Organization of atrial fibrillation using a pure sodium channel blocker: Implications of rotor ablation therapy.

Background: Rotors are the source of atrial fibrillation (AF). However, the ablation of rotors for persistent AF is challenging. The purpose of this study was to identify the dominant rotor by accelerating the organization of AF using a sodium channel blocker and detecting the rotor's preferential area that governs AF. Methods: Overall, 30 consecutive patients with persistent AF who underwent pulmonary vein isolation and still sustained AF were enrolled. Pilsicainide 50 mg was administered. An online real-time phase mapping system (ExTRa Mapping™) was used to identify the meandering rotors and multiple wavelets in 11 left atrial segments. The time ratio of non-passive activation (%NP) was evaluated as the frequency of rotor activity in each segment. Results: Conduction velocity became slower-from 0.46 ± 0.14 to 0.35 ± 0.14 mm/ms (p = .004)-and the rotational period of the rotor was significantly prolonged-156 ± 21 to 193 ± 28 ms/cycle (p < .001). AF cycle length was prolonged from 169 ± 19 to 223 ± 29 ms (p < .001). A decrease in %NP was observed in seven segments. Additionally, 14 patients had at least one complete passive activation area. Of them, the use of high %NP area ablation resulted in atrial tachycardia and sinus rhythm in two patients each. Conclusions: A sodium channel blocker organized persistent AF. In selective patients with a wide organized area, high %NP area ablation could convert AF into atrial tachycardia or terminate AF.

Angiotensin-converting enzyme inhibitor prevents skeletal muscle fibrosis in diabetic mice.

NEW FINDINGS: What is the central question of this study? We questioned whether an angiotensin-converting enzyme (ACE) inhibitor prevents skeletal muscle fibrosis in diabetic mice. What is the main finding and its importance? Administration of ACE inhibitor prevents the increase in skeletal muscle fibrosis during the early phase after induction of diabetes by streptozotocin. Our findings might provide a new therapeutic target for skeletal muscle abnormalities in diabetes. ABSTRACT: Fibrosis is characterized by the excessive production and accumulation of extracellular matrix components, including collagen. Although the extracellular matrix is an essential component of skeletal muscle, fibrosis can have negative effects on muscle function. Skeletal muscle fibrosis was shown to be increased in spontaneously hypertensive rats and to be prevented by an angiotensin-converting enzyme (ACE) inhibitor, an antihypertensive drug, in dystrophic mice or a mouse model of myocardial infarction. In this study, we therefore analysed whether (1) there is increased skeletal muscle fibrosis in streptozotocin (STZ)-induced diabetic mice, and (2) a preventive effect on skeletal muscle fibrosis by administration of an ACE inhibitor. Skeletal muscle fibrosis was significantly increased in STZ-induced diabetic mice compared with control mice from 2 to 14 days post-STZ. The ACE inhibitor prevented both skeletal muscle fibrosis and the reduction in muscle function in STZ-treated mice. Our study demonstrated that administration of an ACE inhibitor prevents the increase in skeletal muscle fibrosis during the early phase after onset of diabetes. Our findings might provide a new therapeutic target for skeletal muscle abnormalities in diabetes. Future studies are required to clarify whether skeletal muscle fibrosis is also linked directly to physical activity.

Inhibition of xanthine oxidase in the acute phase of myocardial infarction prevents skeletal muscle abnormalities and exercise intolerance.

AIMS: Exercise intolerance in patients with heart failure (HF) is partly attributed to skeletal muscle abnormalities. We have shown that reactive oxygen species (ROS) play a crucial role in skeletal muscle abnormalities, but the pathogenic mechanism remains unclear. Xanthine oxidase (XO) is reported to be an important mediator of ROS overproduction in ischaemic tissue. Here, we tested the hypothesis that skeletal muscle abnormalities in HF are initially caused by XO-derived ROS and are prevented by the inhibition of their production. METHODS AND RESULTS: Myocardial infarction (MI) was induced in male C57BL/6J mice, which eventually led to HF, and a sham operation was performed in control mice. The time course of XO-derived ROS production in mouse skeletal muscle post-MI was first analysed. XO-derived ROS production was significantly increased in MI mice from Days 1 to 3 post-surgery (acute phase), whereas it did not differ between the MI and sham groups from 7 to 28 days (chronic phase). Second, mice were divided into three groups: sham + vehicle (Sham + Veh), MI + vehicle (MI + Veh), and MI + febuxostat (an XO inhibitor, 5 mg/kg body weight/day; MI + Feb). Febuxostat or vehicle was administered at 1 and 24 h before surgery, and once-daily on Days 1-7 post-surgery. On Day 28 post-surgery, exercise capacity and mitochondrial respiration in skeletal muscle fibres were significantly decreased in MI + Veh compared with Sham + Veh mice. An increase in damaged mitochondria in MI + Veh compared with Sham + Veh mice was also observed. The wet weight and cross-sectional area of slow muscle fibres (higher XO-derived ROS) was reduced via the down-regulation of protein synthesis-associated mTOR-p70S6K signalling in MI + Veh compared with Sham + Veh mice. These impairments were ameliorated in MI + Feb mice, in association with a reduction of XO-derived ROS production, without affecting cardiac function. CONCLUSION: XO inhibition during the acute phase post-MI can prevent skeletal muscle abnormalities and exercise intolerance in mice with HF.

Type 2 diabetes is an independent predictor of lowered peak aerobic capacity in heart failure patients with non-reduced or reduced left ventricular ejection fraction.

BACKGROUND: Although type 2 diabetes mellitus (T2DM) is one of the most frequent comorbidities in patients with chronic heart failure (CHF), the effects of T2DM on the exercise capacity of CHF patients are fully unknown. Here, we tested the hypothesis that the coexistence of T2DM lowers CHF patients' peak aerobic capacity. METHODS: We retrospectively analyzed the cases of 275 Japanese CHF patients with non-reduced ejection fraction (left ventricular ejection fraction [LVEF] ≥ 40%) or reduced EF (LVEF < 40%) who underwent cardiopulmonary exercise testing. We divided them into diabetic and nondiabetic groups in each CHF cohort. RESULTS: The mean peak oxygen uptake (VO2) value was 16.87 mL/kg/min in the non-reduced LVEF cohort and 15.52 mL/kg/min in the reduced LVEF cohort. The peak VO2 was lower in the diabetics versus the nondiabetics in the non-reduced LVEF cohort with the mean difference (95% confidence interval [95% CI]) of - 0.93 (- 1.82 to - 0.04) mL/kg/min and in the reduced LVEF cohort with the mean difference of - 1.05 (- 1.96 to - 0.15) mL/kg/min, after adjustment for age-squared, gender, anemia, renal function, LVEF, and log B-type natriuretic peptide (BNP). The adjusted VO2 at anaerobic threshold (AT), a submaximal aerobic capacity, was also decreased in the diabetic patients with both non-reduced and reduced LVEFs. Intriguingly, the diabetic patients had a lower adjusted peak O2 pulse than the nondiabetic patients in the reduced LVEF cohort, but not in the non-reduced LVEF cohort. A multivariate analysis showed that the presence of T2DM was an independent predictor of lowered peak VO2 in CHF patients with non-reduced LVEF and those with reduced LVEF. CONCLUSIONS: T2DM was associated with lowered peak VO2 in CHF patients with non-reduced or reduced LVEF. The presence of T2DM has a negative impact on CHF patients' exercise capacity, and the degree of impact is partly dependent on their LV systolic function.

Branched-chain amino acid supplementation ameliorates angiotensin II-induced skeletal muscle atrophy.

AIMS: Sarcopenia is characterized by muscle mass and strength loss and reduced physical activity. Branched-chain amino acids (BCAAs) were recently described as an activator of protein synthesis via mammalian target of rapamycin (mTOR) signaling for muscle atrophy. In cardiovascular diseases, excessive activation of the renin-angiotensin system may induce an imbalance of protein synthesis and degradation, and this plays a crucial role in muscle atrophy. We investigated the effects of BCAAs on angiotensin II (Ang II)-induced muscle atrophy in mice. MATERIALS AND METHODS: We administered Ang II (1000 ng/kg/min) or vehicle to 10-12-week-old male C57BL/6J mice via subcutaneous osmotic minipumps for 4 weeks with or without BCAA supplementation (3% BCAA in tap water). KEY FINDINGS: The skeletal muscle weight/tibial length and cross-sectional area were smaller in the Ang II mice than the vehicle mice; these changes were induced by an imbalance of protein synthesis and degradation signaling such as Akt/mTOR and MuRF-1/Atrogin-1. Compared to the Ang II mice, the mTOR signaling was significantly activated and Ang II-induced muscle atrophy was ameliorated in the Ang II + BCAA mice, and this attenuated the reduction of exercise capacity. Notably, the decrease of muscle weight/tibial length in the fast-twitch dominant muscles (e.g., the extensor digitorum longus) was significantly ameliorated compared to that in the slow-twitch dominant muscles (e.g., soleus). Histologically, the effect of BCAA was larger in fast-twitch than slow-twitch fibers, which may be related to the difference in BCAA catabolism. SIGNIFICANCE: BCAA supplementation could contribute to the prevention of skeletal muscle atrophy induced by Ang II.

Serum Brain-Derived Neurotrophic Factor Levels Are Associated with Skeletal Muscle Function but Not with Muscle Mass in Patients with Heart Failure.

Heart failure (HF) is associated with aberrant skeletal muscle impairments, which are closely linked to the severity of HF. A low level of brain-derived neurotrophic factor (BDNF), a myokine produced in the skeletal muscle, is known to be involved in reduced exercise capacity and poor prognosis in HF. However, little is known about the factors or conditions of skeletal muscle associated with BDNF levels. We investigated the association between serum BDNF levels and the skeletal muscle mass and function in HF patients (n = 60, 63 ± 13 years) and age-matched controls (n = 29, 61 ± 16 years). The serum BDNF level was significantly lower in the HF patients compared to the controls (24.9 ± 0.9 versus 28.6 ± 1.3, P = 0.021). In a univariate analysis, BDNF was significantly correlated with the peak oxygen uptake, estimated glomerular filtration rate, 10-m gait speed, and muscle strength, but not with the body mass index or lean mass in the HF group. A multiple linear regression analysis revealed that BDNF was independently associated with muscle strength (ß-coefficient = 2.80, 95%CI: 1.89-11.8, P = 0.008). Serum BDNF levels were associated with exercise capacity and skeletal muscle function, but not with muscle mass. These novel findings may suggest that BDNF production is controlled by muscle function and activity and consequently regulates exercise capacity, highlighting the importance of adequate training regarding skeletal muscle in HF patients.

Clinical Impact and Associated Factors of Delayed Ambulation in Patients With Acute Heart Failure.

Background: In heart failure (HF) management, early ambulation is recommended to prevent physical deconditioning. The effects of delayed ambulation on later clinical outcomes and the factors linked to delayed ambulation in hospitalized HF patients, however, remain unestablished. Methods and Results: We retrospectively investigated 101 patients (mean age, 66±17 years) who were hospitalized for acute decompensated HF. During the mean follow-up of 244±15 days after hospital discharge, 34 patients had cardiovascular events leading to death or unplanned readmission. Patients with cardiovascular events had longer median days to acquire ambulation than those without cardiovascular events (11 days, IQR, 8-20 days vs. 7 days, IQR, 5-15 days, P<0.001). The optimal cut-off period until initiation of ambulation to discriminate cardiovascular events was 8 days, indicating that longer days (≥8 days) to acquire ambulation was associated with higher rates of cardiovascular events, even after adjustment of multiple confounders. On multivariate analysis, age >65 years (odds ratio [OR], 2.49; 95% confidence interval [CI]: 1.04-6.09) and increase in blood urea nitrogen (BUN; OR, 1.04; 95% CI: 1.01-1.08) were independent predictors of delayed ambulation. Conclusions: Delayed ambulation is associated with older age and increased BUN in patients with acute HF. Time to ambulation in the recovery phase of acute HF is important, and delayed ambulation may increase the rate of cardiovascular events after hospital discharge.

Enhanced Echo Intensity of Skeletal Muscle Is Associated With Exercise Intolerance in Patients With Heart Failure.

BACKGROUND: Skeletal muscle is quantitatively and qualitatively impaired in patients with heart failure (HF), which is closely linked to lowered exercise capacity. Ultrasonography (US) for skeletal muscle has emerged as a useful, noninvasive tool to evaluate muscle quality and quantity. Here we investigated whether muscle quality based on US-derived echo intensity (EI) is associated with exercise capacity in patients with HF. METHODS AND RESULTS: Fifty-eight patients with HF (61 ± 12 years) and 28 control subjects (58 ± 14 years) were studied. The quadriceps femoris echo intensity (QEI) was significantly higher and the quadriceps femoris muscle thickness (QMT) was significantly lower in the patients with HF than the controls (88.3 ± 13.4 vs 81.1 ± 7.5, P= .010; 5.21 ± 1.10 vs 6.54 ±1.34 cm, P< .001, respectively). By univariate analysis, QEI was significantly correlated with age, peak oxygen uptake (VO2), and New York Heart Association class in the HF group. A multivariable analysis revealed that the QEI was independently associated with peak VO2 after adjustment for age, gender, body mass index, and QMT: ß-coefficient = -11.80, 95%CI (-20.73, -2.86), P= .011. CONCLUSION: Enhanced EI in skeletal muscle was independently associated with lowered exercise capacity in HF. The measurement of EI is low-cost, easily accessible, and suitable for assessment of HF-related alterations in skeletal muscle quality.

Empagliflozin restores lowered exercise endurance capacity via the activation of skeletal muscle fatty acid oxidation in a murine model of heart failure.

Decreased exercise capacity, which is an independent predictor of the poor prognosis of patients with heart failure (HF), is attributed to markedly impaired skeletal muscle mitochondrial function and fatty acid oxidation. Previous studies reported that the administration of an inhibitor of sodium-glucose cotransporter 2 (SGLT2) increases ketone body production and fat utilization in type 2 diabetic mice. In this study, we investigated the effects of SGLT2 inhibitor administration on exercise endurance and skeletal muscle mitochondrial function with fatty acid oxidation in a murine model of HF after the induction of myocardial infarction (MI). Two weeks post-MI, HF mice were divided into 2 groups, i.e., with or without treatment with the SGLT2 inhibitor empagliflozin (Empa, 300 mg/kg of food). Consistent with previous studies, urinary glucose and blood beta-hydroxybutyrate levels were increased in the HF+Empa mice compared with the sham and HF mice 4 weeks after the start of Empa administration. Exercise endurance capacity was limited in the HF mice but was ameliorated in the HF+Empa mice, without any effects on cardiac function, food intake, spontaneous physical activity, skeletal muscle strength, and skeletal muscle weight. Mitochondrial oxidative phosphorylation capacity with fatty acid substrates was reduced in the skeletal muscle of HF mice, and this decrease was ameliorated in the HF+Empa mice. Our results demonstrate that SGLT2 inhibitors may be novel therapeutics against reduced exercise endurance capacity in HF, by improving mitochondrial fatty acid oxidation in skeletal muscle.

Protein acetylation in skeletal muscle mitochondria is involved in impaired fatty acid oxidation and exercise intolerance in heart failure.

BACKGROUND: Exercise intolerance is a common clinical feature and is linked to poor prognosis in patients with heart failure (HF). Skeletal muscle dysfunction, including impaired energy metabolism in the skeletal muscle, is suspected to play a central role in this intolerance, but the underlying mechanisms remain elusive. Lysine acetylation, a recently identified post-translational modification, has emerged as a major contributor to the derangement of mitochondrial metabolism. We thus investigated whether mitochondrial protein acetylation is associated with impaired skeletal muscle metabolism and lowered exercise capacity in both basic and clinical settings of HF. METHODS: We first conducted a global metabolomic analysis to determine whether plasma acetyl-lysine is a determinant factor for peak oxygen uptake (peak VO2 ) in HF patients. We then created a murine model of HF (n = 11) or sham-operated (n = 11) mice with or without limited exercise capacity by ligating a coronary artery, and we tested the gastrocnemius tissues by using mass spectrometry-based acetylomics. A causative relationship between acetylation and the activity of a metabolic enzyme was confirmed in in vitro studies. RESULTS: The metabolomic analysis verified that acetyl-lysine was the most relevant metabolite that was negatively correlated with peak VO2 (r = -0.81, P < 0.01). At 4 weeks post-myocardial infarction HF, a treadmill test showed lowered work (distance × body weight) and peak VO2 in the HF mice compared with the sham-operated mice (11 ± 1 vs. 23 ± 1 J, P < 0.01; 143 ± 5 vs. 159 ± 3 mL/kg/min, P = 0.01; respectively). As noted, the protein acetylation of gastrocnemius mitochondria was 48% greater in the HF mice than the sham-operated mice (P = 0.047). Acetylproteomics identified the mitochondrial enzymes involved in fatty acid ß-oxidation (FAO), the tricarboxylic acid cycle, and the electron transport chain as targets of acetylation. In parallel, the FAO enzyme (ß-hydroxyacyl CoA dehydrogenase) activity and fatty acid-driven mitochondrial respiration were reduced in the HF mice. This alteration was associated with a decreased expression of mitochondrial deacetylase, Sirtuin 3, because silencing of Sirtuin 3 in cultured skeletal muscle cells resulted in increased mitochondrial acetylation and reduced ß-hydroxyacyl CoA dehydrogenase activity. CONCLUSIONS: Enhanced mitochondrial protein acetylation is associated with impaired FAO in skeletal muscle and reduced exercise capacity in HF. Our results indicate that lysine acetylation is a crucial mechanism underlying deranged skeletal muscle metabolism, suggesting that its modulation is a potential approach for exercise intolerance in HF.