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.