Objectives Tachycardia-induced relaxation abnormalities were evaluated in myocardium from patients with normal ejection fraction (EF). Background Diastolic dysfunction and left ventricular (LV) hypertrophy are closely linked. Tachycardia can induce heart failure symptoms in otherwise asymptomatic patients. To study the effects of tachycardia on myocardial contractility and relaxation we evaluated the effects of increasing pacing rates in myocardial biopsies obtained from patients with normal EF. Methods LV biopsies were obtained during coronary bypass surgery. Myocardial strip preparations were electrically paced at rates from 60/min to180/min. Diastolic resting tone was assessed by crossbridge deactivation. Calcium transporting systems were functionally examined and myofilament calcium sensitivity was studied. Results Seven preparations developed incomplete relaxation with increased diastolic tension development at increasing pacing rates. This was absent in the remaining seven preparations. Incomplete relaxation was found to be associated with increased LV mass and left atrial volume. Crossbridge deactivation showed that these preparations also had a significant resting tone. Additional functional analyses suggest that incomplete relaxation is associated with disproportionately elevated cellular calcium loads due to a reduced sarcolemmal calcium extrusion reserve. Conclusions Tachycardia-induced incomplete relaxation was associated with increased LV mass and left atrial volumes. We also found a disproportionately increased calcium load at high rates and a substantial resting tone due to diastolic crossbridge cycling. These observations may play a role in reduced exercise tolerance and tachycardia induced diastolic dysfunction.

Background-Patients with chronic heart failure (HF) frequently experience skeletal muscle weakness that limits physical function. The mechanisms underlying muscle weakness, however, have not been clearly defined. Methods and Results-This study examined the hypothesis that HF promotes a loss of myosin protein from single skeletal muscle fibers, which in turn reduces contractile performance. Ten patients with chronic HF and 10 controls were studied. Muscle atrophy was not evident in patients, and groups displayed similar physical activity levels, suggesting that observed differences reflect the effects of HF and not muscle atrophy or disuse. In single muscle fibers, patients with HF showed reduced myosin heavy chain protein content (PϽ0.05) that manifested as a reduction in functional myosin-actin cross-bridges (PϽ0.05). No evidence was found for a generalized loss of myofilament protein, suggesting a selective loss of myosin. Accordingly, single muscle fiber maximal Ca 2ϩ -activated tension was reduced in myosin heavy chain I fibers in patients (PϽ0.05). However, tension was maintained in myosin heavy chain IIA fibers in patients because a greater proportion of available myosin heads were bound to actin during Ca 2ϩ activation (PϽ0.01). Conclusions-Collectively, our results show that HF alters the quantity and functionality of the myosin molecule in skeletal muscle, leading to reduced tension in myosin heavy chain I fibers. Loss of single fiber myosin protein content represents a potential molecular mechanism underlying muscle weakness and exercise limitation in patients with HF. (Circ Heart Fail. 2009;2:700-706.)Key Words: exercise Ⅲ heart failure Ⅲ mechanics Ⅲ myosin Ⅲ skeletal muscle P atients with chronic heart failure (HF) have a reduced capacity for physical work. Although cardiac dysfunction is the primary pathological insult, the resulting syndrome of HF alters numerous physiological systems to impair functional capacity. Alterations in skeletal muscle are of particular importance, most notably atrophy, 1 weakness, 2,3 and reduced endurance. 4 These peripheral skeletal muscle adaptations limit physical function independent of cardiac impairment 5 and persist despite correction of cardiac dysfunction. 6 Clinical Perspective on p 706Aerobic fitness is commonly assumed to be the primary determinant of physical function in patients with HF because exertional fatigue and dyspnea are predominant symptoms. However, aerobic capacity is a relatively poor predictor of performance in activities of daily living. 7 This is because most activities are limited instead by skeletal muscle strength. 8 Accordingly, functional capacity can be increased in patients with HF in the absence of alterations in aerobic capacity by improving muscle strength. 9 Despite its potential relevance to physical disability in patients with HF, few studies have explored the mechanisms underlying reduced skeletal muscle strength.Skeletal muscle weakness in HF is not explained by muscle atrophy 2,10 or reduced motor activation, 2 suggesting d...

Background Relaxation characteristics and Ca2+-homeostasis have not been studied in isolated myocardium from patients with hypertensive heart disease (HHD) and heart failure with preserved ejection fraction (HFpEF). Prolonged myocardial relaxation is believed to play an important role in the pathophysiology of these conditions. In this study we evaluated relaxation parameters, myocardial calcium (Ca2+) and sodium (Na+) handling as well as ion transporter expression and tested the effect of Na+-influx inhibitors on relaxation in isolated myocardium from patients with HHD and HFpEF. Methods and Results Relaxation characteristics were studied in myocardial strip preparations under physiological conditions at stimulation rates of 60/min and 180/min. Intracellular Ca2+ and Na+ was simultaneously assessed using Fura-2 and ANG-2, whereas elemental analysis was utilized to measure total myocardial concentrations of Ca, Na and other elements. Quantitative PCR was used to measure expression levels of key ion transport proteins. The lusitropic effect of Na+-influx inhibitors ranolazine, furosemide and amiloride was evaluated. Myocardial LV biopsies were obtained from 36 control patients (CTR), 29 HHD and 19 HHD+HFpEF. When compared to CTR, half maximal relaxation time (RT50) at 60/min was prolonged by 13% in HHD and by 18% in HHD+HFpEF (both p<0.05). Elevated resting Ca2+-levels and a tachycardia-induced increase in diastolic Ca2+ were associated with incomplete relaxation and an increase in diastolic tension in HHD and HHD+HFpEF. Na+-levels were not increased and expression levels of Ca2+- or Na+-handling proteins were not altered. Na+-influx inhibitors did not improve relaxation or prevent incomplete relaxation at high stimulation rates. Conclusions Contraction and relaxation are prolonged in isolated myocardium from patients with HHD and HHD+HFpEF. This leads to incomplete relaxation at higher rates. Elevated calcium levels in HFpEF are neither due to an impaired Na+-gradient nor to expression changes in key ion transporters and regulatory proteins.

We examined whether factors released from embryonic stem (ES) cells inhibit cardiac and vascular cell apoptosis and stimulate endogenous progenitor cells that enhance neovascularization with improved cardiac function. We generated and transplanted ES-conditioned medium (CM) in the infarcted heart to examine effects on cardiac and vascular apoptosis, activation of endogenous c-kit and FLK-1 +ve cells, and their role in cardiac neovascularization. TUNEL, caspase-3 activity, immunohistochemistry, H&E, and Masson's trichrome stains were used to determine the effect of transplanted ES-CM on cardiac apoptosis and neovascularization. TUNEL staining and caspase-3 activity confirm significantly ( p < 0.05) reduced apoptosis in MI+ES-CM compared with MI+ cell culture medium. Immunohistochemistry demonstrated increased ( p < 0.05, 53%) c-kit +ve and FLK-1 +ve positive cells, as well as increased ( p < 0.05, 67%) differentiated CD31-positive cells in ES-CM groups compared with respective controls. Furthermore, significantly ( p < 0.05) increased coronary artery vessels were observed in ES-CM transplanted hearts compared with control. Heart function was significantly improved following ES-CM transplantation. Next, we observed significantly increased ( p < 0.05) levels of c-kit activation proteins (HGF and IGF-1), anti-apoptosis factors (IGF-1 and total antioxidants), and neovascularization protein (VEGF). In conclusion, we suggest that ES-CM following transplantation in the infarcted heart inhibits apoptosis, activates cardiac endogenous c-kit and FLK-1 +ve cells, and differentiates them into endothelial cells (ECs) that enhances neovascularization with improved cardiac function.