European Journal of Echocardiography 2008 9(1):12-17; doi:10.1016/j.euje.2006.11.004
Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2007. For permissions please email: journals.permissions@oxfordjournals.org.
Segmental atrial contraction in patients restored to sinus rhythm after cardioversion for chronic atrial fibrillation: a colour Doppler tissue imaging study
Anita C. Boyd1,*,
Nelson B. Schiller2,
David L. Ross1 and
Liza Thomas1
1 Department of Cardiology, University of Sydney/Westmead Hospital, Darcy Road, Sydney 2145, NSW, Australia
2 Department of Medicine, Radiology and Anaesthesia, UCSF, California, USA
Received 30 October 2006; accepted after revision 4 November 2006; online publish-ahead-of-print 22 January 2007.
* Corresponding author. Tel: +61 02 98456795; fax: +61 02 98458323. E-mail address: anitaboyd{at}westgate.wh.usyd.edu.au
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Abstract
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Aims: There is little known about segmental atrial function in patients
with atrial arrhythmias. We evaluated segmental atrial contractility
using colour Doppler tissue imaging (CDTI) in patients with
chronic atrial fibrillation (CAF) who were successfully restored
and maintained in sinus rhythm (SR).
Methods and results: We compared the segmental atrial contractility in 39 CAF patients who were successfully cardioverted and maintained in SR for 6 months. Follow up echocardiograms were performed at baseline, 1 week, 1 month and 6 months and compared to a normal age matched cohort (n = 34). Using CDTI, mean peak velocities of atrial contraction were measured from annular, mid and superior segments of lateral and septal walls of the left atrium and right atrium in the apical four-chamber view. Segmental velocities from the posterior and anterior walls of the left atrium were measured from the apical two-chamber view. Segmental left atrial velocities improved over time in the CAF group, with the majority of the recovery occurring in the first month, but failed to normalise even at 6 months. In comparison, the right atrial velocities in the AF group had normalised at 1 month.
Conclusion: Patients with CAF have persistent segmental left atrial dysfunction even 6 months after restoration and maintenance of SR, though right atrial velocities appear to normalise. This differential recovery indicates that left atrial function remains subnormal in patients with CAF despite maintenance of SR, suggesting underlying atrial myopathy or fibrosis as a consequence of CAF.
Keywords: Echocardiography; Colour Doppler tissue imaging; Atrial fibrillation; Atrial segmental function
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Introduction
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Atrial fibrillation (AF) occurs in 0.4% of the general population,
increasing to 5% in those over 65 years of age.
1 AF results
in loss of effective atrial contraction and chamber dilatation
thereby decreasing cardiac function and increasing the risk
of thromboembolism. Direct current electrical cardioversion
(CV) is a common and effective treatment for restoration of
sinus rhythm (SR) in AF.
2,3 Numerous studies have analyzed various
echocardiographic parameters and reported a temporal improvement
in atrial function following CV.
4–6
Colour Doppler tissue imaging (CDTI) is a recently developed technique for the quantification of regional mean peak myocardial velocities. CDTI measures intrinsic myocardial contraction with low velocities (<10 cm/s) and high amplitudes (>40 dB). This method enables simultaneous acquisition of myocardial velocities in multiple segments of the myocardium in the same imaging view and permits offline measurements. CDTI has been used with high reproducibility to quantify regional left ventricular function,7,8 left and right ventricular function after atrial septal defect closure9 and left atrial appendage function.10–12 We have previously reported on the use of this technique to assess regional atrial function and the effect of age in a normal population.13
The aim of this study was to evaluate temporal improvement in segmental atrial contractility in patients restored to SR by direct-current CV. To our knowledge, this study is the first to describe segmental atrial function after restoration and maintenance of SR.
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Methods
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Study approval was obtained from the Committee for Human Research
at Westmead Hospital, Sydney, Australia, and all participants
provided written consent.
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Patient groups
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We studied patients with chronic AF (CAF,
n = 39) who were maintained
in SR for 6 months after CV and compared these to a normal age
matched cohort (normals,
n = 34). The normal subjects had no
history of ischaemic heart disease, significant valvular disease,
peripheral vascular or cerebrovascular disease, hypertension
or diabetes, and were not on cardioactive medications. Follow
up echocardiographic assessment was performed in the CAF group
at baseline (within 4 h after CV), 1 week, 1 month and 6 months
post CV.
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Colour Doppler tissue imaging
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Standard transthoracic echocardiography was performed according
to established clinical laboratory practice using the GE Vivid
5 system. Mitral inflow velocity was obtained by pulsed wave
Doppler examination at a sweep speed of 100 mm/s from the apical
four-chamber view by placing the sample volume at the tips of
the mitral leaflets. Peak velocity of atrial contraction in
late diastole (A-wave velocity) was measured as a traditional
parameter of atrial function. Segmental atrial contraction velocity
was measured offline (GE Echopac 6.2) from colour Doppler tissue
images of the atrium obtained in the apical four- and two-chamber
views, as previously described.
13 Real time colour Doppler was
superimposed on grey scale with a frame rate
110 fps. Special
attention was paid to the Doppler velocity range to avoid aliasing.
Briefly, the left atrium was divided into five segments in both
the apical four- (
Figure 1A) and two-chamber views (
Figure 1B).
The right atrium was divided into three segments (
Figure 1A).
Nine
x nine pixel sampling was used and a tissue velocity profile
throughout the cardiac cycle was displayed in each sample location.
The mean peak velocity of atrial contraction was measured in
each segment following the ‘p’ wave on the ECG and
two consecutive beats were averaged.
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Figure 1 Atrial segments from the two apical echocardiographic views. (A) Apical four-chamber view (1, septal annular segment; 2, septal mid segment; 3, superior segment; 4, lateral mid segment; 5, lateral annular segment; 6, lateral annular RA segment; 7, lateral mid RA segment; 8, superior RA segment). (B) Apical two-chamber view (9, posterior annular segment; 10, posterior mid segment; 11, superior segment; 12, anterior mid segment; 13, anterior annular segment).
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Statistical analysis
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All values are expressed as mean ± SD. Differences between
groups were examined by two-sample Student's
t-test. Differences
in gender between the two groups were assessed by chi-squared
analysis. Temporal assessment was performed by repeated measures
ANOVA and linear mixed effects model. Data were considered significant
if
P < 0.05. Data were analysed using SPSS (version 11.5,
SPSS Inc., Chicago, IL).
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Results
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A total of 73 patients were analyzed as two groups: patients
with CAF (
n = 39) and normal subjects (
n = 34). Mean values
for demographic variables of the two groups are listed in
Table 1.
The normal cohort was both age and heart rate matched to the
CAF group. There were differences in gender between the two
groups, however this did not reach statistical significance.
There were however significant differences between the two groups
in values of body surface area (BSA) and mean arterial pressure
(MAP), which were unavoidable.
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Atrial CDTI velocities (cm/s)
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The velocity of atrial contraction was highest in the annular
segments and lowest at the superior segments. The basal and
mid lateral contraction velocities were higher for both left
and right atria compared to the septum. Right atrial velocities
were higher than left atrial velocities.
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Temporal assessment after CAF
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All segmental atrial velocities significantly improved from
baseline to 1 week, 1 month and 6 months (
Table 2). The
majority of the improvement occurred between baseline and 1
month. Although an increase in segmental velocities was noted
between 1 and 6 months, this failed to reach significance. The
pattern of temporal improvement displayed by CDTI at the septal
annulus was mirrored by the traditional measure of atrial function,
the mitral inflow peak A-wave velocity (
Figure 2).
The improvement in lateral, posterior, and anterior annular
segments after 1 week and 1 month were comparable, while septal
annular improvement was significantly slower (
P = 0.004) than
the other sites (
Figure 3).
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Comparison of normals and CAF
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The normal cohort had significantly higher annular and mid atrial
contraction velocities in the left atrium compared to CAF cohort
at baseline, 1 week, 1 month and 6 months (
Figure 4,
Table 2).
There was a significant difference between the normals and CAF
at baseline for the superior segments, however at 1 and 6 months
no significant difference was noted between the two groups.
Right atrial velocities were significantly lower in the CAF
group at baseline and 1 week compared to normals, but right
atrial contraction velocities normalised at 1 month.
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Discussion
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We have demonstrated that CDTI is a simple, noninvasive technique
for quantifying segmental atrial contraction velocities in both
a normal population and in patients with atrial dysfunction.
CDTI can be used for serial follow up of atrial function following
therapeutic interventions.
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Traditional markers vs TDI
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A temporal improvement in atrial contractility with significant
atrial dysfunction (atrial stunning) immediately after CV was
noted. The maximum improvement in atrial contraction occurred
in the first month after restoration of SR in patients with
CAF, using both traditional measures of peak A-wave velocity
and CDTI. Previous studies have also demonstrated atrial stunning
14 with temporal improvement in atrial function using peak transmitral
A-wave velocity in the first 3–4 weeks following CV.
4–6 However the peak A-wave velocity from transmitral flow normalised
at 1 month.
5,15 In contrast, we have shown that although there
is improvement in intrinsic left atrial contractility it remains
permanently depressed in patients cardioverted and maintained
in SR from CAF compared to a normal population.
Traditional markers of left atrial function have used transmitral peak A-wave velocity, which measures blood flow velocity during atrial contraction. However, newly developed techniques, using tissue Doppler imaging (TDI), may provide a more accurate assessment of atrial function by measuring intrinsic atrial longitudinal contraction.16,17 It has been demonstrated that normal transmitral peak atrial velocity can be evident despite abnormal atrial contractile function as reported in patients with coronary artery disease,16 confirming that TDI markers of atrial function are more sensitive than traditional markers. CDTI has been previously used to quantify regional left ventricular function,7–9 left atrial appendage function,10–12 and regional atrial function.13 We have previously shown that septal TDI measures of A' velocity correlated with atrial fraction and atrial ejection force in a normal cohort.13
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Left atrial vs right atrial recovery
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We have demonstrated that in contrast to the permanently depressed
left atrial contractility, the right atrial function normalises
after 1 month, following restoration and maintenance of SR in
subjects with CAF. This differential recovery in atrial function
suggests that mechanical remodelling or underlying structural
disease caused by CAF may preferentially and permanently affect
the left atrium. This differential atrial dysfunction may also
be the reason for an increase in left atrial thrombi associated
with AF as compared to the occurrence of right atrial thrombi.
Differential atrial function has been previously described in
relation to stunning following CV for AF,
18 and atrial volumes
following atrial septal defect closure.
19,20
Previous studies have shown similar mechanical recovery of the atrium and the subsequent time course of such recovery after CV has been related to the duration of the preceding AF.6,21 Thus the persistently depressed left atrial mechanical function, despite restoration of ‘sinus rhythm’, may be a consequence of atrial mechanical remodelling due to preprocedural AF, pre-existing subclinical atrial myopathy or atrial fibrosis. This inherent inability of left atrial mechanical function to completely recover despite restoration and maintenance of SR may provide the substrate for the recurrence of AF in these individuals.
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Segmental left atrial contractility
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We have demonstrated a differential improvement in segmental
left atrial contractility through the use of CDTI. There was
comparable recovery in the lateral, posterior and anterior annular
segments, whilst recovery in the septal annular segment was
significantly slower than the other positions at both 1 week
and 1 month. The septal segments are relatively less mobile
as compared to the free walls, which may be the cause for the
slower improvement.
Velocities in the superior segments are low at baseline. This may in part represent the relative lack of mobility of the apical segments that are not likely to contribute significantly to longitudinal contraction. Further, as TDI is angle dependent, the contraction velocity obtained from the superior segments is likely underestimated. Regional differences in atrial function has only been reported between the left atrial body and appendage previously.22 This is the first report of the study of segmental atrial function in patients with CAF.
The study of regional or segmental atrial function may be useful in evaluating the success of surgical and catheter based ablation methods to treat AF. These techniques make lines of block within the atria to prevent re-entry circuits.23–26 CDTI may be useful in these instances to detect the lines of block as areas of decreased segmental contractility.
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Limitations
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CDTI is relatively immune to artifacts and noise but is angle
dependent. We tried to minimise the angle dependence of velocity
measurements by careful alignment of the ultrasound beam to
be parallel to the myocardial wall. Further studies using strain
and strain rate estimation may obviate some of the problems
related to cardiac translation and angle dependence. This study
only investigated longitudinal atrial function and did not take
into account radial atrial contractility. Normal subjects enrolled
had a detailed history taken. However a stress test was not
performed to evaluate exercise capacity or subclinical ischaemic
heart disease. The numbers in the present study are small and
thus a predictive value of these results for identifying arrhythmia
recurrences was not possible, however future studies are directed
towards this outcome.
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Conclusion
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CDTI of the atria can be used to quantify regional atrial contraction.
Patients with CAF have significant intrinsic left atrial dysfunction
even 6 months after restoration and maintenance of SR by cardioversion.
Right atrial segmental velocities appear to normalise at 1 month
as opposed to left atrial segmental velocities. This differential
recovery in left and right atrial function indicates that mechanical
remodelling or underlying structural disease associated with
CAF preferentially and permanently affects the left atrium.
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Abstract
Introduction
