Background
The objective of this study was to investigate myocardial deformation of the left atrium (LA) assessed by two-dimensional speckle tracking echocardiography in patients with permanent atrial fibrillation (AF) and its value for risk stratification for stroke.
Methods
We recruited 66 consecutive patients with permanent AF who were referred to our echocardiography laboratory for evaluation. These patients were divided into two groups according to the presence of previous stroke or not.
Results
Peak positive longitudinal strain (LASp) during atrial filling, peak strain rate in the reservoir phase of LA (LASRr), and peak strain rate in the conduit phase (LASRc) were identified from LA strain and strain rate curves. The ratio of peak early filling velocity (E) of mitral inflow to early diastolic annulus velocity (E’) of the medial annulus (E/E’) was calculated. LASp (10.44% ± 4.2% vs. 15.69% ± 5.1%, P < . 001), LASRr (1.09 ± 0.27 1/s vs. 1.37 ± 0.32 1/s, P = .001), and LASRc (−1.28 ± 0.38 1/s vs. −1.62 ± 0.43 1/s, P = .002) were significantly lower in patients with AF with stroke than those without stroke. By multivariate analysis controlling for age, LA volume index, and left ventricular ejection fraction, LASp (OR 0.787, 95% CI, 0.639–0.968, P = .023) and LASRr (OR 0.019, 95% CI, 0.001–0.585, P = .023) were independently associated with stroke but not LASRc, E’, and E/E’ ratio.
Conclusion
Decreased LASp and LASRr were independently associated with stroke in patients with permanent AF.
Atrial fibrillation (AF) is the most common arrhythmia and increases risk of stroke and mortality from myocardial infarction and heart failure. The echocardiographic parameters associated with an elevated risk of embolism are increased left atrium (LA) dimension, decreased LA appendage (LAA) flow velocity, and proof of thrombi or spontaneous echo contrast during transesophageal echocardiography. Although transesophageal echocardiography is a useful method for predicting stroke and deciding on anticoagulation therapy, it is a semi-invasive method and cannot be used as widely as transthoracic echocardiography. A novel approach to quantify regional left ventricular (LV) function from routine gray-scale two-dimensional echocardiographic images, known as speckle tracking two-dimensional strain echocardiography, calculates myocardial strain independently of angle of incidence and has recently been validated against sonomicrometry and tagged magnetic resonance imaging. Speckle tracking echocardiography has also been used for the assessment of LA function. Our recent study showed that decreased LA strain and strain rate assessed by speckle tracking echocardiography were associated with paroxysmal AF. The feasibility of two-dimensional speckle tracking echocardiography for measuring LA deformation in patients with paroxysmal and persistent AF was documented in a recent study, and the LA deformation was inversely related to LA wall fibrosis, as demonstrated by delayed enhancement on magnetic resonance imaging. The objective of this study was to investigate LA deformation assessed by two-dimensional speckle tracking echocardiography in patients with permanent AF and its value for risk stratification for stroke.
Materials and Methods
Study Population
We recruited 79 consecutive patients with permanent AF who were referred to our echocardiography laboratory for evaluation from June to November in 2009. Permanent AF was diagnosed according to the guidelines of the American College of Cardiology, the American Heart Association, and the European Society of Cardiology. Patients with mitral stenosis ( n = 3) and inadequate imaging ( n = 10) were excluded, and 66 patients were included. Patients were carefully evaluated for the presence of ischemic stroke. Stroke was defined by a history of hospital admission and positive image studies from brain computed tomography. All study patients had ischemic stroke; patients with hemorrhagic stroke were excluded. The stroke risk of our patients was assessed by assigning one point each for the presence of congestive heart failure, hypertension, age ≥75 years, and diabetes mellitus, and assigning two points for a history of stroke or transient ischemic attack (CHADS 2 score). The study was approved by the research ethics committee of our hospital, and informed consent was obtained from all subjects.
Echocardiography
Standard echocardiography was performed with Doppler studies (Vivid 7, GE-VingMed, Horten, Norway) with a 3.5-MHz multiphase array probe in subjects lying in a left lateral decubitus position. The LV volume and ejection fraction were measured by the two-dimensional biplane method of discs according to the recommendations of the American Society of Echocardiography. LV mass was measured by the M-mode method. Transmitral Doppler flow velocity was obtained from the apical four-chamber view, and peak early filling velocity (E) was recorded. Pulse tissue Doppler imaging was obtained from the medial annulus, and peak systolic annulus velocity (S) and early diastolic annulus velocity (E’) were measured. The E to E’ ratio (E/E’) was used as an index for LA pressure. Two-dimensional images were acquired from apical four- and two-chamber views for three cardiac cycles and digitally stored with a frame rate of 50–90 frames per second. The images were analyzed off-line by computer software (EchoPac 08, GE-VingMed).
Measurement of LA Volume and Emptying Fraction
LA volume was measured by the biplane area-length method from two-dimensional echocardiography. The maximal LA volume during LV systole (LAVs) and the minimal LV volume during LV diastole (LAVd) were obtained. LA total emptying fraction (LATEF) was calculated as [(LAVs – LAVd)/LAVs] × 100% as total LA function. Measurements were repeated three times in each subject, and the average was used for analysis. LA size was represented by LA maximal LAVs and indexed by body surface area (LA volume index [LAVI]).
Measurement of LA Strain and Strain Rate by Speckle Tracking Echocardiography
The endocardial border was manually defined using a point-and-click technique. An epicardial surface tracing was automatically generated by the system, creating a region of interest, which was manually adjusted to cover the full thickness of the myocardium in the systolic frame. The width of the smallest region of interest was 8 mm. Before processing, a cine loop preview was used to confirm if the internal line of the region of interest followed the LA endocardial border throughout the cardiac cycle. Time-strain and time-strain rate plots were produced automatically by the software. We identified peak positive strain (LASp) and strain rate (LASRr) during ventricular systole as an index for LA reservoir function, and peak negative conduit strain rate (LASRc) in LV early filling was identified from the strain rate curve ( Figures 1 and 2 ). We further divided the LA wall into eight segments, including basal septal, middle septal, basal lateral, and middle lateral segments on four-chamber view and basal inferior, middle inferior, basal anterior, and middle anterior segments on two-chamber view. The average of LASp, LASRr, and LASRc of eight segments was used for analysis. In our echocardiography laboratory, intraobserver and interobserver variability were 6.8% and 8.9% for LA strain and 3.3% and 6.2% for LA strain rate, respectively.
Statistics
Differences between the groups were compared with the Student t test for continuous variables or the chi-square test for categoric variables. Multiple logistic regression analysis was used for independent factors. All data are presented as the mean ± SD. A P value of less than .05 was considered statistically significant. All analyses were performed with SPSS 13.0 for Windows (SPSS Inc., Chicago, IL).
Results
Twenty patients (30%) had a history of stroke. The clinical characteristics did not show any significant differences between patients with and without previous stroke among the those with AF ( Table 1 ). The mean age was 78.10 ± 8.14 years in patients with stroke and 74.96 ± 9.70 years in those without stroke ( P = .210). The CHADS 2 score was significantly higher in patients with stroke than those without stroke (2.0 ± 0.7 vs. 1.5 ± 0.8, P = .021). For the LA parameters, LASp (10.44% ± 4.2% vs. 15.69% ± 5.1%, P < . 001), LASRr (1.09 ± 0.27 1/s vs. 1.37 ± 0.32 1/s, P = .001), and LASRc (−1.28 ± 0.38 1/s vs. −1.62 ± 0.43 1/s, P = .002) were significantly reduced in patients with AF with stroke than those without stroke ( Table 1 ). There were no differences in LAVI and LATEF between patients with or without stroke. By multivariate analysis controlling for age, LAVI, and LV ejection fraction, LASp (OR 0.787, 95% CI, 0.639–0.968, P = .023) and LASRr (OR 0.019, 95% CI, 0.001–0.585, P = .023) were independently associated with stroke but not LASRc, E’, and E/E’ ratio ( Table 2 ). The area under receiver operating characteristic (ROC) curves for diagnosis of stroke in patients with AF was 0.661 for CHADS 2 score, 0.806 for LASp, 0.748 for LASRr, and 0.732 for LASRc ( Figure 3 ). By using LASp <13.5% for diagnosis of stroke, the sensitivity was 80% and specificity 63%. By using LASRr <1.40 1/s for diagnosis of stroke, the sensitivity was 75% and specificity 43%. In patients with a lower CHADS 2 score (CHADS 2 score <2), there were no significant differences in rates of stroke between patients with LASp ≥13.5% and LASp <13.5% (12.5% vs. 27.3%, P = .332). However, in patients with high CHADS 2 score (CHADS 2 score ≥2), those with LASp <13.5% had a significantly higher rates of stroke than those with LASp ≥13.5% (61.9% vs. 12.5%, P = .002) ( Figure 4 ).
| AF with stroke ( n = 20) | AF without stroke ( n = 46) | P value | |
|---|---|---|---|
| Age (y) | 78 ± 8 | 75 ± 10 | .210 |
| Male (%) | 8 (40) | 30 (65) | .057 |
| Hypertension (%) | 15 (75) | 27 (59) | .206 |
| Diabetes mellitus (%) | 8 (40) | 12 (26) | .309 |
| Smoking (%) | 2 (10) | 9 (20) | .304 |
| Hypercholesterolemia (%) | 3 (15) | 8 (17) | .754 |
| Using antiplatelet agent (%) | 6 (30) | 22 (48) | .135 |
| Using anticoagulants (%) | 5 (25) | 4 (9) | .090 |
| BSA (m 2 ) | 1.70 ± 0.18 | 1.69 ± 0.21 | .940 |
| BMI (kg/m 2 ) | 27.2 ± 3.7 | 25.4 ± 6.1 | .368 |
| LVEDVI (mL/m 2 ) | 36 ± 131 | 33 ± 8 | .481 |
| LVESVI (mL/m 2 ) | 16 ± 10 | 13 ± 7 | .260 |
| LVEF (%) | 59 ± 12 | 64 ± 12 | .152 |
| LV mass index (g/m 2 ) | 96.9 ± 18.0 | 109.4 ± 51.1 | .323 |
| E (cm/s) | 110.3 ± 22.1 | 103.6 ± 33.7 | .459 |
| E’ (cm/s) | 7.3 ± 1.6 | 8.7 ± 2.7 | <.001 |
| E/E’ | 15.2 ± 4.6 | 12.4 ± 4.7 | .051 |
| LA volume index (mL/m 2 ) | 75 ± 22 | 71 ± 35 | .774 |
| LA total emptying fraction (%) | 16 ± 8 | 19 ± 11 | .167 |
| LASp (%) | 10.44 ± 4.23 | 15.69 ± 5.08 | <.001 |
| LASRr (1/s) | 1.09 ± 0.27 | 1.37 ± 0.32 | .001 |
| LASRc (1/s) | −1.28 ± 0.27 | −1.64 ± 0.43 | .002 |
| Heart rate (beats/min) | 99 ± 22 | 94 ± 24 | .408 |
| CHADS 2 score | 2.0 ± 0.7 | 1.5 ± 0.8 | .021 |
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