Evaluation of Excitation Propagation in the Rabbit Heart: Optical Mapping and Transmural Microelectrode Recordings

Abstract

BackgroundBecause of the optical features of heart tissue, optical and electrical action potentials are only moderately associated, especially when near-infrared dyes are used in optical mapping (OM) studies.ObjectiveBy simultaneously recording transmural electrical action potentials (APs) and optical action potentials (OAPs), we aimed to evaluate the contributions of both electrical and optical influences to the shape of the OAP upstroke.Methods and ResultsA standard glass microelectrode and OM, using an near-infrared fluorescent dye (di-4-ANBDQBS), were used to simultaneously record transmural APs and OAPs in a Langendorff-perfused rabbit heart during atrial, endocardial, and epicardial pacing. The actual profile of the transmural AP upstroke across the LV wall, together with the OAP upstroke, allowed for calculations of the probing-depth constant (k ~2.1 mm, n = 24) of the fluorescence measurements. In addition, the transmural AP recordings aided the quantitative evaluation of the influences of depth-weighted and lateral-scattering components on the OAP upstroke. These components correspond to the components of the propagating electrical wave that are transmural and parallel to the epicardium. The calculated mean values for the depth-weighted and lateral-scattering components, whose sum comprises the OAP upstroke, were (in ms) 10.18 ± 0.62 and 0.0 ± 0.56 for atrial stimulation, 9.37 ± 1.12 and 3.01 ± 1.30 for endocardial stimulation, and 6.09 ± 0.79 and 8.16 ± 0.98 for epicardial stimulation; (n = 8 for each). For this dye, 90% of the collected fluorescence originated up to 4.83 ± 0.18 mm (n = 24) from the epicardium.ConclusionsThe co-registration of OM and transmural microelectrode APs enabled the probing depth of fluorescence measurements to be calculated and the OAP upstroke to be divided into two components (depth-weighted and lateral-scattering), and it also allowed the relative strengths of their effects on the shape of the OAP upstroke to be evaluated.

Voltage-Sensitive Fluorescence of Indocyanine Green in the Heart

“…The techniques and procedures used for the simultaneous measurement of fluorescence and electrical signals from whole-heart preparations have been described previously (6,7). In brief, experiments were performed on rabbits (New Zealand White) weighing 3.9 5 0.2 kg (n ¼ 12).…”

Effect of Carvacrol, TRP Channels Modulator, on Cardiac Electrical Activity

“…After observing that CAR decreased electrical signal conduction, in our next step, we extended our studies to evaluate possible changes in various AP parameters under stimulation originating from different locations. We have previously demonstrated that when pacing was initiated via the atrial, endocardial, and epicardial surfaces, the spread of electrical activity varied, creating different situations in the myocardium [19]. Atrial pacing allows evaluation of the spread of electrical activity via the atrioventricular (AV) node.…”

“…Heart. New Zealand white rabbits (n = 9) of either sex (~3 kg) were used, and the methods have been detailed previously [19]. Briefly, after intraperitoneal injection of xylazine (10 mg/kg) and heparin (1000 U/kg), intravenous injection of ketamine (10 mg/kg) was performed.…”

“…Microelectrode Recordings. Electrical APs were recorded using glass microelectrodes (filled with 3 M KCl) with long tips (resistance~30-50 MΩ), which were inserted in the LV wall from the epicardial surface [19]. The recorded APs were amplified and digitized by the 16-channel PowerLab system (ADInstruments, Oxford, UK) at a frequency of 20 kHz.…”

“…Optical Recordings. The optical mapping setup was as described previously [19]. Briefly, an NIR VSD, di-4-ANBDQBS, was used to record electrical signals from the heart.…”