuable technique in the investigation of arrhythmia mechanisms, and we concur that significant advances in the field justify a review of recent progress. In their recent review of the topic, Herron et al tackle a presentation of the essential components that are necessary to build state-of-the-arts optical mapping instruments.…”

Effects of mechanical uncouplers, diacetyl monoxime, and cytochalasin-D on the electrophysiology of perfused mouse hearts

“…However, muscle contractions produce movement artifacts that can distort optical signals, raising concerns regarding their validity, particularly of the recovery phase of APs and [Ca 2ϩ ] i transients. Mechanical immobilization of the heart has been extensively used to abate movement artifacts relative to the voltage-dependent component of the optical signal (18,37 (5,14) Unfortunately, these uncouplers are far from ideal and are found to alter the myocardial substrate through changes intracellular Ca 2ϩ handling, ion channels, and AP characteristics in a species-dependent manner.…”

Optical mapping of repolarization and refractoriness from intact hearts.

“…10 The perfusion chamber containing the Langendorff-perfused heart was mounted on a micromanipulator and positioned along the optical axis of a photodiode array scanning apparatus. Light from two 45-W tungstenhalogen lamps was collimated, passed through a 520±20-nm interference filter, reflected off a 450 dichroic mirror, and focused on the left epicardium of the heart with a 35-mm camera lens (50 mm, f 1:1.4, Nikon).…”

“…10 In preliminary reports, we described signal processing techniques to uniquely identify the repolarization time points of fluorescence (F) APs through (d2F/dt2)max of their downstroke. "1 The algorithm was effective to measure repolarization time points even in optical AP recordings containing substantial distortions caused by movement artifacts.…”