Body mass index (BMI) and blood pressure are modifiable factors that could help to slow heart deterioration in patients with Duchenne muscular dystrophy (DMD), according to a retrospective study.
The study, “Increased Blood Pressure and Body Mass Index as Potential Modifiable Factors in The Progression of Myocardial Dysfunction in Duchenne Muscular Dystrophy,” appeared in the Journal of Neuromuscular Diseases.
DMD, the most common type of muscular dystrophy, is caused by the loss of dystrophin, a protein necessary for the stabilization of muscle cells.
Loss of dystrophin in the heart causes progressive cardiomyopathy, overall damage to the heart muscle that weakens it.
In spite of its high prevalence, cardiac damage in DMD patients is often only found after it is already in the advanced stages. Little is known about the factors that might help slow its progression or predict its occurrence.
The most affected part of the heart is the left ventricle, which develops progressive fibrosis (tissue scarring), leading to dysfunction and dilatation. An increased effort to the left ventricle may worsen the condition.
Hypertension and obesity alter the function of the left ventricle (LV) because they increase the afterload — the pressure against which the heart must work to eject blood — in patients without DMD. So these factors could potentially increase the progression of heart damage in DMD patients.
To determine if blood pressure, steroid use, and high BMI were risk factors associated with heart damage in children with DMD, researchers retrospectively analyzed the blood pressure and BMI values of 65 children with DMD, between 4 and 18 years old, obtained in 273 visits.
The median follow-up was five years. Most patients (97%) were on a steroid intermittent regime during follow-up.
Researchers found that systolic blood pressure (pressure in the blood vessels when the heart beats) was higher than normal in all age groups and that it increased with BMI and decreased with the use of heart medication.
Heart medication use in children with DMD usually only starts after the first symptoms of heart damage appear. However, results of this study indicate that preventive use of heart medication could slow the progression of heart damage.
Diastolic blood pressure (pressure in the blood vessels when the heart rests) was higher in patients younger than 10 and tended to decrease with time. Overall, 22-39% of patients between 4 and 16 years old, and 17% of 16-year-old patients had high blood pressure, while no 17-year-olds had this condition.
BMI increased at younger ages and reached its peaks at ages 13-14, then started to decrease. Patients with a higher prevalence of obesity (43%) were between 12 and 14 years old.
“The relationship between higher BMI and reduced GLS [measure of ventricle deformation] in our study suggests that increased BMI may exert an early, negative, effect on left ventricular function in DMD children as well. BMI may therefore be an important modifiable factor in the deterioration of cardiac function in DMD,” the researchers wrote.
Researchers found no relationship between steroid usage and BMI or blood pressure. However, the high number of patients taking these medications might have masked an existing relationship.
“Increased BMI, but not systolic blood pressure, was related to early myocardial deformation,” they said. “Thus, mild increases in afterload caused by high blood pressure may not affect LV function in an early stadium, but only after long-term exposure.”
These data suggest that controlling BMI, and to a lesser extent heart blood pressure, could prevent the appearance of heart damage in patients with DMD.