Restrictive cardiomyopathy

Cardiomyopathy is a category of disorders that affects the cardiac muscle and can cause significant disability for a large segment of the population. It can be classified into dilated, hypertrophic, and restrictive types based on morphology. The purpose of this paper is to review the etiology and classification of cardiomyopathy as well as the current medical and surgical management of this disorder. This paper also discusses recent literature regarding the efficacy of exercise training and testing for persons with cardiomyopathy.

Key Words: cardiomyopathy, exercise

INTRODUCTION

Cardiomyopathy is a disorder that has long been recognized to cause significant disability in persons affected. Hippocrates described it as "dropsy" for the way affected patients acted.1 Literally translated, cardiomyopathy means a disease of the heart muscle. It has been classified by the World Health Organization into 3 types based on anatomical and physiological features-dilated, hypertrophic, and restrictive.2 These diseases are considered to be those that are primary disorders of the myocardium and are not secondary to acquired or congenital heart disease.3 The causes of cardiomyopathy are varied and not completely understood. Current mechanisms under investigation include genetic factors, metabolic disturbances, hormone imbalances, toxins, calcium overload, altered vascular reactivity, hypoxia, free radicals, infection, and immune dysfunction.4 The common mechanical pathology is impaired pump mechanics.

DILATED CARDIOMYOPATHY

Dilated cardiomyopathy is the most common classification, estimated to affect 10 persons in 100,000 per year.5 It is characterized by impaired systolic function of both ventricles4 along with myocardial fiber hypertrophy in some cases.5 This impairment in contractility has been most commonly associated with infection from Coxsackie B viruses, although it also has been seen with other viruses such as influenza, mumps, rubeola, cytomegalovirus, Epstein-Barr virus, and adenovirus.5 Infection with one of these viruses causes myocarditis and is the precipitating factor in cardiomyopathy development for many individuals.6 Other causes for dilated cardiomyopathy include toxins such as ethyl alcohol, chemotherapeutic agents, and illicit catecholamine drugs.6 It also is found in some genetic disorders, primarily of metabolism or neuromuscular diseases, such as progressive muscular dystrophy.6

The dilated cardiomyopathy associated with alcoholism is rather unique in its dose-response relationship. It is generally accepted that alcohol consumption of at least 5 ounces per day for 5 years is necessary for individuals to develop the disorder.6 However, alcoholics with cirrhosis rarely exhibit cardiomyopathy.6 It also appears that other precipitating factors are necessary, such as a viral infection.4 This type of cardiomyopathy also has been found to be reversible after a few months of abstention in over half of affected persons.6 For those who do not stop consuming alcohol, the expected lifespan is less than 3 years.6

Dilated cardiomyopathy has also been attributed to diabetes mellitus and hyperthyroidism in some individuals.6 Diabetes appears to increase the accumulation of collagen, cholesterol, and triglycerides in the myocardium, affecting contractile function, while chronic stimulation from thyroid hormone appears to overstimulate the muscle.6

It has been estimated that 1000 U.S. women will be affected with dilated cardiomyopathy in the peripartum period.7 This has been diagnosed as left ventricular dysfunction that manifests in the last month of pregnancy or within 5 months of delivery.7 It is more common in older, multiparous women and those carrying twins.7 This type of cardiomyopathy has not been associated with any viral infection6 but appears to have an autoimmune component.7 Fortunately, over half of the affected women have spontaneous resolution of symptoms within 6 months, however, the remaining women have as much as an 83% 5-year mortality.6,7 There is also evidence that resolution of symptoms does not imply total recovery of cardiac function7 or exercise tolerance.8 These women should be counseled regarding the risks of future pregnancies as recurrence is common.6,7

The major pathophysiology of dilated cardiomyopathy due to any cause is a loss of elastic recoil of the ventricles.4,6 This overstretched muscle is then placed at a mechanical disadvantage for contraction due to the altered length-tension relationship of the muscle fibers.4,6,9 The main consequence of the altered mechanics is a decrease in ejection fraction.4,9 The heart attempts to compensate in early stages through increasing heart rate, but as the condition worsens, symptoms of low cardiac output become obvious.4,6,9

HYPERTROPHIC CARDIOMYOPATHY

Hypertrophic cardiomyopathy is one of the most dramatic disorders of cardiac muscle. It has been the cause of death in young, extremely fit athletes.10 It has been attributed to 38% of sudden deaths in young competitive athletes.11 This disorder has a strong familial component, with family members having histories of syncope, sudden cardiac death or dangerous arrhythmias.11 The major disorder is a thickened, nondilated left ventricle in the absence of any identifiable cause, such as aortic stenosis.4,11 The wall thickening is similar to that seen in the "athlete's heart," but is excessive (greater than 15 mm).10,11 The muscle fibers themselves are quite disorganized and can become arrhythmogenic.11 In this young, athletic population, symptoms are generally mild or nonexistent until sudden death strikes from ventricular tachycardia or fibrillation, most often during exercise.4,10,11

RESTRICTIVE CARDIOMYOPATHY

Restrictive cardiomyopathy is the rarest form.4 It is characterized by a fibrosis of the myocardium and has been linked to amyloid heart disease, sarcoid heart disease, tumor, and radiation.4 The major dysfunction in this condition is diastolic, with impaired filling of the ventricles.4 It can be distinguished from dilated cardiomyopathy by the presence of congestive symptoms with no evidence of cardiomegaly.4

DIAGNOSIS AND PROGNOSIS OF CARDIOMYOPATHY

Persons with any of the cardiomyopathies most often present to their physicians with symptoms of low cardiac output and congestion.6 These symptoms include slowly decreasing exercise tolerance; although in inactive persons this may not be present until significant loss of cardiac function has occurred.4 Patients also complain of orthopnea, nocturnal cough, dyspnea on exertion, and possibly dependent edema.4,6

Diagnosis is made using chest X-ray to determine cardiomegaly, echocardiography to determine ventricle size, and measurements of cardiac function, such as ejection fraction.4-6 Since cardiomyopathy is a dysfunction that exists in the absence of other causes, it is important to rule out coronary artery disease and infection as a cause of symptoms.4 Although the mechanisms of cardiomyopathy vary with the category, a specific etiology can be identified in less than 20% of patients.6 Therefore, the treatment has been directed to managing the common symptoms of chronic heart failure.12

Prognosis of the patient is dependent on the severity of the symptoms and the degree of cardiac output impairment. Patients with very low ejection fractions have the poorest prognosis.4,6 Treatment alternatives include medications and surgery, including transplantation for those with refractory dysfunction.

MEDICAL MANAGEMENT OF CARDIOMYOPATHY

Diuretics are commonly used to decrease the congestion in the lungs and periphery, particularly when combined with a salt-restricted diet.4,6 Vasodilators have been used to decrease afterload, particularly for those patients with severe systolic dysfunction.4,6,12 The most promising of these vasodilators are the angiotensin converting enzyme (ACE) inhibitors. These drugs appear to aid in remodeling the dilated heart through their influence on growth factors in the myocardium and have been seen to improve survival.4,12

Beta-blockers also are commonly used in conjunction with ACE inhibitors. These drugs used together appear to dramatically improve the ability of the myocardium to remodel toward a more normal length-tension relationship and improve systolic function.4,12 Other medications such as antiarrhythmic agents and inotropes have been used to improve symptoms. Digitalis is currently used with much caution in this population due to the risks of toxicity and multiple drug interactions.4,6 There have been conflicting studies regarding the ability of digitalis to improve exercise performance13,14 and it has been recommended only for those patients with more severe dysfunction.13 Inotropic agents, such as dobutamine, are commonly used for symptomatic relief for patients with severe symptoms, although it is considered a short-term effect.4 One interesting use of this medication has been to identify areas of hibernating myocardium that can predict functional capacity after exercise training.15

Since these patients have decreased cardiac pumping efficiency, they are prone to thromboembolism. Therefore, it is recommended that anticoagulation therapy be instituted.4,6,12 Some patients who demonstrate electrocardiographic abnormalities may also need pacemakers or implanted defibrillators.6

SURGICAL OPTIONS FOR CARDIOMYOPATHY

The current options for patients who don't respond to medical management for their cardiomyopathy include partial left ventriculectomy, cardiomyoplasty, mitral valve repair, implanted left ventricular assist devices (LVAD), laser revascularization, or cardiac transplantation. Since transplantation involves issues of donor shortage, complex medical monitoring, and severe lifestyle changes, it is available to only a small number of patients with cardiomyopathy.9

Dr. Batista, a Brazilian cardiac surgeon, has developed a controversial new procedure called a partial left ventriculectomy. A section of the dilated left ventricle is removed in order to restore a more optimal length-tension relationship of the muscle.9 Since 1994, this procedure has been performed in only a few locations on selected patients. However, reports of improved ejection fraction seen in the operating room immediately following resection are impressive.9 This procedure also involves repairing the mural valve to compensate for the change in position of the papillary muscles following resection of ventricular tissue.9 Currently, this procedure has demonstrated as much as 89.5% survival at 10-month follow-up.9 However, it is currently recommended that an LVAD be available for support, since up to 15% of patients required this device.9

Another procedure sometimes used to treat persons with cardiomyopathy is the dynamic cardiomyoplasty. In this procedure, a section of skeletal muscle, most commonly the latissimus dorsi, is wrapped around the heart to supplement the pumping action.9 The key to this procedure is implanting a cardiomyostimulator device to attempt to change the properties of the skeletal muscle to function more like the fatigue-resistant cardiac muscle.9 The skeletal muscle is stimulated when the device senses an R-wave from the myocardium. The principles underlying improved cardiac function are both improving contraction and preventing excessive dilation during filling.9 Outcomes seen with this procedure were a 12-month survival of 68%, improvements in New York Heart Association classification status, and increased ejection fraction. No improvements were seen in peak oxygen consumption.9 Studies are finding that patients with moderate disease have the best outcome, and thus this procedure should not be considered a substitute for transplantation, but a way to prevent disease progression.9

Mitral valve regurgitation is common in advanced dilated cardiomyopathy, due to the altered shape of the enlarged ventricle.9 Small studies of mitral valve repair have shown ventricular remodeling toward a more normal shape with accompanying improvement in functional classification and ejection fraction.9 It is currently unclear if this procedure should be considered an alternative to transplantation or a palliative procedure for those who are not transplant candidates.9

The use of LVADs originally was to extend life for those patients awaiting donor hearts. However, new evidence is suggesting that LVADs can play an important role in supporting patients with acute cardiomyopathy while awaiting resolution of the disorder.9 The theory of this procedure is to unload the heart and promote remodeling toward normal ventricular architecture.9 Also, permanent LVAD implantation, although not currently approved by the Food and Drug Administration, shows potential as an alternative to transplantation.9 Device-related infections, thromboembolism, and mechanical malfunction are the limiting factors in the long-term use of LVADs.9

The most recent surgical procedure to help manage patients with refractory ischemia seen in some patients with cardiomyopathy is the use of a laser to improve myocardial blood flow.16 Transmyocardial laser revascularization (TMLR) is a procedure that uses a laser to bore small channels through the myocardium, allowing blood from the ventricles to directly perfuse the epicardium. The TMLR is intended to improve myocardial perfusion and decrease angina in patients not treatable by angioplasty or bypass surgery.16 Early results are mixed. Some patients have improved their anginal symptoms, but some experimental evidence indicates the channels may not remain patent.16 Optimal indications and long-term results of TMLR remain to be seen.

EXERCISE IN CARDIOMYOPATHY

For many patients the presenting symptom of cardiomyopathy is a decrease in exercise capacity, thus exercise training is currently recommended as part of the comprehensive approach to the disorder.16-19 However, a search of literature in the last 5 years yielded only 5 studies regarding cardiomyopathy and rehabilitation. Thus, research regarding the effects of exercise in patients with cardiomyopathy is sorely lacking.

One of the most important concepts regarding exercise in these patients is the finding that ejection fraction is poorly correlated to exercise capacity.4,6,18,20,21 However, patients have been found to have abnormalities of other systems that affect exercise. For example, leg blood flow decreases while leg vascular resistance increases during exercise, counter to normal mechanisms.18 Skeletal muscle of persons with cardiomyopathy have also demonstrated abnormalities, such as atrophy of type I fibers, metabolic abnormalities, decreased aerobic enzyme levels, and altered ultrastructural makeup.14,18 Ventilatory abnormalities also have been seen with a higher ventilatory muscle response and respiratory muscle deoxygenation.18 Selective respiratory muscle training has been shown to decrease symptoms of dyspnea and improve exercise capacity.18,22

Some patients with cardiomyopathy have worsening symptoms with exercise testing or training. Patients who demonstrate decreased left ventricular filling pressure during exercise have a higher mortality23 and worsening of symptoms with exercise training.24 In addition, the dysfunction seen during exercise has been demonstrated to last for more than 24 hours following exercise cessation.25 However, some patients have been shown to improve filling pressures with exercise training.24,26 In a study of 36 subjects with dilated cardiomyopathy, a subgroup of 7 subjects who demonstrated a pattern of abnormal ventricular relaxation during doppler studies of exercise were seen to improve the most with an 8-week exercise program at 60% of maximal oxygen consumption performed 3 times per week for one hour.23

Improvements from exercise training are primarily peripheral adaptations such as increased muscle oxygen extraction, improved leg blood flow, reduced lactate levels, and increased cross-sectional leg muscle area.17,18 Some central adaptations, such as enhanced vagal tone, decreased sympathetic nervous system activity and decreased atrial natretic peptide levels have followed exercise training.18,21,27,28 Sullivan et al28 found reductions in resting and submaximal exercise heart rate and a 23% increase in peak oxygen consumption following a 4- to 6-month training program at 75% of peak oxygen consumption performed 4 times per week in 12 patients with severe left ventricular dysfunction. Coats et al27 found increased functional capacity, increased cardiac output and enhanced vagal tone following 8 weeks of home-based bicycle training in patients with chronic heart failure.

In addition, improvements in functional mobility (6minute walk)21 and health-related quality of life19-29,30 have been associated with training, even with patients who have very poor cardiac function. One component of decreased functional status in these patients is likely to be deconditioning due to a decrease in voluntary activities.19-21 Meyer and colleagues examined the effects of training and detraining in 18 hospitalized patients awaiting transplantation.21 They found 65% improvement in 6-minute walk distance and peak oxygen uptake increase of 2.6 ml/kg/min following a 3-week program of 15 minutes of stationary bicycling at 50% of maximum work capacity 5 times per week, treadmill walking and calisthenics performed 3 times per week. The improvements were subsequently lost following 3 weeks of activity restriction. They found the most improvement in those patients who had the lowest baseline function.

Exercise testing has become the gold standard for deciding if a patient can safely undergo cardiac transplantation.18 A minimum of 10 to 12 ml of oxygen consumed per kilogram of body weight per minute is required by many centers.18 For patients with this low level of aerobic fitness, cardiac rehabilitation has been successful in increasing oxygen consumption, and presumably, chance of survival.18 The 6-minute walk test has also been advocated to assess functional capacity and has been found to be a strong, independent predictor of morbidity and mortality.18

Patients with cardiomyopathy also have demonstrated deficits in strength; however, few studies have examined the effect of strengthening exercise on functional capacity.18 In a randomized controlled trial of patients following cardiac transplantation, Braith et al found twice-weekly strength training at 50% of subjects' 1-repetition maximum level was able to prevent the glucocorticoid-induced myopathy seen in the control group.31 This study shows promise for the safety and efficacy of strength training in persons with poor cardiac function and deserves more study. No studies were found that examined the effect of strengthening on patients with cardiomyopathy, although it has been recommended as part of an overall exercise prescription for elderly persons with heart failure.19

Exercise training has been shown to be beneficial for persons with cardiomyopathy. However, the use of cardiac rehabilitation in this population is currently limited by the decision of the Health Care Financing Administration not to reimburse cardiac rehabilitation for persons with chronic heart failure.16

CONCLUSION

Cardiomyopathy is a complex and poorly understood disorder that affects many patients each year. It is classified into 3 types-dilated, hypertrophic and restrictivebased on the pathophysiology and anatomical changes seen. Patients with cardiomyopathy can benefit from skilled exercise intervention to improve their functional ability and quality of life; however, there is a need for more research to quantify optimal exercise mode, intensity, duration, and frequency. Innovative surgical procedures for the management of cardiomyopathy show promise for improving the quality of life for these persons, but more study is needed in this area.

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23. Diaz RA, Obasohan A, Oakley CM. Prediction of outcome in dilated cardiomyopathy. Br Heart J. 1987;58:393-9.

24. Belardinelli R, Georgiou D, Cianci G, et al. Exercise training improves left ventricular diastolic filling in patients with dilated cardiomyopathy. Circulation. 1995;91 :2775-84.

25. Morikawa M, Sato H, Sato H, et al. Sustained left ventricular diastolic dysfunction after exercise in patients with dilated cardiomyopathy. Heart. 1998;80:263-9.

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27. Coats AJS, Adamapoulos S, Radaelli A, et al. Controlled trial of physical training in chronic heart failure: Exercise performance, hemodynamics, ventilation, and autonomic function. Circulation. 1992;85:211931.

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29. Tyni-Lenne R, Gordon A, Jansson E, et al. Skeletal muscle endurance training improves peripheral oxidative capacity, exercise tolerance, and health-related quality of life in women with chronic congestive heart failure secondary to either ischemic cardiomyopathy or idiopathic dilated cardiomyopathy. Am J Cardiol. 1997;80:1025-9.

30. Wielenga RP, Erdman RA, Huisveld IA, et al. Effect of exercise training on quality of life in patients with chronic heart failure. J Psychosom Res. 1998;45:459464.

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Anne K. Swisher, PT, MS1

Rachel Yeater, PhD2

Address correspondence to: Anne K. Swisher PT, MS, Assistant Professor, Division of Physical Therapy, West Virginia University, PO Box 9226, Morgantown, WV 26506-9226. Email: aswisher@wvu.edu

1Assistant Professor, West Virginia University Division of Physical Therapy, Morgantown, WV

2Professor and Chair, West Virginia University Division of Exercise Physiology, Morgantown, WV

Work performed at: Human Performance Laboratory and Mountain State Cystic Fibrosis Center, West Virginia University, Morgantown, WV

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