Regional ion channel gene expression heterogeneity and ventricular fibrillation dynamics in human hearts.

RATIONALE: Structural differences between ventricular regions may not be the sole determinant of local ventricular fibrillation (VF) dynamics and molecular remodeling may play a role. OBJECTIVES: To define regional ion channel expression in myopathic hearts compared to normal hearts, and correlate expression to regional VF dynamics. METHODS AND RESULTS: High throughput real-time RT-PCR was used to quantify the expression patterns of 84 ion-channel, calcium cycling, connexin and related gene transcripts from sites in the LV, septum, and RV in 8 patients undergoing transplantation. An additional eight non-diseased donor human hearts served as controls. To relate local ion channel expression change to VF dynamics localized VF mapping was performed on the explanted myopathic hearts right adjacent to sampled regions. Compared to non-diseased ventricles, significant differences (p<0.05) were identified in the expression of 23 genes in the myopathic LV and 32 genes in the myopathic RV. Within the myopathic hearts significant regional (LV vs septum vs RV) expression differences were observed for 13 subunits: Nav1.1, Cx43, Ca3.1, Cavα2δ2, Cavß2, HCN2, Na/K ATPase-1, CASQ1, CASQ2, RYR2, Kir2.3, Kir3.4, SUR2 (p<0.05). In a subset of genes we demonstrated differences in protein expression between control and myopathic hearts, which were concordant with the mRNA expression profiles for these genes. Variability in the expression of Cx43, hERG, Na(+)/K(+) ATPase ß1 and Kir2.1 correlated to variability in local VF dynamics (p<0.001). To better understand the contribution of multiple ion channel changes on VF frequency, simulations of a human myocyte model were conducted. These simulations demonstrated the complex nature by which VF dynamics are regulated when multi-channel changes are occurring simultaneously, compared to known linear relationships. CONCLUSIONS: Ion channel expression profile in myopathic human hearts is significantly altered compared to normal hearts. Multi-channel ion changes influence VF dynamic in a complex manner not predicted by known single channel linear relationships.

Early ion-channel remodeling and arrhythmias precede hypertrophy in a mouse model of complete atrioventricular block.

Complete atrioventricular block (CAVB) and related ventricular bradycardia are known to induce ventricular hypertrophy and arrhythmias. Different animal models of CAVB have been established with the most common being the dog model. Related studies were mainly focused on the consequences on the main repolarizing currents in these species, i.e. IKr and IKs, with a limited time point kinetics post-AVB. In order to explore at a genomic scale the electrical remodeling induced by AVB and its chronology, we have developed a novel model of CAVB in the mouse using a radiofrequency-mediated ablation procedure. We investigated transcriptional changes in ion channels and contractile proteins in the left ventricles as a function of time (12h, 1, 2 and 5 days after CAVB), using high-throughput real-time RT-PCR. ECG in conscious and anesthetized mice, left ventricular pressure recordings and patch-clamp were used for characterization of this new mouse model. As expected, CAVB was associated with a lengthening of the QT interval. Moreover, polymorphic ventricular tachycardia was recorded in 6/9 freely-moving mice during the first 24h post-ablation. Remarkably, myocardial hypertrophy was only evident 48 h post-ablation and was associated with increased heart weight and altered expression of contractile proteins. During the first 24 hours post-CAVB, genes encoding ion channel subunits were either up-regulated (such as Nav1.5, +74%) or down-regulated (Kv4.2, -43%; KChIP2, -47%; Navß1, -31%; Cx43, -29%). Consistent with the transient alteration of Kv4.2 expression, I(to) was reduced at day 1, but restored at day 5. In conclusion, CAVB induces two waves of molecular remodeling: an early one (≤24 h) leading to arrhythmias, a later one related to hypertrophy. These results provide new molecular basis for ventricular tachycardia induced by AV block.

Autologous myoblast transplantation after myocardial infarction increases the inducibility of ventricular arrhythmias.

BACKGROUND: Small scale clinical trials suggested the feasibility and the efficacy of autologous myoblast transplantation to improve ventricular function after myocardial infarction. However, these trials were hampered by unexpected episodes of life-threatening ventricular tachyarrhythmias (VT). We investigated cardiac electrical stability after myoblast transplantation to the myocardium. METHODS AND RESULTS: Seven days after coronary ligation, Wistar rats were randomized into 3 groups: a control group receiving no further treatment, a vehicle group injected with culture medium into the infarcted myocardium, and a myoblast group injected with autologous myoblasts. Holter monitoring did not discriminate the myoblast from the vehicle groups. Programmed Electrical Stimulation (PES) was performed to evaluate further a cardiac substrate for arrhythmia susceptibility. The occurrence of sustained VT during PES was similar in control and vehicle groups (5/17 and 4/19 rats, respectively; p=0.50). In contrast, 13/20 rats (65%) from the myoblast group showed at least one episode of sustained VT during PES (p<0.05 and p<0.005 versus control and vehicle groups). As a further control group, rats injected with autologous bone marrow mononuclear cells into the infarcted myocardium did not show increased susceptibility to PES. CONCLUSIONS: In an infarcted rat model, myoblast transplantation but not bone marrow mononuclear cells or myocardial injection per se induces electrical ventricular instability. Because ventricular arrhythmias are life-threatening disorders, we suggest that such preclinical evaluation should be conducted for any new source of cells to be injected into the myocardium.