After myocardial infarction (MI), the noninfarcted myocardium undergoes significant hypertrophy as part of the post-MI structural remodeling. Electrophysiological changes associated with the hypertrophied remodeled myocardium may play a key role in arrhythmia generation in the post-MI heart. We investigated the cellular and ionic basis of arrhythmias in remodeled left ventricular (LV) myocardium 3 to 4 weeks after MI in the rat. We analyzed (1) the incidence of induced ventricular tachyarrhythmias (VTs) in the in vivo heart, (2) action potential characteristics and arrhythmia mechanisms in multicellular preparations and isolated remodeled LV myocytes, and (3) the density and kinetics of the L-type Ca ²⁺ current (I _Ca-L ) and the fast and slow components of transient outward K ⁺ currents (I _to-f and I _to-s , respectively). The results were compared with those from sham-operated rats. In vivo, programmed stimulation induced sustained VT in 80% of post-MI rats but not in sham-operated rats. The capacitance of post-MI hypertrophied myocytes was significantly increased compared with myocytes from sham-operated rats. Post-MI myocytes had prolonged action potential duration (APD) with marked heterogeneity of the time course of repolarization. The prolongation of APD could be explained by the significant decrease of the density of both I _to-f and I _to-s . There was no change in the kinetics of both currents compared with control. Both the density and kinetics of I _Ca-L were not significantly different in post-MI remodeled myocytes compared with control. The cellular studies showed that reentrant excitation secondary to dispersion of repolarization and triggered activity from both early and delayed afterdepolarizations are potential mechanisms for VT in the post-MI remodeled heart.

An important advance in the description and understanding of congenital heart block (CHB) came in the 1970s with the observation that mothers of affected infants frequently had autoimmune diseases and, in particular, that many maternal sera contained antibodies to SSA/Ro and SSB/La ribonucleoproteins. Although the molecular biology of the candidate antigens has been extensively defined, the arrhythmogenic and electrophysiological effects of their cognate antibodies on the human fetal heart are unknown. In the present study, we provide evidence that IgG-enriched fractions and anti-52-kD SSA/Ro antibodies affinity-purified from sera of mothers whose children have CHB induce complete atrioventricular (AV) block in the human fetal heart perfused by the Langendorff technique and inhibit L-type Ca ² + currents at the whole-cell and single-channel level. Immunization of female BALB/c mice with recombinant 52-kD SSA/Ro protein generated high-titer antibodies that crossed the placenta during pregnancy and were associated with varying degrees of AV conduction abnormalities, including complete AV block, in the pups. These findings strongly suggest that anti-52-kD SSA/Ro antibodies are causally related to the development of CHB.

Increased proinflammatory interleukin-6 (IL-6) levels are associated with acquired long QT-syndrome (LQTS) in patients with systemic inflammation, leading to higher risks for life-threatening polymorphic ventricular tachycardia such as Torsades de Pointes. However, the functional and molecular mechanisms of this association are not known. In most cases of acquired LQTS, the target ion channel is the human ether-á-go-go-related gene (hERG) encoding the rapid component of the delayed rectifier K current, I_Kr, which plays a critical role in cardiac repolarization. Here, we tested the hypothesis that IL-6 may cause QT prolongation by suppressing I_Kr. Electrophysiological and biochemical assays were used to assess the impact of IL-6 on the functional expression of I_Kr in HEK293 cells and adult guinea-pig ventricular myocytes (AGPVM). In HEK293 cells, IL-6 alone or in combination with the soluble IL-6 receptor (IL-6R), produced a significant depression of I_Kr peak and tail current densities. Block of IL-6R or Janus kinase (JAK) reversed the inhibitory effects of IL-6 on I_Kr. In AGPVM, IL-6 prolonged action potential duration (APD) which was further prolonged in the presence of IL-6R. Similar to heterologous cells, IL-6 reduced endogenous guinea pig ERG channel mRNA and protein expression. The data are first to demonstrate that IL-6 inhibition of I_Kr and the resulting prolongation of APD is mediated via IL-6R and JAK pathway activation and forms the basis for the observed clinical QT interval prolongation. These novel findings may guide the development of targeted anti-arrhythmic therapeutic interventions in patients with LQTS and inflammatory disorders.

Objective Increasing evidence indicates systemic inflammation as a new potential cause of acquired long QT syndrome (LQTS), via cytokine-mediated changes in cardiomyocyte ion channels. Torsade de pointes (TdP) is a life-threatening polymorphic ventricular tachycardia occurring in patients with LQTS, usually when multiple QT-prolonging factors are simultaneously present. Since classical risk factors cannot fully explain TdP events in a number of patients, we hypothesised that systemic inflammation may represent a currently overlooked risk factor contributing to TdP development in the general population. Methods Forty consecutive patients who experienced TdP (TdP cohort) were consecutively enrolled and circulating levels of C-reactive protein (CRP) and proinflammatory cytokines (interleukin-6 (IL-6), tumour necrosis factor alpha (TNFα), interleukin-1 (IL-1)) were compared with patients with active rheumatoid arthritis (RA), comorbidity or healthy controls. An additional 46 patients with different inflammatory conditions (acute infections, n=31; immune-mediated diseases, n=12; others, n=3) and elevated CRP (inflammatory cohort) were prospectively enrolled, and corrected QT (QTc) and cytokine levels were measured during active disease and after a CRP decrease of >75% subsequent to therapy. Results In the TdP cohort, 80% of patients showed elevated CRP levels (median: ~3 mg/dL), with a definite inflammatory disease identifiable in 18/40 cases (acute infections, n=12; immune-mediated diseases, n=5; others, n=1). In these subjects, IL-6, but not TNFα and IL-1, was ~15–20 times higher than in controls, and comparable to RA patients. In the inflammatory cohort, where QTc prolongation was common (mean values: 456.6±30.9 ms), CRP reduction was associated with IL-6 level decrease and significant QTc shortening (−22.3 ms). Conclusion The data are first to show that systemic inflammation via elevated IL-6 levels may represent a novel QT-prolonging risk factor contributing to TdP occurrence in the presence of other classical risk factors. If confirmed, this could open new avenues in antiarrhythmic therapy.