Therapy Insight: Cardiovascular Complications Associated With Muscular Dystrophy

Elizabeth M McNally; Heather MacLeod

Disclosures

Nat Clin Pract Cardiovasc Med. 2005;2(6):301 

In This Article

Summary and Introduction

The muscular dystrophies are commonly associated with cardiovascular complications, including cardiomyopathy and cardiac arrhythmias. These complications are caused by intrinsic defects in cardiomyocyte and cardiac conduction system function, and by the presence of severe skeletal muscle disease, which also contributes to cardiac dysfunction. Unlike the skeletal muscle degenerative process, for which treatment options are currently limited, therapy is available for the cardiovascular complications that accompany muscular dystrophy. New therapies for skeletal muscle degeneration are moving into clinical trials and, ultimately, into clinical practice. These therapies are expected to also improve the cardiac function, longevity and wellbeing of muscular dystrophy patients.

The muscular dystrophies are disorders of progressive skeletal muscle degeneration. Although often considered to be diseases of childhood, adult forms of muscular dystrophy occur and represent a spectrum of disease. Muscular dystrophies are a genetically heterogeneous group of disorders; there are at least 21 different monogenic causes of muscular dystrophy, and cardiovascular complications are commonly associated with some subtypes.[1]

In normal skeletal muscle, there is a robust regenerative response that leads to the formation of new myofibers, but in individuals with muscular dystrophy this regenerative response does not meet the demands created by the degenerative process. Muscular dystrophy is most commonly diagnosed by examining a muscle biopsy, although for some forms of muscular dystrophy, genetic testing is sufficient. Dystrophic muscle biopsy samples show the following features: an abnormally large distribution of myofiber size, indicative of an enhanced degeneration and regeneration; an increased number of myofibers with centrally placed nuclei, also thought to reflect increased regeneration; and replacement of myofibers by adipose and connective tissue. It is the replacement of myofibers by fibrofatty infiltration that effectively reduces myofiber mass and produces muscle weakness. The muscular dystrophies are a subclass of the myopathies, which are broadly defined by muscle weakness arising from a defect in the muscle itself. The processes that underlie muscular dystrophy and myopathy often adversely affect cardiac muscle. In this context, cardiomyocyte degeneration is a known complication of muscular dystrophy and might lead to both cardiomyopathy and disturbances of the cardiac conduction system.

At present, there is no cure for the skeletal muscle degeneration that occurs in muscular dystrophies and myopathies. There are, however, data to support various medical and device-based approaches to management of cardio myopathy, and the cardiomyopathy associated with muscular dystrophy should not be an exception. Cardiomyopathy in the muscular dystrophies most typically takes on a dilated form with enlarged dimensions. Over time, reduced ventricular systolic function can develop. Global or regional impairment of ventricular function can occur in the presence or absence of symptoms of congestive heart failure. Cardiac rhythm disturbances can contribute significantly to the morbidity and mortality associated with muscular dystrophy, and should be paid special attention. In this review we describe briefly the mechanisms of the major forms of muscular dystrophy with cardiac involvement and discuss how to manage patients with these disorders.

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