In vivo ratiometric optical mapping enables high-resolution cardiac electrophysiology in pig models

Abstract

Aims Cardiac optical mapping is the gold standard for measuring complex electrophysiology in ex vivo heart preparations. However, new methods for optical mapping in vivo have been elusive. We aimed at developing and validating an experimental method for performing in vivo cardiac optical mapping in pig models. Methods and results First, we characterized ex vivo the excitation-ratiometric properties during pacing and ventricular fibrillation (VF) of two near-infrared voltage-sensitive dyes (di-4-ANBDQBS/di-4-ANEQ(F)PTEA) optimized for imaging blood-perfused tissue (n = 7). Then, optical-fibre recordings in Langendorff-perfused hearts demonstrated that ratiometry permits the recording of optical action potentials (APs) with minimal motion artefacts during contraction (n = 7). Ratiometric optical mapping ex vivo also showed that optical AP duration (APD) and conduction velocity (CV) measurements can be accurately obtained to test drug effects. Secondly, we developed a percutaneous dye-loading protocol in vivo to perform high-resolution ratiometric optical mapping of VF dynamics (motion minimal) using a high-speed camera system positioned above the epicardial surface of the exposed heart (n = 11). During pacing (motion substantial) we recorded ratiometric optical signals and activation via a 2D fibre array in contact with the epicardial surface (n = 7). Optical APs in vivo under general anaesthesia showed significantly faster CV [120 (63–138) cm/s vs. 51 (41–64) cm/s; P = 0.032] and a statistical trend to longer APD90 [242 (217–254) ms vs. 192 (182–233) ms; P = 0.095] compared with ex vivo measurements in the contracting heart. The average rate of signal-to-noise ratio (SNR) decay of di-4-ANEQ(F)PTEA in vivo was 0.0671 ± 0.0090 min−1. However, reloading with di-4-ANEQ(F)PTEA fully recovered the initial SNR. Finally, toxicity studies (n = 12) showed that coronary dye injection did not generate systemic nor cardiac damage, although di-4-ANBDQBS injection induced transient hypotension, which was not observed with di-4-ANEQ(F)PTEA. Conclusions In vivo optical mapping using voltage ratiometry of near-infrared dyes enables high-resolution cardiac electrophysiology in translational pig models.

High-Resolution Optical Measurement of Cardiac Restitution, Contraction, and Fibrillation Dynamics in Beating vs. Blebbistatin-Uncoupled Isolated Rabbit Hearts

“…(N = 5) pig hearts ex vivo comparing hearts pre-and post-Blebbistatin (concentration unknown). The findings by Brack et al (2013) and Lee et al (2019) are in agreement with our study. Fedorov et al (2007) reported that Blebbistatin does not have any effect onto electrical activity.…”

“…Moreover, we found that, in agreement with the shorter APD, VF dynamics are faster and more complex in contracting rabbit hearts. Our findings confirm previous findings by Brack et al (2013) and Lee et al (2019), who found that ventricular electrophysiology is significantly different in beating vs. contraction-inhibited isolated rabbit and pig hearts uncoupled with Blebbistatin, respectively. More specifically, Brack et al (2013) found that Blebbistatin substantially prolonges (∼ 17 − 25%) the ventricular action potential in isolated New Zealand White rabbit hearts (N = 39), and increases the ventricular fibrillation threshold, or reduces the likeliness of inducing VF, at a concentration of 5µM.…”

“…Our study confirms the findings both directly and indirectly and we found that VF appears to be less aggressive and decelerated in uncoupled hearts, which could in principle explain higher VF thresholds. More recently, Lee et al (2019) reported a substantial prolongation of the ventricular action potential (∼ 15%), as well as a substantial decrease of the conduction velocity (∼ 25%) in Overall, the findings regarding APD difference ( APD) with and without Blebbistatin remain inconclusive and seem to depend on preparations and species.…”

Minimally invasive system to reliably characterize ventricular electrophysiology from living donors

“…Here we show that AP duration and morphology are comparable in slices from transmural core biopsies and tissue blocks from the same pig ventricular regions. Median APD values (117 ms and 111 ms in the biopsy and block slices, respectively) are slightly lower than previously published values in experimental works on multicellular preparations [40][41][42][43][44] , which could be explained by the fact that our pig samples come from www.nature.com/scientificreports/ piglets and young pigs. Indeed, in our APD measures we could observe a trend to shorter APD in those from piglets as compared to those from adult pigs.…”

Cardiac Optical Mapping in Situ in Swine Models: A View of the Current Situation

“…Ratiometry of Cardiogreen optical signals is difficult to achieve as they contain fast and slow components and their characteristics depend on the excitation/emission wavelengths [16,17]. The use of an optical-fibre array (4 × 4) allows the electrical activity of the heart to be recorded in vivo under physiological blood circulation [3]. However, in large animals or humans, the main disadvantage of this method is the small mapping area, which does not permit high-spatial-resolution mapping.…”