Reperfusion Ventricular Arrhythmias Research Articles

Aesculin suppresses the NLRP3 inflammasome-mediated pyroptosis via the Akt/GSK3β/NF-κB pathway to mitigate myocardial ischemia/reperfusion injury

BackgroundAesculin (AES), an effective component of Cortex fraxini, is a hydroxycoumarin glucoside that has diverse biological properties. The nucleotide-binding domain leucine-rich repeat-containing receptor, pyrin domain-containing 3 (NLRP3) inflammasome has been heavily interwoven with the development of myocardial ischemia/reperfusion injury (MIRI). Nevertheless, it remains unclear whether AES makes a difference to the changes of the NLRP3 inflammasome in MIRI. PurposeWe used rats that were subjected to MIRI and neonatal rat cardiomyocytes (NRCMs) that underwent oxygen-glucose deprivation/restoration (OGD/R) process to investigate what impacts AES exerts on MIRI and the NLRP3 inflammasome activation. MethodsThe establishment of MIRI model in rats was conducted using the left anterior descending coronary artery ligation for 0.5 h ischemia and then untying the knot for 4 h of reperfusion. After reperfusion, AES were administered intraperitoneally using 10 and 30 mg/kg doses. We evaluated the development of reperfusion ventricular arrhythmias, hemodynamic changes, infarct size, and the biomarkers in myocardial injury. The inflammatory mediators and pyroptosis were also assessed. AES at the concentrations of 1, 3, and 10 μM were imposed on the NRCMs immediately before the restoration process. We also determined the cell viability and cell death in the NRCMs exposed to OGD/R insult. Furthermore, we also analyzed the levels of proteins that affect the NLRP3 inflammasome activation, pyroptosis, and the AKT serine/threonine kinase (Akt)/glycogen synthase kinase 3 beta (GSK3β)/nuclear factor-kappa B (NF-κB) signaling pathway via western blotting. ResultsWe found that AES notably attenuated reperfusion arrhythmias and myocardia damage, improved the hemodynamic function, and ameliorated the inflammatory response and pyroptosis of cardiomyocytes in rats and NRCMs. Additionally, AES reduced the NLRP3 inflammasome activation in rats and NRCMs. AES also enhanced the phosphorylation of Akt and GSK3β, while suppressing the phosphorylation of NF-κB. Moreover, the allosteric Akt inhibitor, MK-2206, abolished the AES-mediated cardioprotection and the NLRP3 inflammasome suppression. ConclusionsThese findings indicate that AES effectively protected cardiomyocytes against MIRI by suppressing the NLRP3 inflammasome-mediated pyroptosis, which may relate to the upregulated Akt activation and disruption of the GSK3β/NF-κB pathway.

Serum uric acid level is associated with reperfusion ventricular arrhythmias in acute myocardial infarction

Background and aimIn the acute phase of acute myocardial infarction (AMI), reperfusion ventricular arrhythmias such as ventricular tachycardia and ventricular fibrillation (Reperfusion VT/VF) resulting from reperfusion injury are one of the causes of in-hospital death. Predicting Reperfusion VT/VF is clinically important. Previous studies have reported that oxidative stress is the cause of reperfusion injury and reperfusion arrhythmia. There are also reports that xanthine oxidase inhibitors have the effect of preventing reperfusion arrhythmia. We hypothesized that hyperuricemia is a risk factor for reperfusion arrhythmias in AMI.The aim of our study is to investigate whether serum uric acid is associated with Reperfusion VT/VF in acute myocardial infarction. MethodThis is a single-center, retrospective cohort study. We enrolled 612 ST elevation myocardial infarction patients who underwent successful primary percutaneous coronary intervention (PCI). We divided patients into a high serum uric acid group (HUA group) and a low serum uric acid group (LUA group) with a cutoff value of 7.0 mg/dl, which is the standard value of serum uric acid. We compared the frequency of Reperfusion VT/VF in both groups. ResultThere were 111 patients in the HUA group and 512 patients in the LUA group. Creatinine tended to be higher in the HUA group than in the LUA group. (1.12 ± 0.41 mg/dl VS 0.92 ± 1.10 mg/dl P = 0.06). The frequency of Reperfusion VT/VF was significantly higher in the HUA group than in the LUA group (17.1% VS 4.0% P < 0.001). ConclusionElevated serum uric acid is associated with higher frequency of reperfusion ventricular arrhythmia.

Cardioprotective effect of anisodamine against ischemia/reperfusion injury through the mitochondrial ATP-sensitive potassium channel

Previous clinical studies have shown that anisodamine could improve no-reflow phenomenon and prevent reperfusion arrhythmias, but whether this protective effect is related to the antagonism of the M-type cholinergic receptor or other potential mechanisms is uncertain. The aim of the present study was to investigate the role of the mitochondrial ATP-sensitive potassium channel (mitoK ATP ) in cardioprotective effect of anisodamine against ischemia/reperfusion injury. Anisodamine and 5- hydroxydecanoic acid were used to explore the relationship between anisodamine and mitoK ATP . Using a Langendorff isolated heart ischemia/reperfusion injury model, hemodynamic parameters and reperfusion ventricular arrhythmia were evaluated; in addition, changes in myocardial infarct size, cTnI from coronary effluent and myocardial ultrastructure, as well as ATP, MDA and SOD in myocardial tissues, were detected. In the hypoxia/reoxygenation injury model of neonatal rat cardiomyocyte, cTnI release in the culture medium and levels of ATP, MDA and SOD in cardiomyocytes and mitochondrial membrane potential, were analyzed. Overall, anisodamine could significantly improve the hemodynamic indexes of isolated rat heart injured by ischemia/reperfusion, reduce the occurrence of ventricular reperfusion arrhythmia and myocardial infarction area, and improve the ultrastructural damage of myocardium and mitochondria. The in vitro results demonstrated that anisodamine could improve mitochondrial energy metabolism, reduce oxidative stress and stabilize mitochondrial membrane potential. The cardioprotective effects were significantly inhibited by 5-hydroxydecanoic acid. In conclusion, this study suggests that the opening of mitoK ATP could play an important role in the protective effect of anisodamine against myocardial ischemia/reperfusion injury.

The effect of cold crystalloid versus warm blood cardioplegia on the myocardium during coronary artery bypass grafting

Background: The optimal cardioplegic solution is still debated. The objective of this study was to compare the effect of cold crystalloid versus warm blood cardioplegia on the myocardial injury during coronary artery bypass grafting.&#x0D; Methods: The study included 34 consecutive patients who underwent elective primary on-pump isolated coronary artery bypass grafting from 2016 to 2019. We randomly assigned the patients into two groups. Group (ICCC) (n= 17) received intermittent antegrade cold crystalloid cardioplegia and Group (IWBC) (n= 17) received intermittent antegrade warm blood cardioplegia.&#x0D; Results: There was no difference in the preoperative and operative variables between groups. The time taken by the heart to regain normal sinus rhythm was significantly longer in the cold crystalloid group (7.06 ± 1.8 vs. 2.17 ± 0.8 minutes, p&lt;0.001) with a higher rate of reperfusion ventricular arrhythmia (35% versus 6%; p=0.03) compared to the warm blood cardioplegia group. Both coronary sinus acid production and lactate level were significantly higher in the warm blood group than in the cold crystalloid group (p&lt; 0.001 and 0.043, respectively). The ischemic ECG changes and the severity of new segmental wall motion abnormalities were non-significantly different between both groups (p= 0.68 and 0.67, respectively). Postoperative CK-MB and cTnI levels in all-time points were not significantly different between groups (p= 0.46 and 0.37, respectively). ICU (2.29 ± 0.77 vs. 2.41 ± 0.87 days, p= 0.68) and hospital stay (9.28 ± 0.76 vs. 9.42 ± 0.88 days, p= 0.62) were non-significantly different between both groups.&#x0D; Conclusion: Intermittent antegrade cold crystalloid cardioplegia was associated with attenuated myocardial metabolism. However, it was associated with a longer time to regain normal sinus rhythm and more reperfusion ventricular arrhythmias. We did not find differences in the clinical and echocardiographic outcomes and cardiac enzymes between cold crystalloid and warm blood cardioplegia.

Anti-arrhythmic Cardiac Phenotype Elicited by Chronic Intermittent Hypoxia Is Associated With Alterations in Connexin-43 Expression, Phosphorylation, and Distribution.

Remodeling of the cellular distribution of gap junctions formed mainly by connexin-43 (Cx43) can be related to the increased incidence of cardiac arrhythmias. It has been shown that adaptation to chronic intermittent hypobaric hypoxia (IHH) attenuates the incidence and severity of ischemic and reperfusion ventricular arrhythmias and increases the proportion of anti-arrhythmic n-3 polyunsaturated fatty acids (n−3 PUFA) in heart phospholipids. Wistar rats were exposed to simulated IHH (7,000 m, 8-h/day, 35 exposures) and compared with normoxic controls (N). Cx43 expression, phosphorylation, localization and n−3 PUFA proportion were analyzed in left ventricular myocardium. Compared to N, IHH led to higher expression of total Cx43, its variant phosphorylated at Ser368 [p-Cx43(Ser368)], which maintains “end to end” communication, as well as p-Cx43(Ser364/365), which facilitates conductivity. By contrast, expression of non-phosphorylated Cx43 and p-Cx43(Ser278/289), attenuating intercellular communication, was lower in IHH than in N. IHH also resulted in increased expression of protein kinase A and protein kinase G while casein kinase 1 did not change compared to N. In IHH group, which exhibited reduced incidence of ischemic ventricular arrhythmias, Cx43 and p-Cx43(Ser368) were more abundant at “end to end” gap junctions than in N group and this difference was preserved after acute regional ischemia (10 min). We further confirmed higher n-3 PUFA proportion in heart phospholipids after adaptation to IHH, which was even further increased by ischemia. Our results suggest that adaptation to IHH alters expression, phosphorylation and distribution of Cx43 as well as cardioprotective n-3PUFA proportion suggesting that the anti-arrhythmic phenotype elicited by IHH can be at least partly related to the stabilization of the “end to end” conductivity between cardiomyocytes during brief ischemia.

Bursts of reperfusion arrhythmias occur independently of area at risk size and are the first marker of reperfusion injury

BackgroundThe presence of reperfusion ventricular arrhythmias (VA) has been shown to correlate with larger infarct size (IS). However it is unclear whether the initial area at risk (AAR), also a determining factor for IS, is responsible for this correlation. We hypothesized that IS would be significantly larger in the presence of VA, while AAR would not differ. Methods68 STEMI patients from the MAST study with 24-hour, continuous, 12‑lead Holter monitoring initiated prior to primary percutaneous coronary intervention (PCI) resulting in TIMI 3 flow post PCI were included. VA bursts were identified against subject-specific background VA rates using a previously validated statistical outlier method. IS, and infarct endocardial surface area (ESA) were obtained using CMR at mean 4.9 days after admission. Holter and CMR results were determined in core laboratories blinded to all other data. ResultsVA bursts were present in 69% (45/65) of patients. No significant differences were found for demographic characteristics, comorbidities, infarct location, number of diseased coronary vessels, or duration of ischemia between groups with and without VA burst. IS was significantly smaller in the group without VA bursts (median 9.3% vs 17.0%; p = 0.025). Infarct ESA did not significantly differ between the population with and without VA burst; median 24.3% vs 20.0%; p = 0.15. ConclusionVA bursts are a marker for larger IS independent of AAR, assessed by surrogate markers. These findings support the hypothesis that VA bursts are a marker of reperfusion damage occurring downstream at myocellular level.

Atorvastatin protects myocardium against ischemia–reperfusion arrhythmia by increasing Connexin 43 expression: A rat model

Atorvastatin has protective effects against myocardial ischemia–reperfusion injuries and ischemia–reperfusion arrhythmia. This study was designed to investigate whether atorvastatin is able to protect against myocardial ischemia–reperfusion injury by enhancing the expression of Connexin 43 (Cx43) via the activation of the phosphatidylinositol-3-kinase (PI3K)/Akt pathway and mitochondrial ATP-sensitive potassium (KATP) channels. Isolated perfused rat hearts were treated with classic ischemia postconditioning (IPOST), atorvastatin, and atorvastatin combined with inhibitor of PI3K and KATP channels, respectively, after 30min of LAD ischemia and then subjected to reperfusion for 120min. The QRS duration and the ischemia–reperfusion ventricular arrhythmia were assessed. The lactate dehydrogenase (LDH) and creatine kinase isoenzyme (CK-MB) levels were measured and the Cx43 expression was assessed by immunoblotting and immunohistochemistry. After 120min of reperfusion, atorvastatin and IPOST significantly decreased the QRS duration and inhibited ventricular arrhythmia. They also decreased the levels of LDH and CK-MB. Meanwhile, atorvastatin and IPOST also significantly enhanced the Cx43 expression and the phosphorylation of Cx43. Such protective effects were abolished in the presence of the inhibitor of PI3K or the inhibitor of mitochondrial KATP channels. This study suggests that atorvastatin protected against myocardial ischemia–reperfusion injury and enhanced the expression of Cx43 by activating the PI3K/Akt pathway and mitochondrial KATP channels.

Prospective evaluation of where reperfusion ventricular arrhythmia “bursts” fit into optimal reperfusion in STEMI

BackgroundEarly reperfusion of ischemic myocytes is essential for optimal salvage in acute myocardial infarction. VA (ventricular arrhythmia) bursts after recanalization of the culprit vessel have been found to be related to larger infarct size (IS), using SPECT. ObjectiveThe hypothesis was tested that this finding could be confirmed in an independent cohort using a more accurate technique, i.e. delayed-enhancement cardiovascular magnetic resonance imaging (DE-CMR). MethodsAll 196 patients from the PREPARE and MAST studies who had 24-hour, continuous, 12-lead Holter, started before primary percutaneous coronary intervention resulting in brisk TIMI (thrombolysis in myocardial infarction) 3 flow and stable ST-recovery were included. VA bursts were identified against subject-specific background VA rates using a previously published statistical outlier method. IS was assessed using DE-CMR. Angiography, Holter and DE-CMR results were assessed in core laboratories, blinded to all other data. ResultsVA bursts were present in 154/196 (79%) of patients. Baseline characteristics between the groups with and without bursts were similar. VA burst was associated with significantly larger infarct size in the population as a whole (median 11.3% vs 5.3%; p=0.001) and also when divided in non-anterior (median 9.9% vs 4.9%; p=0.003) and anterior myocardial infarction (median 21.4% vs 12.0%; p=0.48), the latter not reaching statistical significance due to the small subset of patients. ConclusionBeyond the classical markers of “optimal” reperfusion such as TIMI 3 flow and stable ST-segment recovery, VA bursts occurring during the reperfusion phase are an early electrobiomarker of larger IS. Clinical trial registration: PREPARE: ISRCTN71104460 http://www.controlled-trials.com/ISRCTN71104460.

Impact of n-3 polyunsaturated fatty acids in predicting ischemia/reperfusion injury and progression of myocardial damage after reperfusion in patients with ST-segment elevation acute myocardial infarction

BackgroundIn animal models of acute myocardial infarction, n-3 polyunsaturated fatty acids (PUFAs) administered before coronary occlusion have been suggested to prevent induction of ventricular arrhythmia and limit infarct size. However, the relation between the serum levels of n-3 PUFAs and ischemia/reperfusion (I/R) injury remains unclear. Methods211 patients with ST-segment elevation acute myocardial infarction received emergency percutaneous coronary intervention (PCI) within 6h from the onset. The patients were divided into two groups according to the sum of serum eicosapentaenoic acid (EPA) levels and docosahexaenoic acid (DHA) levels before PCI: group L (n=106), EPA+DHA <155μg/ml and group H (n=105), EPA+DHA ≥155μg/ml. The Selvester QRS-scoring system was used to estimate the serial change in infarct size. ResultsTime to reperfusion was similar between the 2 groups. The QRS score before PCI was higher in group L than in group H (2.42±2.00 vs 1.85±2.01, p=0.015). The proportion of patients with I/R injury immediately after reperfusion, defined as reperfusion ventricular arrhythmias (25% vs 11%, p=0.006) and ST-segment re-elevation (44% vs 22%, p<0.001), was also higher in group L than in group H, followed by a greater increment in the QRS score during PCI (3.51±2.51 vs 2.54±1.91, p=0.006) and higher peak levels of creatinine phosphokinase (3552±241U/L vs 2660±242U/L, p<0.01). On multivariate analysis, serum level of EPA+DHA was an independent predictor of reperfusion injury (odds ratio 0.985, p=0.032). ConclusionSerum level of n-3 PUFAs before PCI may be a predictor of I/R injury and the resultant extent of myocardial damage. These findings suggest a protective effect of serum n-3 PUFAs on ischemic myocardium.

B-type natriuretic peptide as a predictor of ischemia/reperfusion injury immediately after myocardial reperfusion in patients with ST-segment elevation acute myocardial infarction

In animal models of acute myocardial infarction (AMI), B-type natriuretic peptide (BNP) administered before and during coronary occlusion limits infarct size. However, the relation between plasma BNP levels and ischemia/reperfusion injury remains unclear. 302 patients with ST-segment elevation AMI (STEMI) received emergency percutaneous coronary intervention within six hours from the onset. The patients were divided into two groups according to the plasma BNP level before angiography: group L (n=151), BNP ≤ 32.2 pg/ml; group H (n=151), BNP >32.2 pg/ml. The Selvester QRS-scoring system was used to estimate infarct size. The rate of ischemia/reperfusion injury immediately after reperfusion, defined as reperfusion ventricular arrhythmias (26% vs. 11%, p=0.001) and ST-segment re-elevation (44% vs. 22%, p=0.008), was higher in group L than in group H. Group L had a greater increase in the QRS score during percutaneous coronary intervention (3.55 ± 0.17 vs. 2.09 ± 0.17, p<0.001) and a higher QRS score 1 h after percutaneous coronary intervention (5.77 ± 0.28 vs. 4.51 ± 0.28, p=0.002). On multivariate analysis, plasma BNP levels in the lower 50th percentile were an independent predictor of reperfusion injury (odds ratio, 2.620; p<0.001). The odds ratios of reperfusion injury according to decreasing quartiles of BNP level, as compared with the highest quartile, were 1.536, 3.692 and 4.964, respectively (p trend=0.002). Plasma BNP level before percutaneous coronary intervention may be a predictor of ischemia/reperfusion injury and the resultant extent of myocardial damage. Our findings suggest that high plasma BNP levels might have a clinically important protective effect on ischemic myocardium in patients with STEMI who receive percutaneous coronary intervention.

ASSA14-03-16 ILK attenuates reperfusion ventricular arrhythmias by inhibiting remodelling of Cx 43 in isolated rat hearts

<h3>Objective</h3> To investigate the role of ILK in ventricular arrhythmia after ischemia-reperfusion (I/R) in isolated hearts. <h3>Methods</h3> Langendoff perfused rat hearts were subjected to 30 min of regional ischemia which induced by deligating the left anterior descending coronary artery, then 30 min of reperfusion. After pretreatment with regulator of ILK activity, Surface ECG was used to observe arrhythmia continuously,and the expression and distribution of connexin 43 were detected via western blot and immunofluorescence. <h3>Results</h3> 1. The agonist of ILK could attenuate ventricular arrhythmia after I/R. As compared with I/R group, the agonist could reduce the ventricular arrhythmia score and the incidence of ventricular arrhymia after reperfusion (p &lt; 0.05), in contrast, the ILK inhibitor Cpd22 could increase the ventricular arrhythmia score and the incidence of ventricular arrhymia after reperfusion (p &lt; 0.05) ,and abolish the anti-arrhythmic effect of ILK agonist. 2. There were no significant differences in Cx43 expression among all groups. ILK agonist could inhibit the remoldeling of Cx43 and reduce the lateralization, contrastly, Cpd22 could promote the lateralization of Cx43. <h3>Conclusion</h3> ILK can imprve reperfusion ventricular arrhythmias by inhibiting remodelling of Cx43, and regulating ILK activity may be a potential therapeutic for reperfusion ventricular arrhythmias.

Implications of ventricular arrhythmia "bursts" with normal epicardial flow, myocardial blush, and ST-segment recovery in anterior ST-elevation myocardial infarction reperfusion: a biosignature of direct myocellular injury "downstream of downstream".

Establishing epicardial flow with percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI) is necessary but not sufficient to ensure nutritive myocardial reperfusion. We evaluated whether adding myocardial blush grade (MBG) and quantitative reperfusion ventricular arrhythmia "bursts" (VABs) surrogates provide a more informative biosignature of optimal reperfusion in patients with Thrombolysis in Myocardial Infarction (TIMI) 3 flow and ST-segment recovery (STR). Anterior STEMI patients with final TIMI 3 flow had protocol-blinded analyses of simultaneous MBG, continuous 12-lead electrocardiogram (ECG) STR, Holter VABs, and day 5-14 SPECT imaging infarct size (IS) assessments. Over 20 million cardiac cycles from >4500 h of continuous ECG monitoring in subjects with STR were obtained. IS and clinical outcomes were examined in patients stratified by MBG and VABs. VABs occurred in 51% (79/154) of subjects. Microcirculation (MBG 2/3) was restored in 75% (115/154) of subjects, of whom 53% (61/115) had VABs. No VABs were observed in subjects without microvascular flow (MBG of 0). Of 115 patients with TIMI 3 flow, STR, and MBG 2/3, those with VABs had significantly larger IS (median: 23.0% vs 6.0%, p=0.001). Multivariable analysis identified reperfusion VABs as a factor significantly associated with larger IS (p=0.015). Despite restoration of normal epicardial flow, open microcirculation, and STR, concomitant VABs are associated with larger myocardial IS, possibly reflecting myocellular injury in reperfusion settings. Combining angiographic and ECG parameters of epicardial, microvascular, and cellular response to STEMI intervention provides a more predictive "biosignature" of optimal reperfusion than do single surrogate markers.

Selective heart rate reduction with ivabradine slows ischaemia-induced electrophysiological changes and reduces ischaemia–reperfusion-induced ventricular arrhythmias

Heart rates during ischaemia and reperfusion are possible determinants of reperfusion arrhythmias. We used ivabradine, a selective If current inhibitor, to assess the effects of heart rate reduction (HRR) during ischaemia–reperfusion on reperfusion ventricular arrhythmias and assessed potential anti-arrhythmic mechanisms by optical mapping. Five groups of rat hearts were subjected to regional ischaemia by left anterior descending artery occlusion for 8min followed by 10min of reperfusion: (1) Control n=10; (2) 1μM of ivabradine perfusion n=10; (3) 1μM of ivabradine+5Hz atrial pacing throughout ischaemia–reperfusion n=5; (4) 1μM of ivabradine+5Hz pacing only at reperfusion; (5) 100μM of ivabradine was used as a 1ml bolus upon reperfusion. For optical mapping, 10 hearts (ivabradine n=5; 5Hz pacing n=5) were subjected to global ischaemia whilst transmembrane voltage transients were recorded. Epicardial activation was mapped, and the rate of development of ischaemia-induced electrophysiological changes was assessed. HRR observed in the ivabradine group during both ischaemia (195±11bpm vs. control 272±14bpm, p<0.05) and at reperfusion (168±13bpm vs. 276±14bpm, p<0.05) was associated with reduced reperfusion ventricular fibrillation (VF) incidence (20% vs. 90%, p<0.05). Pacing throughout ischaemia–reperfusion abolished the protective effects of ivabradine (100% VF), whereas pacing at reperfusion only partially attenuated this effect (40% VF). Ivabradine, given as a bolus at reperfusion, did not significantly affect VF incidence (80% VF). Optical mapping experiments showed a delay to ischaemia-induced conduction slowing (time to 50% conduction slowing: 10.2±1.3min vs. 5.1±0.7min, p<0.05) and to loss of electrical excitability in ivabradine-perfused hearts (27.7±4.3min vs. 14.5±0.6min, p<0.05). Ivabradine administered throughout ischaemia and reperfusion reduced reperfusion VF incidence through HRR. Heart rate during ischaemia is a major determinant of reperfusion arrhythmias. Heart rate at reperfusion alone was not a determinant of reperfusion VF, as neither a bolus of ivabradine nor pacing immediately prior to reperfusion significantly altered reperfusion VF incidence. This anti-arrhythmic effect of heart rate reduction during ischaemia may reflect slower development of ischaemia-induced electrophysiological changes.

Sevoflurane postconditioning alleviates action potential duration shortening and L-type calcium current suppression induced by ischemia/reperfusion injury in rat epicardial myocytes.

It has been proved that sevoflurane postconditioning (SpostC) could protect the heart against myocardial ischemia/reperfusion injury, however, there has been few research focused on the electrophysiological effects of SpostC. The objective of the study was to investigate the effects of SpostC on action potential duration (APD) and L-type calcium current (I(Ca, L)) in isolated cardiomyocytes. Langendorff perfused SD rat hearts were randomly assigned to one of the time control (TC), ischemia/reperfusion (I/R, 25 minutes of ischemia followed by 30 minutes of reperfusion), and SpostC (postconditioned with 3% sevoflurane) groups. At the end of reperfusion, epicardial myocytes were dissociated enzymatically for patch clamp studies. Sevoflurane directly prolonged APD and decreased peak I(Ca, L) densities in epicardial myocytes of the TC group (P < 0.05). I/R injury shortened APD and decreased peak I(Ca, L) densities in epicardial myocytes of the I/R group (P < 0.05). SpostC prolonged APD and increased peak I(Ca, L) densities in epicardial myocytes exposed to I/R injury (P < 0.05). SpostC decreased intracellular reactive oxygen species (ROS) levels, reduced the incidence of ventricular tachycardia and ventricular fibrillation, and decreased reperfusion arrhythmia scores compared with the I/R group (all P < 0.05). SpostC attenuates APD shortening and I(Ca, L) suppression induced by I/R injury. The regulation of APD and I(Ca, L) by SpostC might be related with intracellular ROS modulation, which contributes to the alleviation of reperfusion ventricular arrhythmia.

Myocardial protective effect of sevoflurane postconditioning and its mechanism

Background Many evidences have showed that mechanical ischemic and pharmacological postconditioning are protective against myocardial ischemia/reperfusion injury.Sevoflurane,a novel and ideal volatile anesthetic,is most commonly used to maintain the state of general anesthesia.Experiments have proved that sevoflurane postconditioning can protect against myocardial ischemia/reperfusion injury(I/RI).Objective The review elaborates myocardial protection of sevoflurane postconditioning and its mechanism by summarizing studies and researches in recent years.Content Sevoflurane postconditioning can reduce reperfusion myocardial infarct size,mitochondrial damage and ventricular arrhythmia,as well as improve cardiac hemodynamic after reperfusion.The myocardial protection mechanism involves blocking mitochondrial permeability transition pore,activating mitochondrial KATP-Channels(mKATp),extracellular signal-regulated kinase 1/2(ERK 1/2)and phatidylinosito1-3-kinase-serine/threonine kinase(PI3K-Akt)signaling pathway,etc.Trend Researches in future should be taken to further explore of the mechanism of sevoflurane postconditioning.And strengthening the clinical applications of sevoflurane postconditioning will also be helpful to provide a reliable basis for the practice work. Key words: Sevoflurane; Ischemia postconditioning; Ischemia/reperfusion injury; Myocardial protection

CD36 overexpression predisposes to arrhythmias but reduces infarct size in spontaneously hypertensive rats: gene expression profile analysis.

CD36 fatty acid translocase plays a key role in supplying heart with its major energy substrate, long-chain fatty acids (FA). Previously, we found that the spontaneously hypertensive rat (SHR) harbors a deletion variant of Cd36 gene that results in reduced transport of long-chain FA into cardiomyocytes and predisposes the SHR to cardiac hypertrophy. In the current study, we analyzed the effects of mutant Cd36 on susceptibility to ischemic ventricular arrhythmias and myocardial infarction in adult SHR-Cd36 transgenic rats with wild-type Cd36 compared with age-matched SHR controls. Using an open-chest model of coronary artery occlusion, we found that SHR-Cd36 transgenic rats showed profound arrhythmogenesis resulting in significantly increased duration of tachyarrhythmias (207 ± 48 s vs. 55 ± 21 s, P < 0.05), total number of premature ventricular complexes (2,623 ± 517 vs. 849 ± 250, P < 0.05) and arrhythmia score (3.86 ± 0.18 vs. 3.13 ± 0.13, P < 0.001). On the other hand, transgenic SHR compared with SHR controls showed significantly reduced infarct size (52.6 ± 4.3% vs. 72.4 ± 2.9% of area at risk, P < 0.001). Similar differences were observed in isolated perfused hearts, and the increased susceptibility of transgenic SHR to arrhythmias was abolished by reserpine, suggesting the involvement of catecholamines. To further search for possible molecular mechanisms of altered ischemic tolerance, we compared gene expression profiles in left ventricles dissected from 6-wk-old transgenic SHR vs. age-matched controls using Illumina-based sequencing. Circadian rhythms and oxidative phosphorylation were identified as the top KEGG pathways, while circadian rhythms, VDR/RXR activation, IGF1 signaling, and HMGB1 signaling were the top IPA canonical pathways potentially important for Cd36-mediated effects on ischemic tolerance. It can be concluded that transgenic expression of Cd36 plays an important role in modulating the incidence and severity of ischemic and reperfusion ventricular arrhythmias and myocardial infarct size induced by coronary artery occlusion. The proarrhythmic effect of Cd36 transgene appears to be dependent on adrenergic stimulation.

ORAL PRESENTATION

ORAL PRESENTATION

Suppression of Ischemic and Reperfusion Ventricular Arrhythmias by Inhalational Anesthetic-Induced Preconditioning in the Rat Heart

Inhalational anesthetic-induced preconditioning (APC) has been shown to reduce infarct size and attenuate contractile dysfunction caused by myocardial ischemia. Only a few studies have reported the effects of APC on arrhythmias during myocardial ischemia-reperfusion injury, focusing exclusively on reperfusion. Accordingly, the aim of the present study was to examine the influence of APC on ventricular arrhythmias evoked by regional no-flow ischemia. APC was induced in adult male Wistar rats by 12-min exposures to two different concentrations (0.5 and 1.0 MAC) of isoflurane followed by 30-min wash-out periods. Ventricular arrhythmias were assessed in the isolated perfused hearts during a 45-min regional ischemia and a subsequent 15-min reperfusion. Myocardial infarct size was determined after an additional 45 min of reperfusion. The incidence, severity and duration of ventricular arrhythmias during ischemia were markedly reduced by APC. The higher concentration of isoflurane had a larger effect on the incidence of ventricular fibrillation than the lower concentration. The incidence of ventricular tachycardia and reversible ventricular fibrillation during reperfusion was also significantly reduced by APC; the same was true for myocardial infarct size. In conclusion, we have shown that preconditioning with isoflurane confers profound protection against myocardial ischemia- and reperfusion-induced arrhythmias and lethal myocardial injury.

D Modulation of gap junctional coupling as an anti-arrhythmic strategy to prevent reperfusion ventricular arrhythmias

<h3>Background</h3> Reperfusion arrhythmias can occur within seconds of restoration of blood flow to previously ischaemic myocardium. Heterogeneities and abrupt changes in both gap junctional coupling and action potentials during early reperfusion are thought to contribute to their pathophysiology. We tested the hypothesis that modulating gap junctional coupling can reduce the incidence of reperfusion arrhythmias, and used optical mapping to assess the mechanisms of any anti-arrhythmic effect. <h3>Methods</h3> Using a Langendorff apparatus, rat hearts were perfused with either 50 nM AAP10 to increase gap junctional coupling (n=10), 30 μM carbenoxolone (CBX) to reduce coupling (n=13) or control Krebs-Henseleit solution (n=10). Hearts were then subjected to regional ischaemia by occlusion of the left anterior descending artery for 8 min and then reperfused. Ventricular arrhythmia incidence was documented. For optical mapping experiments, a further eighteen hearts were loaded with a voltage-sensitive dye (RH237), perfused with an excitation-contraction uncoupler (10μM blebbistatin) and either AAP10 (n=6), carbenoxolone (n=6) or control (n=6), and then subjected to ischaemia and reperfusion as above whilst transmembrane voltage (V_m) transients were recorded. <h3>Results</h3> Both AAP10 and CBX reduced the incidence of reperfusion VF (AAP10 50%, CBX 77%, Control 90%) and delayed time to onset of reperfusion VF (AAP10 29.0±9.9 s; CBX 52.2±13.2 s; Control 21.8 s±6.4 s) (LogRank p&lt;0.05). AAP10 reduced the dispersion of action potential duration (APD) in ischaemic myocardium (AAP10 2.3±0.8 ms; CBX 5.1±1.2 ms; Control 4.9±2.0 ms, p&lt;0.05). AAP10 also improved conduction across a 0.6 cm² central ischaemic zone in the anterior left ventricle (LV) (Activation time: AAP10 15.3 ± 1.3ms; CBX 25.7 ±2.2 ms; Control 23.2±2.0 ms, p&lt;0.05) immediately prior to reperfusion. CBX slowed conduction and prolonged this activation time post-reperfusion (AAP10 10.3±0.8 ms; CBX 15.8±2.8 ms; Control 9.5±1.2 ms), thus resulting in smaller changes in conduction velocities pre- and post-reperfusion compared with control. <h3>Conclusions</h3> Both increasing and reducing gap junctional coupling, with AAP10 and CBX respectively, reduced the rate and delayed the onset of reperfusion VF. This suggests that the partial uncoupling that occurs during early reperfusion is a determinant of reperfusion arrhythmias, and that both normalising the degree of coupling or further exacerbating uncoupling may be anti-arrhythmic. The anti-arrhythmic effect of increasing gap junctional coupling may be mediated by its dual effect of reducing action potential heterogeneity and improving conduction during reperfusion. Further uncoupling may be protective via attenuation of the abrupt changes in coupling and conduction that occur at reperfusion following ischaemia.

Acute Caloric Restriction is Cardioprotective in Adult Rats

Reduced coronary perfusion in acute coronary syndrome causes myocardial ischemia. Also the effect of reactive oxygen species (ROS) induced ischemia‐reperfusion injury contributes to myocardial lesion. ROS generation in hypoxia is modulated by the redox state. Fasting before exposure to ischemia should increase ketogenesis that consumes reduced coenzymes and consequently reduces free radical damage.We investigated whether the 3‐day fasting affects production of ROS, incidence of ventricular arrhythmias during ischemia/reperfusion and myocardial infarction size.We analyzed production of the lipid peroxidation end products (LFP) in the heart tissue. Open‐chest rats were subjected to 20‐min LAD coronary artery occlusion followed by reperfusion. A single‐lead ECG was recorded and arrhythmias were assessed. The infarction size in excised hearts was determined by triphenyltetrazolium chloride staining and it was normalized to area at risk (IS/AR).Three day fasting reduced LFP production in heart tissue. During early reperfusion the number of premature ventricular complexes was reduced in fasting rats compared to controls, as well as ventricular tachycardia duration. In fasting rats the IS/AR reached 48.5 ± 3.3 % while in controls it was 74.3 ± 2.2 %, p&lt;0.005.Acute caloric restriction limits free radical damage in heart, reperfusion ventricular arrhythmias and myocardial infarction size in rats.Supported by GAUK 60009/2009 and MSMT 1M 0510.