A review study into the impact that Duchenne muscular dystrophy (DMD) has on the heart proposes a new way of classifying cardiac damage caused by DMD, and outlines potential ways of managing treatment to prevent heart failure.
The sweeping review, “Cardiac Involvement Classification and Therapeutic Management in Patients with Duchenne Muscular Dystrophy,” was published in the Journal of Neuromuscular Diseases.
DMD is caused by a mutation in the dystrophin gene, which encodes for an essential muscle protein. The mutation causes no dystrophin protein to be produced, so that muscle cells lose their stability and eventually die — including muscles of the heart. These dying muscles are progressively replaced by scar tissue, so that the heart has to work harder to pump oxygen through the body and eventually results in heart failure.
Complications associated with DMD include arrhythmias and conduction disorders, or problems with the propagation of electrical impulses through the heart that control its beating.
Skeletal muscles are also affected in DMD, reducing patients’ ability to be mobile. Symptoms normally associated with heart muscle disease, such as dizziness and loss of consciousness, are rarely seen in these people. For this reason, it’s very important that heart health in DMD patients be monitored regularly via electro cardiograms (ECG) and echocardiography.
Classification of heart involvement in DMD
Based on clinical, ECG and cardiac magnetic resonance (CMR) findings, the study’s authors constructed a four-stage clinical-radiological classification of heart involvement in DMD:
- Stage 1: Patients who are asymptomatic, or who do not show any symptoms of heart impairment either clinically or in ECG and CMR tests.
- Stage 2: Tachycardia, in which the heart beats faster than normal while at rest.
- Stage 3L Peripheral edema, where the heart in no longer efficiently pumping fluid to the lungs. Fluid accumulates in the legs and feet, causing swelling.
- Stage 4: Anasarca, characterized by extreme generalized edema or widespread swelling of the body.
A good classification of heart involvement in DMD can help clinicians better understand disease pathology and assess how well therapeutic interventions to treat heart problems are working.
Heart problems in DMD, the review noted, can either be treated with drugs or mechanically by using devices.
Drugs used to treat DMD heart problems mainly consist of angiotensin converting enzyme (ACE) inhibitors, such as perindopril, and beta blockers such as Zebeta (bisoprolol), Coreg (carvedilol), and Lopressor (metoprolol).
ACE inhibitors widen and dilate blood vessels, increasing the volume of blood that the heart pumps and decreasing blood pressure. ACE inhibitors also have anti-scarring properties and have been shown to delay the onset of heart muscle disease in patients.
Beta blockers inhibit the effect of epinephrine (also known as adrenaline), a hormone involved in the “fight or flight” response. They allow the heart to beat more slowly and with less force, and they dilate blood vessels — all of which lowers a person’s blood pressure. Research demonstrates that when used together with ACE inhibitors, beta blockers can have a beneficial effect on heart function in DMD.
Recent studies also show that Inspra (eplerenone), a blood pressure lowering medication, can also aid heart function in children with DMD when used together with ACE inhibitors or beta blockers.
Steroid therapy is also thought to possibly have a positive impact on heart muscle, reducing the risk of heart failure, the review said.
Finally, Raxone (idebenone), a drug that increases energy output from the mitochondria (the energy powerhouses of cells) has been associated with a slight improvement in heart function. Raxone use in DMD patients is currently being evaluated in clinical trials.
Treatment with devices
Two main types of mechanical treatments are used to manage heart problems in DMD patients. These are cardiac resynchronization therapy (CRT) and noninvasive ventilation.
In CRT, a small medical device called a defibrillator is placed in the heart and sends tiny electrical signals to muscles to synchronize the heart. It is thought that CRT can benefit patients with symptomatic heart failure. But technical difficulties associated with implanting a defibrillator, as well as a risk of infection, need to be carefully considered.
Noninvasive ventilation is the therapy of choice for respiratory failure in DMD. These patients usually require long-term mechanical ventilation, especially in later stages of the disease.
“Heart failure is a significant complication in DMD,” the authors concluded, adding that how well the heart is working should be assessed each year in all DMD patients older than age 10.
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