Muscular dystrophy is the name given to a group of inherited diseases caused by mutations in different genes that regulate muscle structure and function. The condition is characterized by progressive muscle weakness and wasting.
In addition to skeletal muscles — the muscles used for movement — muscular dystrophy also can cause problems with the muscles of the heart, which pump blood through the body. The most common problems are cardiomyopathy (a disease of the heart muscle), cardiac arrhythmias (abnormal heart rhythms), and heart failure (the inability of the heart to adequately pump blood through the body).
Heart problems in different disease types
Duchenne muscular dystrophy
Virtually all people with Duchenne muscular dystrophy (DMD) will develop some degree of cardiomyopathy by the time they reach adulthood. The first signs of cardiomyopathy can usually be detected through medical tests as early as age 10.
Although cardiomyopathy is frequent in DMD, it is fairly common for symptoms to be delayed or absent because people with DMD tend not to be very mobile, so the heart generally is not strained by exercise.
As the disease progresses, the heart tissue tends to hypertrophy (enlarge), atrophy (waste away), and/or become fibrotic (scarred). Patients often will develop dysfunction of the left ventricle, which is the part of the heart that pumps oxygen-rich blood out to the body. Heart disease is the leading cause of death in DMD.
Becker muscular dystrophy
Cardiomyopathy also is common in people with Becker muscular dystrophy (BMD). It’s estimated that 60%–75% of BMD patients will develop clinically relevant cardiomyopathy, with an average age at onset in the late 20s. Nearly all people with BMD are estimated to have some form of heart disease, though it may not always be clinically detectable.
In some patients, cardiomyopathy may be the main manifestation of disease. Early on, BMD patients may develop dysfunction of the right ventricle — the portion of the heart that pumps blood over to the lungs to pick up oxygen. As the disease progresses, the left ventricle also may become dysfunctional.
Facioscapulohumeral muscular dystrophy
While some individuals, especially older patients, with facioscapulohumeral muscular dystrophy have been reported to develop heart disease, most people with this form of muscular dystrophy do not experience clinically meaningful heart involvement.
Emery-Dreifuss muscular dystrophy
Heart problems are common in people with X-linked Emery-Dreifuss muscular dystrophy. As the disease progresses, normal heart tissue gradually becomes more fatty and fibrotic, particularly in the atria (the parts of the heart that fill with blood before it pumps).
This can cause problems in the heart’s electrical circuitry, resulting in arrhythmias. The implantation of a pacemaker may help to manage these issues.
Limb-girdle muscular dystrophy
Limb-girdle muscular dystrophy comprises a group of conditions characterized by weakness in proximal (near-the-trunk) muscles. Certain types, particularly 2D, 2C, 2E, 2F, and 2I, have been linked to cardiomyopathy and other heart problems.
Myotonic dystrophies can cause a number of heart problems, most commonly cardiomyopathy, abnormal electrical activity, and arrhythmias. Myocardial myotonia, when the heart muscles do not relax normally, can also occur, and is considered the heart equivalent to how these diseases affect skeletal muscle.
Management and treatments
Several treatments can be used to improve heart function in patients with muscular dystrophy. These are summarized below.
ACE inhibitors and ARBs
ACE (angiotensin-converting enzyme) inhibitors and ARBs (angiotensin II receptor blockers) are two classes of medication that lower blood pressure by helping blood vessels to widen and relax. Lowered blood pressure means that the heart has to work less to pump blood through the body.
ACE inhibitors, such as lisinopril, captopril, and enalapril, work by preventing the ACE enzyme from producing angiotensin II, a signaling molecule that triggers blood vessels to narrow. ARBs, such as azilsartan medoxomil and losartan, block the binding of angiotensin II to its receptor proteins on the blood vessels, thereby preventing its action.
Beta blockers such as bisoprolol, carvedilol, and metoprolol act to inhibit the effects of the hormone adrenaline by preventing its binding to beta-adrenergic receptors. These medicines help the heart to relax and beat more slowly, so it has more time to fill and pump more efficiently.
Diuretics such as chlorothiazide, bumetanide, and amiloride lower blood pressure by helping the body to remove extra water and salt (sodium) in urine. This reduces the amount of fluid that’s in circulation, thereby reducing the pressure on the blood vessels.
Antimineralcorticoids such as eplerenone, spironolactone, and aldactone are a specific type of diuretic that act by blocking the action of the hormone aldosterone.
Cardiac resynchronization therapy
Cardiac resynchronization therapy is used to correct heart conduction issues. A pacemaker device that delivers electrical signals to the heart is implanted in the chest. In some cases, the device may contain an implantable cardioverter-defibrillator, which delivers stronger electrical shocks when the heart rhythm becomes dangerously erratic.
These devices prompt the heart chambers to contract in a normal, coordinated rhythm, which helps maximize the amount of blood pumped out of the heart.
Last updated on Jan. 10, 2022, by Marisa Wexler MS
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