Cardiac and skeletal myopathy associated with cardiac dysrhythmias

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.

Late-onset multiple acyl-CoA dehydrogenase deficiency with cardiac syncope: A case report

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an uncommon autosomal recessive disorder of mitochondrial fatty acid beta-oxidation. Syncope is a transient loss of consciousness due to acute global cerebral hypoperfusion. Late-onset MADD with syncope has not been reported previously.

CASE SUMMARY

We report a 17-year-old girl with exercise intolerance and muscle weakness. She felt palpitation and shortness of breath after short bouts of exercise. She also suffered from a transient loss of consciousness many times. Muscle biopsy showed lipid storage. Genetic mutation analysis indicated a compound heterozygous mutation c.250G > A (p.A84T) and c.872T > G (p.V291G) in the ETFDH gene. The results of Holter electrocardiogram monitoring showed supraventricular tachycardia when the patient experienced a loss of consciousness. After treatment with riboflavin and carnitine, muscle weakness and palpitation symptoms improved rapidly. No loss of consciousness occurred, and the Holter electrocardiogram monitoring was normal.

CONCLUSION

Late-onset MADD with supraventricular tachycardia can cause cardiac syncope. Carnitine and riboflavin supplement were beneficial for treating the late-onset MADD with cardiac syncope. Attention should be paid to the prevention of cardiac syncope when diagnosing late-onset MADD.

[Cardiac involvement in polymyositis]

Cardiovascular involvement in polymyositis constitutes a major cause of death. However, the cardiac location is rarely symptomatic and does not usually represent the principle clinical feature at the time of the initial presentation. We present here an unusual case of polymyositis with severe and polymorph cardiac disturbances that predominant the muscular signs.

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.

Effects of dietary fat and L-carnitine on plasma and whole blood taurine concentrations and cardiac function in healthy dogs fed protein-restricted diets

OBJECTIVE

To evaluate plasma taurine concentrations (PTC), whole blood taurine concentrations (WBTC), and echocardiographic findings in dogs fed 1 of 3 protein-restricted diets that varied in fat and L-carnitine content.

ANIMALS

17 healthy Beagles.

DESIGN

Baseline PTC and WBTC were determined, and echocardiography was performed in all dogs consuming a maintenance diet. Dogs were then fed 1 of 3 protein-restricted diets for 48 months: a low-fat (LF) diet, a high-fat and L-carnitine supplemented (HF + C) diet, or a high-fat (HF) diet. All diets contained methionine and cystine concentrations at or above recommended Association of American Feed Control Officials (AAFCO) minimum requirements. Echocardiographic findings, PTC, and WBTC were evaluated every 6 months.

RESULTS

The PTC and WBTC were not significantly different among the 3 groups after 12 months. All groups had significant decreases in WBTC from baseline concentrations, and the HF group also had a significant decrease in PTC. One dog with PT and WBT deficiency developed dilated cardiomyopathy (DCM). Taurine supplementation resulted in significant improvement in cardiac function. Another dog with decreased WBTC developed changes compatible with early DCM.

CONCLUSIONS AND CLINICAL RELEVANCE

Results revealed that dogs fed protein-restricted diets can develop decreased taurine concentrations; therefore, protein-restricted diets should be supplemented with taurine. Dietary methionine and cystine concentrations at or above AAFCO recommended minimum requirements did not prevent decreased taurine concentrations. The possibility exists that AAFCO recommended minimum requirements are not adequate for dogs consuming protein-restricted diets. Our results also revealed that, similar to cats, dogs can develop DCM secondary to taurine deficiency, and taurine supplementation can result in substantial improvement in cardiac function.

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.

Mechanisms and therapy of complex arrhythmias in pediatric patients

In recent years, the distinction between the diagnostic and therapeutic techniques used in the assessment and management of pediatric and adult patients with arrhythmias has gradually blurred. Nonetheless, arrhythmias in the pediatric patient are still often different from the adult patient in one of two important ways. First, a variety of arrhythmia mechanisms remain relatively unique to the pediatric population, some because of developmental issues and others because of early presentation of an incessant tachycardia. Second, the presentation and management of certain arrhythmias is sometimes markedly affected by patient age or the presence of structural congenital heart disease. A sampling from each of the above categories is reviewed and discussed.

Corticosteroid therapy for ventricular tachycardia in children with silent lymphocytic myocarditis

OBJECTIVE

The objective of our study was to describe the efficacy of corticosteroids for ventricular tachycardia in four children with structurally normal hearts in whom endomyocardial biopsy revealed histologic changes of lymphocytic myocarditis.

PATIENTS

The four patients had unexplained ventricular tachycardia. Three dysrhythmias were sustained, and one was inducible by exercise. Patient ages ranged from 4 months to 12 years. Three of the four patients had no symptoms. In two of them, ventricular tachycardia was identified by mass screening for heart disease. Two patients received oral steroids and two received pulse steroid therapy.

RESULTS

In all four patients, significant underlying diseases were not found by noninvasive evaluation. Right ventricular endomyocardial biopsy revealed abnormal histologic findings of chronic lymphocytic myocarditis in all patients. Steroid therapy was effective in all four patients, two of whom received methylprednisolone pulse therapy.

CONCLUSIONS

We conclude that unexplained ventricular tachycardia may be the only manifestation of clinically silent myocarditis. Steroid therapy should therefore be considered if conventional antiarrhythmic medication is not effective and histologic findings confirm the presence of lymphocytic myocarditis.

Supraventricular tachycardia mechanisms and their age distribution in pediatric patients

To better define the natural history of supraventricular tachycardia (SVT) in young patients, age distribution of SVT mechanisms was examined in 137 infants, children and adolescents. Patients with a history of cardiac surgery or neuromuscular diseases were excluded. An electrophysiologic study was performed in each patient: transesophageal (110 patients) or transvenous (14 patients) or both (13 patients). Mechanisms were classified as SVT using accessory atrioventricular (AV) connection (SVT using accessory connection, including orthodromic and antidromic reciprocating tachycardia), primary atrial tachycardia (including chaotic, automatic and reentrant atrial tachycardia), and tachycardia due to reentry within the AV node. SVT using accessory connection occurred in 100 of 137 patients (73%) and was the most prevalent mechanism. Primary atrial tachycardia and reentry within the AV node were present in 19 of 137 (14%) and 18 of 137 (13%) patients, respectively. Using a multinomial logit model, relative probabilities for tachycardia mechanisms for 5 age groups--prenatal, less than 1, 1 to 5, 6 to 10 and greater than 10 years--were determined. Primary atrial tachycardia (11 to 16%) and SVT using accessory connection (58 to 84%) appeared throughout infancy, childhood and adolescence. On the other hand, tachycardia due to reentry within the AV node (0 to 31%) rarely appeared before age 2 years. Mechanisms of SVT appear to have age-dependent distributions. SVT using accessory connection is the most common mechanism in young patients. We speculate that the propensity to tachycardia due to reentry within the AV node occurs during postnatal development.

Ventricular arrhythmias in children with an apparently normal heart

Ventricular ectopy occurs frequently in normal children. In the presence of a normal heart, these arrhythmias, including asymptomatic, nonsustained ventricular tachycardia, carry a benign prognosis and are not associated with sudden, unexpected death. However, complex ventricular arrhythmias frequently indicate the presence of underlying cardiac disease; patients with such arrhythmias must undergo an appropriately thorough evaluation before decisions regarding prognosis and the need for therapy can be made.

Type 1 fiber abnormalities in skeletal muscle of patients with hypertrophic and dilated cardiomyopathy: evidence of subclinical myogenic myopathy

Abnormalities of skeletal muscle have been described in patients with dilated and hypertrophic cardiomyopathy. Eleven patients with dilated and eight with hypertrophic cardiomyopathy without overt symptomatic skeletal myopathy underwent extensive neuromuscular studies. Quantitative electromyography showed abnormal reduction of motor unit potential duration, indicative of myogenic myopathy, in four patients (36%) with dilated and in three (37%) with hypertrophic cardiomyopathy. Values were 21% to 40% (mean 28%) lower than those in age-matched normal control subjects. The presence of normal nerve conduction velocities and of normal motor unit fiber density in all patients indicated lack of neurogenic abnormalities. Skeletal muscle biopsy was performed in five patients with dilated and in four with hypertrophic cardiomyopathy. In all nine patients light and electron microscopy showed central hyporeactive cores, selective atrophy and mitochondrial abnormalities of type 1 fibers but not of type 2 fibers. The degree of impairment of left ventricular function in patients with electromyographic abnormalities was similar to that of those without (percent fractional shortening at two-dimensional echocardiography 21 +/- 9 versus 25 +/- 10, ejection fraction at angiography 39 +/- 13% versus 42 +/- 13% and left ventricular end-diastolic pressure 21 +/- 6 versus 21 +/- 8 mm Hg) as well as symptom duration (9 +/- 4 versus 12 +/- 8 months). Thus, subclinical electromyographic alterations indicative of myogenic myopathy are frequent in patients with dilated and hypertrophic cardiomyopathy and are unrelated to the degree of impairment of left ventricular function. The concomitant histologic alterations, characterized by selective type 1 atrophy, are similar to those observed in congenital and idiopathic myopathies, but different from those described in secondary heart failure.

Myocardial carnitine in end-stage congestive heart failure

To test the hypothesis that carnitine is decreased in the myocardial tissue of patients with end-stage congestive heart failure (CHF), left ventricular myocardial carnitine was measured in 51 patients undergoing orthotopic cardiac transplantation. The study group included patients with idiopathic dilated cardiomyopathy, coronary artery disease, myocarditis and rheumatic heart disease. Myocardial carnitine varied in different cardiac chambers. In normal control hearts, the left and right ventricular total carnitine was similar, but the ventricles had higher levels than the atria (p less than 0.005); in 30 hearts in CHF, the left ventricular total carnitine was higher than in the right ventricle (p less than 0.001) and both ventricles had higher total carnitine than the atria (p less than 0.005). Only 7 of 51 patients with CHF had low myocardial carnitine, whereas plasma carnitine was elevated in all diagnostic groups of end-stage CHF studied.

Cardiac manifestations in disorders of fat and carnitine metabolism in infancy

The prognosis of patients with cardiomyopathy associated with hypocarnitinemia is uncertain. Cardiac hemodynamics, histologic findings and response to oral L-carnitine therapy were retrospectively evaluated in 11 children with cardiomyopathy associated with abnormal carnitine metabolism. Three had systemic carnitine deficiency, two familial hypocarnitinemia with neutropenia, three transient neonatal hypocarnitinemia and three a carnitine insufficiency syndrome. Six had a hypertrophic and five a dilated cardiomyopathy. Hypotonia was present in seven (64%). The cardiothoracic ratio was greater than 0.60 in eight (73%). The most frequent abnormality on the electrocardiogram was ST-T wave inversion in the left precordial leads with various degrees of left ventricular hypertrophy. Echocardiographically, two patients with hypertrophic cardiomyopathy had decreased left ventricular function and two patients with dilated cardiomyopathy had increased thickness of the left ventricular wall. Histologic evaluation (two autopsies and one endomyocardial biopsy) revealed striking lipid accumulation within hypertrophied myocytes. Six of eight patients on carnitine replacement therapy had improvement echocardiographically during a 3 month to 2 year follow-up period. In summary, both hypertrophic and dilated cardiomyopathy can result from abnormal carnitine metabolism. The determination of plasma carnitine concentrations and fatty acid metabolism by-products should be performed in all patients with either form of cardiomyopathy of unknown etiology because carnitine supplementation may lead to improvement.

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

Results of cardiac muscle and skeletal muscle biopsies were compared in 22 patients with cardiomyopathy; 11 patients presented with symptoms secondary to ventricular tachycardia (Group 1) and 11 had symptoms of severe congestive heart failure (Group 2). No patient had structural or ischemic cardiac disease. In Group 1 patients, hemodynamic abnormalities were subtle, but invasive study demonstrated dilated cardiomyopathy in two patients and restrictive cardiomyopathy in nine. In Group 2, eight patients had dilated cardiomyopathy and three had restrictive cardiomyopathy. Cardiac biopsy results were abnormal in all 22 patients and the abnormalities were similar for the two groups. Cardiac histologic study revealed a spectrum of abnormalities including fibrosis, dilated sarcoplasmic reticulum, increased numbers of intercalated discs and mitochondrial abnormalities. Histologic abnormalities of skeletal muscle were similar in each group, consisting of endomysial fibrosis and increased lipid deposits. Slightly more than half of the Group 1 and Group 2 patients also had a low concentration of skeletal muscle long chain acylcarnitine. These data demonstrate that abnormalities of both cardiac and skeletal muscle are common in patients with cardiomyopathy; abnormalities are similar whether initial symptoms are due to ventricular tachycardia or congestive heart failure. It is suggested that these patients with cardiomyopathy may have a generalized myopathy.

Ventricular tachycardia in a young population without overt heart disease

Since 1974, 24 young patients presenting with ventricular tachycardia and without clinical evidence of heart disease were evaluated and followed. Sixteen patients (67%) were symptomatic. Clinical episodes of ventricular tachycardia were sustained in 18, incessant in four, and nonsustained in two patients. The rate of tachycardia ranged from 130 to 300 beats/min (mean = 200 beats/min). Subtle abnormalities of cardiac size or function were present at cardiac catheterization in 16 of 23 patients (70%). During electrophysiologic studies, spontaneous ventricular tachycardia was present in six patients. The clinical ventricular tachycardia was inducible by programmed stimulation in 13 of 18 patients. The site of origin of tachycardia based on endocardial mapping in 17 patients was the right ventricle in 14, the ventricular septum in one, and indeterminate in two patients. Seventeen patients were treated based on results of short-term drug testing. During a mean follow-up period of 7.5 years, three patients died suddenly; none of these patients were receiving antiarrhythmic medication at the time of death. We conclude that in a young population without clinical evidence of heart disease, ventricular tachycardia may be the first manifestation of cardiomyopathy, since at least two-thirds of these patients have abnormalities at cardiac catheterization. Without treatment mortality in this population may be as high as 13% over an 8 year period. Presently we recommend treatment of ventricular tachycardia in any symptomatic patient, with therapy guided by electrophysiologic and treadmill testing. In addition, we recommend treatment for any asymptomatic patient with exercise-related tachycardia, since this group appears to be at increased risk for sudden death.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymyositic heart disease

There is an apparent correlation between the severity and duration of skeletal muscle involvement, cardiac manifestations and the extent of conduction system disease in polymyositis. Cardiac involvement during the course of polymyositis has been recognized as one of the typical features of skeletal muscle myositis. We report a patient with polymyositis in whom bifascicular block, prolonged P-R interval and congestive heart failure appeared three years before any clinical or laboratory evidence of active skeletal muscle myositis. To the best of our knowledge, this is the first report of polymyositis where cardiac manifestations preceded those of skeletal muscle myositis.