“How might I apply this information?”
Study of cardiomyopathy in Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) is increasingly important. Life expectancy in DMD is into the third, fourth, and fifth decades for some,1 as respiratory issues previously causing mortality are managed more successfully, and cardiac issues emerge as causes of mortality in DMD/BMD.2 Lack of correlation between skeletal and cardiac muscle involvement supports early cardiac evaluation.2 Cardiomyopathy, arrhythmias, abnormalities of calcium regulation, fibrosis, fatty infiltration, and conduction abnormalities typically progress to dilated cardiomyopathy with arrhythmias including ventricular tachycardia.2 Because of limited physical activity, symptoms of cardiomyopathy may not present clinically until cardiac involvement is advanced.2 Guidelines recommend early preventative management.3 Exercise concerns relate to metabolic and structural abnormalities including membrane instability, muscle fragility, and increased susceptibility to mechanical stress2 and nitric oxide abnormalities contributing to ischemia and muscle damage, especially during exercise.4 Cardiopulmonary exercise testing (CPET) showed moderate to severely reduced exercise capacity in all 9 participants, though 6 of the 9 had normal or mildly impaired functional capacity and motor function. This study supports the use CPET for individuals with DMD/BMD, who might have reduced exercise capacity even when functioning well, and supports early referral to cardiology for identification and preventative management of cardiomyopathy.
“What might I be mindful about when applying this information?”
Preliminary information does not yet offer support for use of CPET in exercise prescription, but in the future, as disease-modifying treatments may increase safe exercise capacity, assessments such as the CPET may be important in monitoring exercise.
Laura E. Case, PT, DPT, MS, PCS, C/NDT
Andrea S. Hartzell, PT, DPT, MHS
Durham, North Carolina
1. O'Brien L, Varadi R, Goldstein RS, Evans RA. Cardiac management of ventilator-assisted individuals with Duchenne muscular dystrophy. Chron Respir Dis. 2014;11(2):103–110.
2. Yilmaz A, Sechtem U. Cardiac involvement in muscular dystrophy: advances in diagnosis and therapy. Heart. 2012;98(5):420–429.
3. Romfh A, McNally EM. Cardiac assessment in Duchenne and Becker muscular dystrophies. Curr Heart Fail Rep. 2010;7(4):212–218.
4. Rando TA. Role of nitric oxide in the pathogenesis of muscular dystrophies: a “two hit” hypothesis of the cause of muscle necrosis. Microsc Res Tech. 2001;55(4):223–235.