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.
Heart dysfunction and heart disease are commonly encountered in several types of muscular dystrophy. The most common problems are cardiomyopathy (disease of the heart muscle), cardiac arrhythmias (abnormal heart rhythms as a result of electrical conduction issues in the heart), and heart failure (the inability of the heart to pump blood adequately).
Early diagnosis and treatment of heart problems are critical because they can significantly affect daily activities and increase life expectancy.
Symptoms of heart disease
Heart problems in different muscular dystrophies
Heart disease in Duchenne muscular dystrophy (DMD) generally involves some degree of cardiomyopathy in all patients by age 18. The first signs of cardiomyopathy can be detected as early as age 10. Some patients show hypertrophic cardiomyopathy because of thickened heart muscles. The heart muscles become progressively fibrotic, leading to heart arrhythmias and eventually cardiomyopathy.
In Becker muscular dystrophy (BMD), nearly 40 percent of patients may be diagnosed with dilated cardiomyopathy where the left ventricle becomes enlarged and thin, and cannot pump blood properly, by age 30.
In X-linked Emery-Dreifuss muscular dystrophy (EDMD), conduction defects are common where there is impaired electrical conduction between the atrial and ventricle chambers of the heart. This causes atrial arrhythmias with symptoms of atrial fibrillation (irregular heartbeat) and flutter. Cardiomyopathy is less common in X-linked EDMD. These issues can be resolved by a pacemaker that reduces the incidence of sudden death.
In autosomal dominant EDMD, a progressive decrease of left ventricle function is seen in addition to arrhythmias and conduction defects. The incidence of sudden death due to ventricular arrhythmia is high.
In facioscapulohumeral muscular dystrophy (FSHMD), conduction abnormalities and cardiomyopathies are rare, but few cases of atrial arrhythmias are seen. However, the incidence of cardiac abnormalities is lower in FSHMD.
Patients with the autosomal dominant form of limb-girdle muscular dystrophy (LGMD) are more prone to arrhythmias and conduction issues rather than cardiomyopathies. While types 2A and 2B LGMD are not associated with significant heart complications, cardiomyopathy is common in type 2C LGMD patients with low incidence rates of arrhythmias.
Herat involvement is common in myotonic dystrophy type 1 (DM1) and is often the cause of death. Atrial flutter, atrial fibrillation, and atrial tachycardias (higher heart rate than normal) are noted in up to 25 percent of patients. Patients are generally monitored for syncope (temporary loss of consciousness because of insufficient blood supply to the heart) because of a high rate of sudden death in these patients. Patients with myotonic dystrophy type 2 (DM2) share similar traits to those with DM1 with frequent incidences of arrhythmias and syncope.
Management and treatments
There are several treatments available that can be used to improve heart function in patients with muscular dystrophy. These are summarized below.
ACE inhibitors and angiotensin 2 receptor blockers (ARBs)
ACE (angiotensin-converting enzyme) inhibitors such as lisinopril, captopril, and enalapril lower blood pressure by preventing the ACE enzyme from producing angiotensin 2, which narrows blood vessels and increases blood pressure. ARBs such as azilsartan medoxomil and losartan block the binding of angiotensin 2 to its receptor proteins on the blood vessels, thereby preventing its action. These medicines help the blood vessels leading from the heart to open wider, which allows the heart to pump blood throughout the body using less pressure.
Beta blockers such as bisoprolol, carvedilol, and metoprolol act by blocking 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). This reduces the blood volume, thereby reducing the pressure on the blood vessels.
Medicines such as eplerenone, spironolactone, and aldactone help lower blood pressure by blocking the action of the hormone aldosterone, thereby reducing the reabsorption of sodium and water, which also decreases blood volume.
Cardiac resynchronization therapy (CRT) is used to correct heart conduction issues. In CRT, a pacemaker device that delivers electrical signals to both ventricles (lower chambers of the heart) is implanted in the chest. In some cases, the device may contain an implantable cardioverter-defibrillator (ICD), which delivers stronger electrical shocks when the heart rhythm becomes dangerously erratic. These devices help the heart chambers contract at the same time and maximize the amount of blood pumped out of the heart.
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