Assessment of Ventricular Function by Ejection Fraction: A Major Limitation
CMR LVEF assessment of global ventricular function is accurate and reproducible and is consider the reference standard for evaluation of cardiac function 78. LVEF by CMR has become the gold standard test for assessing global function in acquired and congenital heart disease including DMD patients to monitor disease progression and treatment efficacy. Tandon et al reported on a large series of 335 DMD patients and concluded that LVEF by CMR decline with age and disease progression and is related to scar burden 79. The presence of global dysfunction by LVEF (define as < 55%) is however uncommon before 10 years of age (Fig. 2). The number of DMD patients with abnormal LVEF increases with age (Fig 3). This data suggest that, although LVEF is a good tool it may not be sensitive enough to detect occult cardiac dysfunction in younger DMD patients32, 33, 48, 53, 56, 80, 81. LVEF is late finding in the DMD-CM process when the heart no longer squeezes normally. The presence of DMD-CM is evident with the presence myocardial fibrosis (LGE) before age 10 years and increased with age (Fig 4) 33, 56. LVEF remains normal until more than 6 of 16 segments of the myocardium is affected with LGE79. As such, LVEF for global cardiac function is insensitive to alterations in regional contractility and may conceal underlying regional dysfunction due to the regional myocardial fibrosis seen in DMD-CM53, 54, 73. The lack of this ability means that regional contraction cannot be measure by traditional techniques like LVEF. Region dysfunction by myocardial strain (ε), which is the fractional change in the length of a small myocardial segment can be abnormal in the presence of normal LVEF and is a sign of subclinical cardiac dysfunction73, 82.