Spiral Waves and Reentry Dynamics in an In Vitro Model of the Healed Infarct Border Zone

Abstract

Rationale Reentry underlies most ventricular tachycardias (VT) seen post-myocardial infarction (MI). Mapping studies reveal that the majority of VTs late post-MI arise from the infarct border-zone (IBZ). Objective To investigate reentry dynamics and the role of individual ion channels on reentry in in vitro models of the healed IBZ. Methods and Results We designed in vitro models of the healed IBZ by co-culturing skeletal myotubes (SkM) with neonatal rat ventricular myocytes (NRVMs) and performed optical mapping at high temporal and spatial resolution. In culture, NRVMs mature to form striated myocytes and electrically uncoupled SkMs simulate fibrosis seen in the healed IBZ. High resolution mapping revealed that SkMs produced localized slowing of conduction velocity (CV), increased dispersion of CV and directional-dependence of activation delay without affecting myocyte excitability. Reentry was easily induced by rapid pacing in co-cultures; treatment with lidocaine, a Na+ channel blocker, significantly decreased reentry rate and CV, increased reentry pathlength and terminated 30% of reentrant arrhythmias (n=18). In contrast, nitrendipine, an L-type Ca2+ channel (LTCC) blocker terminated 100% of reentry episodes while increasing reentry cycle length and pathlength and decreasing reentry CV (n=16). K+ channel blockers increased reentry APD, but infrequently terminated reentry (n=12). Conclusions Co-cultures reproduce several architectural and EP features of the healed IBZ. Reentry termination by LTCC, but not Na+ channel blockers suggests a greater Ca2+-dependence of propagation. These results may help explain the low efficacy of pure Na+ channel blockers in preventing and terminating clinical VTs late after MI.

Antiarrhythmic Potential of Mesenchymal Stem Cell Is Modulated by Hypoxic Environment

“…Hypoxic PM modulates Ca 2؉ -regulatory ion channels and proteins. Alteration of Ca 2ϩ -regulatory ion channels and proteins in the border zone contribute to triggering easily focal activity and may affect electrical conduction (16,17). We observed a marked decrease in messenger ribonucleic acid (mRNA) levels of L-type calcium channel (LTCC), sarcoplasmic/endoplasmic reticulum calcium adenosine triphosphatase 2a, Na ϩ /K ϩ adenosine triphosphatase, and the calcium-binding proteins, calreticulin and calmodulin in the border zone, which was significantly restored in hypoxic PM-treated area and moderately in normoxic PM-treated area (Fig.…”

A novel, minimally invasive, segmental myocardial infarction with a clear healed infarct borderzone in rabbits

“…understanding of post-MI arrhythmias, we believe that these previous reports may have been limited in their insight into borderzone dynamics due to pericardial adhesions and fibrosis in the borderzone after the pericardium was opened during the coronary ligation procedure. Furthermore, while the role of individual ion channels in formation of arrhythmias has been studied (14,32,48) effects of manipulation of individual currents has been limited as a result of the lack of a transgenic infarct model (8). We suggest that use of a reproducible closed-chest model MI in the rabbit, with available transgenically modified repolarization currents (3), may significantly enhance the investigator's ability to image and thus study the important peri-infarct zone in a model that allows for manipulation of repolarization currents.…”

Optical Mapping: Its Impact on Understanding Arrhythmia Mechanisms

“…Cultured rat neonate myocytes have been extensively studied in patterned cell growth in strands [11], monolayers [12] with controlled fiber orientations [13] and in co-cultures with fibroblasts [14] and skeletal myotubes [ 15] as surrogates of fibrosis. Contact fluorescence imaging systems were developed to record optical action potentials (APs) from confluent monolayers of rat neonate myocytes by placing the recording chamber directly above a hexagonal (17 mm) bundle of light guide fibers.…”

“…Each light guide was directly coupled to a photodiode to record action potentials from 1 × 1 mm 2 of cells [16] (Figure 8.1). In an attempt to model arrhythmias following a myocardial infarct, monolayers of rat neonate myocytes were co-cultured with electrically uncoupled skeletal myoctubes to simulate fibrosis that is typically seen in the healed infarct border zone [15]. Electrically uncoupled skeletal myotubes produced localized slowing down of conduction velocity (CV), and enhanced the vulnerability to reentry by rapid pacing, without altering the excitability of the cardiac myocytes [15].…”