Electrical remodeling of the ventricular myocardium in myocarditis: studies of rat experimental autoimmune myocarditis

The natural history of CVB3 myocarditis in C57BL/6J mice: an extended in-depth characterization

BACKGROUND AND AIMS

Viral infections are the leading cause of myocarditis. Besides acute cardiac complications, late-stage sequelae such as myocardial fibrosis may develop, importantly impacting the prognosis. Coxsackievirus B3 (CVB)-induced myocarditis in mice is the most commonly used translational model to study viral myocarditis and has provided the majority of our current understanding of the disease pathophysiology. Nevertheless, the late stages of disease, encompassing fibrogenesis and arrhythmogenesis, have been underappreciated in viral myocarditis research to date. The present study investigated the natural history of CVB-induced myocarditis in C57BL/6J mice, expanding the focus beyond the acute phase of disease. In addition, we studied the impact of sex and inoculation dose on the disease course.

METHODS AND RESULTS

C57BL/6J mice (12 weeks old; n=154) received a single intraperitoneal injection with CVB to induce viral myocarditis, or vehicle (PBS) as control. Male mice (n=92) were injected with 5 × 105 (regular dose) (RD) or 5 × 106 (high dose) (HD) plaque-forming units of CVB, whereas female mice received the RD only. Animals were sacrificed 1, 2, 4, 8, and 11 weeks after CVB or PBS injection. Virally inoculated mice developed viral disease with a temporary decline in general condition and weight loss, which was less pronounced in female animals (P<.001). In male CVB mice, premature mortality occurred between days 8 and 23 after inoculation (RD: 21%, HD: 20%), whereas all female animals survived. Over the course of disease, cardiac inflammation progressively subsided, with faster resolution in female mice. There were no substantial group differences in the composition of the inflammatory cell infiltrates: predominance of cytotoxic T cells at day 7 and 14, and a switch from arginase1-reactive macrophages to iNOS-reactive macrophages from day 7 to 14 were the main findings. There was concomitant development and maturation of different patterns of myocardial fibrosis, with enhanced fibrogenesis in male mice. Virus was almost completely cleared from the heart by day 14. Serum biomarkers of cardiac damage and cardiac expression of remodeling genes were temporarily elevated during the acute phase of disease. Cardiac CTGF gene upregulation was less prolonged in female CVB animals. In vivo electrophysiology studies at weeks 8 and 11 demonstrated that under baseline conditions (i.e. in the absence of proarrhythmogenic drugs), ventricular arrhythmias could only be induced in CVB animals. The cumulative arrhythmia burden throughout the entire stimulation protocol was not significantly different between CVB and control groups.

CONCLUSION

CVB inoculation in C57BL/6J mice represents a model of acute self-limiting viral myocarditis, with progression to different patterns of myocardial fibrosis. Sex, but not inoculation dose, seems to modulate the course of disease.

Soluble suppression of tumorigenicity 2 associated with major adverse cardiac events in children with myocarditis

Objective

Soluble suppression of tumorigenicity 2 (sST2) is associated with the prognosis of some cardiac diseases, but studies on sST2 and the prognosis of patients with myocarditis are rare. This study investigated the relationship between major adverse cardiovascular events (MACEs) and sST2 during hospitalization in pediatric patients with myocarditis.

Methods

This was a single-center retrospective cohort study. A total of 252 patients aged ≤14 years diagnosed with myocarditis were enrolled. Events during the hospitalization were defined as MACEs (all-cause death > new heart failure > ventricular arrhythmia).

Results

A total of 25 people had MACEs during their hospital stay. The mortality during hospitalization was 6/23 (26%) in patients with heart failure and 3/10 (30%) in patients with ventricular arrhythmias. After including these risk factors in a multivariate logistic regression analysis, NT-proBNP (OR 4.323; 95% CI, 2.433-7.679; p < 0.001) and sST2 (OR 1.020; 95% CI, 1.003-1.037; p = 0.022) remained statistically significant and were independent risk factors for MACEs during hospitalization in pediatric myocarditis patients.

Conclusions

Elevated levels of NT-proBNP and sST2 were independently associated with major adverse cardiovascular events during hospitalization in children with myocarditis, and both showed good predictive efficacy.

Imbalance of Pro- and Anti-inflammatory Cytokines Induced Different Types of Recurrent Atrial Arrhythmias after Drug Eluting Coronary Stent Implantation

BACKGROUND

Atrial arrhythmias are associated with an increased risk of stroke and death in the elderly. The risk and predictive factors of recurrent atrial arrhythmias in elderly patients after coronary stenting are not well known.

OBJECTIVE

This research sought to investigate the roles of pro- and anti-inflammatory cytokine imbalances in different types of recurrent atrial arrhythmias in elderly patients defined as individuals aged 65 years or older after sirolimus eluting stent (Cordis, Warren, New Jersey) implantation.

METHODS

We measured interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), interleukin-17 (IL-17), interleukin-13 (IL-13) and interleukin- 37 (IL-37) in elderly patients with recurrent atrial arrhythmias and assessed the impact of pro- and antiinflammatory cytokine imbalances on recurrent atrial arrhythmias in elderly patients after coronary stenting.

RESULTS

Levels of IL-1 β, IL-6, IL-8, and TNF-α were remarkably increased (p<0.001), and IL-10, IL- 17, IL-13, and IL-37 were remarkably lowered (p<0.001) in elderly patients with recurrent atrial arrhythmias after coronary stent implantation. Imbalance of pro- and anti-inflammatory cytokines induced recurrent atrial arrhythmias after coronary stenting. Pro- and anti-inflammatory cytokine imbalances may be used to identify elderly patients who have an increased risk of developing recurrent atrial arrhythmias after coronary stenting.

CONCLUSION

The imbalance of pro- and anti-inflammatory cytokines was associated with recurrent atrial arrhythmias in elderly patients after coronary stenting. Pro- and anti-inflammatory cytokines may be clinically useful biomarkers for predicting recurrent atrial arrhythmias in elderly patients after coronary stent implantation.

Viral Myocarditis: Classification, Diagnosis, and Clinical Implications

Myocarditis is an inflammatory disease of the myocardium with focal or diffuse involvement. Viral infections are the most common cause of myocarditis, especially in Western countries. A recent viral illness with gastroenteric or upper respiratory symptoms often precedes myocarditis. The absence of specific pathognomonic features in conjunction with the wide spectrum of clinical manifestations that range from subclinical cases to sudden cardiac death (SCD) makes myocarditis diagnosis particularly challenging. Moreover, myocarditis might represent a cause of initially unexplained dilated cardiomyopathy (DCM) and heart failure (HF), especially among children and young adults. Cardiac magnetic resonance imaging (CMR) is crucial for myocarditis diagnosis, because of its ability to detect interstitial edema during acute inflammation. Assessment of subepicardial or mid-myocardial fibrosis by late gadolinium enhancement (LGE) is typical for myocarditis. Cardiac arrhythmias are frequent events that may arise especially in more severe myocarditis cases. The most common form of arrhythmia is atrial fibrillation, followed by ventricular tachycardia. Documented arrhythmias have been reported more commonly with HIV myocarditis than other more common infections such as Adenovirus, Parvovirus B19, human Herpes virus 6, and Enterovirus. The mechanisms of arrhythmogenesis in myocardial inflammation are not fully understood; in the acute phase, the spectrum of arrhythmogenesis ranges from a direct effect on cardiomyocytes that leads to electrical instability and ion channel impairment to ischemia from coronary macro- or microvascular disease. In chronic myocarditis, instead, myocardial replacement with fibrosis promotes scar-mediated re-entrant ventricular arrhythmias. Observational data suggested the important role of CMR, with LGE being the strongest independent predictor of SCD, cardiac, and all-cause mortality. In acute myocarditis, the most common localization of subepicardial LGE dwells in the lateral wall. Patients with myocarditis that develop HF and arrhythmias usually show a larger LGE distribution involving several myocardial segments. Moreover, a mid-layer LGE in the interventricular septum is more frequent in acute myocarditis than in acute coronary syndromes cases. The risk of SCD in patients with wide areas of LGE is significant, and a shared decision-making approach is warranted. Nevertheless, there is no formal consensus about the extension of LGE to justify implantable cardioverter defibrillator (ICD) implantation in primary prevention.

Diagnosis, treatment and predictors of prognosis of myocarditis. A narrative review

Although it has been recognized for almost two centuries, myocarditis is still a challenging diagnosis due to the wide heterogeneity of its clinical manifestations and evolution. Moreover, the diagnostic gold standard, endomyocardial biopsy (EMB), is infrequently used, making hard to determine the exact incidence of myocarditis. Clinical presentation includes a wide range of symptoms, ranging from asymptomatic or subclinical disease with mild dyspnea and chest pain to sudden death, due to cardiogenic shock or malignant ventricular arrhythmias. Equally, the evolution of myocarditis largely varies: albeit short-term prognosis is usually good, with complete or partial recovery, dilated cardiomyopathy with chronic heart failure is the major long-term consequence of myocarditis, developing often several years after the acute onset. This narrative review aims to summarize the current knowledge about myocarditis, with a particular attention to predictors of short- and long-term prognosis, in order to provide a rational and practical approach to the diagnosis, evaluation and treatment of suspected myocarditis.

Impact of ventricular arrhythmias on outcomes in children with myocarditis

Children affected with acute myocarditis may progress rapidly into profound ventricular dysfunction and ventricular arrhythmias. The objective of this study is to assess the impact of ventricular arrhythmias on in-hospital mortality and the use of mechanical circulatory support in patients with myocarditis. Pediatric patients (age 0-18 years) admitted with myocarditis were identified from the National Inpatient Sample dataset for the years 2002-2015. A total of 12,489 patients with myocarditis were identified. Of them, 1627 patients were with ventricular arrhythmias and 10,862 patients without ventricular arrhythmias. Mortality was higher in those with ventricular arrhythmias (19.5% vs. 2.8%, OR = 8.47; 95% CI 7.16-10.04; p < 0.001). The median length of stay and the median cost of hospitalization were higher in the ventricular arrhythmias group (9 days vs. 4 days, p < 0.001 and $121,826 vs. $37,658, p < 0.001, respectively). There was a substantial increase in the utilization of extracorporeal membrane oxygenation (ECMO) in patients with ventricular arrhythmias (25.4% vs. 2.7%, OR = 12.40; 95% CI 10.55-14.57; p < 0.001). The use of ventricular assist devices (VADs) was higher in patients with ventricular arrhythmias (4.5% vs. 1.3%, OR = 3.76; 95% CI 2.82-5.01; p < 0.001). An improvement in discharge survival was observed over the years of study in both VA and non-VA groups; associated with this decline in mortality, there was a rising trend of ECMO utilization.Conclusion: Development of ventricular arrhythmia in children with myocarditis is a strong predictor for mortality and ECMO utilization. What is Known: • The clinical presentation of pediatric myocarditis varies from no symptoms of myocardial dysfunction to a rapidly progressing severe congestive heart failure. • Little is known about the predictors of mortality in children with suspected myocarditis. What is New: • Development of ventricular arrhythmia in children with myocarditis is a strong predictor for mortality and ECMO utilization. • Improvement in discharge survival was observed over the years of study; associated with this decline in mortality, there was a rising trend of ECMO utilization.

Heart Infection Prognosis Analysis by Two-dimensional Spot Tracking Imaging

Cardiovascular death is one of the leading causes worldwide; an accurate identification followed by diagnosing the cardiovascular disease increases the chance of a better recovery. Among different demonstrated strategies, imaging on cardiac infections yields a visible result and highly reliable compared to other analytical methods. Two-dimensional spot tracking imaging is the emerging new technology that has been used to study the function and structure of the heart and test the deformation and movement of the myocardium. Particularly, it helps to capture the images of each segment in different directions of myocardial strain values, such as valves of radial strain, longitudinal strain, and circumferential strain. In this overview, we discussed the imaging of infections in the heart by using the two-dimensional spot tracking.

High Risk of Sustained Ventricular Arrhythmia Recurrence After Acute Myocarditis

Acute myocarditis is associated with cardiac arrhythmia in 25% of cases; a third of these arrhythmias are ventricular tachycardia (VT) or ventricular fibrillation (VF). The implantation of a cardiac defibrillator (ICD) following sustained ventricular arrhythmia remains controversial in these patients. We sought to assess the risk of major arrhythmic ventricular events (MAEs) over time in patients implanted with an ICD following sustained VT/VF in the acute phase of myocarditis compared to those implanted for VT/VF occurring on myocarditis sequelae. Our retrospective observational study included patients implanted with an ICD following VT/VF during acute myocarditis or VT/VF on myocarditis sequelae, from 2007 to 2017, in 15 French university hospitals. Over a median follow-up period of 3 years, MAE occurred in 11 (39%) patients of the acute myocarditis group and 24 (60%) patients of the myocarditis sequelae group. Kaplan–Meier MAE rate estimates at one and three years of follow-up were 19% and 45% in the acute group, and 43% and 64% in the sequelae group. Patients who experienced sustained ventricular arrhythmias during acute myocarditis had a very high risk of VT/VF recurrence during follow-up. These results show that the risk of MAE recurrence remains high after resolution of the acute episode.

Sudden cardiac death in patients with myocarditis: Evaluation, risk stratification, and management

Myocarditis is a major cause of sudden cardiac death (SCD) and dilated cardiomyopathy (DCM) in young adults. Cardiac magnetic resonance is the established tool for the diagnosis of myocarditis, and late gadolinium enhancement detected on cardiac magnetic resonance imaging is the strongest independent predictor of SCD, all-cause mortality, and cardiac mortality. Several other factors have been associated with SCD or cardiac transplantation including New York Heart Association functional class III/IV, reduced left ventricular ejection fraction <35%, and right ventricular ejection fraction ≤45%. A fragmented QRS and a prolonged QTc interval on an electrocardiogram are predictors of VAs. The postulated mechanism of VA in acute myocarditis is ion channel dysfunction and inflammation that alter intracellular signaling, producing interstitial edema and fibrosis and thereby causing conduction abnormalities. VAs in chronic myocarditis are generally due to scar-mediated reentry. Treatment of myocarditis is tailored toward supportive care and symptomatic relief. The subset of patients who develop DCM should be treated with heart failure medications according to professional guideline recommendations. Indications for an implantable cardioverter-defibrillator are similar to those for nonischemic cardiomyopathy; however, an implantable cardioverter-defibrillator should be held in the acute phase of myocarditis to allow left ventricular ejection fraction recovery, and a wearable cardioverter-defibrillator may be beneficial for some patients. Antiarrhythmic medications are reserved for patients with symptomatic nonsustained or sustained VAs. Radiofrequency ablation appears to be an effective treatment option for VAs; however, more data on its safety and effectiveness are needed. This review addresses risk factors of SCD and VAs in patients with myocarditis with special emphasis on treatment and prevention of these outcomes.

Myocarditis in Athletes Is a Challenge: Diagnosis, Risk Stratification, and Uncertainties

Presentation of myocarditis in athletes is heterogeneous and establishing the diagnosis is challenging with no current uniform clinical gold standard. The combined information from symptoms, electrocardiography, laboratory testing, echocardiography, cardiac magnetic resonance imaging, and in certain cases endomyocardial biopsy helps to establish the diagnosis. Most patients with myocarditis recover spontaneously; however, athletes may be at higher risk of adverse cardiac events. Based on scarce evidence and mainly autopsy studies and expert's opinions, current recommendations generally advise abstinence from competitive sports ranging from a minimum of 3 to 6 months. However, the dilemma poses that (un)necessary prolonged disqualification of athletes to avoid adverse cardiac events can cause considerable disruption to training schedules and tournament preparation and lead to a decline in performance and ability to compete. Therefore, better risk stratification tools are imperatively needed. Using latest available data, this review contrasts existing recommendations and presents a new proposed diagnostic flowchart putting a greater focus on the use of cardiac magnetic resonance imaging in athletes with suspected myocarditis. This may enable cardiac caregivers to counsel athletes with suspected myocarditis more systematically and furthermore allow for pooling of more unified data. To modify recommendations regarding sports behavior in athletes with myocarditis, evidence, based on large multicenter registries including cardiac magnetic resonance imaging and endomyocardial biopsy, is needed. In the future, physicians might rely on combined novel risk stratification methods, by implementing both noninvasive and invasive tissue characterization methods.

Linagliptin Suppresses Electrical and Structural Remodeling in the Isoproterenol Induced Myocardial Injury Model

The effect of DPP-4 inhibitor on the electrical and structural remodeling in myocardial injury has not been evaluated. We hypothesized that linagliptin, DPP-4 inhibitor, suppresses myocardial remodeling in the isoproterenol (ISP)-induced myocardial injury model.Sprague-Dawley rats were assigned to 3 groups: 1) sham group, 2) ISP group (subcutaneous ISP injection of 70 mg/kg), and 3) ISP + linagliptin (ISP + Lin) (5 mg/kg/day, p.o.) group. Serum was sampled on day 1 (acute phase) and day 7 (sub-acute phase) to evaluate derivatives of reactive oxidative metabolites (d-ROMs). The electrophysiological study was performed in sub-acute phase for the evaluation of the ventricular effective refractory period (VERP) and monophasic action potential duration (MAPD). The VERP and MAPD were markedly prolonged in the ISP group in comparison with the sham (MAPD20: 14 ± 6 versus 11 ± 3 ms, MAPD90: 57 ± 8 versus 44 ± 7 ms, VERP: 74 ± 22 versus 38 ± 10 ms, P < 0.05). In contrast in the ISP + Lin group, such prolongations were suppressed, and the parameters were shorter than the ISP group (MAPD20: 9 ± 2 ms, MAPD90: 35 ± 6 ms, VERP: 52 ± 13 ms, P < 0.05). ISP treatment induced myocardial injury. The injured area was reduced in the ISP + Lin group in comparison with the ISP group (P < 0.05). Serum d-ROMs level in acute phase was higher in ISP group than the other 2 groups (sham: 214 ± 55 versus ISP: 404 ± 45 versus ISP + Lin: 337 ± 20 U.CARR, P < 0.05).Linagliptin suppressed structural and electrical changes, possibly through the antioxidative effect, in this myocardial injury model.

Increased risk of ventricular tachycardia and cardiovascular death in patients with myocarditis during the long-term follow-up: A national representative cohort from the National Health Insurance Research Database

The incidence of acute myocarditis complicated with ventricular tachycardia (VT) is unknown. This study aimed to investigate the association between myocarditis and the incidence of VT and mortality. We also aimed to determine the independent predictors that increased the VT risk in those patients. From 2000 to 2004, 13,250 patients with a history of myocarditis were identified from the Taiwan National Health Insurance Research Database. The same number of individuals without heart disease with a matched sex and underlying diseases were selected as the control group. The long-term risks of life-threatening ventricular arrhythmias and mortality in patients with a history of myocarditis were investigated by an adjusted Cox proportional hazards regression. After a mean follow-up of 10.4 ± 2.94 years (interquartile range: 12, 10.19-12), the myocarditis patients showed a higher incidence of new onset VT events compared with healthy controls (5.4% [519 per 100,000 person-year] in the myocarditis group vs, 0.47% [43 per 100,000 person-year] in the healthy controls; adjusted hazard ratio [HR]: 16.1, 95% confidence interval [CI]: 12.4-20.9; P < .001). A higher incidence of cardiovascular death was noted in the myocarditis group than healthy controls (6.52% vs 3.18%; HR: 2.42, 95% CI: 2.14-2.73; P < .001) after adjusting for the multivariate confounders including sex, age, underlying comorbidities, and medications. The results of this study suggested that there was higher incidence of life-threatening VT and mortality during the very long-term follow-up in patients with a history of myocarditis. Future work should focus on an in-depth risk stratification of VT in myocarditis patients.

What Is the Arrhythmic Substrate in Viral Myocarditis? Insights from Clinical and Animal Studies

Sudden cardiac death (SCD) remains an unsolved problem in the twenty-first century. It is often due to rapid onset, ventricular arrhythmias caused by a number of different clinical conditions. A proportion of SCD patients have identifiable diseases such as cardiomyopathies, but for others, the causes are unknown. Viral myocarditis is becoming increasingly recognized as a contributor to unexplained mortality, and is thought to be a major cause of SCD in the first two decades of life. Myocardial inflammation, ion channel dysfunction, electrophysiological, and structural remodeling may play important roles in generating life-threatening arrhythmias. The aim of this review article is to examine the electrophysiology of action potential conduction and repolarization and the mechanisms by which their derangements lead to triggered and reentrant arrhythmogenesis. By synthesizing experimental evidence from pre-clinical and clinical studies, a framework of how host (inflammation), and viral (altered cellular signaling) factors can induce ion electrophysiological and structural remodeling is illustrated. Current pharmacological options are mainly supportive, which may be accompanied by mechanical circulatory support. Heart transplantation is the only curative option in the worst case scenario. Future strategies for the management of viral myocarditis are discussed.

Arrhythmias in viral myocarditis and pericarditis

Acute viral myocarditis and acute pericarditis are self-limiting conditions that run a benign course and that may not involve symptoms that lead to medical assessment. However, ventricular arrhythmia is frequent in viral myocarditis. Myocarditis is thought to account for a large proportion of sudden cardiac deaths in young people without prior structural heart disease. Identification of acute myocarditis either with or without pericarditis is therefore important. However, therapeutic interventions are limited and nonspecific. Identifying those at greatest risk of a life-threatening arrhythmia is critical to reducing the mortality. This review summarizes current understanding of this challenging area in which many questions remain.

Increased phosphorylation of Ca(2+) handling proteins as a proarrhythmic mechanism in myocarditis

BACKGROUND

Because fatal arrhythmia is an important cause of death in patients with myocarditis, we investigated the proarrhythmic mechanisms of experimental autoimmune myocarditis. METHODS AND RESULTS: Myocarditis was induced by injection of 2 mg porcine cardiac myosin into the footpads of adult Lewis rats on days 1 and 8 (Myo, n=15) and the results compared with Control rats (Control, n=15). In an additional 15 rats, 6 mg/kg prednisolone was injected into the gluteus muscle before the injection of porcine cardiac myosin on days 1 and 8 (MyoS, n=15). Hearts with myocarditis had longer action potential duration (APD), slower conduction velocity (CV; P<0.01 vs. Control), higher CV heterogeneity, greater fibrosis, higher levels of immunoblotting of high-mobility group protein B1, interleukin 6 and tumor necrosis factor-α proteins. Steroid treatment partially reversed the translations for myocarditis, CV heterogeneity, reduced APD at 90% recovery to baseline, increased CV (P<0.01), and reversed fibrosis (P<0.05). Programmed stimulation triggered sustained ventricular tachycardia in Myo rats (n=4/5), but not in controls (n=0/5) or Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitor (KN93) treated Myo rats (n=0/5, P=0.01). CaMKII autophosphorylation at Thr287 (201%), and RyR2 phosphorylation at Ser2808 (protein kinase A/CaMKII site, 126%) and Ser2814 (CaMKII site, 21%) were increased in rats with myocarditis and reversed by steroid.

CONCLUSIONS

The myocarditis group had an increased incidence of arrhythmia caused by increased phosphorylation of Ca(2+)handling proteins. These changes were partially reversed by an antiinflammatory treatment and CaMKII inhibition.

Mortality and morbidity in different immunization protocols for experimental autoimmune myocarditis in rats

AIM

We aimed to investigate the histological and clinical presentations of experimental autoimmune myocarditis (EAM) induced by different immunization schemes.

METHODS

Male young Lewis rats were divided into five groups immunized by porcine myocardial myosin: subcutaneously (SC) 2 mg (in two 1-mg doses on day 0 and 7), 0 mg (sham group) subcutaneously into rear footpads (RF), 0.25 mg RF, 0.5 mg RF or 1 mg RF (all RF once on day 0). On day 21, left ventricular (LV) function was assessed by cardiac magnetic resonance imaging and cardiac catheterization. The type and degree of myocardial inflammatory infiltrates were determined by conventional histology and immunohistochemistry.

RESULTS

In the SC immunized rats and in the RF sham group, we observed 0% mortality, while in the actively RF immunized rats, mortality was 20, 20 and 44% for the 0.25 mg, 0.5 mg and 1 mg myosin doses respectively. Morbidity as defined by inflammatory infiltrates on haematoxylin and eosin (HE) staining was 22% in the SC immunized rats, 0% in the RF sham group and 100% in all actively RF immunized groups. We observed augmented relative ventricle weight and spleen weight, increased LV end-diastolic pressure, reduced LV developed pressure and reduced LV ejection fraction in all with myosin-immunized RF groups without any systematic dose effect.

CONCLUSION

Subcutaneous immunization to the neck and flanks did not induce a reproducible EAM, while RF myosin administration reliably led to EAM. Lower myosin doses seem to induce the complete histological and clinical picture of EAM while being associated with lower mortality, non-specific symptoms and animal distress.

Drug-Refractory Ventricular Tachycardias After Myocarditis

Background—

Ventricular tachycardia (VT) is a significant therapeutic challenge in patients with myocarditis. This study aimed to assess the efficacy and safety of radiofrequency catheter ablation (RFCA) of VT in patients with myocarditis.

Methods and Results—

We enrolled 20 patients (15 men; age, 42 [28–52] years) with a history of biopsy-proven viral myocarditis and drug-refractory VT; 5 patients presented with electrical storm. The median left ventricular ejection fraction was 55% (45–60%). All patients underwent endocardial RFCA with an irrigated catheter, using contact electroanatomic mapping. Recurrence of sustained VT after endocardial RFCA was treated with additional epicardial RFCA. Endocardial RFCA was acutely successful in 14 patients (70%) while in the remaining 6 (30%) clinical VT was successfully ablated by epicardial RFCA. In 1 patient, hemodynamic instability required an intra-aortic balloon pump to complete RFCA. No major complication occurred during or after RFCA. Over a median follow-up time of 28 (11–48) months, 18 patients (90%) remained free of sustained VT; 2 patients (10%, both with baseline left ventricular ejection fraction ≤35%) died of acute heart failure unrelated to ventricular arrhythmias.

Conclusions—

In patients with myocarditis, RFCA of drug-refractory VT is feasible, safe, and effective. Epicardial RFCA should be considered as an important therapeutic option to increase success rate.

Progression of ventricular remodeling and arrhythmia in the primary hyperoxidative state of glutathione-depleted rats

BACKGROUND

Although oxidative stress is considered to promote arrhythmogenic substrates in diseased model animals, it is difficult to evaluate its primary role. In this study, we evaluated the promotion of arrhythmogenic substrates in the primary hyperoxidative state.

METHODS AND RESULTS

Sprague-Dawley rats were treated with L-buthionine-sulfoximine (BSO, 30 mmol · L(-1) · day(-1)) for 14 days. On day 7 or 14, the serum levels of derivatives of reactive oxygen metabolites (d-ROM) were measured, and immune staining of 8-hydroxy-2'-deoxyguanosine (8O HdG) was performed to assess oxidative stress. The ventricular effective refractory period (ERP), monophasic action potential duration (MAPD), and the inducibility of ventricular arrhythmia were also evaluated. BSO rats exhibited higher serum d-ROM and clearer 8OHdG staining than the controls. The inducibility of ventricular arrhythmia was higher in the BSO rats than in the controls. The ERP was shorter in the BSO rats than the control (day 14, 32 ± 1 vs. 36 ± 1 ms, P<0.05), whereas the MAPD(90) was longer in the BSO rats (day 14, 76 ± 5 vs. 55 ± 4 ms, P<0.05). The mRNA levels of Kv4.2, erg, and SERCA2a were downregulated in the BSO rats (P < 0.05), and Western blot analysis exhibited the downregulation of erg and SERCA2 expression in the BSO rats (P < 0.05).

CONCLUSIONS

Systemic oxidative stress might be one of the primary factors promoting cardiac electrophysiological remodeling and increasing the inducibility of arrhythmia independently of major organ disorders.

Atrial natriuretic peptide (ANP) suppresses acute atrial electrical remodeling in the canine rapid atrial stimulation model

OBJECTIVES

Atrial electrical remodeling is considered to play an important role in the appearance of atrial fibrillation. The effect of atrial natriuretic peptide (ANP) on atrial electrical remodeling was evaluated in a canine atrial stimulation model.

METHODS

In 15 beagle dogs, electrodes for pacing and recording were fixed on the atrial surface. In 10/15 dogs, rapid atrial stimulation (400 bpm) was performed for 7 h at the right atrial appendage (RAA) and the remaining 5 were used as the sham without rapid pacing. In 5/10 dogs with rapid pacing, human atrial natriuretic peptide (ANP) was infused (1.0 microg/kg/min). The effective refractory period (ERP) and the monophasic action potential duration (MAP) were evaluated at 0, 3, and 7 h after rapid pacing. The expression levels of mRNAs of ion channels or transporters were evaluated from the atrial samples of sham and after a 7 hour pacing.

RESULTS

In the control group with rapid pacing (n=5), the atrial ERP and MAP duration were shortened at all atrial sites, e.g., ERP from 148+/-14 ms to 109+/-8 ms at RAA, P=0.006. In contrast in the ANP group, neither the ERP nor MAP duration showed a significant shortening and the effect of ANP on hemodynamic parameter was relatively small. Expression levels of the mRNA were not significantly different between the control and ANP groups.

CONCLUSIONS

Administration of ANP prevented the shortening of the ERP and MAP duration in the rapid atrial stimulation model. The effect of ANP on atrial electrical remodeling was considered to be due to its direct action on the myocardium.

Contactless magnetocardiographic mapping in anesthetized Wistar rats: evidence of age-related changes of cardiac electrical activity

Magnetocardiography (MCG) is the recording of the magnetic field (MF) generated by cardiac electrophysiological activity. Because it is a contactless method, MCG is ideal for noninvasive cardiac mapping of small experimental animals. The aim of this study was to assess age-related changes of cardiac intervals and ventricular repolarization (VR) maps in intact rats by means of MCG mapping. Twenty-four adult Wistar rats (12 male and 12 female) were studied, under anesthesia, with the same unshielded 36-channel MCG instrumentation used for clinical recordings. Two sets of measurements were obtained from each animal: 1) at 5 mo of age (297.5 ± 21 g body wt) and 2) at 14 mo of age (516.8 ± 180 g body wt). RR and PR intervals, QRS segment, and QTpeak, QTend, JTpeak, JTend, and Tpeak-end were measured from MCG waveforms. MCG imaging was automatically obtained as MF maps and as inverse localization of cardiac sources with equivalent current dipole and effective magnetic dipole models. After 300 s of continuous recording were averaged, the signal-to-noise ratio was adequate for study of atrial and ventricular MF maps and for three-dimensional localization of the underlying cardiac sources. Clear-cut age-related differences in VR duration were demonstrated by significantly longer QTend, JTend, and Tpeak-end in older Wistar rats. Reproducible multisite noninvasive cardiac mapping of anesthetized rats is simpler with MCG methodology than with ECG recording. In addition, MCG mapping provides new information based on quantitative analysis of MF and equivalent sources. In this study, statistically significant age-dependent variations in VR intervals were found.

Tumor Necrosis Factor-.ALPHA. Downregulates the Voltage Gated Outward K+ Current in Cultured Neonatal Rat Cardiomyocytes A Possible Cause of Electrical Remodeling in Diseased Hearts

BACKGROUND

Inflammatory cytokines have been reported to contribute to the progression of cardiac remodeling in various heart diseases and a remarkable prolongation of the monophasic action potential duration and reductions in the expression of Kv4.2 and K+ channel-interacting protein-2 (KChIP-2) in a rat autoimmune myocarditis model have been documented. In this study, the effect of tumor necrosis factor-alpha (TNF-alpha) on cultured cardiomyocytes was evaluated, focusing on the change in the voltage-gated outward K+ current and expression of related molecules.

METHODS AND RESULTS

Cardiomyocytes isolated from 1-day-old Lewis rats were cultured for 72 h and treated with TNF-alpha (50 ng/ml) for an additional 48 h. The myocytes treated with TNF-alpha showed a 22% reduction in the peak K+ current, which consisted of a transient outward K+ current (Ito) and 1.4-fold enhancement of the cell-capacitance in comparison with the control. Among the cardiac ion channel related molecules evaluated in this study, Kv4.2 and KChIP-2 mRNA exhibited remarkable reductions (p < 0.05).

CONCLUSIONS

Treatment with TNF-alpha induced reductions in Ito as well as cellular hypertrophy in neonatal cultured myocytes, which indicates that TNF-alpha might play a role in promoting electrical remodeling of cardiomyocytes under inflammatory conditions.

Electrical remodeling of cardiac myocytes from mice with heart failure due to the overexpression of tumor necrosis factor-alpha

Mice that overexpress the inflammatory cytokine tumor necrosis factor-alpha in the heart (TNF mice) develop heart failure characterized by atrial and ventricular dilatation, decreased ejection fraction, atrial and ventricular arrhythmias, and increased mortality (males > females). Abnormalities in Ca2+ handling, prolonged action potential duration (APD), calcium alternans, and reentrant atrial and ventricular arrhythmias were previously observed with the use of optical mapping of perfused hearts from TNF mice. We therefore tested whether altered voltage-gated outward K+ and/or inward Ca2+ currents contribute to the altered action potential characteristics and the increased vulnerability to arrhythmias. Whole cell voltage-clamp recordings of K+ currents from left ventricular myocytes of TNF mice revealed an approximately 50% decrease in the rapidly activating, rapidly inactivating transient outward K+ current Ito and in the rapidly activating, slowly inactivating delayed rectifier current IK,slow1, an approximately 25% decrease in the rapidly activating, slowly inactivating delayed rectifier current IK,slow2, and no significant change in the steady-state current Iss compared with controls. Peak amplitudes and inactivation kinetics of the L-type Ca2+ current ICa,L were not altered. Western blot analyses revealed a reduction in the proteins underlying Kv4.2, Kv4.3, and Kv1.5. Thus decreased K+ channel expression is largely responsible for the prolonged APD in the TNF mice and may, along with abnormalities in Ca2+ handling, contribute to arrhythmias.

Autoimmune myocarditis: cellular mediators of cardiac dysfunction

Immune mediators play a critical role in the pathogenesis and outcomes of a number of cardiac diseases. This review summarizes recent findings on the composition of the inflammatory infiltrate and the role of different types and subtypes of immune cells and their products in mediating cardiac dysfunction in experimental autoimmune myocarditis (EAM). CD4+ T cells are required for initiation of myocarditis and their numbers in the heart infiltrate correlate with systolic dysfunction during disease progression. Other immune cells, including CD8+ T cells, granulocytes, and mast cells, can directly affect cardiomyocyte function. When regulatory mechanisms fail, the local damage leads to cardiomyocyte death, replacement fibrosis and overall cardiac dysfunction. EAM provides insights into the role of the immune system in the development of dilated cardiomyopathy (DCM) and heart failure and may serve as a general paradigm for autoimmune organ-specific tissue damage.

Gene expression of cardiac mast cell chymase and tryptase in a murine model of heart failure caused by viral myocarditis

This study examined the gene expression of mouse mast cell proteases to clarify their role in the pathophysiology of viral myocarditis. Male DBA/2 mice were inoculated intraperitoneally with the encephalomyocarditis virus and the gene expression of mast cell chymase, mouse mast cell protease (mMCP)-4 and -5, and tryptase, mMCP-6, matrix metalloproteinase (MMP)-9 and type-I procollagen was measured by real-time quantitative RT-PCR analysis. The gene expression of mMCP-4, -5 and -6 mRNA was increased at 5 days, and continued to increase to day 14, coinciding with a prominent inflammatory reaction and extensive myocardial necrosis and fibrosis. The gene expression of MMP-9 was also increased, and there was a significant correlation between upregulation of mast cell proteases and MMP-9. The gene expression of type-I procollagen was increased at 5 days and continued to increase to day 14, suggesting that a fibrotic process had already begun during the acute stage of viral myocarditis. These findings suggest that mast cell chymase and tryptase participate in the acute inflammation and remodeling process of viral myocarditis.