Cardiac and skeletal muscle abnormalities in cardiomyopathy: comparison of patients with ventricular tachycardia or congestive heart failure

Cardiac rehabilitation in heart failure with severely reduced ejection fraction: effects on mortality

Thirty years ago, patients with low ejection fraction (EF) have often been excluded from rehabilitation programs due to concern about possibility of sudden death or other adverse cardiovascular events during exercise sessions. Recent studies have highlighted the fact that cardiac rehabilitation could improve exercise capacity, cardiac function, and health-related quality of life in congestive heart failure patients. This encouraged us to write a review article and update our latest knowledge about the outcome of rehabilitation program in patients with severely depressed cardiac function. We were particularly interested in effect of cardiac rehabilitation on exercise capacity, quality of life, vascular effects, neuro-hormonal changes, and mortality. We also conducted a mini-systematic review and meta-analysis on randomized controlled trials comparing exercise training with usual care in patients with severely reduced left ventricular ejection fraction, for the mortality subsection to obtain precise estimates of overall treatment benefit on mortality. It is our privilege to submit our manuscript for possible publication in your prestigious journal.

Insights into myosin regulatory and essential light chains: a focus on their roles in cardiac and skeletal muscle function, development and disease

The activity of cardiac and skeletal muscles depends upon the ATP-coupled actin-myosin interactions to execute the power stroke and muscle contraction. The goal of this review article is to provide insight into the function of myosin II, the molecular motor of the heart and skeletal muscles, with a special focus on the role of myosin II light chain (MLC) components. Specifically, we focus on the involvement of myosin regulatory (RLC) and essential (ELC) light chains in striated muscle development, isoform appearance and their function in normal and diseased muscle. We review the consequences of isoform switching and knockout of specific MLC isoforms on cardiac and skeletal muscle function in various animal models. Finally, we discuss how dysregulation of specific RLC/ELC isoforms can lead to cardiac and skeletal muscle diseases and summarize the effects of most studied mutations leading to cardiac or skeletal myopathies.

Iron status, catabolic/anabolic balance, and skeletal muscle performance in men with heart failure with reduced ejection fraction

BACKGROUND

Metabolic derangements related to tissue energetics constitute an important pathophysiological feature of heart failure. We investigated whether iron deficiency and catabolic/anabolic imbalance contribute to decreased skeletal muscle performance in men with heart failure with reduced ejection fraction (HFrEF), and whether these pathologies are related to each other.

METHODS

We comprehensively examined 23 men with stable HFrEF (median age [interquartile range]: 63 [59-66] years; left ventricular ejection fraction: 28 [25-35]%; New York Heart Association class I/II/III: 17/43/39%). We analyzed clinical characteristics, iron status, hormones, strength and fatigability of forearm flexors and quadriceps (surface electromyography), and exercise capacity (6-minute walking test).

RESULTS

None of the patients had anemia whereas 8 were iron-deficient. Flexor carpi radialis fatigability correlated with lower reticulocyte hemoglobin content (CHR, p < 0.05), and there was a trend towards greater fatigability in patients with higher body mass index and lower serum ferritin (both p < 0.1). Flexor carpi ulnaris fatigability correlated with lower serum iron and CHR (both p < 0.05). Vastus medialis fatigability was related to lower free and bioavailable testosterone (FT and BT, respectively, both p < 0.05), and 6-minute walking test distance was shorter in patients with higher cortisol/FT and cortisol/BT ratio (both p < 0.05). Lower ferritin and transferrin saturation correlated with lower percentage of FT and BT. Men with HFrEF and iron deficiency had higher total testosterone, but lower percentage of FT and BT.

CONCLUSIONS

Iron deficiency correlates with lower bioactive testosterone in men with HFrEF. These two pathologies can both contribute to decreased skeletal muscle performance in such patients.

Angiotensin-converting-enzyme inhibitor prevents skeletal muscle fibrosis in myocardial infarction mice

BACKGROUND

Transforming growth factor beta (TGF-β)-Smad2/3 is the major signaling pathway of fibrosis, which is characterized by the excessive production and accumulation of extracellular matrix (ECM) components, including collagen. Although the ECM is an essential component of skeletal muscle, fibrosis may be harmful to muscle function. On the other hand, our previous studies have shown that levels of angiotensin II, which acts upstream of TGF-β-Smad2/3 signaling, is increased in mice with myocardial infarction (MI). In this study, we found higher skeletal muscle fibrosis in MI mice compared with control mice, and we investigated the mechanisms involved therein. Moreover, we administered an inhibitor based on the above mechanism and investigated its preventive effects on skeletal muscle fibrosis.

METHODS

Male C57BL/6 J mice with MI were created, and sham-operated mice were used as controls. The time course of skeletal muscle fibrosis post-MI was analyzed by picrosirius-red staining (days 1, 3, 7, and 14). Mice were then divided into 3 groups: sham + vehicle (Sham + Veh), MI + Veh, and MI + lisinopril (an angiotensin-converting enzyme [ACE] inhibitor, 20 mg/kg body weight/day in drinking water; MI + Lis). Lis or Veh was administered from immediately after the surgery to 14 days postsurgery.

RESULTS

Skeletal muscle fibrosis was significantly increased in MI mice compared with sham mice from 3 to 14 days postsurgery. Although mortality was lower in the MI + Lis mice than the MI + Veh mice, there was no difference in cardiac function between the 2 groups at 14 days. Skeletal muscle fibrosis and hydroxyproline (a key marker of collagen content) were significantly increased in MI + Veh mice compared with the Sham + Veh mice. Consistent with these results, protein expression of TGF-β and phosphorylated Smad2/3 in the skeletal muscle during the early time points after surgery (days 1-7 postsurgery) and blood angiotensin II at 14 days postsurgery was increased in MI mice compared with sham mice. These impairments were improved in MI + Lis mice, without any effects on spontaneous physical activity, muscle strength, muscle weight, and blood pressure.

CONCLUSIONS

ACE inhibitor administration prevents increased skeletal muscle fibrosis during the early phase after MI. Our findings indicate a new therapeutic target for ameliorating skeletal muscle abnormalities in heart diseases.

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: β-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.

Diagnosis of myocarditis: Current state and future perspectives

Myocarditis, i.e. inflammation of the myocardium, is one of the leading causes of sudden cardiac death (SCD) and dilated cardiomyopathy (DCM) in young adults, and is an important cause of symptoms such as chest pain, dyspnea and palpitations. The pathophysiological process of disease progression leading to DCM involves an ongoing inflammation as a result of a viral-induced auto-immune response or a persisting viral infection. It is therefore crucial to detect the disease early in its course and prevent persisting inflammation that may lead to DCM and end-stage heart failure. Because of the highly variable clinical presentation, ranging from mild symptoms to severe heart failure, and the limited available diagnostic tools, the evaluation of patients with suspected myocarditis represents an important clinical dilemma in cardiology. New approaches for the diagnosis of myocarditis are needed in order to improve recognition, to help unravel its pathophysiology, and to develop new therapeutic strategies to treat the disease. In this review, we give a comprehensive overview of the current diagnostic strategies for patients with suspected myocarditis, and demonstrate several new techniques that may help to improve the diagnostic work-up.

Extracardiac medical and neuromuscular implications in restrictive cardiomyopathy

Restrictive cardiomyopathy (RCMP) is characterized by restrictive filling and reduced diastolic volume of either or both ventricles with normal or near-normal systolic function and wall thickness. It may occur idiopathically or as a cardiac manifestation of systemic diseases such as scleroderma, amyloidosis, Churg-Strauss syndrome, cystinosis, sarcoidosis, lymphoma, Gaucher's disease, hemochromatosis, Fabry's disease, pseudoxanthoma elasticum, hypereosinophilic syndrome, carcinoid, Noonan's syndrome, reactive arthritis, or Werner's syndrome and various neuromuscular disorders. Whereas in idiopathic RCMP the therapeutic options are only treatment of cardiac congestion, in cases with an underlying disorder, a causal therapy may be available. Patients with RCMP should be investigated as soon as the cardiac diagnosis is established for extracardiac diseases to detect a possibly treatable cause of RCMP before the disease becomes intractable. These investigations include a diligent clinical history and examination, blood tests, and ophthalmologic, otologic, dermatologic, gastroenterologic, nephrologic, hematologic, and neurologic examinations. If extracardiac examinations do not reveal a plausible cause for RCMP, endomyocardial biopsy is indicated.

Effects of chronic heart disease on skeletal muscle fiber size

Size changes in muscle fibers of subjects with chronic heart disease (CHD) have been reported, although a consensus has not been achieved. The aims of the present study were to investigate a possible association between CHD and fiber size changes in the brachial biceps compared to subjects without heart disease. Forty-six muscle samples were obtained in autopsies of individuals (13 to 84 years) without neuromuscular disorders, 19 (10 males and 9 females) with, and 27 (14 males and 13 females) without CHD. In all cases muscle sections were stained with hematoxylin and eosin and processed for the visualization of myofibrillar ATPase activity. The lesser diameter of type 1 and type 2 fibers was obtained tracing their outlines (at least 150 fibers of each type per sample) onto an image analyzer connected to a computer. The results were analyzed statistically comparing males and females with and without CHD. Type 1 fiber mean lesser diameters were 51.51 and 54.52 microm in males (normal range 34-71 microm) and 45.65 and 55.42 microm in females (normal range 34-65 microm) without and with CHD, respectively; type 2 fibers measured 54.31, 58.23, 41.15, and 49.57 microm, respectively (normal range 36-79 microm for males and 32-59 microm for females). No significant difference in fiber size was detected in 24 males with and without CHD, while in 22 females there was a significant increase in size in those with cardiomyopathy. We concluded that CHD does not determine significant changes in fiber size. However, in females, there is some hypertrophy which, despite within normal range, may reflect morphologic heterogeneity of the sample, or the daily life activities in the upper limbs as a compensatory mechanism to fatigability that affect predominantly the lower limbs in subjects with CHD.

Skeletal muscle abnormalities in chronic heart failure patients: relation to exercise capacity and therapeutic implications

Recent studies suggest that changes in the periphery, like those occurring in the skeletal muscles of patients with chronic heart failure, might play an important role in the origin of symptoms and exercise intolerance in this condition. Biochemical and histologic changes in the skeletal muscles of chronic heart failure patients relate with the degree of exercise intolerance better than hemodynamics parameters. A reduction in skeletal muscle mass represents another important determinant of exercise intolerance in chronic heart failure patients. The relationship between skeletal muscle changes and exercise intolerance suggests the possibility of modifying the peripheral changes in order to improve functional capacity in chronic heart failure patients. Recent studies have shown that the administration of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers can improve the properties of the skeletal muscles. Similarly, exercise training allows improvement in peak oxygen consumption, which parallels important biochemical and histologic changes in the skeletal muscles.

Preoperative assessment and management of pediatric heart transplantation

The period of preoperative management of the pediatric cardiac transplant patient can be divided into three phases: determination of transplant feasibility, listing, and medical management. Chronic infection, irreversible elevation of pulmonary vascular resistance, and intractable disease in other organ systems may all be contraindications for transplantation. The United Network for Organ Sharing has recently changed its listing guidelines. Adolescent donors are now preferentially, to some extent, allocated to adolescent recipients. Management of pediatric patients awaiting cardiac transplantation encompasses optimization of cardiac output through the use of vasodilators and oral and intravenous inotropic agents. For those patients listed for transplantation who have single ventricle lesions, such as hypoplastic left heart syndrome, management of heart failure also includes balancing systemic and pulmonary blood flows. Mechanical support of the circulation with extracorporeal membrane oxygenation or ventricular assist devices can be used as a bridge to transplant in pediatric patients.

Skeletal muscle dysfunction in chronic obstructive pulmonary disease and chronic heart failure: underlying mechanisms and therapy perspectives

Low exercise tolerance has a large influence on health status in chronic obstructive pulmonary disease and chronic heart failure. In addition to primary organ dysfunction, impaired skeletal muscle performance is a strong predictor of low exercise capacity. There are striking similarities between both disorders with respect to the muscular alterations underlying the impairment. However, different alterations occur in different muscle types. Histologic and metabolic data show that peripheral muscles undergo a shift from oxidative to glycolytic energy metabolism, whereas the opposite is observed in the diaphragm. These findings are in line with the notion that peripheral and diaphragm muscle are limited mainly by endurance and strength capacity, respectively. In both diseases, muscular impairment is multifactorially determined; hypoxia, oxidative stress, disuse, medication, nutritional depletion, and systemic inflammation may contribute to the observed muscle abnormalities and each factor has its own potential for innovative treatment approaches.

Pulmonary function and respiratory muscle strength in chronic heart failure: comparison between ischaemic and idiopathic dilated cardiomyopathy

OBJECTIVE

To compare pulmonary function and respiratory muscle strength in patients with ischaemic and idiopathic dilated cardiomyopathy, well matched for indices of heart failure.

METHODS

The study involved 30 patients with ischaemic cardiomyopathy and 30 with idiopathic dilated cardiomyopathy. The groups were well matched for age, weight, and clinical severity of cardiac dysfunction as assessed by ejection fraction and the New York Heart Association functional class. There were more smokers in the ischaemic group (p < 0.05), but indices of pulmonary function were comparable.

RESULTS

Mean (SD) maximum static inspiratory pressure was lower in dilated cardiomyopathy than in ischaemic cardiomyopathy (73 (20) v 84 (22) cm H2O, p < 0.05), as was the maximum static expiratory pressure (90 (20) v 104 (21) cm H2O, p < 0.05).

CONCLUSIONS

For a given degree of cardiac dysfunction, the respiratory muscles are weaker in patients with idiopathic dilated cardiomyopathy than in those with ischaemic cardiomyopathy.

Leg blood flow and increased potassium release during exercise in chronic heart failure: effect of physical training

BACKGROUND

Exercise-induced hyperkalemia, which may contribute to exercise hyperpnea and exertional fatigue, is increased in patients with chronic heart failure (CHF). This study examined whether differences in leg blood flow during exercise could be responsible for alterations in the level of hyperkalaemia, as well as the effect of physical training.

METHODS AND RESULTS

We studied 10 subjects with CHF (ejection fraction 23 +/- 3.9%; mean +/- SD) and 10 subjects with normal left ventricular function (NLVF) who had undergone previous coronary bypass graft surgery (ejection fraction 64 +/- 8.0%; mean +/- SD). Subjects performed incremental cycle exercise to exhaustion before and after physical training. The rises in femoral venous potassium concentration ([K+]), heart rate, lactate, and ventilation (VI) with exercise were all greater in the subjects with CHF than in those with NLVF (P < .05). There was no difference between the groups in leg blood flow during submaximal exercise but peak leg flow was greater in the group with NLVF (P < .01). Physical training was well tolerated and both groups increased their peak VO2 (8 +/- 3.2% CHF (P < .05); 11 +/- 2.7% NLVF (P < .01); mean +/- SE). Training resulted in a reduced rise in femoral venous [K+] and VI (P < .05), but did not affect leg blood flow during submaximal exercise in either group.

CONCLUSIONS

The rise in the femoral venous [K+] with exercise is increased in patients with CHF and can be reduced by physical training. These changes are not a consequence of different leg blood flows, either between groups or with training. The study also suggests that femoral venous [K+] is not a powerful regulator of leg blood flow during exercise.

Skeletal muscle myosin heavy chains in heart failure: correlation between magnitude of the isozyme shift, exercise capacity, and gas exchange measurements

BACKGROUND

Patients with congestive heart failure (CHF) have a reduced exercise capacity because of the early appearance of fatigue and dyspnea. Qualitative changes in the skeletal muscle composition and metabolism can be responsible for the origin of symptoms

METHODS

We correlated the myosin heavy chain (MHC) composition of the gastrocnemius in 20 patients with different degrees of CHF to NYHA class, diuretic consumption, echocardiographic parameters, and expiratory gases measured during cardiopulmonary exercise testing. MHC composition was determined electrophoretically in skeletal muscle needle microbiopsies and the percent distribution was calculated by densitometry. Maximal cardiopulmonary exercise testing was performed on a treadmill with a modified Naughton protocol. A capnograph was used.

RESULTS

There was no correlation between ejection fraction, left ventricular end systolic diameter, left ventricular end diastolic diameter, and MHC composition. We found a significant positive correlation between the percentage of MHC 1 (slow aerobic isoform) and NYHA class (r2 = 0.62, p < 0.0001), peak VO2 (r2 = 0.5, p < 0.0004), ventilatory threshold (VT) (r2 = 0.33, p = 0.008) and O2 pulse (peak VO2/HR) (r2 = 0.40, p = 0.003). There was a negative correlation between both MHC2a (fast oxidative) and MHC2b (fast glycolytic) with peak VO2 (r2 = 0.38, p = 0.004 and r2 = 0.37, p = 0.004, respectively), VT (r2 = 0.2, p = 0.046 and r2 = 0.34, p = 0.007, respectively), and O2 pulse (peak VO2/HR) (r2 = 0.39, p = 0.003 and r2 = 0.23, p = 0.03). NYHA class was also correlated positively with MHC2a and MHC2b (r2 = 0.46, p = 0.001 and r2 = 0.41, p < 0.006, respectively) and negatively with the same clinical and functional parameters.

CONCLUSIONS

The correlation between the magnitude of the MHC shift from the slow aerobic to the fast glycolytic and fast oxidative with both functional and objective measurements of exercise capacity (peak VO2, VT, O2 pulse) seem to suggest that changes in skeletal muscle composition may play a determining role in exercise tolerance in patients with CHF.

Skeletal muscle function and its relation to exercise tolerance in chronic heart failure

OBJECTIVES

This study sought to define the relation between muscle function and bulk in chronic heart failure (HF) and to explore the association between muscle function and bulk and exercise capacity.

BACKGROUND

Skeletal muscle abnormalities have been postulated as determinants of exercise capacity in chronic HF. Previously, muscle function in chronic HF has been evaluated in relatively small numbers of patients and with variable results, with little account being taken of the effects of muscle wasting.

METHODS

One hundred male patients with chronic HF and 31 healthy male control subjects were studied. They were matched for age (59.0 +/- 1.0 vs. 58.7 +/- 1.7 years [mean +/- SEM]) and body mass index (26.6 +/- 0.4 vs. 26.3 +/- 0.7 kg/m2). We assessed maximal treadmill oxygen consumption (VO2), quadriceps maximal isometric strength, fatigue (20-min protocol, expressed in baseline maximal strength) and computed tomographic cross-sectional area (CSA) at midthigh.

RESULTS

Peak VO2 was lower in patients (18.0 +/- 0.6 vs. 33.3 +/- 1.4 ml/min per kg, p < 0.0001), although both groups achieved a similar respiratory exchange ratio at peak exercise (1.15 +/- 0.01 vs. 1.19 +/- 0.03, p = 0.13). Quadriceps (582 vs. 652 cm2, p < 0.05) and total leg muscle CSA (1,153 vs. 1,304 cm2, p < 0.005) were lower in patients with chronic HF. Patients were weaker than control subjects (357 +/- 12 vs. 434 +/- 18 N, p < 0.005) and also exhibited greater fatigue at 20 min (79.1% vs. 92.1% of baseline value, p < 0.0001). After correcting strength for quadriceps CSA, significant differences persisted (5.9 +/- 0.2 vs. 7.0 +/- 0.3 N/cm2, p < 0.005), indicating reduced strength per unit muscle. In patients, but not control subjects, muscle CSA significantly correlated with peak absolute VO2 (R = 0.66, p < 0.0001) and is an independent predictor of peak absolute VO2.

CONCLUSIONS

Patients with chronic HF have reduced quadriceps maximal isometric strength. This weakness occurs as a result of both quantitative and qualitative abnormalities of the muscle. With increasing exercise limitation there is increasing muscle weakness. This progressive weakness occurs predominantly as a result of loss of quadriceps bulk. In patients, this muscular atrophy becomes a major determinant of exercise capacity.

Multicore myopathy with restrictive cardiomyopathy

A 10-y-old girl is presented who suffered mild muscular weakness and exercise intolerance from the age of 1 y onwards, with progression appearing from the age of about 8 y. Multicore myopathy and restrictive cardiomyopathy were diagnosed. Literature concerning the coexistence of multicore myopathy and cardiomyopathy is reviewed.

Changes in skeletal muscle histology and metabolism in patients undergoing exercise deconditioning: effect of propionyl-L-carnitine

To define the skeletal muscle abnormalities in patients undergoing exercise deconditioning and evaluate the metabolic effect of propionyl-L-carnitine (PLC), muscle biopsies were obtained from 28 patients with effort angina and 31 control subjects. Coronary artery disease patients received either placebo (n = 12), PLC (1.5 g i.v. followed by infusion of 1 mg/kg/min for 30 min, n = 10), or L-carnitine (1 g i.v. followed by infusion of 0.65 mg/kg/min for 30 min, n = 6) for 2 days. Exercise deconditioned patients treated with placebo showed normal muscle content of total carnitine and glycogen, and decrease in percentage of type 1 fibers (P < 0.01) and in the activity of citrate synthase (P < 0.05), succinate dehydrogenase (P < 0.05), and cytochrome oxidase (P < 0.05), as compared to controls. Both PLC and L-carnitine did not modify muscle fiber composition or enzyme activities, but significantly increased muscle levels of total carnitine by 42% and 31%, respectively (P < 0.05). Moreover, PLC significantly increased glycogen muscle content (P < 0.01), while the equimolar dose of L-carnitine did not. This effect, probably due to the anaplerotic activity of the propionic group of PLC, suggests that this drug may be effective in improving energy metabolism of muscles with impaired oxidative capacity.

Cardiac troponin I and T alterations in hearts with severe left ventricular remodeling

Cardiac troponin T (cTnT) and troponin I (cTnI) have been suggested as new, more specific markers of myocardial cellular damage. The objective of this study was to examine how the distributions of cTnI and cTnT were affected in postinfarction left ventricular remodeled (LVR) myocardium. At 2 months postinfarct in a porcine heart failure model, both Western blot and biochemical assay analyses were performed on left ventricular myocardium remote from the infarct zone in ligation animals (n = 8). Results were compared with data from the left ventricular myocardium from similar sized healthy (control) pigs (n = 7). Autoradiograms from Western blot analysis showed that the protein mass for cTnI and cTnT in LVR hearts decreased 80% (P &lt;0.001) and 40% (P &lt;0.02), respectively, when compared with nondiseased tissue. Similarly, the concentrations for cTnI and cTnT in LVR hearts decreased 42% (P &lt;0.05) and 70% (P &lt;0.001), respectively, compared with nondiseased normal tissue. The clinical assumption is that the appearance of cTnI and cTnT in the blood is proportional to chronic loss of cTnI and cTnT from injured myocardium associated with left ventricular remodeling.

Cardiac arrhythmias as presenting symptoms in patients with limb-girdle muscular dystrophy

Clinically manifest muscular dystrophy is often accompanied by functional and anatomic derangements in the myocardium which often have prognostic significance. We describe two young patients who had unrecognized limb-girdle muscular dystrophy who presented with cardiac arrhythmia. One developed dilated cardiomyopathy complicated by ventricular tachyarrhythmia. The other patient had atrial paralysis requiring permanent pacing. It is important to consider the possibility of underlying muscular dystrophy in patients who present with cardiac arrhythmia without an obvious cause.

Exercise limitation in chronic heart failure: central role of the periphery

The symptoms of chronic heart failure (CHF) are predominantly shortness of breath and fatigue during exercise and reduced exercise capacity. Disturbances of central hemodynamic function are no longer considered to be the major determinants of exercise capacity. The two symptoms of fatigue and breathlessness are often considered in isolation. A pulmonary abnormality is usually considered to be the cause of abnormal ventilation, and increased dead space ventilation has come to be accepted as a major cause of the increased ventilation relative to carbon dioxide production seen in CHF. Rather than decreased skeletal muscle perfusion, an intrinsic muscle abnormality is considered to be responsible for fatigue. Another abnormality seen in CHF is persistent sympathetic nervous system activation, which is difficult to explain on the basis of baroreflex activation. There is increasing evidence for the importance of skeletal muscle ergoreceptors or metaboreceptors in CHF. These receptors are sensitive to work performed, and activation results in increased ventilation and sympathetic activation. The ergoreflex appears to be greatly enhanced in CHF. We put forward the "muscle hypothesis" as an explanation for many of the pathophysiologic events in CHF. Impaired skeletal muscle function results in ergoreflex activation. In turn, this causes increased ventilation, thus linking the symptoms of breathlessness and fatigue. Furthermore, ergoreflex stimulation may be responsible for persistent sympathetic activation.

Explaining fatigue in congestive heart failure

Fatigue is a prominent symptom in patients with chronic heart failure, limiting physical activity and impairing quality of life. Although the underlying mechanisms are not clearly identified, alterations associated with peripheral adaptation in heart failure appear to play an important role, including a variably impaired peripheral perfusion during exercise, reduced oxidative capacity of skeletal muscle, impaired muscle strength, and possibly reflex mechanisms associated with alterations in the metabolism of skeletal muscle. Exercise training can, in part, reverse these peripheral alterations, improve exercise capacity, and alleviate fatigue.

Exercise capacity and skeletal muscle structure and function before and after balloon mitral valvuloplasty

This study evaluated the effects of balloon mitral valvuloplasty (BMV) on exercise capacity and skeletal muscle structure and function in 10 subjects with mitral stenosis (mean age +/- SD 33 +/- 5.5). Measurements were obtained before, and 2 weeks and 4 months after BMV to provide baseline data, to examine the effects of improved hemodynamics, and to examine the effects of resumption of normal physical activity, respectively. Valvuloplasty caused an increase in mitral valve area (0.89 +/- 0.04 to 1.75 +/- 0.07 cm2; mean +/- SE), and an increase in resting cardiac output (3.8 +/- 0.18 to 4.6 +/- 0.19 L/min, p < 0.05). At early follow-up after 2 weeks, subjects did more work (31% increase, p < 0.01) and had greater maximal oxygen consumption (11% increase, p < 0.01). However, measurements reflecting skeletal muscle histology, biochemistry, and function were unaltered at this stage. Four months after BMV, subjects had a further increase in exercise capacity compared with both baseline (58% increase, p < 0.01) and early follow-up (20% increase, p < 0.05). There were associated late increases compared with baseline in quadriceps cross-sectional area (66 +/- 5.8 vs 61 +/- 5.5 cm2, p < 0.05) and torque production (125 +/- 14 vs 118 +/- 16 Nm, p < 0.05). The percentage of slow twitch type I fibers increased compared with baseline (41 +/- 2.0% vs 33 +/- 3.1%, p < 0.05), as did the size of type II fibers (5.9 +/- 0.49 vs 4.9 +/- 0.57 microns2 x 10(3), p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities of skeletal muscle metabolism during nerve stimulation determined by 31P nuclear magnetic resonance spectroscopy in severe congestive heart failure

These data confirm the presence of abnormal skeletal muscle metabolic function in patients with chronic heart failure. These changes are independent of patient compliance and central hemodynamic response to conventional exercise, and may explain, in part, the marked decrease in exercise tolerance often observed in patients with chronic severe heart failure. The etiology of these abnormalities of metabolic function and nutritive flow remains uncertain. TNS may prove useful in further elucidation of the peripheral metabolic consequences of chronic heart failure.

Cardiac dysrhythmias in children with idiopathic dilated or hypertrophic cardiomyopathy

To assess the incidence and prognostic significance of cardiac dysrhythmias in children with idiopathic dilated or hypertrophic cardiomyopathy, the clinical course of 59 patients was retrospectively reviewed over a period of 27 years. Dilated cardiomyopathy (DCM) was diagnosed in 28 patients and hypertrophic cardiomyopathy (HCM) in 31 patients. The mean age at the time of diagnosis was 2.8 +/- 0.7 years in DCM patients and 6.7 +/- 0.8 years in HCM patients. Mean follow-up time after diagnosis of cardiomyopathy was 4.1 +/- 1.0 years in DCM patients and 6.6 +/- 0.8 years in HCM patients. Clinically significant cardiac dysrhythmias were found in 17 of 59 patients (29%): 7 of 28 patients (25%) with DCM and 10 of 31 patients (32%) with HCM. The initial diagnosis of a cardiac dysrhythmia was made by standard electrocardiography in 12 of 17 patients (71%) and by 24-hour Holter monitoring in 5 of 17 patients (29%). Ventricular dysrhythmias were present in 5 of 7 patients with dilated cardiomyopathy and in 5 of 10 patients with hypertrophic cardiomyopathy. During the followup time, death occurred in 18 of 59 patients (31%): 8 of 59 patients (14%) died from congestive heart failure and 10 of 59 patients (17%) died suddenly. Among the sudden deaths were 4 of 28 patients (14%) with dilated cardiomyopathy and 6 of 31 patients (19%) with hypertrophic cardiomyopathy. Cardiac dysrhythmias had been documented in 6 of the 10 patients dying suddenly (3 of 4 patients with DCM and 3 of 6 patients with HCM).(ABSTRACT TRUNCATED AT 250 WORDS)

Results of biventricular endomyocardial biopsy in survivors of cardiac arrest with apparently normal hearts

Seventeen young patients (10 males and 7 females, aged 14 to 38 years, mean 26.4) without overt organic heart disease, who had been resuscitated from sudden cardiac arrest and referred to our institution during the period 1984 to 1993 for diagnostic evaluation and electrophysiologic study-guided antiarrhythmic therapy, were studied. Patients underwent noninvasive (electrocardiography, echocardiography [2-dimensional and Doppler], and magnetic resonance imaging) and invasive (left ventricular [LV], right ventricular [RV], and coronary angiography, ergonovine testing, electrophysiologic study, and biventricular endomyocardial biopsy) cardiac studies. Six to 8 biopsy fragments per patient were processed for histology and electron microscopy and read by a pathologist blinded to clinical data. Antiarrhythmic drug testing included amiodarone, propafenone, and metoprolol. A cardioverter-defibrillator was implanted in patients with persistently inducible sustained ventricular tachycardia or ventricular fibrillation. Sequential cardiac biopsy specimens were obtained in patients with active myocarditis undergoing immunosuppressive treatment. Periodic 3-month follow-ups included echocardiography and Holter monitoring. Two groups of patients were distinguished by invasive and noninvasive examinations: group I consisted of 9 patients with entirely normal parameters; group II consisted of 8 patients with structural, nonspecific cardiac abnormalities. In this latter group, mild to moderate dilatation and hypokinesia of the left ventricle were documented in 4 patients, concentric LV hypertrophy was seen in three patients, and RV dysfunction was noted in 1 patient. Histologic examination was abnormal in in all patients and revealed specific lesions in 65% of them; LV biopsy specimens allowed a diagnosis in 3 of 7 myocarditic patients with normal RV histology.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistence of ventricular arrhythmia after resolution of occult myocarditis in children and young adults

OBJECTIVES

We sought to examine whether resolution of occult myocarditis in children with associated ventricular arrhythmia correlated with the presence of arrhythmia at late follow-up.

BACKGROUND

Complex ventricular arrhythmias have been documented in children with myocarditis. Therapy is aimed at controlling the arrhythmia and any associated ventricular dysfunction. However, no reported studies have documented whether resolution of myocarditis in children is associated with resolution of the associated arrhythmias.

METHODS

We performed a retrospective analysis of 12 patients (mean age 12 years) with myocarditis. Ambulatory electrocardiographic (Holter) monitors were reviewed for ventricular arrhythmias at presentation and follow-up. Patients were assigned to Group I if they received corticosteroids in addition to any antiarrhythmic agents and to Group II if they did not receive steroids. Follow-up endomyocardial biopsy was performed in some patients, and results were analyzed in relation to the presence of arrhythmias at follow-up.

RESULTS

Eleven patients had ventricular tachycardia, and one had multiform couplets. Corticosteroids were given to seven patients (Group I). Follow-up biopsy was performed in seven patients (six received steroids), with resolution of inflammation in all; four of the seven still had ventricular arrhythmias but with improved control. Of the five patients without follow-up biopsy, three had persistent arrhythmia. Absence of inflammation at follow-up biopsy did not correlate with loss of ventricular arrhythmias, and there was no difference between Group I and II patients with respect to resolution of arrhythmia (Fisher exact test, p = 0.70, power 11%).

CONCLUSIONS

Complex ventricular arrhythmias persist after apparent resolution of occult myocarditis in children. Although these arrhythmias are easier to control after such resolution, the patients may require long-term antiarrhythmic therapy.

Relation of pathophysiologic mechanisms to outcome in heart failure

Advances in the treatment of heart failure with angiotensin-converting enzyme inhibitors have been accompanied by an improved understanding of the pathophysiology of heart failure. The inability of the heart to act as a pump is determined in some patients by alterations to the architecture of the heart and changes in the extracellular space, particularly fibrosis. The degree to which the failure of the heart as a pump can be attributed to a reduced ability of the myocyte to contract is contentious. The origin of symptoms is still uncertain but does relate to identified changes in the lung, increased peripheral resistance and atrophy of skeletal muscle. The mechanisms of action of angiotensin-converting enzyme inhibitors are numerous and do not yet account easily for the clinical benefits. Further epidemiologic studies are needed to ascertain the proportion of patients who manifest progressive heart failure rather than deterioration due to further cardiac events. Understanding the pathophysiology of heart failure will allow therapy to be tailored to the requirements of the individual patient.

Decreased proportion of type I myofibers in skeletal muscle of dogs with chronic heart failure

BACKGROUND

Whether biochemical and histological abnormalities of skeletal muscle (SM) develop in patients with chronic heart failure (HF) remains controversial. In the present study, dogs with chronic HF were used to examine potential alterations of SM fiber type, fiber size, number of capillaries per fiber (C/F), beta-adrenergic receptor density (Bmax), and fiber ultrastructural integrity.

METHODS AND RESULTS

HF was produced in 17 dogs by sequential intracoronary microembolizations. Biopsies of the lateral head of the triceps muscle were used in all studies. Type I and type II fibers were differentiated by myofibrillar ATPase (pH 9.4 or 4.2). Bmax was assessed by radioligand binding and SM ultrastructure by transmission electron microscopy. Comparisons were made with biopsies obtained from nine control dogs. The percentage of SM type I fibers was reduced in HF dogs compared with control dogs (19 +/- 2% versus 32 +/- 5%) (p < 0.001), whereas the percentage of SM type II fibers was increased (81 +/- 2% versus 68 +/- 5%) (p < 0.001). The change in fiber type composition was not associated with a preferential atrophy or hypertrophy of either fiber type. There was no difference in SM Bmax (198.9 +/- 14.3 versus 186.8 +/- 17.3 fmol/mg protein) or in C/F (5.37 +/- 0.26 versus 5.84 +/- 0.21) between HF dogs and control dogs. No ultrastructural abnormalities were present in SM fibers of HF dogs.

CONCLUSIONS

In dogs with HF, there is a decrease in the relative composition of the slow-twitch type I SM fibers and an increase in fast-twitch type II fibers. The shift in fiber type composition is not associated with preferential atrophy of either fiber type or with a reduction in C/F, beta-adrenergic receptor density, or structural abnormalities of the myofibers.

Effect of balloon mitral valvuloplasty on exercise capacity, ventilation and skeletal muscle oxygenation

OBJECTIVES

The short- and long-term effects of valvuloplasty on exercise capacity, ventilation and skeletal muscle oxygenation were investigated to determine whether a dissociation between hemodynamic improvement and exercise capacity occurs in patients with mitral stenosis.

BACKGROUND

Percutaneous balloon mitral valvuloplasty in patients with mitral stenosis results in immediate hemodynamic improvement at rest and with exercise. Improved exercise capacity has been described at 3 months after valvuloplasty. In patients with left ventricular dysfunction, acute therapeutic interventions that produce hemodynamic benefit do not immediately improve exercise capacity.

METHODS

Maximal bicycle exercise with measurement of respiratory gases was performed in 11 patients with mitral stenosis before and at 48 h and 3 months after successful percutaneous balloon mitral valvuloplasty. Respiratory and leg skeletal muscle oxygenation were assessed by monitoring changes in light absorption of the serratus anterior and vastus lateralis muscles using near-infrared spectroscopy and were expressed as percent deoxygenation.

RESULTS

Mitral valvuloplasty significantly increased mean mitral valve area from 1.0 +/- 0.2 to 1.7 +/- 0.3 cm2 (p < 0.05). Immediately after valvuloplasty, peak exercise oxygen consumption (VO2), VO2 at the anaerobic threshold, ventilation, peak respiratory and leg muscle deoxygenation all remained unchanged. At submaximal work loads, respiratory muscle deoxygenation was attenuated (25 W: before 12 +/- 4%; 48 h 4 +/- 3%; 50 W: before 10 +/- 5%; 48 h 5 +/- 4%; both p < 0.05). At 3 months, significant improvement in peak VO2 (before 10.9 +/- 5%; 3 months 14.6 +/- 6.2 ml/kg per min; p < 0.05) and VO2 at the anaerobic threshold (before 7.1 +/- 2.4; 3 months 8.4 +/- 2.3; p < 0.05) were observed, whereas ventilation remained unchanged. No further improvement was seen in respiratory muscle deoxygenation. Vastus lateralis deoxygenation at submaximal work loads tended to be decreased.

CONCLUSIONS

Long-term changes in skeletal muscle and the lungs preclude immediate enhancement of exercise performance after balloon mitral valvuloplasty. Immediate symptomatic improvement probably results from an immediate decrease in the work of breathing. Long-term symptomatic improvement results from changes that occur in the peripheral skeletal musculature as well as from the reduced work of breathing.

Cardiomyopathy and myocarditis in children with ventricular ectopic rhythm

OBJECTIVE

The objective of this study was to evaluate the histologic features of the myocardium in children with abnormal ventricular ectopic rhythm but a structurally normal heart.

BACKGROUND

Abnormal ventricular ectopic rhythm in children with a structurally normal heart is an uncommon but serious condition. Previous studies in adults with these findings have shown that approximately 10% have "primary electrical disease" and that 40% to 100% of these have abnormal histologic findings.

METHODS

Endomyocardial biopsy samples were obtained prospectively in 33 subjects presenting with ventricular ectopic rhythm but a structurally normal heart by physical examination and noninvasive studies. Biopsy specimens were evaluated for histologic changes consistent with dilated cardiomyopathy or myocarditis and these results were compared with noninvasive and invasive clinical findings.

RESULTS

Of the 33 subjects, 16 (48%) had normal myocardial histologic features (Group A), 14 (42%) had changes similar to the histologic features seen with idiopathic dilated cardiomyopathy (Group B) and 3 (9%) had lymphocytic myocarditis (Group C). Presenting clinical symptoms, surface electrocardiograms (ECGs), exercise stress testing and electrophysiologic stimulation tests failed to predict the biopsy results. Twenty-four-hour ambulatory ECGs showed a statistical difference between sustained and nonsustained ventricular tachycardia in Group A versus Group B (p less than 0.007), with Group A having more sustained ventricular tachycardia. Left ventricular function measured by fractional shortening on echocardiography did not differ between groups, but left ventricular end-diastolic dimension was greater in the subjects with abnormal histologic findings (Group B) (p less than 0.03).

CONCLUSIONS

These results provide evidence that approximately 50% of children with abnormal ventricular ectopic rhythm but a structurally normal heart may have subclinical cardiomyopathy or unsuspected myocarditis.

Alterations of skeletal muscle in chronic heart failure

BACKGROUND

The present study was designed to define the prevalence and characteristics of skeletal muscle alterations in patients with chronic heart failure (CHF) and their relation to exercise capacity.

METHODS AND RESULTS

The ultrastructure of skeletal muscle was analyzed by ultrastructural morphometry in 57 patients with CHF and 18 healthy controls. The volume density of mitochondria (Vvm) and the surface density (Svmc) of mitochondrial cristae were evaluated as a structural correlate of oxidative capacity of skeletal muscle. Vvm and Svmc were reduced by approximately 20% in patients with severe CHF irrespective of age and etiology. The cytochrome oxidase activity in mitochondria as determined by cytochemistry and subsequent morphometry in a subset of patients (n = 10) was significantly decreased in heart failure (p less than 0.01). The capillary length density of skeletal muscle was reduced in CHF (n = 12, p less than 0.05), and the fiber type distribution was shifted to type II fibers (n = 15, p less than 0.05). Vvm and Svmc were significantly related to peak exercise VO2 (r = 0.56, p less than 0.001, n = 60) and to VO2 at anaerobic threshold (r = 0.535, p less than 0.0001, n = 60). In 16 patients with severe heart failure, Vvm was inversely related to the duration of heart failure (r = 0.545, p less than 0.03). In 11 patients who underwent repeat biopsies after 4 months, a correlation was observed between the change in Vvm and the change in peak exercise VO2 (r = 0.89, p less than 0.001).

CONCLUSIONS

These findings indicate that patients with CHF develop significant ultrastructural abnormalities of skeletal muscle reflecting a depressed oxidative capacity of working muscle. It appears that these alterations of skeletal muscle contribute to the decreased exercise capacity of these patients but are, in principle, reversible by an effective treatment regimen.

Grading the severity of congestive heart failure in infants

To determine which variables most accurately define congestive heart failure (CHF) in infants, 41 patients (median age 2.5 months) were graded by four pediatric cardiologists for the presence and severity of CHF based on the following variables: amount of formula consumed per feeding, feeding time, history of diaphoresis or tachypnea, growth parameters, respiratory and heart rates, respiratory pattern, perfusion, presence of edema, diastolic filling sounds, and hepatomegaly. There were 19 patients graded as having no CHF, nine as mild, seven moderate, and six severe CHF. The most sensitive and specific variables (p less than 0.0001) for the presence of CHF were a history of less than 3.5 oz/feed, respiratory rate greater than 50/min, an abnormal respiratory pattern, diastolic filling sounds, and hepatomegaly. Moderate to severe CHF was present when patients took less than 3 oz/feed or greater than 40 min/feed, had an abnormal respiratory pattern with a resting respiratory rate greater than 60/min, and had a diastolic filling sound and moderate hepatomegaly. Severe CHF was accompanied by a heart rate greater than 170/min, decreased perfusion, and severe hepatomegaly. Thus, the grading of the severity of CHF in infants should include an accurate description of these historical and clinical variables.

Complex ventricular ectopic activity in patients less than 20 years of age with or without syncope, and the role of ventricular extrastimulus testing

To assess the potential for ventricular tachycardia (VT), ventricular extrastimulus testing was performed in 33 young patients with complex ventricular ectopic activity defined as multiform ventricular premature complexes (VPCs), couplets or nonsustained VT, or a combination, found during electrocardiographic monitoring. There were 21 male and 12 female patients with a mean age of 11 years (range 1 to 18). Patients were divided into 2 groups based on the presence (14 patients) or absence (19 patients) of syncope. Patients with syncope had ostensibly normal hearts (9 patients) or miscellaneous heart disease (5 patients). Patients without syncope had ostensibly normal hearts (8 patients) or miscellaneous heart disease (11 patients). Ventricular stimulation protocol consisted of burst pacing and 1 to 4 programmed extrastimuli decreasing to refractoriness at 3 drive-train cycle lengths, and at 2 pacing sites (right ventricular apex and outflow tract) during the drug-free baseline state and isoproterenol infusion. No patient had VT induced with 1 or 2 extrastimuli. VT was induced in 13 of 14 patients (93%) with syncope, and in 9 of 19 patients (47%) without syncope (p less than 0.05). Using a 3-extrastimuli protocol, 8 of 14 patients (57%) with and 3 of 19 patients (16%) without syncope had VT induced (p less than 0.05). These findings suggest that VT may be the cause of syncope in young patients with complex ventricular ectopic activity.

Ultrastructural abnormalities of mitochondria and deficiency of myocardial cytochrome c oxidase in a patient with ventricular tachycardia

A 30-year-old woman presented with life-threatening ventricular tachycardia without overt heart disease. Ultrastructural investigation of endomyocardial biopsy disclosed abnormally structured and often enlarged mitochondria. Morphometry revealed the ratio of volume density of mitochondria to myofibrils to be markedly increased to 0.667 as compared with five controls (mean: 0.46; range: 0.445-0.479). Investigation of mitochondrial respiratory chain enzymes revealed a 90% reduction in activity of cytochrome c oxidase. Our data suggest that mitochondrial cardiomyopathy may induce malignant ventricular arrhythmias.