Clinical & Medical Imaging - Juniper Publishers
Abstract
Left ventricular hypertrophy (LVH) is a frequently
diagnosed cardiac condition, which may result from physiological
adaptation as well as from chronic pressure overload in various
etiologies. Its differentiation has important prognostic implications
for the patient. However, in clinical practice the identification of the
underlying cause of disease is challenging. Myocardial contraction
fraction (MCF) as an easily available parameter has the ability to offer
additional diagnostic and prognostic information on LVH. The goal of
this mini review is to provide a comprehensive overview of MCF
performance in LVH assessed by cardiac magnetic resonance (CMR).
Keywords: Myocardial contraction fraction, Left ventricular hypertrophy, Cardiac magnetic resonance, Cardiac amyloidosis
Intrоductiоn
Left ventricular hypertrophy (LVH) is a common
condition and associated with a poor cardiovascular prognosis [1,2].
Various etiologies cause LVH and their differentiation has prognostic
implications for the patients. Physiological adaptation to chronic
pressure overload in conditions such as aortic stenosis or arterial
hypertension (AH) present the most common cause of LVH. In addition,
genetically determined hypertrophic cardiomyopathy (HCM) as well as
infiltrative myocardial disease, such as cardiac amyloidosis (CA), may
also result in apparent LVH. In clinical practice, the non-invasive
measurement of LVH assessed by two-dimensional (2D) M-mode
echocardiography leads to the diagnosis of LVH. However, the
echocardiographic differentiation of the underlying disease is not
perennially feasible by echocardiography alone and patients are referred
to cardiac magnetic resonance (CMR) for further diagnostic evaluation.
CMR is the modality of choice for the quantitative assessment of
ventricular mass and myocardial tissue characterization using Late
gadolinium enhancement (LGE) images as well as T1 mapping with
calculation of extracellular volume (ECV) [3]. Both techniques have been
introduced for identification of myocardial fibrosis. Different pattern
of fibrosis have been reported according to the underlying etiology
[4-6]. However, the assessment of LGE as well as ECV requires the
injection of contrast agents, which holds the risk of
gadolinium-associated nephrogenic systemic fibrosis in patients with
severe renal dysfunction. Especially, patients with CA suffer from renal
failure and application of gadolinium-based contrast agents is often
limited. Furthermore, tissue characterization may not represent enough
information on functional abnormalities in LVH, especially subtle
regional or global dysfunction for disease detection. Therefore,
additional parameter for characterization of LVH are desirable. The goal
of this mini review is to provide a comprehensive overview of
myocardial contraction fraction (MCF) diagnostic and prognostic
performance in LVH assessed by CMR.
Discussion
Introduction of myocardial contraction fraction (MCF)
MCF is an easily available quantitative marker,
dictated from standard cine CMR images, without the need for contrast
agents or specific post-processing software. MCF is a simple imaging
parameter, reflecting the relationship between stroke volume (SV) and
left ventricle (LV) mass. It is calculated by dividing
LV SV (LV enddiastolic volume - LV endsystolic volume) by LV
myocardial volume and multiplicated by 100. LV myocardial
mass divided by the mean density of myocardium of 1.05g/ml
presents LV myocardial volume (Figure 1).
MCF reference values are defined in a large cohort of an
age- and gender-matched healthy population [7]. The normal
MCF mean values are higher in women (155 ± 18.7 %) than in
men (126.6 ± 21.2%). These data consistent with Framingham
Heart Study data [8]. Furthermore, the study demonstrated an
association of higher MCF values with cardiovascular events.
MCF measured by different modalities
The first description of MCF exists from King et. al. and
introduces MCF as a novel marker for investigating myocardial
performance in LVH [9]. The estimation of MCF, as a ratio of
SV to myocardial volume, is performed by freehand contours
and 3D echocardiographic LV reconstruction algorithms.
Echocardiography measurements of LV mass by M-mode or 2D
echocardiography based on geometric assumptions has been
hampered by poor accuracy, especially when compared to CMR as
the accepted gold [10]. Major advantage of CMR is accuracy and
reproducibility by using 3D approach. Even 3D echocardiography
shows only limited performance compared to CMR, suffering
from substantial variability and underestimation [11]. CMR is
considered the reference standard for LV mass measurements
[12,13]. Therefore, MCF derived from CMR images may present
a more accurate and reproducible parameter than from 3D
echocardiography.
Diagnostic performance of MCF in LVH
In a recent published study, we could demonstrate that
MCF has a good diagnostic accuracy to identify LVH and
discriminate heart failure patients with CA from patients with
other forms of LVH [7]. Therefore, we analyzed CMR images of
a heterogenous study population consisted of patients with CA,
HCM, hypertensive heart disease (HHD). The diagnostic accuracy
of MCF was compared to that of left ventricular ejection fraction
(LVEF) and mass index. The results demonstrated a significant
reduction of MCF values in LVH. Thereby, MCF performed better
than LVEF in discriminating LVH from controls. In addition, MCF
outperformed standard functional marker, such as LVEF and LV
mass index, in discrimination of LVH etiologies. A cut-off value
for MCF < 50% was identified for patients with high probability
for CA. Similar to our analysis, a study by King et al presented
lower values of MCF in patients with LVH compared with normal
subjects [9]. The echocardiographic MCF measurements was
performed in a heterogeneous group with various pathologies
and controls. The authors concluded that MCF may be useful
in assessing differences in myocardial performance in other
patients with LVH. In both studies the decrease in MCF indicated
an abnormal LV function, although LVEF remained normal
even in advanced stages because the progressive reduction in
ventricular capacitance. Therefore, measurement of LVEF alone
may not give a complete representation of the complex cardiac
dysfunction especially in LVH.
Prognostic performance of MCF amyloidosis
After identification of MCF as a discriminator for CA, the
prognostic value of MCF was studied in a separate population
of systemic immunoglobulin light chain (AL) amyloidosis [14].
Seventy-four subjects with biopsy-proven AL amyloidosis and
LGE pattern characteristic for CA were analyzed. The median
follow-up was 41 months. The results showed a reduced
transplant-free survival and higher rates of death in AL patients
with lower MCF values. In addition, the determination of MCF
could further risk stratify subjects with AL amyloidosis. Related
results were achieved in an additional study by Tendler et al.
[15]. The authors proved the prognostic value of MCF in CA in
standard 2D echocardiography and concluded the superiority
of MCF to LVEF in predicting overall survival among patients
with AL amyloidosis. The same method for MCF calculation was
utilized by Rubin et al. in 30 subjects with wild-type or mutant
ATTR from the THAOS registry. The recent published data could
also demonstrate superiority of MCF to LVEF in predicting
mortality [16]. These few investigations existing are indicating
that MCF is a relevant prognostic marker in CA.
Conclusion
MCF calculated by CMR has a good diagnostic accuracy
compared with LV mass and it presents a great prognostic marker
in patients with CA. MCF is easily determined from standard cine
CMR images, without the need for specific sequences, contrast
agents or post-processing software. MCF remains as a routinely
available clinical marker with a strong potential. However, further
studies of MCF performance are required before it becomes part
of clinical routine in the evaluation of LVH.
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