Cardiac Arrhythmogenic Remodeling in a Rat Model of Long-Term Intensive Exercise Training

Unraveling the role of high-intensity resistance training on left ventricle proteome: Is there a shift towards maladaptation?

High-intensity resistance training (RT) induces adaptations that improve physiological function. However, high intensity, volume and/or frequency may lead to injury and other health issues such as adverse cardiac effects. The aim of this study was to evaluate the effect of RT on left ventricle proteome, and to identify the pathways involved on the harmful adaptations induced by this protocol. Male Wistar rats were randomized into 2 groups: Trained (T) and Sedentary (S). Animals from T group were trained for 6weeks, and then all the animals were sacrificed and left ventricle was isolated for analysis. We identified 955 proteins, and 93 proteins were considered; 36 were expressed exclusively in T group, and 4 in S group. Based on quantitative analysis, 42 proteins were found overexpressed and 11 underexpressed in T group compared with S group. Using the Gene Ontology to relate the biological processes in which these proteins are involved, we conclude that RT protocol promotes changes similar to those found in the initial phase of heart failure, but we also observed a concomitant increased expression of protective proteins, suggesting the activation of pathways to avoid major damages on left ventricle and delay the onset of pathological hypertrophy.

STATEMENT OF SIGNIFICANCE OF THE STUDY

Our study shows that high-intensity RT protocol changes left ventricle proteome, modifying metabolic profile of heart tissue and inducing the expression of proteins that acts against cardiac injury. We hypothesize that these adaptations occur to prevent the onset of cardiac dysfunction. Despite highly significant, it remains to be determined whether these adaptations are sufficient to further keep left ventricle function and exert cardioprotection, and whether this panel will be shifted towards maladaptation, and heart failure.

Incremental Value of Left Atrial Global Longitudinal Strain for Prediction of Post Stroke Atrial Fibrillation in Patients with Acute Ischemic Stroke

Background

Atrial fibrillation (AF) is a well-established risk factor for stroke. Interestingly, ischemic stroke increases risk of incident AF in patients without prior diagnosed AF. For better risk stratification for post-stroke AF, we studied left atrial (LA) size and mechanical function using two-dimensional (2D) speckle tracking imaging in patients with acute ischemic stroke.

Methods

A total of 227 patients (132 males, age 67 ± 12) with acute ischemic stroke without a history of AF underwent 2D transthoracic echocardiography and speckle tracking imaging for the assessment of LA volume index and global LA longitudinal strain (LALS). From clinical variables, the CHA₂DS₂-VASc score and National Institute of Health Stroke Scale (NIHSS) were calculated in each patient. Post-stroke AF was defined as newly diagnosed AF during the course after ischemic stroke.

Results

Post-stroke AF occurred in 25 patients (11%). Patients with post-stroke AF were older and showed a higher tendency of CHA₂DS₂-VASc score, significantly higher log NIHSS, larger LA volume index and lower global LALS than those without. In multivariate analysis, global LALS was an independent predictor for post-stroke AF (hazard ratio 0.90, 95% confidence interval 0.83.0.97, p < 0.01) after controlling for confounding factors. Furthermore, global LALS provided incremental predictive value for post-stroke AF over the CHA₂DS₂-VASc score, NIHSS, and LA volume index. The global LALS < 14.5% better distinguished post-stroke AF (area under the curve 0.837, sensitivity 60%, specificity 95%, p < 0.01) than CHA₂DS₂-VASc score.

Conclusion

Global LALS as a marker of LA mechanical function has incremental predictive value for post-stroke AF in patients with acute ischemic stroke.

MicroRNAs as Biomarkers for Acute Atrial Remodeling in Marathon Runners (The miRathon Study--A Sub-Study of the Munich Marathon Study)

Introduction

Physical activity is beneficial for individual health, but endurance sport is associated with the development of arrhythmias like atrial fibrillation. The underlying mechanisms leading to this increased risk are still not fully understood. MicroRNAs are important mediators of proarrhythmogenic remodeling and have potential value as biomarkers in cardiovascular diseases. Therefore, the objective of our study was to determine the value of circulating microRNAs as potential biomarkers for atrial remodeling in marathon runners (miRathon study).

Methods

30 marathon runners were recruited into our study and were divided into two age-matched groups depending on the training status: elite (ER, ≥55 km/week, n = 15) and non-elite runners (NER, ≤40 km/week, n = 15). All runners participated in a 10 week training program before the marathon. MiRNA plasma levels were measured at 4 time points: at baseline (V1), after a 10 week training period (V2), immediately after the marathon (V3) and 24h later (V4). Additionally, we obtained clinical data including serum chemistry and echocardiography at each time point.

Results

MiRNA plasma levels were similar in both groups over time with more pronounced changes in ER. After the marathon miR-30a plasma levels increased significantly in both groups. MiR-1 and miR-133a plasma levels also increased but showed significant changes in ER only. 24h after the marathon plasma levels returned to baseline. MiR-26a decreased significantly after the marathon in elite runners only and miR-29b showed a non-significant decrease over time in both groups. In ER miRNA plasma levels showed a significant correlation with LA diameter, in NER miRNA plasma levels did not correlate with echocardiographic parameters.

Conclusion

MiRNAs were differentially expressed in the plasma of marathon runners with more pronounced changes in ER. Plasma levels in ER correlate with left atrial diameter suggesting that circulating miRNAs could potentially serve as biomarkers of atrial remodeling in athletes.

Sports in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy and desmosomal mutations

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a rare cardiomyopathy associated with life-threatening arrhythmias and an increased risk of sudden cardiac death. In addition to mutations in desmosomal genes, environmental factors such as exercise and sport have been implicated in the pathogenesis of the disease. Recent studies have shown that exercise may be associated with adverse outcomes in patients with ARVD/C. On the basis of current evidence, patients with ARVD/C are recommended to limit exercise irrespective of their mutation status. Some studies have suggested the presence of an entirely acquired form of the disease caused by exercise, which has been dubbed "exercise-induced ARVD/C."

Physiologic and pathophysiologic changes in the right heart in highly trained athletes

Exercise causes changes in the heart in response to the hemodynamic demands of increased systemic and pulmonary requirements during exercise. Understanding these adaptations is of great importance, since they may overlap with those caused by pathological conditions. Initial descriptions of athlete's heart focused mainly on chronic adaptation of the left heart to training. In recent years, the substantial structural and functional adaptations of the right heart have been documented, highlighting the complex interplay with left heart. Moreover, there is evolving evidence of acute and chronic cardiac damage, mainly involving the right heart, which may predispose subjects to atrial and ventricular arrhythmias, configuring an exercise-induced cardiomyopathy. The aim of this article is to review the current knowledge on the physiologic and pathophysiologic changes in the right heart in highly trained athletes.

Are There Deleterious Cardiac Effects of Acute and Chronic Endurance Exercise?

Multiple epidemiological studies document that habitual physical activity reduces the risk of atherosclerotic cardiovascular disease (ASCVD), and most demonstrate progressively lower rates of ASCVD with progressively more physical activity. Few studies have included individuals performing high-intensity, lifelong endurance exercise, however, and recent reports suggest that prodigious amounts of exercise may increase markers for, and even the incidence of, cardiovascular disease. This review examines the evidence that extremes of endurance exercise may increase cardiovascular disease risk by reviewing the causes and incidence of exercise-related cardiac events, and the acute effects of exercise on cardiovascular function, the effect of exercise on cardiac biomarkers, including "myocardial" creatine kinase, cardiac troponins, and cardiac natriuretic peptides. This review also examines the effect of exercise on coronary atherosclerosis and calcification, the frequency of atrial fibrillation in aging athletes, and the possibility that exercise may be deleterious in individuals genetically predisposed to such cardiac abnormalities as long QT syndrome, right ventricular cardiomyopathy, and hypertrophic cardiomyopathy. This review is to our knowledge unique because it addresses all known potentially adverse cardiovascular effects of endurance exercise. The best evidence remains that physical activity and exercise training benefit the population, but it is possible that prolonged exercise and exercise training can adversely affect cardiac function in some individuals. This hypothesis warrants further examination.

Atrial Fibrillation In Athletes: Pathophysiology, Clinical Presentation, Evaluation and Management

Atrial fibrillation (AF) is the most common cardiac arrhythmia in athletes, especially in middle-aged athletes. Studies have demonstrated that athletes who engage in endurance sports such as runners, cyclists and skiers are more prone to AF than other athletes. The effects of exercise on the onset and progression of AF is complex. Triggers of AF in athletes may include atrial ectopy and sports supplements. Substrates for AF in athletes include atrial remodeling, fibrosis, and inflammation. Modulators of AF in athletes include autonomic activation, electrolyte abnormalities, and possibly, gastroesophageal reflux. Management of AF in athletes with rate-controlling agents and antiarrhythmic drugs remains a challenge and can be associated with impaired athletic performance. The value of catheter ablation is emerging and should be considered in suitable athletes with AF.

Exercise and the heart--the harm of too little and too much

Physical activity and exercise training are underutilized by much of Westernized society, and physical inactivity may be the greatest threat to health in the 21st century. Many studies have shown a linear relationship between one's activity level and heart health, leading to the conclusion that "if some exercise is good, more must be better." However, there is evolving evidence that high levels of exercise may produce similar or less overall cardiovascular (CV) benefits compared with those produced by lower doses of exercise. Very high doses of exercise may be associated with increased risk of atrial fibrillation, coronary artery disease, and malignant ventricular arrhythmias. These acute bouts of excessive exercise may lead to cardiac dilatation, cardiac dysfunction, and release of troponin and brain natriuretic peptide. The effects of too little and too much exercise on the heart are reviewed in this article, along with recommendations to optimize the dose of exercise to achieve heart health.

Effects of Running on Chronic Diseases and Cardiovascular and All-Cause Mortality

Considerable evidence has established the link between high levels of physical activity (PA) and all-cause and cardiovascular disease (CVD)-specific mortality. Running is a popular form of vigorous PA that has been associated with better overall survival, but there is debate about the dose-response relationship between running and CVD and all-cause survival. In this review, we specifically reviewed studies published in PubMed since 2000 that included at least 500 runners and 5-year follow-up so as to analyze the relationship between vigorous aerobic PA, specifically running, and major health consequences, especially CVD and all-cause mortality. We also made recommendations on the optimal dose of running associated with protection against CVD and premature mortality, as well as briefly discuss the potential cardiotoxicity of a high dose of aerobic exercise, including running (eg, marathons).

Exercise and Health: Dose and Response, Considering Both Ends of the Curve

Over the past 60 years, an enormous body of data has demonstrated that exercise is good for health. Recently, however, there has been concern that repetitive intense exercise may have deleterious cardiovascular effects. To evaluate this possibility, I have reviewed the health response to exercise, with particular attention to the body's minimum daily requirement and to the maximum amount that is safe and effective.

Right Ventricular Adaptation Is Associated with the Glu298Asp Variant of the NOS3 Gene in Elite Athletes

Nitric oxide (NO), an important endogenous pulmonary vasodilator is synthetized by the endothelial NO synthase (NOS3). Reduced NO bioavailability and thus the Glu298Asp polymorphism of NOS3 may enhance right ventricular (RV) afterload and hypertrophic remodeling and influence athletic performance. To test this hypothesis world class level athletes (water polo players, kayakers, canoeists, rowers, swimmers, n = 126) with a VO2 maximum greater than 50ml/kg/min were compared with non-athletic volunteers (n = 155). Cardiopulmonary exercise tests and cardiac magnetic resonance imaging (cMRI) were performed to determine structural or functional changes. Genotype distribution of the NOS3 Glu298Asp polymorphism was not affected by gender or physical performance. Cardiac MRI showed increased stroke volume with eccentric hypertrophy in all athletes regardless of their genotype. However, the Asp allelic variant carriers had increased RV mass index (32±6g versus 27±6g, p<0.01) and larger RV stroke volume index (71±10ml versus 64±10ml, p<0.01) than athletes with a Glu/Glu genotype. Genotype was not significantly associated with athletic performance. In the non-athletic group no genotype related differences were detected. The association between the NOS3 Glu298Asp polymorphism and RV structure and dimension in elite athletes emphasizes the importance of NOS3 gene function and NO bioavailability in sport related cardiac adaptation.

The potential protective effect of green, black, red and white tea infusions against adverse effect of cadmium and lead during chronic exposure - A rat model study

The protective effect of green (GT), black (BT), red (RT) and white (WT) tea infusions on the lungs, brains, hearts, livers and kidneys of adult Wistar rats exposed to Cd (7 mg/kg) and Pb (50 m/kg) was studied. The degree of reduction in the absorption of Cd and Pb in the organs compared to control group and the activity of SOD, CAT and GPx as well as GSH level was evaluated. It was determined that tea significant reduced the accumulation of Cd in the tissues. A significant reduction in the accumulation of Pb was recorded in the brain (WT), liver (GT, WT) and kidneys (BT, GT, RT, WT). A significant increase was observed in the activity of SOD, CAT and GPx in the organs of all rats from tea groups. It was found that the results obtained in rats receiving black, red and white tea were overall not worse than those recorded for rats receiving green tea. The obtained results suggest that drinking tea could be an effective method of reducing the adverse effect of environmental Cd and Pb pollution on the human body.

The Impaired Function of Macrophages Induced by Strenuous Exercise Could Not Be Ameliorated by BCAA Supplementation

The aim of this study was to evaluate the effect of strenuous exercise on the functions of peritoneal macrophages in rats and to test the hypothesis that branched-chain amino acid (BCAA) supplementation will be beneficial to the macrophages of rats from strenuous exercise. Forty male Wistar rats were randomly divided into five groups: (C) Control, E) Exercise, (E1) Exercise with one week to recover, (ES) Exercise + Supplementation and (ES1) Exercise + Supplementation with 1 week to recover. All rats except those of the sedentary control were subjected to four weeks of strenuous exercise. Blood hemoglobin, serum testosterone and BCAA levels were tested. Peritoneal macrophages functions were also determined at the same time. The data showed that hemoglobin, testosterone, BCAA levels, and body weight in group E decreased significantly as compared with that of group C. Meanwhile, phagocytosis capacity (decreased by 17.07%, p = 0.031), reactive oxygen species (ROS) production (decreased by 26%, p = 0.003) and MHC II mRNA (decreased by 22%, p = 0.041) of macrophages decreased in the strenuous exercise group as compared with group C. However, the chemotaxis of macrophages did not change significantly. In addition, BCAA supplementation could slightly increase the serum BCAA levels of rats from strenuous exercise (increased by 6.70%, p > 0.05). Moreover, the body weight, the blood hemoglobin, the serum testosterone and the function of peritoneal macrophages in group ES did not change significantly as compared with group E. These results suggest that long-term intensive exercise impairs the function of macrophages, which is essential for microbicidal capability. This may represent a novel mechanism of immunosuppression induced by strenuous exercise. Moreover, the impaired function of macrophage induced by strenuous exercise could not be ameliorated by BCAA supplementation in the dosing and timing used for this study.

Exercise has a disproportionate role in the pathogenesis of arrhythmogenic right ventricular dysplasia/cardiomyopathy in patients without desmosomal mutations

Background

Exercise is associated with age‐related penetrance and arrhythmic risk in carriers of arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C)‐associated desmosomal mutations; however, its role in patients without desmosomal mutations (gene‐elusive) is uncertain. This study investigates whether exercise is (1) associated with onset of gene‐elusive ARVD/C and (2) has a differential impact in desmosomal and gene‐elusive patients.

Methods and Results

Eighty‐two ARVD/C patients (39 desmosomal, all probands) were interviewed about regular physical activity from age 10. Participation in endurance athletics, duration (hours/year), and intensity (MET‐Hours/year) of exercise prior to clinical presentation were compared between patients with desmosomal and gene‐elusive ARVD/C. All gene‐elusive patients were endurance athletes. Gene‐elusive patients were more likely to be endurance athletes (P<0.001) and had done significantly more intense (MET‐Hrs/year) exercise prior to presentation (P<0.001), particularly among cases presenting < age 25 (P=0.027). Family history was less prevalent among gene‐elusive patients (9% versus 40% desmosomal, P<0.001), suggesting a greater environmental influence. Gene‐elusive patients without family history did considerably more intense exercise than other ARVD/C patients (P=0.004). Gene‐elusive patients who had done the most intense (top quartile MET‐Hrs/year) exercise prior to presentation had a younger age of presentation (P=0.025), greater likelihood of meeting ARVD/C structural Task Force Criteria (100% versus 43%, P=0.02), and shorter survival free from a ventricular arrhythmia in follow‐up (P=0.002).

Conclusions

Gene‐elusive, non‐familial ARVD/C is associated with very high intensity exercise suggesting exercise has a disproportionate role in the pathogenesis of these cases. As exercise negatively modifies cardiac structure and promotes arrhythmias, exercise restriction is warranted.

Comparison of Nigella sativa- and exercise-induced models of cardiac hypertrophy: structural and electrophysiological features

Exercise training is employed as supplementary therapeutic intervention for heart failure, due to its ability to induce physiological cardiac hypertrophy. In parallel, supplementation with Nigella sativa (N. sativa) was found to enhance myocardial function and induce cardiac hypertrophy. In this study, we aim to compare the morphological and electrophysiological changes associated with these patterns of cardiac hypertrophy and the possible changes upon administration of N. sativa to exercise-trained animals. Fifty-six adult Wistar rats were divided into: control, Nigella-treated (N), exercise-trained (E), and Nigella-treated-exercise-trained (NE) rats. Daily 800 mg/kg N. sativa was administered orally to N and NE. E and NE ran on treadmill, 2 h/day. At the end of 8 weeks ECG, body weight (BW), heart weight (HW), and left ventricular weight (LVW) were recorded. Hematoxylin and Eosin and periodic acid-Schiff sections were prepared to study the histology of left ventricles and to measure diameter of cardiomyocytes (Cdia). HW/BW, LVW/BW, and mean Cdia were significantly higher in all experimental animals compared to the controls. Histology showed normal cardiomyocytes with no fibrosis. ECG showed significantly lower heart rates, higher QRS amplitude, and ventricular specific potential in NE group compared to control group. Supplementation of N. sativa demonstrated a synergistic effect with exercise training as Nigella-exercise-induced cardiac hypertrophy had lower heart rate and well-matched electrical activity of the heart to its mass. Therefore, this model of cardiac hypertrophy might be introduced as a new therapeutic strategy for treatment for heart failure with superior advantages to exercise training.

Aldehyde dehydrogenase-2 protects against myocardial infarction-related cardiac fibrosis through modulation of the Wnt/β-catenin signaling pathway

Background

Aldehyde dehydrogenase-2 (ALDH2) has a protective effect on ischemic heart disease. Here, we examined the protective effects of ALDH2 on cardiac fibrosis through modulation of the Wnt/β-catenin signaling pathway in a rat model of myocardial infarction (MI).

Methods

Wistar rats were divided into the sham (control), MI (model), and ALDH2 activator (Alda-1) groups. After 10 days of treatment, the left ventricular (LV) remodeling parameters of each animal were evaluated by echocardiography. Myocardial fibrosis was evaluated by Masson’s trichrome staining and Sirius Red staining. Expression levels of collagen types I and III and α-smooth muscle actin (α-SMA) were examined. Finally, the expression and activity of ALDH2 and the levels of several Wnt-related proteins and genes, such as phosphoglycogen synthase kinase (GSK)-3β, GSK-3β, β-catenin, Wnt-1, WNT1-inducible signaling-pathway protein 1, and tumor necrosis factor (TNF)-α, were also analyzed.

Results

After MI, the heart weight/body weight ratio, LV dimension at end diastole, and LV dimension at end systole were decreased, while the LV ejection fraction and LV fractional shortening were increased in the Alda-1 group. Myocardial fibrosis was also reduced in the Alda-1 group, accompanied by decreased expression collagen types I and III and α-SMA. β-Catenin, phosphorylated GSK-3β, and Wnt-1 levels were significantly increased in the model group. Interestingly, this alteration was partly reversed by Alda-1 treatment. Immunohistochemical staining showed that numerous WNT1-inducible signaling-pathway protein 1 (WISP-1)- and TNF-α-positive cells were found in the model group. However, few WISP-1- and TNF-α-positive cells were detected in the Alda-1 group.

Conclusion

The reduction of cardiac fibrosis and the down-regulation of β-catenin, phosphorylated GSK-3β, Wnt-1, and WISP-1 may be mediated by increased ALDH2 activity, leading to reduction of MI-related cardiac fibrosis.

Patterns of leisure-time physical activity using multivariate finite mixture modeling and cardiovascular risk factors in the Northern Manhattan Study

PURPOSE

Physical activity is currently commonly summarized by simple composite scores of total activity, such as total metabolic equivalent score (METS), without further information about the many specific aspects of activities. We sought to identify more comprehensive physical activity patterns, and their association with cardiovascular disease risk factors.

METHODS

The Northern Manhattan Study is a multiethnic cohort of stroke-free individuals. Questionnaires were used to capture multiple dimensions of leisure-time physical activity. Participants were grouped into METS categories and also into clusters by multivariate mixture modeling of activity frequency, duration, energy expenditure, and number of activity types. Associations between clusters and risk factors were assessed using χ(2) tests.

RESULTS

Using data available in 3293 participants, we identified six model-based clusters that were differentiated by frequency and diversity of activities, rather than activity duration. High activity clusters had lower prevalence of the risk factors compared with those with lower activity; associations with obesity and hypertension remained significant after adjusting for METS (P = .027, .043). METS and risk factors were not significantly associated after adjusting for the clusters.

CONCLUSIONS

Data-driven clustering method is a principled, generalizable approach to depict physical activity and form subgroups associated with cardiovascular risk factors independently of METS.

Intermittent cardiac overload results in adaptive hypertrophy and provides protection against left ventricular acute pressure overload insult

The present study aimed to test whether a chronic intermittent workload could induce an adaptive cardiac phenotype Chronic intermittent workload induced features of adaptive hypertrophy This was paralleled by protection against acute pressure overload insult The heart may adapt favourably to balanced demands, regardless of the nature of the stimuli. The present study aimed to test whether submitting the healthy heart to intermittent and tolerable amounts of workload, independently of its nature, could result in an adaptive cardiac phenotype. Male Wistar rats were subjected to treadmill running (Ex) (n = 20), intermittent cardiac overload with dobutamine (ITO) (2 mg kg(-1) , s.c.; n = 20) or placebo administration (Cont) (n = 20) for 5 days week(-1) for 8 weeks. Animals were then killed for histological and biochemical analysis or subjected to left ventricular haemodynamic evaluation under baseline conditions, in response to isovolumetric contractions and to sustained LV acute pressure overload (35% increase in peak systolic pressure maintained for 2 h). Baseline cardiac function was enhanced only in Ex, whereas the response to isovolumetric heartbeats was improved in both ITO and Ex. By contrast to the Cont group, in which rats developed diastolic dysfunction with sustained acute pressure overload, ITO and Ex showed increased tolerance to this stress test. Both ITO and Ex developed cardiomyocyte hypertrophy without fibrosis, no overexpression of osteopontin-1 or β-myosin heavy chain, and increased expression of sarcoplasmic reticulum Ca(2+) protein. Regarding hypertrophic pathways, ITO and Ex showed activation of the protein kinase B/mammalian target of rapamycin pathway but not calcineurin. Mitochondrial complex IV and V activities were also increased in ITO and Ex. Chronic submission to controlled intermittent cardiac overload, independently of its nature, results in an adaptive cardiac phenotype. Features of the cardiac overload, such as the duration and magnitude of the stimuli, may play a role in the development of an adaptive or maladaptive phenotype.

The U-shaped relationship between exercise and cardiac morbidity

Exercise confers a plethora of health benefits that are well documented, whereas physical inactivity is a leading risk factor for cardiovascular morbidity and mortality. The dose of physical activity required to achieve these benefits is relatively modest and equates to jogging at a pace of 15min per mile for 20-30min daily. In the current era, most athletes engage in a volume and intensity of exercise that is at least 5-10-fold greater than the general recommendations for physical activity. Such practice is evidenced by the fact that many sportsmen have achieved athletic feats that were considered impossible only 2 decades ago. Numerous studies in retired athletes have consistently shown a reduced incidence of heart disease and an increased longevity of life. Occasionally, however, intense exercise is associated with sudden deaths in athletes harboring quiescent yet potentially sinister cardiac diseases. Despite the visibility afforded by such catastrophes, the reputation of exercise remains unscathed because most deaths can be accounted for by an underlying cardiac abnormality where exercise is a mere trigger for a fatal arrhythmia rather than the actual cause of death. More recently, there have been an emerging number of reports suggesting that intense exercise may have an adverse impact on an otherwise normal heart. This article will review the morbidity and mortality associated with sport and pose the question whether one can have "too much of a good thing."

Relationship between Inflammatory Cytokines and Indices of Cardiac Dysfunction following Intense Endurance Exercise

Objectives

Pro-inflammatory cytokines have been noted to increase following exercise but their relationship to exercise-induced cardiac dysfunction has not previously been investigated. We sought to evaluate whether exercise-induced cardiac dysfunction was associated with increases in cytokines, particularly the pro-inflammatory cytokines IL-1β, IL-12p70 and TNFα, which have been most implicated in cardiac pathology.

Methods

40 well-trained endurance athletes underwent evaluation prior to and immediately following one of four endurance sporting events ranging from 3 to 11 hours duration. Cytokines (IL-1β, IL-6, IL-8, IL-10, IL-12p70 and TNFα) were analyzed by flow cytometry from serum samples collected within 50 minutes of race completion. Cardiac troponin (cTnI) and B-type natriuretic peptide were combined with an echocardiographic assessment of cardiac function, and a composite of cTnI > 0.04 μg/L, BNP increase > 10 ng/L and a decrease in right ventricular ejection (RVEF) > 10% were prospectively defined as evidence of myocardial dysfunction.

Results

Relative to baseline, IL-6 IL-8 and IL-10 increased 8.5-, 2.9-, and 7.1-fold, respectively, P<0.0001. Thirty-one (78%), 19 (48%) and 18 (45%) of the athletes met the pre-specified criteria for significant cTnI, BNP and RVEF changes, respectively. TNFα, IL-12p70 were univariate predictors of ΔRVEF and ΔBNP whilst none of the anti-inflammatory cytokines were significantly associated with these measures. Ten athletes (25%, all athletes competing in the endurance event of longest duration) met criteria for exercise-induced myocardial dysfunction. In these 10 athletes with myocardial dysfunction, as compared to those without, there was significantly greater post-race expression of the pro-inflammatory cytokines IL-12p70 (8.1±3.8pg/ml vs. 2.5±2.6pg/ml, P<0.0001) and TNFα (6.5±3.1pg/ml vs. 2.0±2.5pg/ml, P<0.0001).

Conclusion

Cardiac dysfunction following intense endurance exercise was associated with increased expression of pro-inflammatory cytokines. This does not prove a causal relationship but provides rationale for further investigations into whether inflammation mediates exercise-induced myocardial dysfunction.

Exercise-induced right ventricular dysfunction is associated with ventricular arrhythmias in endurance athletes

AIMS

Intense exercise places disproportionate strain on the right ventricle (RV) which may promote pro-arrhythmic remodelling in some athletes. RV exercise imaging may enable early identification of athletes at risk of arrhythmias.

METHODS AND RESULTS

Exercise imaging was performed in 17 athletes with RV ventricular arrhythmias (EA-VAs), of which eight (47%) had an implantable cardiac defibrillator (ICD), 10 healthy endurance athletes (EAs), and seven non-athletes (NAs). Echocardiographic measures included the RV end-systolic pressure-area ratio (ESPAR), RV fractional area change (RVFAC), and systolic tricuspid annular velocity (RV S'). Cardiac magnetic resonance (CMR) measures combined with invasive measurements of pulmonary and systemic artery pressures provided left-ventricular (LV) and RV end-systolic pressure-volume ratios (SP/ESV), biventricular volumes, and ejection fraction (EF) at rest and during intense exercise. Resting measures of cardiac function were similar in all groups, as was LV function during exercise. In contrast, exercise-induced increases in RVFAC, RV S', and RVESPAR were attenuated in EA-VAs during exercise when compared with EAs and NAs (P < 0.0001 for interaction group × workload). During exercise-CMR, decreases in RVESV and augmentation of both RVEF and RV SP/ESV were significantly less in EA-VAs relative to EAs and NAs (P < 0.01 for the respective interactions). Receiver-operator characteristic curves demonstrated that RV exercise measures could accurately differentiate EA-VAs from subjects without arrhythmias [AUC for ΔRVESPAR = 0.96 (0.89-1.00), P < 0.0001].

CONCLUSION

Among athletes with normal cardiac function at rest, exercise testing reveals RV contractile dysfunction among athletes with RV arrhythmias. RV stress testing shows promise as a non-invasive means of risk-stratifying athletes.

Exercise training-induced bradycardia: evidence for enhanced parasympathetic regulation without changes in intrinsic sinoatrial node function

The mechanisms responsible for exercise-induced reductions in baseline heart rate (HR), known as training bradycardia, remain controversial. Therefore, changes in cardiac autonomic regulation and intrinsic sinoatrial nodal (SAN) rate were evaluated using dogs randomly assigned to either a 10- to 12-wk exercise training (Ex, n = 15) or an equivalent sedentary period (Sed, n = 10). Intrinsic HR was revealed by combined autonomic nervous system (ANS) blockade (propranolol + atropine, iv) before and after completion of the study. At the end of the study, SAN function was further evaluated by examining the SAN recovery time (SNRT) following rapid atrial pacing and the response to adenosine in anesthetized animals. As expected, both the response to submaximal exercise and baseline HR significantly (P < 0.01) decreased, and heart rate variability (HRV; e.g., high-frequency R-R interval variability) significantly (P < 0.01) increased in the Ex group but did not change in the Sed group. Atropine also induced significantly (P < 0.01) greater reductions in HRV in the Ex group compared with the Sed group; propranolol elicited similar HR and HRV changes in both groups. In contrast, neither intrinsic HR (Ex before, 141.2 ± 6.7; Ex after, 146.0 ± 8.0 vs. Sed before, 143.3 ± 11.1; Sed after, 141.0 ± 11.3 beats per minute), the response to adenosine, corrected SNRT, nor atrial fibrosis and atrial fibrillation inducibility differed in the Ex group vs. the Sed group. These data suggest that in a large-animal model, training bradycardia results from an enhanced cardiac parasympathetic regulation and not from changes in intrinsic properties of the SAN.

Relationship between arrhythmogenic right ventricular dysplasia and exercise

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is rare cardiomyopathy associated with life-threatening arrhythmias and increased risk of sudden cardiac death. In addition to mutations in desmosomal genes, environmental factors such as exercise have been implicated in the pathogenesis of the disease. Recent studies have shown that exercise may be associated with adverse outcomes in ARVD/C patients. Based on current evidence, ARVD/C patients are recommended to limit exercise irrespective of their mutation status. In addition, some studies have suggested the presence of an entirely acquired form of the disease caused by exercise that has been dubbed exercise-induced ARVD/C.

High-intensity interval and endurance training are associated with divergent skeletal muscle adaptations in a rodent model of hypertension

Skeletal muscle is extremely adaptable to a variety of metabolic challenges, as both traditional moderate-intensity endurance (ET) and high-intensity interval training (HIIT) increases oxidative potential in a coordinated manner. Although these responses have been clearly demonstrated in healthy individuals, it remains to be determined whether both produce similar responses in the context of hypertension, one of the most prevalent and costly diseases worldwide. Therefore, in the current study, we used the Dahl sodium-sensitive rat, a model of hypertension, to determine the molecular responses to 4 wk of either ET or HIIT in the red (RG) and white gastrocnemius (WG) muscles. In the RG, both ET and HIIT increased the content of electron transport chain proteins and increased succinate dehydrogenase (SDH) content in type I fibers. Although both intensities of exercise shifted fiber type in RG (increased IIA, decreased IIX), only HIIT was associated with a reduction in endothelial nitric oxide synthase and an increase in HIF-1α proteins. In the WG, both ET and HIIT increased markers of the electron transport chain; however, HIIT decreased SDH content in a fiber-specific manner. ET increased type IIA, decreased IIB fibers, and increased capillarization, while, in contrast, HIIT increased the percentage of IIB fibers, decreased capillary-to-fiber ratios, decreased endothelial nitric oxide synthase, and increased hypoxia inducible factor-1α (HIF-1α) protein. Altogether, these data show that unlike in healthy animals, ET and HIIT have divergent effects in the skeletal muscle of hypertensive rats. This suggests ET may be optimal at improving the oxidative capacity of skeletal muscle in animals with hypertension.

Is exercise good for the right ventricle? Concepts for health and disease

There is substantial evidence supporting the prescription of exercise training in patients with left-sided heart disease, but data on the effects of exercise are far more limited for conditions that primarily affect the right ventricle. There is evolving evidence that right ventricular (RV) function is of critical importance to circulatory function during exercise. Even in healthy individuals with normal pulmonary vascular function, the hemodynamic load on the right ventricle increases relatively more during exercise than that of the left ventricle, and this disproportionate load is far greater in patients with pulmonary hypertension. Exercise-induced increases in pulmonary artery pressures can exceed RV contractile reserve (so-called arterioventricular uncoupling), resulting in attenuated cardiac output and exercise intolerance. In this review, we explore the spectrum of RV reserve-from transient RV dysfunction observed in athletes after extreme bouts of intense endurance exercise to RV failure with minimal exertion in patients with advanced pulmonary hypertension. Recent advances and novel approaches to echocardiographic and cardiac magnetic resonance imaging have provided more accurate means of assessing the right ventricle and pulmonary circulation during exercise such that quantification of exercise reserve may provide a valuable means of assessing prognosis and response to therapies. We discuss the potential benefits and risks of exercise training in both health and disease while recognizing the need for prospective studies that assess the long-term efficacy and safety of exercise interventions in patients with pulmonary vascular and RV pathologic conditions.

The response of the pulmonary circulation and right ventricle to exercise: exercise-induced right ventricular dysfunction and structural remodeling in endurance athletes (2013 Grover Conference series)

There is unequivocal evidence that exercise results in considerable health benefits. These are the result of positive hormonal, metabolic, neuronal, and structural changes brought about by the intermittent physiological challenge of exercise. However, there is evolving evidence that intense exercise may place disproportionate physiological stress on the right ventricle (RV) and the pulmonary circulation. Both echocardiographic and invasive studies are consistent in demonstrating that pulmonary arterial pressures increase progressively with exercise intensity, such that the harder one exercises, the greater the load on the RV. This disproportionate load can result in fatigue or damage of the RV if the intensity and duration of exercise is sufficiently prolonged. This is distinctly different from the load imposed by exercise on the left ventricle (LV), which is moderated by a greater capacity for reductions in systemic afterload. Finally, given the increasing RV demand during exercise, it may be hypothesized that chronic exercise-induced cardiac remodeling (the so-called athlete's heart) may also disproportionately affect the RV. Indeed, there is evidence, although somewhat inconsistent, that RV volume increases may be relatively greater than those for the LV. Perhaps more importantly, there is a suggestion that chronic endurance exercise may cause electrical remodeling, predisposing some athletes to serious arrhythmias originating from the RV. Thus, a relatively consistent picture is emerging of acute stress, prolonged fatigue, and long-term remodeling, which all disproportionately affect the RV. Thus, we contend that the RV should be considered a potential Achilles' heel of the exercising heart.

Obligatory role of neuronal nitric oxide synthase in the heart's antioxidant adaptation with exercise

Excessive oxidative stress in the heart results in contractile dysfunction. While antioxidant therapies have been a disappointment clinically, exercise has shown beneficial results, in part by reducing oxidative stress. We have previously shown that neuronal nitric oxide synthase (nNOS) is essential for cardioprotective adaptations caused by exercise. We hypothesize that part of the cardioprotective role of nNOS is via the augmentation of the antioxidant defense with exercise by positively shifting the nitroso-redox balance. Our results show that nNOS is indispensable for the augmented anti-oxidant defense with exercise. Furthermore, exercise training of nNOS knockout mice resulted in a negative shift in the nitroso-redox balance resulting in contractile dysfunction. Remarkably, overexpressing nNOS (conditional cardiac-specific nNOS overexpression) was able to mimic exercise by increasing VO2max. This study demonstrates that exercise results in a positive shift in the nitroso-redox balance that is nNOS-dependent. Thus, targeting nNOS signaling may mimic the beneficial effects of exercise by combating oxidative stress and may be a viable treatment strategy for heart disease.

Effects of allopurinol on exercise-induced muscle damage: new therapeutic approaches?

Intensive muscular activity can trigger oxidative stress, and free radicals may hence be generated by working skeletal muscle. The role of the enzyme xanthine oxidase as a generating source of free radicals is well documented and therefore is involved in the skeletal muscle damage as well as in the potential transient cardiovascular damage induced by high-intensity physical exercise. Allopurinol is a purine hypoxanthine-based structural analog and a well-known inhibitor of xanthine oxidase. The administration of the xanthine oxidase inhibitor allopurinol may hence be regarded as promising, safe, and an economic strategy to decrease transient skeletal muscle damage (as well as heart damage, when occurring) in top-level athletes when administered before a competition or a particularly high-intensity training session. Although continuous administration of allopurinol in high-level athletes is not recommended due to its possible role in hampering training-induced adaptations, the drug might be useful in non-athletes. Exertional rhabdomyolysis is the most common form of rhabdomyolysis and affects individuals participating in a type of intense exercise to which they are not accustomed. This condition can cause exercise-related myoglobinuria, thus increasing the risk of acute renal failure and is also associated with sickle cell trait. In this manuscript, we have reviewed the recent evidence about the effects of allopurinol on exercise-induced muscle damage. More research is needed to determine whether allopurinol may be useful for preventing not only exertional rhabdomyolysis and acute renal damage but also skeletal muscle wasting in critical illness as well as in immobilized, bedridden, sarcopenic or cachectic patients.

What do we know about the cardiac benefits of exercise?

Exercise has long been considered an essential element for sustaining cardiovascular health. A vast literature of clinical studies suggests that exercise serves as an effective intervention for the primary and secondary prevention of cardiovascular disease, although the optimal nature, intensity, and duration of exercise for maximizing these cardiovascular benefits remain unclear. On a molecular level, exercise induces physiologic growth of the heart primarily by driving cardiomyocyte hypertrophy, notably through the interconnected IGF-1-PI3K-AKT1 and C/EBPβ-CITED4 pathways. Here, we explore the range of clinical evidence supporting the cardiovascular benefits of exercise and outline the molecular pathways that play major roles in regulating these protective effects.