Histologic and biochemical correlates of left ventricular chamber dynamics in man

Integrated Functions of Cardiac Energetics, Mechanics, and Purine Nucleotide Metabolism

Purine nucleotides play central roles in energy metabolism in the heart. Most fundamentally, the free energy of hydrolysis of the adenine nucleotide adenosine triphosphate (ATP) provides the thermodynamic driving force for numerous cellular processes including the actin-myosin crossbridge cycle. Perturbations to ATP supply and/or demand in the myocardium lead to changes in the homeostatic balance between purine nucleotide synthesis, degradation, and salvage, potentially affecting myocardial energetics and, consequently, myocardial mechanics. Indeed, both acute myocardial ischemia and decompensatory remodeling of the myocardium in heart failure are associated with depletion of myocardial adenine nucleotides and with impaired myocardial mechanical function. Yet there remain gaps in the understanding of mechanistic links between adenine nucleotide degradation and contractile dysfunction in heart disease. The scope of this article is to: (i) review current knowledge of the pathways of purine nucleotide depletion and salvage in acute ischemia and in chronic heart disease; (ii) review hypothesized mechanisms linking myocardial mechanics and energetics with myocardial adenine nucleotide regulation; and (iii) highlight potential targets for treating myocardial metabolic and mechanical dysfunction associated with these pathways. It is hypothesized that an imbalance in the degradation, salvage, and synthesis of adenine nucleotides leads to a net loss of adenine nucleotides in both acute ischemia and under chronic high-demand conditions associated with the development of heart failure. This reduction in adenine nucleotide levels results in reduced myocardial ATP and increased myocardial inorganic phosphate. Both of these changes have the potential to directly impact tension development and mechanical work at the cellular level. © 2024 American Physiological Society. Compr Physiol 14:5345-5369, 2024.

Inefficient Batteries in Heart Failure: Metabolic Bottlenecks Disrupting the Mitochondrial Ecosystem

Mitochondrial abnormalities have long been described in the setting of cardiomyopathies and heart failure (HF), yet the mechanisms of mitochondrial dysfunction in cardiac pathophysiology remain poorly understood. Many studies have described HF as an energy-deprived state characterized by a decline in adenosine triphosphate production, largely driven by impaired oxidative phosphorylation. However, impairments in oxidative phosphorylation extend beyond a simple decline in adenosine triphosphate production and, in fact, reflect pervasive metabolic aberrations that cannot be fully appreciated from the isolated, often siloed, interrogation of individual aspects of mitochondrial function. With the application of broader and deeper examinations into mitochondrial and metabolic systems, recent data suggest that HF with preserved ejection fraction is likely metabolically disparate from HF with reduced ejection fraction. In our review, we introduce the concept of the mitochondrial ecosystem, comprising intricate systems of metabolic pathways and dynamic changes in mitochondrial networks and subcellular locations. The mitochondrial ecosystem exists in a delicate balance, and perturbations in one component often have a ripple effect, influencing both upstream and downstream cellular pathways with effects enhanced by mitochondrial genetic variation. Expanding and deepening our vantage of the mitochondrial ecosystem in HF is critical to identifying consistent metabolic perturbations to develop therapeutics aimed at preventing and improving outcomes in HF.

Cardioprotective effects of early intervention with sacubitril/valsartan on pressure overloaded rat hearts

Left ventricular remodeling due to pressure overload is associated with poor prognosis. Sacubitril/valsartan is the first-in-class Angiotensin Receptor Neprilysin Inhibitor and has been demonstrated to have superior beneficial effects in the settings of heart failure. The aim of this study was to determine whether sacubitril/valsartan has cardioprotective effect in the early intervention of pressure overloaded hearts and whether it is superior to valsartan alone. We induced persistent left ventricular pressure overload in rats by ascending aortic constriction surgery and orally administrated sacubitril/valsartan, valsartan, or vehicle one week post operation for 10 weeks. We also determined the effects of sacubitril/valsartan over valsartan on adult ventricular myocytes and fibroblasts that were isolated from healthy rats and treated in culture. We found that early intervention with sacubitril/valsartan is superior to valsartan in reducing pressure overload-induced ventricular fibrosis and in reducing angiotensin II-induced adult ventricular fibroblast activation. While neither sacubitril/valsartan nor valsartan changes cardiac hypertrophy development, early intervention with sacubitril/valsartan protects ventricular myocytes from mitochondrial dysfunction and is superior to valsartan in reducing mitochondrial oxidative stress in response to persistent left ventricular pressure overload. In conclusion, our findings demonstrate that sacubitril/valsartan has a superior cardioprotective effect over valsartan in the early intervention of pressure overloaded hearts, which is independent of the reduction of left ventricular afterload. Our study provides evidence in support of potential benefits of the use of sacubitril/valsartan in patients with resistant hypertension or in patients with severe aortic stenosis.

Quantifying the effect of dobutamine stress on myocardial Pi and pH in healthy volunteers: A 31 P MRS study at 7T

Purpose

Phosphorus spectroscopy (³¹P‐MRS) is a proven method to probe cardiac energetics. Studies typically report the phosphocreatine (PCr) to adenosine triphosphate (ATP) ratio. We focus on another ³¹P signal: inorganic phosphate (Pi), whose chemical shift allows computation of myocardial pH, with Pi/PCr providing additional insight into cardiac energetics. Pi is often obscured by signals from blood 2,3‐diphosphoglycerate (2,3‐DPG). We introduce a method to quantify Pi in 14 min without hindrance from 2,3‐DPG.

Methods

Using a ³¹P stimulated echo acquisition mode (STEAM) sequence at 7 Tesla that inherently suppresses signal from 2,3‐DPG, the Pi peak was cleanly resolved. Resting state UTE‐chemical shift imaging (PCr/ATP) and STEAM ³¹P‐MRS (Pi/PCr, pH) were undertaken in 23 healthy controls; pH and Pi/PCr were subsequently recorded during dobutamine infusion.

Results

We achieved a clean Pi signal both at rest and stress with good 2,3‐DPG suppression. Repeatability coefficient (8 subjects) for Pi/PCr was 0.036 and 0.12 for pH. We report myocardial Pi/PCr and pH at rest and during catecholamine stress in healthy controls. Pi/PCr was maintained during stress (0.098 ± 0.031 [rest] vs. 0.098 ± 0.031 [stress] P = .95); similarly, pH did not change (7.09 ± 0.07 [rest] vs. 7.08 ± 0.11 [stress] P = .81). Feasibility for patient studies was subsequently successfully demonstrated in a patient with cardiomyopathy.

Conclusion

We introduced a method that can resolve Pi using 7 Tesla STEAM ³¹P‐MRS. We demonstrate the stability of Pi/PCr and myocardial pH in volunteers at rest and during catecholamine stress. This protocol is feasible in patients and potentially of use for studying pathological myocardial energetics.

Cardiac metabolic imaging: current imaging modalities and future perspectives

In this review, current imaging techniques and their future perspectives in the field of cardiac metabolic imaging in humans are discussed. This includes a range of noninvasive imaging techniques, allowing a detailed investigation of cardiac metabolism in health and disease. The main imaging modalities discussed are magnetic resonance spectroscopy techniques for determination of metabolite content (triglycerides, glucose, ATP, phosphocreatine, and so on), MRI for myocardial perfusion, and single-photon emission computed tomography and positron emission tomography for quantitation of perfusion and substrate uptake.

Unveiling differences between patients with acute coronary syndrome with and without ST elevation through fingerprinting with CE-MS and HILIC-MS targeted analysis

Differences in the degree and severity of Acute Coronary Syndrome, associated to differences in the electrocardiogram, together with blood tests of biomarkers classify patients for diagnosis and treatment. Cases where the electrocardiogram and/or biomarkers are not conclusive still appear, and there is a need for complementary biomarkers for routine determinations. Metabolomics approaches with blind fingerprinting could reveal differences in metabolites, which must be confirmed by means of targeted determinations. CE-MS and HILIC-MS are well suited for the determination of highly polar compounds, like those from to the intermediate metabolism, altered due to acute stress induced by myocardial infarction. Serum from patients with ST-elevated and non-ST elevated myocardial infarction was collected at intensive care and emergency units, and fingerprinted with CE-MS. Data pretreatment and analysis showed up carnitine-related compounds and amino acids differentially present in both groups. Acylcarnitines and amino acids were then quantitatively measured with HILIC-MS-QqQ. The significance of the differences and the sensitivity/specificity of each compound were individually evaluated. The ratio of free carnitine to acylcarnitines, together with the ratios of acetylcarnitine to betaine, to threonine, and to citrulline, showed high significance and area under the curve in the respective receiver operating characteristic curves. This study opens new possibilities for defining new sets of biomarkers for refining the diagnosis of the patients with difficult classification.

Ultrastructural calcium distribution and myocardial calcium content in human idiopathic dilated cardiomyopathy

Myocardial calcium overload in chronic heart failure is still a debatable issue. The aim of this study was to investigate the myocardial calcium content and intracellular calcium distribution in end-stage dilated cardiomyopathy. The explanted hearts of 13 patients (9 male, 4 female, mean age 49 ± 12 years) undergoing heart transplantation because of end-stage dilated cardiomyopathy were examined. Samples were obtained from the right and left ventricular free wall and from the septum. Calcium and magnesium content were measured by atomic absorption spectrophotometry. Ultrastructural calcium distribution was examined in dilated cardiomyopathy using the phosphate-pyroantimonate method. Ultrastructural calcium distribution was also examined in left ventricular biopsies obtained from 3 patients (male, mean age 47 ± 3.6 years) with nonfailing hearts. The number of mitochondrial calcium precipitates was estimated morphometrically by a point counting method. Myocardial calcium and magnesium content in dilated cardiomyopathy did not differ significantly among the right and left ventricles and septum ranging from 8.5 to 10.8 mmol/kg dry weight. The phosphate-pyroantimonate method visualized calcium precipitates being confined to the sarcolemma, T-tubules, intercalated disks, and mitochondria in both nonfailing myocardium and dilated cardiomyopathy. Because mitochondria may act as buffers of cytoplasmic calcium, mitochondrial calcium precipitates served as a criterion for a possible cellular calcium overload. No differences in the amount of mitochondrial calcium deposits were observed between dilated cardiomyopathy and nonfailing hearts. The data suggest that there is no global myocardial calcium overload in human eng-stage dilated cardiomyopathy.

Possible involvement of mitochondrial energy-producing ability in the development of right ventricular failure in monocrotaline-induced pulmonary hypertensive rats

The present study was undertaken to explore the possible involvement of alterations in the mitochondrial energy-producing ability in the development of the right ventricular failure in monocrotaline-administered rats. The rats at the 6th week after subcutaneous injection of 60 mg/kg monocrotaline revealed marked myocardial hypertrophy and fibrosis, that is, severe cardiac remodeling. The time-course study on the cardiac hemodynamics of the monocrotaline-administered rat by the cannula and echocardiographic methods showed a reduction in cardiac double product, a decrease in cardiac output index, and an increase in the right ventricular Tei index, suggesting that the right ventricular failure was induced at the 6th week after monocrotaline administration in rats. The mitochondrial oxygen consumption rate of the right ventricular muscle isolated from the monocrotaline-administered animal was decreased, which was associated with a reduction in myocardial high-energy phosphates. Furthermore, the decrease in mitochondrial oxygen consumption rate was inversely related to the increase in the right ventricular Tei index of the monocrotaline-administered rats. These results suggest that impairment of the mitochondrial energy-producing ability is involved in the development of the right ventricular failure in monocrotaline-induced pulmonary hypertensive rats.

Mitochondrial uncoupling protein 3 and its role in cardiac- and skeletal muscle metabolism

Uncoupling protein 3 (UCP3), is primarily expressed in skeletal muscle mitochondria and has been suggested to be involved in mediating energy expenditure via uncoupling, hereby dissipating the mitochondrial proton gradient necessary for adenosine triphosphate (ATP) synthesis. Although some studies support a role for UCP3 in energy metabolism, other studies pointed towards a function in fatty acid metabolism. Thus, the protein is up regulated or high when fatty acid supply to the mitochondria exceeds the capacity to oxidize fatty acids and down regulated or low when oxidative capacity is high or improved. Irrespective of the exact operating mechanism, UCP3 seems to protect mitochondria against lipid-induced oxidative stress, which makes this protein a potential player in the development of type 2 diabetes mellitus. Next to skeletal muscle, UCP3 is also expressed in cardiac muscle where its role is relatively unexplored. Interestingly, energy deficiency in cardiac muscle is associated to heart failure and UCP3 might contribute to this energy deficiency. It has been suggested that UCP3 decreases energy status via uncoupling of mitochondrial respiration, but the available data does not provide a unified answer. In fact, the results obtained regarding cardiac UCP3 are very similar as in skeletal muscle, implying that its physiological function can be extrapolated. Therefore, cardiac UCP3 can just as well serve to protect the heart against lipid-induced oxidative stress, similar to the function described for skeletal muscle UCP3. The present review will deal with the available literature on both skeletal muscle- and cardiac UCP3 to elucidate its physiological function in these tissues.

Redox proteomic identification of oxidized cardiac proteins in adriamycin-treated mice

Adriamycin (ADR) is a potent anticancer drug, but its use is limited by a dose-dependent cardiotoxicity. Oxidative stress is regarded as the mediating mechanism of ADR cardiotoxicity. However, cardiac proteins that are oxidatively modified have not been well characterized. We took a redox proteomics approach to identify increasingly oxidized murine cardiac proteins after a single injection of ADR (ip, 20 mg/kg body wt). The specific carbonyl levels of three proteins were significantly increased, and these proteins were identified as triose phosphate isomerase (TPI), beta-enolase, and electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). TPI and enolase are key enzymes in the glycolytic pathway, and ETF-QO serves as the transporter for electrons derived from a variety of oxidative processes to the mitochondria respiratory chain. Cardiac enolase activity in ADR-treated mice was reduced by 25%, whereas the cardiac TPI activity remained unchanged. Oxidation of purified enolase or TPI via Fenton chemistry led to a 17 or 23% loss of activity, respectively, confirming that a loss of activity was the consequence of oxidation. The observation that these cardiac enzymes involved in energy production are more oxidized resulting from ADR treatment indicates that the bioenergetic pathway is an important target in ADR-initiated oxidative stress.

Potential role of ubiquinone (coenzyme Q10) in pediatric cardiomyopathy

Pediatric cardiomyopathy (PCM) represents a group of rare and heterogeneous disorders that often results in death. While there is a large body of literature on adult cardiomyopathy, all of the information is not necessarily relevant to children with PCM. About 40% of children who present with symptomatic cardiomyopathy are reported to receive a heart transplant or die within the first two years of life. In spite of some of the advances in the management of PCM, the data shows that the time to transplantation or death has not improved during the past 35 years. Coenzyme Q10 is a vitamin-like nutrient that has a fundamental role in mitochondrial function, especially as it relates to the production of energy (ATP) and also as an antioxidant. Based upon the biochemical rationale and a large body of data on patients with adult cardiomyopathy, heart failure, and mitochondrial diseases with heart involvement, a role for coenzyme Q10 therapy in PCM patients is indicated, and preliminary results are promising. Additional studies on the potential usefulness of coenzyme Q10 supplementation as an adjunct to conventional therapy in PCM, particularly in children with dilated cardiomyopathy, are therefore warranted.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Effects of simvastatin on blood lipids, vitamin E, coenzyme Q10 levels and left ventricular function in humans

BACKGROUND

As statin therapy has been reported to reduce antioxidants such as vitamin E and coenzyme Q10 and there are indications that this reduction may cause impairment of left ventricular function (LVF), we studied the influence of simvastatin on LVF and serum vitamin E and coenzyme Q10 levels in humans.

MATERIAL AND METHODS

We assessed the effect of simvastatin on left ventricular function and coenzyme Q10 levels in 21 (11 male, 10 female) hypercholesterolaemic subjects (mean age = 56 years) with normal LVF, over a period of 6 months. Subjects were re-tested after a 1-month wash-out period (7 months). Echocardiography was performed on all subjects before commencement of simvastatin (20 mg day(-1)), and at 1, 3, 6 and 7 months after initiation of treatment. Fasting blood samples were also collected at these intervals to assess lipids, apoproteins, vitamin E and coenzyme Q10.

RESULTS

Serum lipids showed the expected reductions. Plasma vitamin E and coenzyme Q10 levels were reduced by 17 +/- 4% (P < 0.01) and 12 +/- 4% (P < 0.03) at 6 months. However, the coenzyme Q10/LDL-cholesterol ratio and vitamin E/LDL-cholesterol ratio increased significantly. Left ventricular ejection fraction (EF) decreased transiently after 1 month, while no significant change was observed at 3 and 6 months. Other markers of left ventricular function did not change significantly at any time point.

CONCLUSION

Despite reduced plasma vitamin E and coenzyme Q10, 20 mg of simvastatin therapy is associated with a significantly increased coenzyme Q10/LDL-cholesterol ratio and vitamin E/LDL-cholesterol ratio. Simvastatin treatment is not associated with impairment in left ventricular systolic or diastolic function in hypercholesterolaemic subjects after 6 months of treatment.

Effects of sulfonylurea hypoglycemic agents and adenosine triphosphate dependent potassium channel antagonists on ventricular arrhythmias in patients with decompensated heart failure

Hypoglycemic sulfonylureas block cardiac ATP-sensitive potassium channels (K(ATP)). The opening of these channels in cardiomyocytes can induce arrhythmias. In animal studies, sulfonylureas exert an antiarrhythmic effect on the ischemic myocardium, but data on human arrhythmic events are lacking. The study population included 207 patients (age 61 +/- 14 years) admitted for decompensated CHF. The severity of ventricular arrhythmias was assessed by 24-hour Holter monitoring. None of the patients were on parenteral vasoactive therapy or antiarrhythmics during Holter recording. Diabetic patients comprised 48% of the study population, and 34% of diabetic patients were prescribed sulfonylureas. The mean hourly ventricular pairs (3.6 +/- 0.5 vs 1.8 +/- 0.3, P = 0.03), the mean hourly repetitive ventricular beats (5.7 +/- 1.0 vs 2.6 +/- 0.1, P = 0.03), and the frequency of ventricular tachycardia episodes per 24 hours (4.7 +/- 0.8 vs 2.2 +/- 0.4, P = 0.03) were significantly lower in patients with diabetes who were receiving sulfonylureas compared with nondiabetics. No significant difference occurred between patients with diabetes who were not receiving sulfonylureas and nondiabetic patients. Multivariate regression revealed a negative independent relationship between sulfonylurea therapy and hourly ventricular pairs (P = 0.03), the mean hourly repetitive ventricular beats (P = 0.03), and ventricular tachycardia episodes (P = 0.04). In a multiple logistic regression, sulfonylurea therapy was a negative predictor of repetitive ventricular beats (P = 0.01, adjusted OR, 0.31; 95% CI, 0.12-0.78). Concomitant sulfonylurea therapy may reduce the occurrence of complex ventricular ectopy in the setting of severe CHF. These results suggest that cardiac K(ATP) channel activation may be involved in the genesis of ventricular arrhythmias in CHF.

The energy metabolism in the right and left ventricles of human donor hearts across transplantation

OBJECTIVE

Brain death appears to predominantly affect the right ventricle (RV) and right ventricular failure is a common complication of clinical cardiac transplantation. It is not clear to what extent myocardial energy stores are affected in the operative sequence. We aimed to describe the time-dependent variation in high energy phosphate (HEP) metabolism of the two ventricles, and the relationship with endothelial activation and postoperative functional recovery.

METHODS

Fifty-two human donors had serial biopsies from the RV and the left ventricle (LV) at (1) initial evaluation, (2) after haemodynamic optimisation, (3) end of cold ischaemia, (4) end of warm ischaemia, (5) reperfusion, and (6) at 1 week postoperatively. HEP was measured by chemiluminescence in biopsies 1-5 and adhesion molecules (P-selectin, E-selectin, VCAM-1) and thrombomodulin were analysed by immunohistochemistry in biopsies 5-6. Seventeen donors and five recipients had RV intraoperative pressure-volume recordings by a conductance catheter. Six patients served as live controls.

RESULTS

Brain death did not affect HEP metabolism quantitatively. There was no difference between the RV and LV at any time point, but significant time-dependent changes were observed. The RV was prone to HEP depletion at retrieval, with ATP/ADP falling from 3.89 to 3.13, but recovered during cold ischaemia. During warm ischaemia the ATP/ADP ratio fell by approximately 50%, from 5.48 for the RV and 4.26 for the LV, with partial recovery at reperfusion (P<0.005). Hearts with impaired function in the recipient showed marked variations in HEP levels at reperfusion, and those organs with RV dysfunction failed to replenish their energy stores. However, these organs were not different from normally functioning allografts in terms of endothelial activation and clinical risk factors. There was poor correlation between pressure-volume and HEP data in either donor or recipient studies. Hearts followed-up with HEP and pressure-volume studies showed improvement in the recipient, despite functioning against a higher pulmonary vascular resistance.

CONCLUSIONS

HEP are preserved over a wide range of contractile performance in the donor heart, with no metabolic difference between the two ventricles. No correlation with endothelial activation was seen either. Preservation efforts should be directed to the vulnerable periods of implantation and reperfusion.

Absolute concentrations of high-energy phosphate metabolites in normal, hypertrophied, and failing human myocardium measured noninvasively with (31)P-SLOOP magnetic resonance spectroscopy

OBJECTIVE

The purpose of the present study was to measure absolute concentrations of phosphocreatine (PCr) and adenosine triphosphate (ATP) in normal, hypertrophied, and failing human heart.

BACKGROUND

Conflicting evidence exists on the extent of changes of high-energy phosphate metabolites in hypertrophied and failing human heart. Previous reports using phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) have quantified metabolites in relative terms only. However, this analysis cannot detect simultaneous reductions.

METHODS

Four groups of subjects (n = 10 each), were studied: volunteers and patients with hypertensive heart disease (HHD), aortic stenosis, and dilated cardiomyopathy (DCM). Left ventricular (LV) function and mass were measured by cine magnetic resonance imaging. Absolute and relative concentrations of PCr and ATP were determined by (31)P-MRS with spatial localization with optimum point spread function.

RESULTS

Left ventricular ejection fraction remained normal in HHD and aortic stenosis, but was severely reduced to 18% in DCM; LV mass was increased by 55%, 79%, and 68% respectively. In volunteers, PCr and ATP concentrations were 8.82 +/- 1.30 mmol/kg wet weight and 5.69 +/- 1.02 mmol/kg wet weight, and the PCr/ATP ratio was 1.59 +/- 0.33. High-energy phosphate levels were unaltered in HHD. In aortic stenosis, PCr was decreased by 28%, whereas ATP remained constant. In DCM, PCr was reduced by 51%, ATP by 35%, and reduction of the PCr/ATP ratio by 25% was of borderline significance (p = 0.06). Significant correlations were observed among energetic and functional variables, with the closest relations for PCr.

CONCLUSIONS

In human heart failure due to DCM, both PCr and ATP are significantly reduced. Ratios of PCr to ATP underestimate changes of high-energy phosphate levels.

Energy metabolism in the normal and failing heart: potential for therapeutic interventions

The chronically failing heart has been shown to be metabolically abnormal, in both animal models and in patients. Little data are available on the rate of myocardial glucose, lactate and fatty acid metabolism and oxidation in heart failure patients, thus at present, it is not possible to draw definitive conclusions about cardiac substrate preference in the various stages and manifestations of the disease. Normal cardiac function is dependent on a constant resynthesis of ATP by oxidative phosphorylation in the mitochondria. The healthy heart gets 60-90% of its energy for oxidative phosphorylation from fatty acid oxidation, with the balance from lactate and glucose. There is some indication that compensated NYHA Class III heart failure patients have a significantly greater rate of lipid oxidation, and decreased glucose uptake and carbohydrate oxidation compared to healthy age-matched individuals, and that therapies that acutely switch the substrate of the heart away from fatty acids result in improvement in left ventricular function. Clinical studies using long-term therapy with beta-adrenergic receptor antagonists show improved left ventricular function that corresponds with a switch away from fatty acid oxidation towards more carbohydrate oxidation by the heart. These findings suggest that chronic manipulation of myocardial substrate oxidation toward greater carbohydrate oxidation and less fatty acid oxidation may improve ventricular performance and slow the progression of left ventricular dysfunction in heart failure patients. At present, this intriguing hypothesis requires further evaluation.

Abnormal myocardial free fatty acid utilization deteriorates with morphological changes in the hypertensive heart

The left ventricle's morphological adaptation to high blood pressure is classified into 4 patterns based on mass and wall thickness. The geometric changes caused by maladaptation to pressure overload possibly relate to progression of contractile dysfunction with abnormal energy metabolism. The present study assessed whether the geometric adaptation of the left ventricle (LV) to high blood pressure relates to changes in myocardial energy metabolism, especially free fatty acid (FFA) utilization. Thirty-five patients with essential hypertension underwent echocardiography and dual isotopes myocardial scintigraphy using iodine-123 labeled 15-p-iodophenyl-3-(R,S)-methylpentadecanoic acid (BMIPP, an analogue of a FFA) and thallium-201 (Tl-201). Systolic (endocardial fractional shortening; %FS) and diastolic indices (the ratio of early to atrial filling waves; E/A) of LV function were also assessed. Quantitative myocardial BMIPP uptake was evaluated by the BMIPP/TI-201 myocardial uptake ratio (B/T). The subjects were divided into 4 groups based on LV mass and wall thickness: (1) concentric hypertrophy (CH), (2) eccentric hypertrophy (EH), (3) concentric remodeling (CR), and (4) normal geometry (N). The %FS was lower in the EH group than in the other groups. The mitral E/A ratio in the CH group was lowest. B/T was significantly decreased in the EH group compared with the N group (p < 0.05). B/T correlated with the mitral E/A ratio significantly (p < 0.05, r = 0.42), whereas there was no relationship between %FS and B/T. These results indicate that the geometric changes occurring in hypertensive hearts strongly correlate with alternations in cardiac function and with abnormal myocardial FFA metabolism, and that the latter is associated with diastolic abnormality, but not with systolic function.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Abnormal mitochondrial respiration in failed human myocardium

Chronic heart failure (HF) is associated with morphologic abnormalities of cardiac mitochondria including hyperplasia, reduced organelle size and compromised structural integrity. In this study, we examined whether functional abnormalities of mitochondrial respiration are also present in myocardium of patients with advanced HF. Mitochondrial respiration was examined using a Clark electrode in an oxygraph cell containing saponin-skinned muscle bundles obtained from myocardium of failed explanted human hearts due to ischemic (ICM, n=9) or idiopathic dilated (IDC, n=9) cardiomyopathy. Myocardial specimens from five normal donor hearts served as controls (CON). Basal respiratory rate, respiratory rate after addition of the substrates glutamate and malate (V(SUB)), state 3 respiration (after addition of ADP, V(ADP)) and respiration after the addition of atractyloside (V(AT)) were measured in scar-free muscle bundles obtained from the subendocardial (ENDO) and subepicardial (EPI) thirds of the left ventricular (LV) free wall, interventricular septum and right ventricular (RV) free wall. There were no differences in basal and substrate-supported respiration between CON and HF regardless of etiology. V(ADP)was significantly depressed both in ICM and IDC compared to CON in all the regions studied. The respiratory control ratio, V(ADP)/V(AT), was also significantly decreased in HF compared to CON. In both ICM and IDC, V(ADP)was significantly lower in ENDO compared to EPI. The results indicate that mitochondrial respiration is abnormal in the failing human heart. The findings support the concept of low myocardial energy production in HF via oxidative phosphorylation, an abnormality with a potentially impact on global cardiac performance.

Mitochondrial respiratory chain activity in idiopathic dilated cardiomyopathy

BACKGROUND

Cardiomyopathy is well recognized in mitochondrial diseases in which it has been associated with defects of mitochondrial function, including cytochrome-c oxidase (COX) deficiencies. This study explores the respiratory chain activity, particularly of COX, in patients with cardiomyopathy to determine whether a relationship exists between respiratory enzyme activity and cardiac function.

METHODS AND RESULTS

Myocardial specimens from the left ventricular wall of explanted hearts were obtained from subjects with ischemic (n = 6) or nonischemic dilated (n = 8) cardiomyopathy. Assays for citrate synthase (CS) and complexes II/III and IV activity were performed on cardiac mitochondria and homogenate. Enzyme activities were normalized to CS activity and compared with control activities (n = 10). A significant reduction in COX and/or CS activity was identified in mitochondrial preparations from the transplant group and correlated significantly with ejection fraction (P < .05), although this does not prove a causal relationship. Significantly reduced CS activity in homogenate was identified, suggesting decreased mitochondrial volume in addition to decreased COX activity. Measurements in cardiac homogenates failed to show a significant reduction in COX activity (P > .05) in the transplant group, suggesting that the use of prefrozen tissue homogenates may underestimate existing mitochondrial respiratory defects in cardiac tissue.

CONCLUSIONS

Mitochondrial function is altered at a number of levels in end-stage cardiomyopathy. Defective COX activity resulting in deficient adenosine triphosphate generation may contribute to impaired ventricular function in heart failure. Agents capable of improving mitochondrial function may find an adjuvant role in the treatment of cardiac failure.

Progressive loss of myocardial ATP due to a loss of total purines during the development of heart failure in dogs: a compensatory role for the parallel loss of creatine

BACKGROUND

Whether myocardial ATP content falls in heart failure is a long-standing and controversial issue. The mechanism(s) to explain any decrease in ATP content during heart failure have not been identified.

METHODS AND RESULTS

Cardiac dysfunction, heart failure, and a prolonged steady state of heart failure were induced by chronic right ventricular pacing for 1 to 2 weeks, 3 to 4 weeks, and 7 to 9 weeks in dogs. Cardiac function and myocardial O(2) consumption (Mf1.gif" BORDER="0">O(2)) were measured with the dogs in the conscious state. ATP, total purine, and creatine were measured in biopsy specimens obtained at each stage. ATP and the total purine pool progressively fell at rates of 0.12 and 0.15 nmol. mg protein(-1). d(-1), despite an increase in Mf1.gif" BORDER="0">O(2). The rate of loss of creatine was 1.06 nmol. mg protein(-1). d(-1), 7 times faster than the depletion of total purine.

CONCLUSIONS

(1) ATP contents progressively decreased during heart failure as a result of a loss of the total purine pool. The loss of purines may be due to inhibition of de novo purine synthesis. (2) Loss of creatine is an early marker of heart failure and may serve as a compensatory mechanism minimizing the reduction of the total purine pool in the failing heart.

Changes in myocardial protein expression in pacing-induced canine heart failure

Canine rapid ventricular pacing produces a low output cardiomyopathic state which is similar to dilated cardiomyopathy. In this study dogs were paced at 245 beats per minute (bpm) for 3-4 weeks until signs of heart failure were apparent. Unpaced dogs were used as controls. A previous study identified myocardial protein changes in the pH region 4-7 following ventricular pacing by using two-dimensional electrophoresis (2-DE) (Heinke et al., Electrophoresis 1998 19, 2021-2030). Many of these proteins were associated with mitochondria, energy metabolism within the cardiomyocyte, the cytoskeleton and calcium cycling. The present study aimed to examine the proteins migrating in the more basic region of the 2-DE pattern using immobilised pH gradient 3-10 strips to separate myocardial proteins. The expression of 31 proteins was altered in the paced myocardium: 21 were decreased and 10 increased. Following the identification of 23 of these spots by either amino acid compositional analysis or peptide mass fingerprinting or a combination of both, we confirm that many of the proteins whose expression is altered following ventricular pacing are associated with the mitochondria and energy production within the cardiomyocyte, including creatine kinase M, triosephosphate isomerase, phosphoglycerate mutase, cytochrome c oxidase, cytochrome b5, hydroxymethyl glutaryl CoA synthase, myoglobin, and 3,2-trans-enoyl-CoA transferase. Additionally, the cytoskeletal protein actin was increased in the paced hearts. These results strongly support the notion that energy production is impaired and mitochondrial dysfunction is involved in the development of heart failure in the paced dog.

Myocardial adenine nucleotides, glycogen, and Na, K-ATPase in patients with idiopathic dilated cardiomyopathy requiring mechanical circulatory support

Acute decompensation leading to progressive pump failure is a main cause of death in patients with congestive heart failure. To find possible metabolic defects associated with the onset of this fatal occurrence, we measured myocardial adenine nucleotides, glycogen, and Na,K-ATPase in patients with end-stage idiopathic dilated cardiomyopathy. The biopsy specimens were obtained from the right ventricle of beating hearts during implantation of a biventricular assistance device in 23 patients (group I) suffering from irreversible cardiogenic shock and during heart transplantation in 20 patients (group II) in compensated heart failure. Left ventricular ejection fraction (LVEF) was determined preoperatively by echocardiography. Left ventricular function in group I was more severely impaired than in group II (LVEF 16.8%+/-4.6% vs 22.1%+/-5.1 %; p <0.01). Myocardial adenosine triphosphate (ATP) in group I was significantly reduced in comparison with group II (119.4+/-10.2 vs 27.7+/-7.4 nmol/mg noncollagen protein; p <0.01). There was no difference in glycogen levels. Na,K-ATPase concentration in group I (n = 8) was lower than that of group II (n = 20) (425+/-80 vs 498+/-75 pmol/g wet weight; p <0.05). Linear regression analyses showed a significant correlation between adenosine triphosphate (ATP) and LVEF (r = 0.41, p <0.01) and between Na,K-ATPase and LVEF (r = 0.55, p <0.01). These results indicate that loss of myocardial ATP and Na,K-ATPase could partially contribute to the development of spontaneous deterioration of the chronically overloaded heart.

Is the failing heart energy depleted?

This article takes three different approaches to the question of whether the failing heart is in an energy-starved state. A brief historical overview introduces the issue and points out problems in both models and methods. Second, current information regarding the energetic state of the failing heart is examined. Finally, the mechanistic and therapeutic implications of a defect in energy production are described.

Ventricular remodeling: from bedside to molecule

The multiple mechanisms that bring about the decompensation of the hypertrophic remodeled myocardium are synergistic and not fully understood. Our current hypothesis is that the increased stress on the ventricle is initially offset by compensatory myocardial hypertrophy. In many instances, however, progressive ventricular dilatation and heart failure occur as a result of maladaptive hypertrophy (abnormal myosin-actin production), programmed cell death (apoptosis) and/or changes in the interstitial vasculature and collagen composition. The molecular and genetic background to these processes includes changes in myocardial gene expression, activation of the local tissue renin-angiotensin and other neurohormonal systems, increased matrix metalloproteinase activity (including collagenase), and expression of certain components of the immune system, such as TNF-alpha. Future research will hopefully provide better methods for limiting the remodeling-ventricular dilatation process by novel pharmacotherapies, gene therapy and, possibly, surgical therapy, and determine the impact of such interventions on survival.

Inotropic agents in the treatment of heart failure: despair or hope?

Depression of myocardial contractility plays an important role in the development of heart failure; therefore, intensive interest and passion have been generated to develop cardiotonic agents to improve the contractile function of the failing heart. Inotropic agents that increase cyclic AMP, either by increasing its synthesis or reducing its degradation, exert dramatic short-term hemodynamic benefits, but these acute effects cannot be extrapolated into long-term improvement of the clinical outcome in patients with advanced heart failure. Administration of these agents to an energy-starved failing heart would be expected to increase myocardial energy use and could accelerate disease progression. The role of digitalis in the management of heart failure has been controversial, but ironically the drug has now been proved to favorably affect the neurohormonal disorders and its reevaluation is now being intensively investigated. More recently, attention has been focused on other inotropic agents that have a complex and diversified mechanism. Recent clinical studies have demonstrated that they are potentially useful in the long-term treatment of heart failure patients. These agents have some phosphodiesterase-inhibitory action but also possess additional effects, including acting as cytokine inhibitors, immunomodulators, or calcium sensitizers. However, their therapeutic ratio is narrow and further studies are warranted to establish their optimal doses and their eventual status in the treatment of heart failure.

Long-term 1-carnitine treatment prolongs the survival in rats with adriamycin-induced heart failure

BACKGROUND

The most serious consequence of heart failure is the shortened life expectancy, which may be associated with myocardial energy starvation.

METHODS AND RESULTS

Eight-week-old male Sprague-Dawley rats received 6 intraperitoneal injections of adriamycin (group A: total dose; 15 mg/kg body weight) or vehicle (group C) over 2 weeks. Rats then received either 272 mg/kg daily of oral 1-carnitine (A-LC and C-LC groups) or saline (A-S and C-S groups) for 6 weeks. The cumulative mortality rate in the A-LC group was significantly lower than in the A-S group (13 vs 42%, P = .028). Myocardial levels of high-energy phosphate compounds (ATP and creatine phosphate) and fatty acid metabolites (free carnitine, short-chain and long-chain acylcarnitine, and long-chain acyl CoA) in the left ventricle were measured the day after the last dose of drug or vehicle was administered. ATP was decreased by 73%, creatine phosphate by 61%, free carnitine by 52%, short-chain acylcarnitine by 48%, and long-chain acylcarnitine by 56% in the A-S group compared to the C-S group. Long-chain CoA was increased by 168% in the A-S group. Levels of myocardial high-energy phosphate compounds and fatty acid metabolites were near normal in adriamycin- and 1-carnitine-treated rats.

CONCLUSIONS

Preservation of the myocardial level of carnitine by 1-carnitine treatment prolonged survival of rats with adriamycin-induced failure by improving the myocardial metabolism of fatty acids.

Medical therapy can improve the biological properties of the chronically failing heart. A new era in the treatment of heart failure

Myocardial failure has been considered to be an irreversible and progressive process characterized by ventricular enlargement, chamber geometric alterations, and diminished pump performance. However, more recent evidence has suggested that certain types of medical therapy may lead to retardation and even reversal of the cardiomyopathic process. In the failing heart, long-term neurohormonal/autocrine-paracrine activation results in abnormalities in myocyte growth, energy production and utilization, calcium flux, and receptor regulation that produce a progressively dysfunctional, mechanically inefficient heart. Interventions such as ACE inhibition and beta-blockade result in a reduction in the harmful long-term consequences of neurohormonal/autocrine-paracrine effects and retard the progression of left ventricular dysfunction or ventricular remodeling. Furthermore, in subjects with idiopathic dilated or ischemic cardiomyopathy, antiadrenergic therapy with beta-blocking agents appears to be able to partially reverse systolic dysfunction and ventricular remodeling. Although the precise mechanisms underlying this latter effect have not yet been elucidated, the general mechanism appears to be via improvement in the biological function of the cardiac myocyte. Such an improvement in the intrinsic defect(s) responsible for myocardial failure will likely translate into important clinical benefits.

Creatine kinase system in failing and nonfailing human myocardium

BACKGROUND

The creatine kinase (CK) reaction is important for rapid resynthesis of ATP when the heart increases its work. Studies defining the CK system in human failing and nonfailing myocardium are limited and in conflict. To resolve this conflict, we measured the activities of CK and its isoenzymes and the contents of creatine and CK-B in homogenates of human myocardium.

METHODS AND RESULTS

Myocardium was sampled from 23 subjects who underwent heart transplant, 36 subjects maintained in an intensive care unit before heart harvesting, 13 accident victims, and 2 patients undergoing heart surgery. Since the characteristics of myocardium of potential organ donors differed from those of myocardium of accident victims, data are presented for three groups: failing, donor, and control. CK activity was 7.7 +/- 1.9 and 6.0 +/- 1.4 IU/mg protein in left (LV) and right (RV) ventricles of failing, 9.4 +/- 2.5 and 10.7 +/- 2 IU/mg protein in LV and RV of donor, and 11.6 +/- 2.4 IU/mg protein in LV of control hearts. CK-MM and the mitochondrial isoenzyme activities were lower in failing and donor LV, and CK-MB activity and CK-B content were higher in failing and donor hearts. Creatine contents were 64 +/- 25 and 56 +/- 18.6 nmol/mg protein in LV and RV of failing, 96 +/- 30 and 110 +/- 24 nmol/mg protein in LV and RV of donor, and 131 +/- 28 nmol/mg protein in LV of control hearts.

CONCLUSIONS

In failing and nonfailing donor human myocardium, there is a combined decrease of CK activity and creatine that may impair the ability to deliver ATP to energy-consuming systems.

Cardiac energy metabolism at several stages of adriamycin-induced heart failure in rats

To evaluate the changes in myocardial energy metabolism in the progressively failing myocardium, we measured myocardial level of adenosine triphosphate (ATP) using high-performance liquid chromatography (HPLC), and levels of lactate, alanine and free carnitine using 1H-nuclear magnetic resonance (NMR) spectroscopy in rats injected with adriamycin. The drug was injected intraperitoneally 2.5 mg/kg 6 times over a period of 2 weeks. Measurements were obtained 1 day (1 d), 3 weeks (3 w) and 6 weeks (6 w) after the last injection. No deaths were observed until the end of the 3rd week. The cumulative mortality rate 6 weeks after the last injection was 48%. ATP and free carnitine levels were not significantly changed at 1 d, while myocardial lactate was increased by 33% from the control values (P < 0.05). Lactate levels were reduced significantly, but not progressively, at 3 w (31% of control values) and at 6 w (69% of control values). Similar changes were observed in alanine levels. Free carnitine levels were progressively decreased at 3 w (74% of control values) and at 6 w (57% of control values). Changes in ATP levels paralleled those of free carnitine. Data suggest that a decrease in the myocardial level of free carnitine may be involved in progression of the heart failure induced by adriamycin in rats.

Applicability of small endomyocardial biopsies for evaluation of high energy phosphates and glycogen in the heart

To evaluate variability of biochemical determination of energy stores in endomyocardial biopsies, we compared myocardial contents of high energy phosphates and glycogen in endomyocardial and transmural myocardial biopsies from 12 75-kg pigs before, during, and after cardioplegia. Before cardioplegia, comparable amounts of adenine nucleotides and glycogen were found in left and right ventricular endomyocardial and left ventricular transmural biopsies. Phosphocreatine levels were lower in endomyocardial than in transmural biopsies. Significant correlations were observed between endomyocardial and transmural adenine nucleotide and glycogen contents but not phosphocreatine content. During cardioplegia, myocardial ATP and phosphocreatine contents increased and glycogen concentration tended to decrease. During reperfusion, ATP and glycogen levels decreased, whereas phosphocreatine levels increased remarkably. Transmural changes in left ventricular adenine nucleotide and glycogen levels were reflected in endomyocardial biopsies but those in phosphocreatine were not. By increasing the number of endomyocardial biopsies from one to three, within-subject variance was reduced from 33-47% to 14-23% of total variance whereas four or more biopsies only added minor further reduction in variability. In conclusion, endomyocardial biopsies yield representative estimates of the average myocardial content of adenine nucleotides and glycogen but not of phosphocreatine in the normal heart. Endomyocardial biopsies offer a sensitive estimate of the changes in myocardial adenine nucleotides and glycogen induced by cardioplegia and reperfusion. However, metabolite content in endomyocardial biopsies shows a high variability. Three or more endomyocardial biopsies are necessary to reduce variability to acceptable levels.

Bioenergetics in the pathogenesis, progression and treatment of cardiovascular disorders

The aim of this manuscript is to review perturbations in bioenergetics that are redundant denominators in the diversity of factors mediating the pathogenesis and progression of coronary heart disease (CHD), congestive heart failure (CHF), hypertension and arrhythmias. This paper likewise assesses the pharmacodynamics of widely prescribed drugs that enhance cellular respiration, maintain positive inotropic, chronotropic, dromotropic cardiac effects, sustain myocardial biosynthesis, reverse the morbidity of heart disease, and assure low levels of toxicity commensurate with the agent's biocompatability. Conversely, it is essential to delineate the modality of xenobiotic drugs that inhibit energy transformations, enhance the pathogenesis of CHD, worsen survival in CHF, provoke arrhythmogenic effects, and induce serious side-effects. Documented evidence, derived from biochemical, physiological and pharmacological data sources, consistently links inhibited mitochondrial decarboxylation to aberrations in cholesterol metabolism, biosynthesis, and calcium balance. Underutilized citrates evolved from inhibited decarboxylation are degraded to acetyl CoA. The acetate is the source of steroid synthesis; its carbon atoms form the molecular basis for all endogenous cholesterol. Myocardial anoxia, a consequence of the atheromatous plaque, inhibits ATP production, impairs biosynthesis, induces negative cardiac inotropic and chronotropic effects, and enhances the pathogenesis of CHF. Inhibited decarboxylation is likewise a factor in the mobilization of in situ cardiac Ca2+, resulting in arrhythmias provoked by the cation's deficiency. The restoration of calcium homeostasis decreases peripheral vasotension, reducing hypertension. Parameters drawn from endocrinopathies and the new physiological dimension of microgravity are developed to illustrate the detrimental effect of inhibited bioenergetics on cardiac pathomorphism and cardiovascular dysfunction. In conclusion, anabolic agents, adjunctive to a productive life-style, can provide the rational basis for the prevention and treatment of cardiac diseases. Failure to understand mechanisms generating cardiovascular morbidity eventuates in ineffective and empirical treatment.

Modulation of intramitochondrial free Ca2+ concentration by antagonists of Na(+)-Ca2+ exchange

Evidence has accumulated in the past decade suggesting that Ca2+ acts as a second messenger not only in the cytosol of the heart to regulate contractility, but also within the mitochondria to regulate the rate of oxidative ATP synthesis. Just as elucidation of the second messenger pathways for Ca2+ in the cytosol has led to the development of pharmacological interventions that alter mechanical functioning of the heart, understanding the role of Ca2+ as a second messenger within the mitochondria and the mechanisms by which this organelle transports and regulates Ca2+ has exciting potential for developing pharmacological interventions that alter myocardial energy metabolism. In this article, David Cox and Mohammed Matlib discuss the potential consequences of pharmacologically increasing the intramitochondrial Ca2+ concentration on myocardial energy metabolism, and suggest some pathological conditions in which such an effect may be beneficial.

Effect of enoximone alone and in combination with metoprolol on myocardial function and energetics in severe congestive heart failure: improvement in hemodynamic and metabolic profile

The hemodynamic and myocardial metabolic effects of enoximone (phosphodiesterase III inhibitor), alone or in combination with metoprolol (beta-adrenergic blocker), were studied in patients with congestive heart failure. Ten patients (New York Heart Association Class III-IV) underwent right heart and coronary sinus catheterization, and parameters were assessed at basal condition, at peak enoximone response (mean intravenous loading dose = 2.2 mg/kg), and after the combination with metoprolol (mean intravenous dose = 8.5 mg). Heart rate tended to increase during enoximone administration (from 102 +/- 16 to 107 +/- 16 min-1, ns) and was reduced during enoximone plus metoprolol (to 88 +/- 15 min-1, p < 0.05 vs. basal). Cardiac index was increased during enoximone (from 2.2 +/- 0.2 to 3.8 +/- 0.5 1/min/m2, p < 0.05) and decreased during enoximone plus metoprolol (to 2.8 +/- 0.5 1/min/m2, p < 0.05 vs. enoximone). Mean pulmonary wedge pressure fell during enoximone and remained reduced during enoximone plus metoprolol (from 27 +/- 9 to 9 +/- 3 and to 13 +/- 4 mmHg, respectively, both p < 0.05). Myocardial oxygen consumption did not change during enoximone (from 27 +/- 8 to 25 +/- 13 ml/min, ns) and was reduced during enoximone plus metoprolol (to 19 +/- 8 ml/min, p < 0.05 vs. basal). Myocardial lactate extraction tended to be lower during enoximone and during enoximone plus metoprolol conditions (from 38 +/- 17% to 26 +/- 20% and to 29 +/- 24%, respectively), but no statistical significance was found. Myocardial efficiency was increased during enoximone and during enoximone plus metoprolol (from 9 +/- 3% to 15 +/- 6% and to 14 +/- 6%, respectively, both p < 0.05). Thus in patients with congestive heart failure enoximone improves hemodynamics and, in most cases, it does not influence energetics. The addition of metoprolol to enoximone reduces heart rate, cardiac index, and myocardial oxygen consumption without any other major changes, producing a more physiologic hemodynamic and metabolic profile.

31P magnetic resonance spectroscopy in dilated cardiomyopathy and coronary artery disease. Altered cardiac high-energy phosphate metabolism in heart failure

BACKGROUND

The purpose of this work was to further define the value of cardiac 31P magnetic resonance (MR) spectroscopy for patients with coronary artery disease and dilated cardiomyopathy.

METHODS AND RESULTS

Blood-corrected and T1-corrected 31P MR spectra of anteroseptal myocardium were obtained at rest using image-selected in vivo spectroscopy localization, a selected volume of 85 +/- 12 cm3, and a field strength of 1.5 T. Nineteen volunteers had a creatine phosphate (CP)/ATP ratio of 1.95 +/- 0.45 (mean +/- SD) and a PDE/ATP ratio of 1.06 +/- 0.53; in four patients with left anterior descending coronary artery (LAD) stenosis, six patients with chronic anterior wall infarction, and four patients with chronic posterior wall infarction, CP/ATP and phosphodiester (PDE)/ATP ratios did not differ from those in volunteers. Twenty-five measurements of 19 patients with dilated cardiomyopathy yielded a CP/ATP of 1.78 +/- 0.51 and a PDE/ATP of 0.98 +/- 0.56 (p = NS versus volunteers). When these patients were grouped according to the severity of heart failure, however, CP/ATP was 1.94 +/- 0.43 in mild (p = NS versus volunteers) and 1.44 +/- 0.52 in severe DCM (p < 0.05), respectively. No correlation was found between CP/ATP and left ventricular ejection fraction or fractional shortening, but correlation of CP/ATP with the New York Heart Association (NYHA) class was significant (r = 0.60, p < 0.005). Six patients with dilated cardiomyopathy were studied repeatedly before and after 12 +/- 6 weeks of drug treatment leading to clinical recompensation with improvement of the NYHA status by 0.8 +/- 0.3 classes. Concomitantly, CP/ATP increased from 1.51 +/- 0.32 to 2.15 +/- 0.27 (p < 0.01), whereas PDE/ATP did not change significantly.

CONCLUSIONS

Cardiac high-energy phosphate metabolism at rest is normal in LAD stenosis and chronic myocardial infarction in the absence of heart failure. The CP/ATP ratio has low specificity for the diagnosis of dilated cardiomyopathy. However, CP/ATP correlated with the clinical severity of heart failure and may improve during clinical recompensation.

Heart failure in 2001: a prophecy

Understanding of heart failure has developed through 3 paradigms involving organ, cell, and gene. The first views heart failure as an abnormality of organ (pump) function leading to salt and water retention and vasoconstriction. Therapy to correct these circulatory abnormalities is well accepted and effective. The second considers heart failure as a disordered cellular function, mainly impaired contraction and relaxation. Efforts to correct the biochemical and biophysical abnormalities responsible for these disorders of myocardial performance have, however, been less successful. Recent emphasis on efforts to improve prognosis as well as symptoms in patients with chronic heart failure demonstrates that it is a lethal disease with problems of survival similar to those in malignancies. The third paradigm of abnormal gene expression, which in the failing heart represents a cardiomyopathy of overload, appears to be a major cause of poor prognosis in these patients. Evidence that the angiotensin-converting enzyme inhibitors have important effects on cell growth, as well as on vascular tone, suggests that their ability to prolong survival in patients with heart failure may be due largely to the inhibition of detrimental effects of angiotensin II on cardiac gene expression. Thus, it seems likely that work focused on the third paradigm will uncover specific abnormalities of gene expression that are responsible for poor survival of patients with heart failure. By 2001, I predict that heart failure will be viewed as an abnormality of cell growth and this will lead to the development of therapies to retard, if not reverse, the clinical deterioration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of simultaneous alterations in preload and afterload on measurements of left ventricular contractility in patients with dilated cardiomyopathy: comparisons of ejection phase, isovolumetric and end-systolic force-velocity indexes

OBJECTIVES

The study was designed to critically evaluate the clinical utility of ejection phase and nonejection phase indexes of contractile state in patients with severe left ventricular dysfunction.

BACKGROUND

Ejection phase indexes of left ventricular systolic performance are unable to differentiate contractility changes from alterations in loading conditions. Isovolumetric and end-systolic force-velocity indexes have been proposed as alternative measurements of contractile state that are load independent.

METHODS

Seventeen patients with nonischemic dilated cardiomyopathy were studied during cardiac catheterization. High fidelity central aortic and left ventricular pressure measurements were made with simultaneous echocardiographic recordings of chamber minor- and long-axis dimensions and wall thickness. Data were acquired under control conditions, during nitroprusside infusion and with dopamine (6 micrograms/kg per min).

RESULTS

Patients were classified into those without (group 1, n = 10) and those with (group 2, n = 7) a decrease in end-diastolic circumferential wall stress in response to dopamine. There were no baseline differences between the groups in functional class, left ventricular chamber geometry or cardiovascular hemodynamics. Ejection phase indexes were variably altered by changes in preload, afterload and heart rate, thereby complicating physiologic interpretation of data. Dopamine increased the commonly used isovolumetric index, maximal rate of rise in left ventricular pressure (dP/dtmax), by 64% for group 1 but by only 16% for group 2 (p less than 0.001), resulting in an underestimation of contractile state change in 41% of patients. In contrast, the left ventricular end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation, which incorporates afterload, ventricular wall mass and heart rate in its analysis, was a sensitive contractility measurement that was preload independent and equally augmented by dopamine for both groups.

CONCLUSIONS

Of the left ventricular contractility indexes evaluated, the end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation was the most physiologically appropriate for assessing pharmacologically induced changes in inotropic state that were accompanied by complex alterations in loading conditions in patients with dilated cardiomyopathy.

Myocardial adenine nucleotide concentrations and myocardial norepinephrine content in patients with heart failure secondary to idiopathic dilated or ischemic cardiomyopathy

It has been suggested that chronically reduced myocardial adenosine triphosphate (ATP) content causes contractile dysfunction in dilated cardiomyopathy. Because total adenine nucleotides (ATP, adenosine diphosphate and monophosphate) may reflect chronic changes in energy metabolism better than may ATP alone, myocardial ATP, and adenosine diphosphate and monophosphate were determined in endomyocardial biopsy specimens from 19 patients with dilated cardiomyopathy, and decreased left (30 +/- 2%) and right (34 +/- 3%) ventricular ejection fractions, and from 11 patients with ischemic cardiomyopathy (left ventricular ejection fraction 38 +/- 3%), and compared with those from 28 normal control subjects (ejection fraction greater than 55%) to assess myocardial energy metabolism in heart failure. Myocardial norepinephrine was measured simultaneously in the same biopsy specimens to assess if the myocardium studied for adenine nucleotide content was metabolically altered. Myocardial total adenine nucleotides as well as ATP levels in 19 patients with dilated cardiomyopathy (39 +/- 3 and 23 +/- 3 nmol/mg of noncollagen protein, respectively) were unchanged in comparison with those of control subjects (37 +/- 4 and 23 +/- 3, respectively); patients with ischemic cardiomyopathy were not significantly different (30 +/- 3 and 19 +/- 3, respectively). Myocardial norepinephrine in the same biopsy specimens from patients with dilated (5.8 +/- 1.1 pg/micrograms of noncollagen protein) or ischemic (5.7 +/- 1.3) cardiomyopathy was significantly decreased compared with that of normal control subjects (12 +/- 1.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic response of the human heart to inotropic stimulation: in vivo phosphorus-31 studies of normal and cardiomyopathic myocardium

In order to determine if an increase in myocardial oxygen consumption is accompanied by changes in high energy phosphates in normal subjects and patients with dilated cardiomyopathy, phosphorus-31 spectra were acquired under resting conditions and during dobutamine infusion. In seven normal subjects, dobutamine raised the rate-pressure product to 226% of control. The ratio of PCr/ATP was 1.86 +/- 0.17 (mean +/- SE) under resting conditions and 1.90 +/- 0.22 (P = 0.44) with dobutamine infusion. In eight patients with dilated cardiomyopathy, dobutamine raised the rate-pressure product to 161% of control. As in the normal subjects, the ratio of PCr/ATP under resting conditions (1.63 +/- 0.24) was unchanged during dobutamine infusion (1.57 +/- 0.24, P = 0.38). These data indicate that increases in cardiac work do not have a major effect on high energy phosphate concentrations in normal subjects or in patients with clinically compensated dilated cardiomyopathy.

Adenine nucleotide metabolism and contractile dysfunction in heart failure--biochemical aspects, animal experiments, and human studies

In myocardial hypertrophy and heart failure a series of adaptational changes occur some multiplying contractile units, others slowing shortening velocity and increasing economy of contraction. The demonstration of energy-saving mechanisms in heart failure has prompted further investigations of energy providing and utilizing metabolic pathways. The use of myocardial ATP as a substrate occurs mainly at the myosin-ATPase and at the Ca-ATPase of the sarcoplasmic reticulum. As the Michaelis constant of both enzymes for ATP is in the micromolar (microM) range, whereas cellular ATP content is about 5000 microM, these enzymes are not controlled by the availability of ATP as a substrate. In experimental heart failure in large animals, normal or reduced creatine phosphate levels (in most cases together with normal adenine nucleotides) have been described. Reduced creatine phosphate is found in models with increased oxygen consumption, and creatine phosphate may buffer the ATP pool in these models. In human heart failure due to dilated cardiomyopathy, where resting oxygen consumption per unit mass and lactate extraction are normal in most patients, normal adenine nucleotides, creatine phosphate, and mitochondrial function have been described in the initial studies. These results have been challenged by one study showing decreased ATP levels in dilated cardiomyopathy, correlating with the decrease in ejection fraction. However, only ATP has been measured in this study, whereas total adenine nucleotides may be a more suitable parameter. Recently published results have again demonstrated normal ATP and total adenine nucleotides in human heart failure. In the same patients, significantly decreased myocardial norepinephrine was measured, indicating that metabolic changes had occurred in these hearts, but were independent of adenine nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

Dysfunction of the ADP/ATP carrier as a causative factor for the disturbance of the myocardial energy metabolism in dilated cardiomyopathy

The adenine nucleotide translocator (ADP/ATP carrier) plays a key role in nucleotide transport across the mitochondrial membrane. The quantity and function of this transport protein were investigated in myocardium from hearts with endstage failing dilated and ischemic cardiomyopathy, and were compared to measurements in nonfailing myocardium. In addition, lactate dehydrogenase (LDH) isoenzymes were determined. The concentration of the ADP/ATP carrier was significantly increased by 48% in myocardium from dilated cardiomyopathic hearts compared to control myocardium. The concentration of the carrier in explanted hearts with ischemic cardiomyopathy did not differ from values in the normal human hearts. Analysis of carrier function revealed similar nucleotide exchange rates in control hearts and hearts with ischemic cardiomyopathy, whereas carrier function was reduced in most hearts with dilated cardiomyopathy. Compared to control hearts, in hearts with dilated cardiomyopathy and decreased nucleotide exchange rate, the carrier content was significantly higher, whereas the carrier content was only slightly increased compared to control in cardiomyopathy hearts with unchanged transport activity. Compared to hearts, in dilated cardiomyopathy there was a significant increase in LDH5 and a decrease in LDH1 isoforms, indicating more anaerobic metabolism in failing dilated cardiomyopathic hearts. In summary, in hearts with dilated cardiomyopathy disturbed function of the ADP/ATP-carrier may result in altered myocardial energy metabolism and, thus, may be the cause of impaired myocardial function.