rotigaptide and Ventricular-Fibrillation

Therapeutic hypothermia (TH) may increase the susceptibility to ventricular arrhythmias by decreasing ventricular conduction velocity (CV) and facilitating arrhythmogenic spatially discordant alternans (SDA).. The purpose of this study was to test the hypothesis that rotigaptide, a gap junction enhancer, can increase ventricular CV, delay the onset of SDA, and decrease the susceptibility to pacing-induced ventricular fibrillation (PIVF) during TH.. Langendorff-perfused isolated rabbit hearts were subjected to 30-minute moderate hypothermia (33°C) followed by 20-minute treatment with rotigaptide (300 nM, n = 8) or vehicle (n = 5). The same protocol was also performed at severe hypothermia (30°C; n = 8 for rotigaptide, n = 5 for vehicle). Using an optical mapping system, epicardial CV and SDA threshold were evaluated by S1 pacing. Ventricular fibrillation inducibility was evaluated by burst pacing for 30 seconds at the shortest pacing cycle length (PCL) that achieved 1:1 ventricular capture.. Rotigaptide increased ventricular CV during 33°C (PCL 300 ms, from 76 ± 6 cm/s to 84 ± 7 cm/s, P = .039) and 30°C (PCL 300 ms, from 62 ± 6 cm/s to 68 ± 4 cm/s, P = .008). Rotigaptide decreased action potential duration dispersion at 33°C (P = .01) and 30°C (P = .035). During 30°C, SDA thresholds (P = .042) and incidence of premature ventricular complexes (P = .025) were decreased by rotigaptide. PIVF inducibility was decreased by rotigaptide at 33°C (P = .039) and 30°C (P = .042). Rotigaptide did not change connexin43 expressions and distributions during hypothermia.. Rotigaptide protects the hearts against ventricular arrhythmias by increasing ventricular CV, delaying the onset of SDA, and reducing repolarization heterogeneity during TH. Enhancing cell-to-cell coupling by rotigaptide might be a novel approach to prevent ventricular arrhythmias during TH.

Topics: Animals; Anti-Arrhythmia Agents; Connexin 43; Gap Junctions; Heart Conduction System; Heart Ventricles; Hypothermia, Induced; Models, Cardiovascular; Oligopeptides; Rabbits; Treatment Outcome; Ventricular Fibrillation; Voltage-Sensitive Dye Imaging

The present study investigated the effects of rotigaptide (ZP123) on the expression, distribution and phosphorylation of connexin43 (Cx43) in myocardial cell membranes in cardioversion of ventricular fibrillation (VF). A model of prolonged VF (8, 12 and 30 min) was established in mongrel dogs (n=8/group), following treatment with ZP123 or normal saline (NS control). A sham control was included. Cardiopulmonary resuscitation was begun at the start of VF followed by defibrillation. Animals received a maximum of three defibrillations of increasing energy (70, 100 and 150 J biphasic shock) as required. The average defibrillation energy, defibrillation success rate, return of spontaneous circulation and survival rate were recorded. Cx43 and phosphorylated (p-)Cx43 expression in cardiomyocyte membranes was detected by western blot and immunofluorescence analyses. Compared with the NS-treated control groups, the success defibrillation rate in the 8-min and 12-min ZP123 groups was significantly higher (P<0.05), while the average defibrillation energy was significantly lower (P<0.05). Cx43 expression in the VF groups was significantly lower than that in the sham control group (P<0.05). Cx43 expression was higher in the 12-min and 30-min ZP123 groups than that in the NS control group (P<0.05), while p-Cx43 expression decreased, although the levels were significantly higher than those in the control groups (P<0.05). Cx43 expression was positively correlated with the defibrillation success rate (r=0.91; P<0.01) and negatively with the mean defibrillation energy (r=-0.854; P<0.01), while p-Cx43 expression was positively correlated with the success rate of the previous three defibrillations (r=0.926; P<0.01).In conclusion, ZP123 reduced Cx43 remodeling through regulating the expression, distribution and phosphorylation of Cx43, thereby reducing the defibrillation energy required for successful cardioversion.

Topics: Animals; Anti-Arrhythmia Agents; Cardiopulmonary Resuscitation; Connexin 43; Diastole; Dogs; Electric Countershock; Electrocardiography; Female; Gene Expression Regulation; Heart Ventricles; Hemodynamics; Male; Myocytes, Cardiac; Oligopeptides; Phosphorylation; Systole; Ventricular Fibrillation

Spiral-wave (SW) reentry is a major organizing principle of ventricular tachycardia/fibrillation (VT/VF). We tested a hypothesis that pharmacological modification of gap junction (GJ) conductance affects the stability of SW reentry in a two-dimensional (2D) epicardial ventricular muscle layer prepared by endocardial cryoablation of Langendorff-perfused rabbit hearts. Action potential signals were recorded and analyzed by high-resolution optical mapping. Carbenoxolone (CBX; 30 μM) and rotigaptide (RG, 0.1 μM) were used to inhibit and enhance GJ coupling, respectively. CBX decreased the space constant (λ) by 36%, whereas RG increased it by 22-24% (n = 5; P < 0.01). During centrifugal propagation, there was a linear relationship between the wavefront curvature (κ) and local conduction velocity (LCV): LCV = LCV(0) - D·κ (D, diffusion coefficient; LCV(0), LCV at κ = 0). CBX decreased LCV(0) and D by 27 ± 3 and 57 ± 3%, respectively (n = 5; P < 0.01). RG increased LCV(0) and D by 18 ± 3 and 54 ± 5%, respectively (n = 5, P < 0.01). The regression lines with and without RG crossed, resulting in a paradoxical decrease of LCV with RG at κ > ~60 cm(-1). SW reentry induced after CBX was stable, and the incidence of sustained VTs (>30 s) increased from 38 ± 4 to 85 ± 4% after CBX (n = 18; P < 0.01). SW reentry induced after RG was characterized by decremental conduction near the rotation center, prominent drift and self-termination by collision with the anatomical boundaries, and the incidence of sustained VTs decreased from 40 ± 5 to 17 ± 6% after RG (n = 13; P < 0.05). These results suggest that decreased intercellular coupling stabilizes SW reentry in 2D cardiac muscle, whereas increased coupling facilitates its early self-termination.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Carbenoxolone; Cell Communication; Disease Models, Animal; Electrophysiologic Techniques, Cardiac; Gap Junctions; Heart Conduction System; Oligopeptides; Perfusion; Rabbits; Tachycardia, Ventricular; Time Factors; Ventricular Fibrillation; Voltage-Sensitive Dye Imaging

In ventricular fibrillation, the uncoupling of gap junctions slows conduction velocity and increases action-potential dispersion, which slows and diminishes defibrillation. We studied how the peptide ZP123, a gap-junction enhancer, might lower defibrillation-energy requirements during ventricular fibrillation in live pigs. We randomly assigned 33 pigs into 3 groups: ZP123 (receiving a 1-µg/kg bolus and 10 µg/kg/hr of ZP123), control (receiving saline solution), and sham (undergoing a sham operation). After a 30-min administration of agents, ventricular fibrillation was induced and left untreated for 8 min. Biphasic defibrillation of 50 J was increased by 50-J increments as necessary. Defibrillation-energy requirements were defined as the lowest energy required to achieve defibrillation. Electrocardiographic values were obtained before and after the administration of agents. Western blot and immunofluorescence analyses were performed on ventricular myocardial samples. All but one pig survived. The ZP123 treatment did not alter electrocardiographic variables. In the ZP123 group, the average required defibrillation energy was lower than that in the control group (327.28±269.6 vs 610±192.64 J; P=0.015), and the cumulative percentage of successful defibrillation at upper energy levels was higher (P<0.05). Supraventricular rhythm occurred more often in the ZP123 group than in the control group (72.7% vs 50%, P=0.042). Western-blot and immunofluorescence results showed that ZP123 did not alter the total amount of connexin43 but did prevent its dephosphorylation. We conclude that ZP123 can reduce defibrillation-energy requirements by preventing connexin43 remodeling during prolonged ventricular fibrillation.

Topics: Animals; Connexin 43; Disease Models, Animal; Electric Countershock; Electrocardiography; Female; Male; Oligopeptides; Swine; Treatment Outcome; Ventricular Fibrillation; Ventricular Remodeling

It was the aim of this study to investigate the effect of ZP123 on prolonged ventricular fibrillation (VF) in swine.. VF was electrically induced in 20 pigs. The animals randomly received either ZP123 or saline control infusion before VF. After 8 min of untreated VF, cardiopulmonary resuscitation and biphasic defibrillation shocks were applied. VF mean frequency (VF(mf)) and mean amplitude (VF(ma)), hemodynamics, outcome of defibrillation and the rate of return of spontaneous circulation (ROSC) were analyzed.. Compared with the control group, VF(mf) was higher but VF(ma) lower during the 8 min of VF in the drug group (11.8 ± 2.1 vs. 10.4 ± 2.0 Hz and 0.24 ± 0.10 vs. 0.31 ± 0.16 mV, respectively; p < 0.05). Hemodynamic variables in the 2 groups were comparable (p > 0.05). The defibrillation threshold was lower and the rate of successful defibrillation was higher in the drug group compared with the control group (92.2 ± 26.4 vs. 133.3 ± 28.9 J and 90 vs. 30%, respectively; p < 0.05). The rate of ROSC was not different between the 2 groups (40 vs. 30%; p > 0.05).. In prolonged VF, ZP123 could decrease the defibrillation threshold and improve the rate of successful defibrillation. However, it could not improve the rate of ROSC - which may be due to its side effect of decreasing VF(ma).

Topics: Animals; Blood Pressure; Disease Models, Animal; Electric Countershock; Female; Gap Junctions; Male; Oligopeptides; Sus scrofa; Swine; Time Factors; Ventricular Fibrillation

To observe changes in connexin 43 (Cx43) after ventricular fibrillation (VF) and the effects of rotigaptide (ZP123) on Cx43.. Thirty domestic pigs were randomly assigned to three groups (10 in each group): sham group, model group and ZP123 group. VF was induced by an 80 V AC transthoracic shock for 5 seconds with the use of subcutaneous needles. Before the induction of VF, animals in ZP123 group were administered with ZP123 (1 μg/kg bolus+10 μg×kg(-1)×h(-1) dissolved in 50 ml normal saline and pumped for 15 minutes ). Those in model group received 50 ml normal saline pumped for 15 minutes. For pigs in sham group VF was not induced and no fluid was given. After 8 minutes of VF, animals were euthanized and myocardial tissues were harvested along the long axis of each left ventricular free wall. Immunofluorescence combined with laser scanning confocal microscope was used to detect the distribution of Cx43. Western blotting was used for quantitative determination of Cx43 protein expression.. Immunofluorescence signals for Cx43 in sham group were strong and regularly distributed. In model group, Cx43 signals were weak and distributed in heterogeneity, while in ZP123 group, Cx43 signals were enhanced and their distribution were much more orderly. Compared with sham group, the percentage area and the optical densities (A value) of Cx43 fluorescence signals and Cx43 protein expression were significantly decreased in model group [the percentage area: (0.64±0.36)% vs.(1.27±0.19)%, A value: 15 201± 2 613 vs. 30 634±4 975, Cx43 protein expression: 0.72±0.08 vs. 0.97±0.07, all P<0.05]. The level of Cx43 expression in ZP 123 group [the percentage area (0.96±0.16)%, A value 22 100±4 404, Cx43 protein expression 0.82±0.04] was much higher than model group (all P<0.05).. During VF, down-regulation of myocardial Cx43 expression occurred, which could be attenuated by administration of ZP123.

Topics: Animals; Connexin 43; Disease Models, Animal; Myocardium; Oligopeptides; Swine; Ventricular Fibrillation

The gap junction modifier Rotigaptide (ZP123), which promotes cellular coupling, was hypothesized to decrease defibrillation thresholds during prolonged ventricular fibrillation (VF). Thirty-two New Zealand white rabbits were randomized to receive saline (control, n = 16) or Rotigaptide (n = 16). Following 4 min of untreated VF, biphasic defibrillation shocks were applied through chest wall patches, starting either at 300 volts (V) (n = 16) or 500 V (n = 16), with 200 V increasing steps to 900 V in case of shock failure. Rotigaptide significantly decreased defibrillation voltage requirements (average cumulative voltage of all shocks: 1206 +/- 709 V in control group vs. 844 +/- 546 V in treated group, P = .002). Rotigaptide had no effect on heart rate, QRS duration, QT interval, ventricular effective refractory period, monophasic action potential duration or on connexin 43 density using immunofluorescence. Rotigaptide improves the ability to defibrillate after untreated VF.

Topics: Action Potentials; Animals; Blood Pressure; Connexin 43; Disease Models, Animal; Electric Countershock; Electric Stimulation; Electrocardiography; Fluorescent Antibody Technique; Gap Junctions; Heart Arrest; Heart Rate; Injections, Intravenous; Male; Myocytes, Cardiac; Oligopeptides; Rabbits; Random Allocation; Resuscitation; Ventricular Fibrillation