Introduction: Is CMR ready for Primetime?
Mitral regurgitation (MR) is the most common valvular heart disorder.
(1) About 9% of the general population aged more than 75 years in the
USA have MR. As the incidence of MR increases with age, the number of
patients with MR who require intervention and inpatient care will only
increase in the coming decades. (2) MR is generally divided into two
categories: primary organic MR, which occurs as a result of an
intrinsically abnormal mitral valve, and secondary or functional MR,
which develops secondary to left ventricular (LV) dysfunction or annular
dilatation prohibiting normal valve closure.(3,4) Differentiating
between these phenotypes of severe MR by imaging modalities is critical
to allow accurate diagnosis as well as guidance in choosing timing and
type of intervention.(5)
Untreated severe MR is associated with poor outcomes due to the adverse
consequences of long-standing volume overload on the left ventricle. It
can cause LV volume overload, which may lead to progressive dilatation
of the left ventricle and left atrium, heart failure, and pulmonary
hypertension.(5) Echocardiography
and CMR play a complementary role in the diagnosis and understanding the
mechanism of MR. They also help define prognosis along with the optimal
treatment strategies for MR. (6,7)
Decisions regarding surgical interventions, being mitral valve repair or
replacement, rely on symptomatology as well as the regurgitation
severity, LV ejection fraction (LVEF), and LV end‐systolic diameter
(LVESD).(8,9) The role of imaging is as follows: to identify the
etiology of the MR; to quantify the severity of the regurgitation; to
assess the response of the left ventricle to the volume overload; and to
determine the feasibility of durable repair.(4-7)
Transthoracic echocardiography (TTE) remains the first line modality per
ASE/ACC/AHA guidelines. The quantitative methods for assessment of MR
severity via TTE involves the assessment of several independent data
points as indicated in the ASE guidelines which includes, but is not
limited to, flow convergence-based effective regurgitant orifice area
(EROA) and regurgitant volume, pulse Doppler-based regurgitant volume,
and the vena contracta.(4,10-13) Many assumptions underlie the
assessment of MR by echocardiography and hence this assessment has
several important limitations which arise from mitral regurgitation
characteristics such as temporal change in orifice geometry, the
possibility of multiple jets, the direction of the jet itself, and the
ultrasound settings including angle dependence. (4, 10) In addition,
significant inter-observer and intra-observer variability in the
echocardiographic parameters of MR severity is a well-known limitation
of this modality. (10-14) What may be the most important limitation of
the echocardiographic assessment of MR is that there is no single
reproducible parameter for severity of regurgitation, and in fact the
assessment is reached by integrating multiple parameters which may be
discordant from each other. It is as a result of these limitations that
echocardiography often lacks accuracy as well as reproducibility in the
assessment of MR. (4)