Download Left atrium phasic volume assessment: Its application in stroke patients

Available online at www.sciencedirect.com
Journal of the Chinese Medical Association 76 (2013) 535e536
www.jcma-online.com
Editorial
Left atrium phasic volume assessment: Its application in stroke patients
Stroke is one of the most common causes of morbidity and
mortality. The survivors of stroke have a risk of recurrence that
leads to long-term disability and death. Embolism with a
cardiac origin, however, is difficult to document, but accounts
for approximately 20% of ischemic stroke. The emboli are
most likely to originate either from atria, ventricles, or cardiac
valves. The left atrial appendage (LAA) as an embryological
remnant functioning as a reservoir is the prevalent site of
thrombi in patients with atrial fibrillation (AF) or rheumatic
mitral valve disease. The specific LAA morphology with or
without organized atrial systole is independently associated
with an increased risk of stroke.1 Beyond morphology, LAA
functions, indexed by spontaneous echocardiographic contrast
and the peak flow velocity, are independently associated with
higher thromboembolic risk in patients with AF.
Despite the well-established methodology of measuring
LAA structures and functions, the assessment depends mostly
on invasive transesophageal echocardiography. Complete
structural and functional evaluations of the LAA are inherently
prone to substantial variability during data acquisition, particularly pulsed-wave Doppler interrogation, because of anatomical challenges. The left atrium (LA) attached by LAA is
easily evaluated by transthoracic echocardiography. The
morphological changes of LA were a significant predictor of
AF recurrence after transcatheter ablation. Regardless of the
presence of AF or valvular abnormalities, LA enlargement is
independently associated with cardiovascular events, particularly ischemic stroke, across various populations and
genders.2,3
The LA modulates left ventricle (LV) filling by serving as a
reservoir or a conduit delivering blood from pulmonary veins
to LV as well as an active contractile chamber in late diastole
and a suction source in early systole.4 Growing evidence
suggests an association between LA enlargement and ventricular, arterial, and arrhythmic disorders.5,6 In addition, LA
dysfunction occurs in patients with patent foramen ovale,
which is associated with cryptogenic stroke. An enlarged LA
may be a marker of the complexity of other cardiovascular
conditions that could also increase stroke risk.
Conventionally, echocardiographic assessment measuring
maximum anteroposterior dimension on M-mode or 2D
echocardiography in the parasternal long axis used extensively
in clinical practice is an inaccurate presentation of the true
LA size or volume; in particular, enlargement occurs
asymmetrically in the medialelateral or superioreinferior
axes.7,8 The American Society of Echocardiography, in conjunction with the European Association of Echocardiography,
recommended either an ellipsoid model or the Simpson’s
method for LA volume measurement.9 LA volume evaluated
by recently developed three dimensional (3D) echocardiography has more favorable agreement in testeretest, intraobserver, and interobserver variations than other
echocardiographic techniques.10 The major disadvantage of
the 2D or 3D echocardiographic methodology is that procedures are time consuming and thus not practical in clinical
practice. Moreover, the size of LA varies during the cardiac
cycle.4 Total LA volume is a composite of phasic volume
changes reflecting LA dynamic functions.4,11 The LA passive
emptying volume represents early diastolic filling; the LA
conduit volume is the amount of blood transited from pulmonary veins to LA whereas mitral valve is open; the LA
active emptying volume represents blood actively propelled
into LV.11
Velocity vector imaging (VVI) is a novel image quantitative
analysis technique using a speckle tracking echocardiographic
method that assesses details of regional and global myocardial
functions. VVI involves complex signal processing but
requires only a single frame tracing of endocardial borders for
an easy assessment of the timeevolume information.12 VVI
provided a highly correlated evaluation of LA volume with a
reduction in time of measurement as compared with the conventional 2D methodology. Furthermore, VVI assesses LA
phasic function beyond maximum and minimum LA volume
and LAA function.13,14
In this issue of the Journal of the Chinese Medical Association, Dr Chen and his colleagues prospectively enrolled
healthy controls and patients with various types of stroke in
sinus rhythm. The phasic LA volumes were assessed by VVI
and were compared across 20 controls and 87 stroke
patients.15 The LA function assessed by pulmonary venous
flow was of no significant difference among healthy controls
and stroke patients of all types. However, LV diastolic function
was impaired in stroke patients. In spite of similar maximum
LA volume, minimum LA volume was elevated in the stroke
patients. Compared to controls, patients with stroke had
impaired LA reservoir function as well as depressed passive
emptying function whereas the active emptying function had
greater contribution in LV filling. The same observation
1726-4901/$ - see front matter Copyright Ó 2013 Elsevier Taiwan LLC and the Chinese Medical Association. All rights reserved.
http://dx.doi.org/10.1016/j.jcma.2013.06.007
536
Editorial / Journal of the Chinese Medical Association 76 (2013) 535e536
occurred in stroke patients as the elevated mitral A indicated
an increased LA contractile function in the setting of LV
diastolic dysfunction. LA phasic functions were not different
in the subtypes of stroke. The authors concluded that their
findings suggest that functional changes of LA may occur
without significant structural changes.
There are several points that need to be addressed. First, LA
volume assessed by VVI has not been compared to the gold
standard indexed by cardiac magnetic resonance imaging or
computed tomography. Previous analyses indicate that the
VVI method tends to overestimate maximum LA volume and
to underestimate minimum LA volume.12 Second, VVI analyses were performed utilizing the 4-chamber view. However,
the conventional 2D echocardiography using the biplane
analysis is more accurate for LA volume assessment. In
addition, the LA volumes presented in this study were not
indexed to the measure of body size, which are preferred by
the guideline.9 Third, the contribution of LA phasic function to
LV filling is dependent on diastolic properties.4 Besides reservoir and contractile functions, LA conduit function accounts
for 35% of LV filling in the normal heart and decreases in
abnormal LV relaxation. The conduit function was not evaluated in the current study. Finally, in spite of atrial phasic
function assessed by volume changes, the current information
indicates that maximum and minimum LA volume occurring
prior to mitral valve opening and closure is associated with the
development of adverse cardiovascular outcomes.4,8
References
1. Di Biase L, Santangeli P, Anselmino M, Mohanty P, Salvetti I, Gili S,
et al. Does the left atrial appendage morphology correlate with the risk of
stroke in patients with atrial fibrillation? Results from a multicenter study.
J Am Coll Cardiol 2012;60:531e8.
2. Kizer JR, Bella JN, Palmieri V, Liu JE, Best LG, Lee ET, et al. Left atrial
diameter as an independent predictor of first clinical cardiovascular events
in middle-aged and elderly adults: the Strong Heart Study (SHS). Am
Heart J 2006;151:412e8.
3. Kohsaka S, Sciacca RR, Sugioka K, Sacco RL, Homma S, Di Tullio MR.
Electrocardiographic left atrial abnormalities and risk of ischemic stroke.
Stroke 2005;36:2481e3.
4. Abhayaratna WP, Seward JB, Appleton CP, Douglas PS, Oh JK, Tajik AJ,
et al. Left atrial size: physiologic determinants and clinical applications. J
Am Coll Cardiol 2006;47:2357e63.
5. Pritchett AM, Mahoney DW, Jacobsen SJ, Rodeheffer RJ, Karon BL,
Redfield MM. Diastolic dysfunction and left atrial volume: a populationbased study. J Am Coll Cardiol 2005;45:87e92.
6. Vaziri SM, Larson MG, Lauer MS, Benjamin EJ, Levy D. Influence of
blood pressure on left atrial size. The Framingham Heart Study. Hypertension 1995;25:1155e60.
7. Pritchett AM, Jacobsen SJ, Mahoney DW, Rodeheffer RJ, Bailey KR,
Redfield MM. Left atrial volume as an index of left atrial size: a
population-based study. J Am Coll Cardiol 2003;41:1036e43.
8. Tsang TS, Abhayaratna WP, Barnes ME, Miyasaka Y, Gersh BJ,
Bailey KR, et al. Prediction of cardiovascular outcomes with left atrial
size: is volume superior to area or diameter? J Am Coll Cardiol
2006;47:1018e23.
9. Lang RM, Bierig M, Devereux RB, Flachskampf FA, Foster E,
Pellikka PA, et al. Recommendations for chamber quantification: a report
from the American Society of Echocardiography’s Guidelines and
Standards Committee and the Chamber Quantification Writing Group,
developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc
Echocardiogr 2005;18:1440e63.
10. Jenkins C, Bricknell K, Marwick TH. Use of real-time three-dimensional
echocardiography to measure left atrial volume: comparison with other
echocardiographic techniques. J Am Soc Echocardiogr 2005;18:991e7.
11. Leung DY, Boyd A, Ng AA, Chi C, Thomas L. Echocardiographic evaluation of left atrial size and function: current understanding, pathophysiologic correlates, and prognostic implications. Am Heart J 2008;156:
1056e64.
12. Valocik G, Druzbacká L, Valocikova I, Mitro P. Velocity vector imaging to
quantify left atrial function. Int J Cardiovasc Imaging 2010;26:641e9.
13. Ogawa K, Hozumi T, Sugioka K, Iwata S, Otsuka R, Takagi Y, et al.
Automated assessment of left atrial function from time-left atrial volume
curves using a novel speckle tracking imaging method. J Am Soc Echocardiogr 2009;22:63e9.
14. Tamura H, Watanabe T, Nishiyama S, Sasaki S, Wanezaki M, Arimoto T,
et al. Prognostic value of low left atrial appendage wall velocity in patients
with ischemic stroke and atrial fibrillation. J Am Soc Echocardiogr
2012;25:576e83.
15. Chen CW, Chen SY, Tung RN, Chen YT, Chiang YY, Hsu HY. Changes of
left atrial functional indexes in ischemic stroke patients. J Chin Med Assoc
2013;76:564e9.
Kang-Ling Wang
Chern-En Chiang*
General Clinical Research Center, Taipei Veterans
General Hospital, Taipei, Taiwan, ROC
Division of Cardiology, Taipei Veterans
General Hospital, Taipei, Taiwan, ROC
School of Medicine, National Yang-Ming University,
Taipei, Taiwan, ROC
*Corresponding author. Dr. Chern-En Chiang, General
Clinical Research Center, Taipei Veterans General Hospital,
201, Section 2, Shih-Pai Road, Taipei 112, Taiwan, ROC.
E-mail address: [email protected] (C.-E. Chiang)