Role of the Purkinje-Muscle Junction on the Ventricular Repolarization Heterogeneity in the Healthy and Ischemic Ovine Ventricular Myocardium

Abstract

Alteration of action potential duration (APD) heterogeneity contributes to arrhythmogenesis. Purkinje-muscle junctions (PMJs) present differential electrophysiological properties including longer APD. The goal of this study was to determine if Purkinje-related or myocardial focal activation modulates ventricular repolarization differentially in healthy and ischemic myocardium. Simultaneous epicardial (EPI) and endocardial (ENDO) optical mapping was performed on sheep left ventricular (LV) wedges with intact free-running Purkinje network (N = 7). Preparations were paced on either ENDO or EPI surfaces, or the free-running Purkinje fibers (PFs), mimicking normal activation. EPI and ENDO APDs were assessed for each pacing configuration, before and after (7 min) of the onset of no-flow ischemia. Experiments were supported by simulations. In control conditions, maximal APD was found at endocardial PMJ sites. We observed a significant transmural APD gradient for PF pacing with PMJ APD = 347 ± 41 ms and EPI APD = 273 ± 36 ms (p < 0.001). A similar transmural gradient was observed when pacing ENDO (49 ± 31 ms; p = 0.005). However, the gradient was reduced when pacing EPI (37 ± 20 ms; p = 0.005). Global dispersion of repolarization was the most pronounced for EPI pacing. In ischemia, both ENDO and EPI APD were reduced (p = 0.005) and the transmural APD gradient (109 ± 55 ms) was increased when pacing ENDO compared to control condition or when pacing EPI (p < 0.05). APD maxima remained localized at functional PMJs during ischemia. Local repolarization dispersion was significantly higher at the PMJ than at other sites. The results were consistent with simulations. We found that the activation sequence modulates repolarization heterogeneity in the ischemic sheep LV. PMJs remain active following ischemia and exert significant influence on local repolarization patterns.

Mechanical stimulation of endocardial Purkinje fibres can trigger ventricular arrhythmias

“…The activation map given in Fig. 4D in response to mechanical stimulation of a PF shows a broad activation pattern, consistent with rapid conduction through an extended portion of the distal Purkinje network (Martinez et al, 2018) and electrical stimulation of the same PF gave a similar activation pattern (Suppl. Fig.…”

“…Sheep studies were carried out as previously described (Martinez et al, 2018) and in accordance with the recommendations of the Directive 2010/63/EU of the European Parliament on the protection of animals used for scientific purposes and the local ethical committee of Bordeaux CEEA50. Hearts were obtained from female adult sheep (N = 4; 42-55kg).…”

“…The electrodes were insulated by a 3μm kapton sheath (electrode OD 0.356mm) exposing a tip of length 5mm and tip diameter of 1-2μm (World Precision instruments, ref TM33B20KT). They were placed either in the endocardial surface, or in a chosen PF (Martinez et al, 2018). Preparations were stimulated at 0.5Hz with 5ms pulses which were increased in amplitude until regular capture was achieved.…”

Gap Junctional Communication via Connexin43 between Purkinje Fibers and Working Myocytes Explains the Epicardial Activation Pattern in the Postnatal Mouse Left Ventricle

“…On the other hand, during development small amounts of Cx40 are present also in the compact myocardium [ 36 , 37 ], making Cx40 Purkinje-myocyte coupling a possibility during the embryonic and early postnatal stages. These junctions, as well as PFs in general, can be a source of arrhythmias [ 38 , 39 ].…”

“…Epicardial optical mapping shows apex-to-base activation with the first activated regions located near ventricular apices [ 37 , 40 , 41 ], corresponding to bundle branches’ terminations. Transmural activation is clearly dependent on intramural PFs in the hearts where those are present, e.g., in Ungulates [ 38 ]. However, neither the human, nor the mouse has intramural PFs [ 42 ], and little hard data is available on the actual nature of physiological propagation of the transmural activation wave [ 43 , 44 , 45 , 46 ].…”