Chronic treatment with carvedilol improves Ca(2+)-dependent ATP consumption in triton X-skinned fiber preparations of human myocardium

Heart Failure with Improved Ejection Fraction: Insight into the Variable Nature of Left Ventricular Systolic Function

The progress of contemporary cardiovascular therapy has led to improved survival in patients with myocardial disease. However, the development of heart failure (HF) represents a common clinical challenge, regardless of the underlying myocardial pathology, due to the severely impaired quality of life and increased mortality comparable with malignant neoplasms. Left ventricular ejection fraction (LVEF) is the main index of systolic function and a key predictor of mortality among HF patients, hence its improvement represents the main indicator of response to instituted therapy. The introduction of complex pharmacotherapy for HF, increased availability of cardiac-implantable electronic devices and advances in the management of secondary causes of HF, including arrhythmia-induced cardiomyopathy, have led to significant increase in the proportion of patients with prominent improvement or even normalization of LVEF, paving the way for the identification of a new subgroup of HF with an improved ejection fraction (HFimpEF). Accumulating data has indicated that these patients share far better long-term prognoses than patients with stable or worsening LVEF. Due to diverse HF aetiology, the prevalence of HFimpEF ranges from roughly 10 to 40%, while the search for reliable predictors and genetic associations corresponding with this clinical presentation is under way. As contemporary guidelines focus mainly on the management of HF patients with clearly defined LVEF, the present review aimed to characterize the definition, epidemiology, predictors, clinical significance and principles of therapy of patients with HFimpEF.

Time and technology will tell: the pathophysiologic basis of neurohormonal modulation in heart failure

The central roles of neurohormonal abnormalities in the pathobiology of heart failure have been defined in recent decades. Experiments have revealed both systemic involvement and intricate subcellular regulation by circulating effectors of the sympathetic nervous system, the renin-angiotensin-aldosterone system, and others. Randomized clinical trials substantiated these findings, establishing neurohormonal antagonists as cornerstones of heart failure pharmacotherapy, and occasionally offering further insight on mode of benefit. This review discusses the use of β-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone receptor antagonists in the treatment of heart failure, with particular attention to the pathophysiologic basis and mechanisms of action.

β-adrenergic blockade attenuates cardiac dysfunction and myofibrillar remodelling in congestive heart failure

Although β-adrenoceptor (β-AR) blockade is an important mode of therapy for congestive heart failure (CHF), subcellular mechanisms associated with its beneficial effects are not clear. Three weeks after inducing myocardial infarction (MI), rats were treated daily with or without 20 and 75 mg/kg atenolol, a selective β₁-AR antagonist, or propranolol, a non-selective β-AR antagonist, for 5 weeks. Sham operated rats served as controls. All animals were assessed haemodynamically and echocardiographically and the left ventricle (LV) was processed for the determination of myofibrillar ATPase activity, α- and β-myosin heavy chain (MHC) isoforms and gene expression as well as cardiac troponin I (cTnI) phosphorylation. Both atenolol and propranolol at 20 and 75 mg/kg doses attenuated cardiac hypertrophy and lung congestion in addition to increasing LV ejection fraction and LV systolic pressure as well as decreasing heart rate, LV end-diastolic pressure and LV diameters in the infarcted animals. Treatment of infarcted animals with these agents also attenuated the MI-induced depression in myofibrillar Ca²⁺-stimulated ATPase activity and phosphorylated cTnI protein content. The MI-induced decrease in α-MHC and increase in β-MHC protein content were attenuated by both atenolol and propranolol at low and high doses; however, only high dose of propranolol was effective in mitigating changes in the gene expression for α-MHC and β-MHC. Our results suggest that improvement of cardiac function by β-AR blockade in CHF may be associated with attenuation of myofibrillar remodelling.

Increased Ca2+ sensitivity of myofibrillar tension in ischaemic vs dilated cardiomyopathy

1. There is evidence that different aetiologies of heart failure, especially ischaemic vs dilated cardiomyopathy (ICM and DCM, respectively), may influence the prognosis of patients with this disease. Patients with ICM have a worse prognosis than those with DCM; the mechanisms underlying this difference have not yet been clarified. The aim of the present study was to investigate whether there are changes in myofibrillar function depending on the aetiology of human heart failure. 2. Ca(2+) -dependent tension (DT) and actomyosin ATPase activity (MYO) in Triton X-skinned fibre preparations of the left ventricular myocardium from patients with heart failure due to ICM (n=5) and DCM (n=5) were measured. Tension-dependent ATP consumption was calculated by the ratio of DT and MYO ('tension cost'). Non-failing myocardium (NF) from donor hearts, which could not be transplanted because of technical reasons, was evaluated as a control. 3. Although DT was reduced, the myofibrillar Ca(2+) sensitivity of DT and MYO, as well as tension cost, were increased in preparations from ICM and DCM myocardium compared with NF. The Ca(2+) sensitivity of DT and MYO was significantly increased in ICM compared with DCM preparations, resulting in more economic cross-bridge cycling in ICM than in DCM. 4. In conclusion, ICM is associated with an increased Ca(2+) sensitivity of myofibrillar tension and ATPase activity accompanied by decreased tension cost compared with DCM. Thus, the worse prognosis associated with ICM does not seem to be due to differences in myofibrillar function.

Energy metabolism in heart failure and remodelling

Myocytes of the failing heart undergo impressive metabolic remodelling. The time line for changes in the pathways for ATP synthesis in compensated hypertrophy is: flux through the creatine kinase (CK) reaction falls as both creatine concentration ([Cr]) and CK activity fall; increases in [ADP] and [AMP] lead to increases in glucose uptake and utilization; fatty acid oxidation either remains the same or decreases. In uncompensated hypertrophy and in other forms of heart failure, CK flux and fatty acid oxidation are both lower; any increases in glucose uptake and utilization are not sufficient to compensate for overall decreases in the capacity for ATP supply and [ATP] falls. Metabolic remodelling is under transcriptional and post-transcriptional control. The lower metabolic reserve of the failing heart contributes to impaired contractile reserve.

Reduced troponin I phosphorylation and increased Ca(2+)-dependent ATP-consumption in triton X-skinned fiber preparations from Galphaq overexpressor mice

Overexpression of the Galphaq-protein has been shown to result in hypertrophic and dilated cardiomyopathy. This study investigated Ca(2+ )sensitivity of tension and myosin-ATPase activity in skinned fiber preparations of male and female wildtype (WT; n = 12) and transgenic mice with a cardiac specific overexpression of the Galphaq-protein (Galphaq-OE; n = 11). In addition, the phosphorylation status of troponin I was measured. Ca(2+) sensitivity of tension was increased in Galphaq-OE with a significant reduction in the half-maximum Ca(2+) concentration (EC(50)) compared to WT. Similarly, Ca(2+) sensitivity of myosin ATPase activity was increased in Galphaq-OE when comparing Galphaq-OE to WT. Maximum Ca(2+)-dependent tension and ATPase activity were both enhanced in Galphaq-OE compared to WT littermates. Phosphorylation of troponin I was significantly reduced in Galphaq-OE compared to WT. In the above experiments, no gender specific differences were observed in either Gaq-OE or in WT. We conclude that, in mice, increased expression of the Galphaq-protein induces alterations of myofibrillar function and energy consumption, which are also characteristics of human heart failure. This may result from a decreased phosphorylation of troponin I in Galphaq-OE.