Download Tissue Mitral Annular Displacement—A Novel Descriptor of Global

Technology & Services Section
Tissue Mitral Annular Displacement—A Novel Descriptor of
Global Left Ventricular Function
a report by
A r u m u g a m N a ra y a n a n , M D , Je f f re y C H i l l , R D C S a n d G e ra rd P A u r i g e m m a , M D
Non-invasive Laboratory, University of Massachusetts Memorial Healthcare and the Division of Cardiology, Department of Medicine, University of Massachusetts
Medical Scool, Worcester, Massachusetts
Systolic ejection of the left ventricle (LV) is a complex co-ordinated action,
which involves fiber shortening in multiple directions along with systolic
torsion (see Figure 1). These actions produce wall thickening and blood
displacement, thus generating a stroke volume. The most commonly used
index of LV contractile function is the ejection fraction (EF), which represents
volume strain—a change in volume divided by initial volume. EF, by
definition, is ‘internally’ normalized, and does not require correction for
body size. Therefore, the EF of a normal–sized adult can be compared with
that of an infant and, likewise, systolic function in small, experimental
animals can be compared with that of humans. Furthermore, a large volume
of published literature supports the clinical utility of the EF in clinical
medicine. However, the EF does not convey information about regional
function,1 which is important in diagnosing coronary artery disease.
Furthermore, chronic changes in left ventricular geometry also affect
myocardial function, but may not be detected by the EF. Such geometric
changes are common among patients with hypertension, aortic stenosis and
diastolic heart failure.2
How Prevalent is Hypertrophic Remodeling Among Patients
with Diastolic Heart Failure?
A recent survey of patients admitted to the New York area hospitals with
heart failure and a normal EF showed that left ventricular hypertrophy was
present in over 80% of such patients.3 Our laboratory has devoted much
attention to the study of LV systolic function in hypertensive heart disease,
valvular heart disease and diastolic heart failure—three conditions that are
commonly associated with hypertrophic remodeling. As noted above, a
Dr Gerard P Aurigemma has been director of Non-invasive
Cardiology at UMass Memorial Health Care, Worcester, MA
since 1992. He is currently Professor of Medicine and
Radiology at the University of Massachusetts Medical School
and has directed its cardiology fellowship program since
1990. He has served as course director for the ASE Board
Review Course for several years and has edited a board exam
review CD on the behalf of the ASE. He has also served on
the editorial board of several cardiology journals, and on the
board of directors of the American Society of Echocardiography (ASE). Dr Aurigemma is the
author of over 100 peer-reviewed original articles and reviews on left ventricle (LV) function and
other topics in cardiology, and has served as an associate editor of the textbook Cardiology and
editor of a monograph on stress echocardiography. He has a long-standing interest in LV systolic
and diastolic function in hypertension, valvular heart disease, and diastolic heart failure, and has
devoted much of his career to applying non-invasive imaging techniques to the study of these
disorders. He completed his fellowship in cardiovascular diseases at the Hospital of the
University of Pennsylvania in 1987, and joined the faculty at the University of Massachusetts
Medical School that year. He is a graduate of Harvard College (1975) and Harvard Medical
School (1979) and he completed his medical residency at the University of California at San
Francisco and as Chief Medical Resident there following residency.
© TOUCH BRIEFINGS 2007
Figure 1: The Mechanisms Underlying the Generation of Stroke
Volume in Systole.
The final output, namely stroke volume, represents the product of co-ordinated activities
circumferential fiber shortening and long axis shortening, which lead to wall thickening and
displacement of blood in the cavity.
common theme has been that the EF may not demonstrate systolic
dysfunction in situations in which the LV has undergone geometric
remodeling. We believe that identifying such systolic function
abnormalities is important, as they may help the clinician to identify
individuals at high risk for a poor outcome. However, to demonstrate
these subtle, and most likely, pre-clinical abnormalities, sophisticated
measures of intra-mural function are required. With the prevalence of
hypertension cases considered to be as high as 40 million in the US, and
with rates of obesity and type II diabetes rising, identifying subclinical LV
dysfunction might prove to be important in attenuating the rise in heart
failure cases. The available techniques for measuring myocardial function
each have their strengths and weaknesses
M-mode Techniques Applied to the Study of Myocardial Function
In order to identify pre-clinical abnormalities in systolic function in
hypertensives, over a decade ago we studied a group of patients with
concentric remodeling of the LV all of whom had a normal EF.4 We
demonstrated that both long axis and circumferential shortening, in these
individuals with concentric remodeling, was abnormal despite a normal EF
and a normal endocardial fractional shortening. These results supported
prior work utilizing magnetic resonance imaging (MRI) tagging for regional
function analysis. However, at the time we had no direct ultrasound
measure of either circumferential or longitudinal shortening of the LV.
Accordingly, we derived circumferential shortening using the ‘modified’
midwall fractional shortening (FSmw) technique, and longitudinal
1
Technology & Services Section
contraction using an M-mode derived technique. The longitudinal shortening
measured as mitral annular descent (MAD) was indexed for the LV length (see
Figures 2 and 3). These measures were time-consuming and indirect, and it is
clear that direct measures of long-axis shortening might be preferable. In the
mid-1990s, such measures became available with tissue Doppler techniques.
Figure 2: M-mode Technique Used to Measure Long Axis Function.
mostly to measure regional, as opposed to global LV systolic function.
Standard tissue Doppler imaging allows a Doppler sample volume—
region of interest—to be placed in any myocardial structure as long as it
is reasonably parallel to the ultrasound beam. For this reason, regional
shortening and lengthening are usually measured in the longitudinal, and
more recently, in the radial direction. Myocardial longitudinal strain,
expressed as a percentage, throughout the cardiac cycle can be derived
from the velocity gradient, or strain rate, between any two points.
Conceptually, it should be kept in mind that strain rate represents the
rate of systolic deformation and strain represents the normalized extent
of deformation in this region of interest.
Advantages/Disadvantages of Doppler Imaging in the Study of
Myocardial Function
Tethered Myocardium
Strain rate imaging has the advantage of measuring a vector component of
regional myocardial contraction independent of the effect of tethering and
translation. However, analysis of regional function by velocity and/or
displacement measurements is bedeviled by inability to discriminate between
actively contracting and ‘tethered’ myocardium. In this situation, an akinetic
segment may demonstrate motion if it is pulled by an adjacent segment that
is functioning normally.
The M-mode cursor is placed in the mitral annulus, and the systolic excursion is measured. The
descent of the annulus toward the apex is related to the integrity of systolic function. If the
distance between the annulus and the chest wall at end diastole is known, the mitral annular
descent (MAD) as a fraction of the initial length represents ‘strain’. This principle was exploited
in the use of mitral annular descent to derive and index long axis function. Newer techniques,
such as Tissue Mitral Annular Displacement, permit direct measurement of MAD and can be
normalized to an initial length to derive long axis shortening.
Figure 3: Bar Graph of Longitudinal and Circumferential Shortening in
Normal and Left Ventricular Hypertrophy.
The results of this study demonstrate that shortening abnormalities exist in patients with left
ventricular hypertrophy and normal ejection fraction (65%). There was a similar reduction in both
circumferential shortening at the midwall and long axis shortening, derived from mitral annular
descent.
Tissue Doppler Techniques in the Study of Myocardial Function
Fundamentally, the tissue Doppler technique is based on measurements of
regional length and velocity, which when normalized to initial length, can be
used to derive strain and strain rate. Tissue Doppler techniques have been used
2
Need for Normalization
It is also important to realize that neither velocity nor displacement
measurements are normalized for segment length or size. Systolic
displacement and velocity of a given region would presumably be greater in
the heart of a larger subject than a smaller subject. The absence of
consideration of such normalization is a limitation of studies of long axis
shortening in patients with diastolic heart failure, published to date. The
principles of normalization have been applied in a variety of clinical and
experimental studies; such results expressed in dimensionless terms, provide
more consistent and reliable functional information than non-normalized data
(expressed, in centimeters or cm/sec). For example, some investigators have
concluded that myocardial velocities at the base of the heart are substantially
greater than those at the mid-ventricular level. If, however, these velocities had
been normalized for the initial diastolic length, the velocities would have been
similar in these two regions. The tissue Doppler methods, providing strain rate
and its integral strain, would likely provide more reliable information than the
non-normalized data found in these studies. Strain and strain rate
measurements are also appropriately normalized and are therefore more
accurate than standard tissue Doppler velocity imaging, in assessing regional
myocardial function.
Speckle Tracking—Advantages Compared with Tissue Doppler
Techniques
Speckle tracking imaging is a novel systolic function technique that may
permit better quantification of regional left ventricular function than
more traditional tissue Doppler methodology. This technique, which is
based on B-mode signal intensity, is angle independent and thereby
permits the measurement of strain vectors that are not parallel to the
ultrasound beam. Hence, speckle tracking imaging for the first time,
permits direct ultrasound measurement of circumferential, longitudinal
as well as radial strain (see Figure 4).5
US CARDIOVASCULAR DISEASE 2007
Tissue Mitral Annular Displacement—A Novel Descriptor of Global Left Ventricular Function
Figure 4: Speckle Tracking Imaging in a Normal Subject.
individually along with the displacement of the midpoint between the
two annular ROIs. Displacement of the midpoint towards the apex is
directly expressed in millimeters. This displacement, as we have
hypothesized with tissue Doppler methods, is likely to be confounded by
individual ventricular size and, in particular, LV length (individuals at
extremes of height). In order to normalize for the LV length, the software
permits an expression of the total displacement as a ratio of the
longitudinal chamber length at end-diastole. The image also provides
parametric imaging of mitral annulus excursion, both in systole as well as
diastole (See Figure 5).
Following previous work with TMAD, DeCara et al. evaluated MAD in
comparison with biplane EF using the method of discs.6 They found a
Figure 6: Tissue Mitral Annular Displacement in Dilated Cardiomyopathy.
Circumferential strain obtained from the short axis image at the papillary muscle level using 2-D
speckle imaging.
Tissue Mitral Annular Displacement—a Novel Technique for
Measuring Global Systolic Function
We believe that Tissue Mitral Annular Displacement (TMAD) introduces a
potentially important descriptor to the field of systolic function analysis.
TMAD utilizes speckle tracking technique to measure strain vectors.
Longitudinal shortening is measured in the apical four chamber view, where
the annulus and apex are well-visualized. Images are obtained using 2-D
Doppler technology with a harmonic transducer, and stored as digital cine
loops. The native data format is analyzed using off-line QLAB software
(Philips Medical Systems). Three regions of interest (ROI) or points are
placed—two at the mitral annulus where it meets the lateral and septal
leaflets, and the third ROI at the apex. These ROIs are tracked during cardiac
motion. The motion of the annular ROIs toward the apex is measured
Figure 5: TMAD in a Normal Subject.
The annular midpoint shows an excursion of 13.0mm and a long axis shortening of 14.9%.
US CARDIOVASCULAR DISEASE 2007
The annular midpoint shows an excursion of 1.5mm and a long axis shortening of 1.4%. The
displacement curves for the septal and lateral region of interest are not only unequal, but their
peaks are quite dispersed in time (0.23sec).
Figure 7: Tissue Mitral Annual Displacemnt in Left Ventricular
Hypertrophy with a Normal Ejection Fraction.
The annular midpoint shows an excursion of 8.3mm and a long axis shortening of 9.2%. This
example describes the role of longitudinal shortening in detecting abnormal myocardial function
in the presence of a normal ejection fraction.
3
Technology & Services Section
significant correlation between both measures of systolic function, MAD
and biplane EF, in 65 subjects that included both normal, as well as patients
with LV dysfunction, and some with regional wall motion abnormalities.
The interobserver variability for the MAD technique was low.
Potential Advantages of Tissue Mitral Annular Displacement
TMAD is a rapid and reproducible method of determining global systolic
function. It can be performed on most, if not all patients, as the mitral
annulus is an easily detectable echo-dense structure. As shown by
DeCara and colleagues, it is likely that it correlates with ventricular
systolic function even in individuals with hypertrophy, and may exclude
the effect of LV geometry. It is plausible that TMAD measurements are
likely to be altered in patients with regional abnormalities involving either
the septum or the lateral wall—one more than the other. However,
TMAD might enable a better description of global function in the face of
1.
2.
3.
4
Aurigemma GP, Zile MR, Gaasch WH, Contractile behavior of the
left ventricle in diastolic heart failure – with emphasis on regional
systolic function. Circulation. 2006;113(2):296–304..
Aurigemma GP, Gaasch WH, Clinical practice. Diastolic heart
failure. N Engl J Med. 2004;351(11):1097–105.
Klapholz M, Maurer M, Lowe AM, et al,. Hospitalization for
heart failure in the presence of a normal left ventricular
4.
5.
regional abnormalities as it samples the motion of both annuli.
Conclusions/Clinical Applications
An ideal method of measuring systolic function would be rapid, sensitive
and reproducible. Ultrasound technology has expanded to the
remarkable point where it is now possible to measure regional
myocardial strain and strain rate, non-invasively in humans with and
without heart disease. In the future, such measurements will provide a
more complete description of left ventricular regional and global
function. Regional myocardial strain and strain rate should be particularly
useful in the evaluation of spatial and temporal non-uniformity, not only
in patients with coronary heart disease but, also in those with
cardiomyopathy or valvular heart disease■
Disclosures
Research grant support from Omron Healthcare, Toshiba Medical, Novartis, and Philips Medical Systems.
ejection fraction: results of the New York Heart Failure
Registry, J Am Coll Cardiol. 2004;43(8):1432–8.
Aurigemma GP, Silver KH, Priest MA, et al. Geometric changes
allow normal ejection fraction despite depressed myocardial
shortening in hypertensive left ventricular hypertrophy. J Am Coll
Cardiol. 1995;26(1):195–202.
Hurlburt HM, Aurigemma GP, Hill JC et al. Direct ultrasound
6.
measurement of longitudinal, circumferential, and radial strain
using 2-dimensional strain imaging in normal adults,
Echocardiography. 2007; in press.
DeCara JM, Toledo E, Salgo IS, et al, Evaluation of left
ventricular systolic function using automated angleindependent motion tracking of mitral annular displacement, J
Am Soc Echocardiogr, 2005;18(12):1266–9.
US CARDIOVASCULAR DISEASE 2007