In patients with severe mitral regurgitation (MR) referred for cardiac surgery, left atrial (LA) remodeling and enlargement are accompanied by mechanical stress, mediated cellular hypertrophy, and interstitial fibrosis that finally lead to LA failure. Speckle tracking echocardiography is a novel non–Doppler-based method that allows an objective quantification of LA myocardial deformation, becoming useful for LA functional analysis. We conducted a study to evaluate the relation between the traditional and novel atrial indexes and the extent of ultrastructural alterations, obtained from patients with severe MR who were undergoing surgical correction of the valvular disease. The study population included 46 patients with severe MR, referred to our echocardiographic laboratory for a diagnostic examination before cardiac surgery. The global peak atrial longitudinal strain (PALS) was measured in all subjects by averaging all atrial segments. LA tissue samples were obtained from all patients. Masson’s trichrome staining was performed to assess the extent of the fibrosis. The LA endocardial thickness was measured. A close negative correlation between the global PALS and grade of LA myocardial fibrosis was found (r = −0.82, p <0.0001), with poorer correlations for the LA indexed volume (r = 0.51, p = 0.01), LA ejection fraction (r = 0.61, p = 0.005), and E/E′ ratio (0.14, p = NS). Of these indexes, global PALS showed the best diagnostic accuracy to detect LA fibrosis (area under the curve 0.89), and it appears to be a strong and independent predictor of LA fibrosis. Furthermore, we also demonstrated an inverse correlation between the global PALS and LA endocardial thickness (r = −0.66, p = 0.0001). In conclusion, in patients with severe MR referred for cardiac surgery, impairment of LA longitudinal deformation, as assessed by the global PALS, correlated strongly with the extent of LA fibrosis and remodeling.
Recently, speckle tracking echocardiography (STE), an echocardiographic technique that uses standard B-mode images for the analysis of myocardial deformation, has extended its application to the study of the left atrium. Speckle tracking echocardiographic analysis allows an excellent assessment of the atrial deformation profile during an entire cardiac cycle, closely following the LA physiology. Considering the limitations of the classic indexes of LA function, assessment of LA strain using STE might represent a relatively rapid and easy-to-perform technique to explore LA function, because of its semiautomated and angle-independent nature and its off-line processing. Hence, the parameter of LA longitudinal strain (peak atrial longitudinal strain [PALS]) becomes the first parameter useful for functional analysis of the left atrium. The aim of our study was to evaluate the correlation between LA longitudinal function calculated using STE and the histopathologic findings obtained through the analysis and anatomic study of LA biopsy specimens obtained from patients with severe mitral regurgitation (MR), undergoing surgical correction of valvular disease.
Methods
Patients with severe MR, who were referred to our echocardiographic laboratory for a diagnostic examination before cardiac surgery from September of 2011 to March of 2012, were included in the present study. MR was graded using the Doppler quantitative method and, according to the American Society of Echocardiography criteria, was defined as severe if the mitral regurgitant fraction was >50%. To be eligible, all patients were required to have no arterial hypertension, diabetes mellitus, overt coronary artery disease (defined by ≥1 of the following: a history of effort angina, acute coronary syndrome, or revascularization procedures; evidence of a positive exercise stress test; segmental wall abnormalities at echocardiography), present atrial fibrillation, atrial flutter, or other major arrhythmias, hypertrophic cardiomyopathy, left bundle branch block, pacemaker implantation, heart transplantation, a history of cerebrovascular events, inadequate acoustic windows, previous mitral valve replacement, and no other valvulopathy findings. Samples of the LA free wall were obtained from each patient during mitral valve surgery. The tissue samples were subsequently prepared for histopathologic examination.
All subjects gave their written informed consent for participation in the present study. All work was in compliance with the Declaration of Helsinki.
Echocardiographic studies were performed using a high-quality echocardiograph (Vivid 7, GE, Waukesha, Wisconsin), equipped with a 2.5-MHz transducer. The subjects were studied in the left lateral recumbent position. Measurements of the left ventricular (LV) and LA dimensions, LV ejection fraction, and diastolic LV filling velocities were made in accordance with the current recommendations of the American Society of Echocardiography. The LV ejection fraction, measured using Simpson’s method, was used as a standard index of global LV systolic function. The ratio between the peak early (E) and late (A) diastolic LV filling velocities was used as the standard index of LV diastolic function.
LV longitudinal function was explored using pulsed tissue Doppler imaging, placing the sample volume at the level of the mitral lateral annulus from the apical 4-chamber view. The peak systolic (S′), early diastolic (E′), and late diastolic (A′) annular velocities were obtained. S′ was considered as a relatively load-independent index of LV longitudinal systolic function. The E/E′ ratio was also calculated and used as a reliable index of the LV filling pressure. M-mode measurements of mitral annular plane systolic excursion was performed by placing the cursor perpendicular to the lateral site of the annulus.
For speckle tracking analysis, apical 4- and 2-chamber views images were obtained using conventional 2-dimensional gray-scale echocardiography, during breath hold and with a stable electrcardiographic recording. Care was taken to obtain true apical images using standard anatomic landmarks in each view and not to foreshorten the left atrium, allowing a more reliable delineation of the atrial endocardial border. Three consecutive heart cycles were recorded and averaged. The frame rate was set at 60 to 80 frames/second. The analysis of files recorded was performed off-line by a single experienced and independent echocardiographer, who was not directly involved in the image acquisition and had no knowledge of the other echocardiographic parameters, using a commercially available semiautomated 2-dimensional strain software program (EchoPac, GE, Milwaukee, Wisconsin). As previously described, and as stated in the current American Society of Echocardiography/European Association of Echocardiography Consensus, the PALS was measured at the end of the reservoir phase and was calculated by averaging the values observed in all LA segments (global PALS) and by separately averaging the values observed in the 4- and 2-chamber views (4- and 2-chamber average PALS). In patients in whom some segments were excluded because of the impossibility of achieving adequate tracking, the PALS was calculated by averaging the values measured in the remaining segments. The reproducibility and feasibility of speckle tracking measurement of LA longitudinal strain has been previously reported by studies conducted in our echocardiographic laboratory.
Regarding the histopathologic analysis, samples of the LA free wall, measuring about 1 × 0.5 cm each, were obtained during cardiac surgery from patients undergoing mitral valve surgical intervention for severe MR secondary to mitral valve prolapse. The samples for histopathologic examination were fixed in 10% buffered formalin, embedded in paraffin, and cut into slices of 4 μm thickness for hematoxylin-eosin and Masson’s trichrome staining. For Masson’s staining, the slices were dewaxed with xylol (2 steps for 2 minutes each and soaked in a series of a gradient concentrations from 99% to 95% alcohol). All slices were washed in distilled water and put in a solution of hematoxylin for 3 minutes. Subsequently, color change was performed with lithium carbonate. The slices were washed in pure water and colored with red panceau staining (oven at 30°C for 20 seconds at 45 kW). Next, the slices were put into acid water and phosphomolybdic acid for 1 minute. The last passage included the addition of green light and washing with acid water. The extent of fibrosis was assessed in the sections collected. The ratio of the fibrotic area to the total surface area of each section was used to assess the degree of LA fibrosis (percentage) as (fibrosis area − total area) × 100.
Concerning statistical analysis, the data are shown as the mean ± SD. p Values <0.05 were considered statistically significant. Pearson’s correlation coefficients were calculated to assess the relations between the continuous variables. The sensitivity and specificity were calculated using standard definitions, receiver operating characteristic curves were constructed, and the area under the curve was calculated for the prediction of LA fibrosis >50%. Multiple regression analysis was performed to explore the independent determinants of LA fibrosis. Included in the model were age, gender, body mass index, systolic blood pressure, diastolic blood pressure, effective regurgitant orifice area, systolic pulmonary artery pressure, LV ejection fraction, LA area, LA indexed volume, LA ejection fraction, and global PALS. Analyses were performed using the Statistical Package for Social Sciences software, release 12.0 (SPSS, Chicago, Illinois).
Results
Of 75 patients screened, 46 (24 women and 22 men) met the eligibility criteria for the present study. The admitting diagnosis was exclusively chronic MR secondary to mitral valve prolapse. Of these patients, 18 were excluded because of overt coronary disease, hypertension, and/or diabetes, 10 because of nonsinus rhythm, and 1 because of a poor echocardiographic window. The clinical and echocardiographic characteristics of the study population are listed in Tables 1 to 3 . All patients were in sinus rhythm at echocardiographic examination.
| Variable | Study Population |
|---|---|
| Age (yrs) | 68 ± 9 |
| Women (%) | 47 |
| Height (cm) | 165 ± 9 |
| Weight (kg) | 70 ± 12 |
| Body surface area (m 2 ) | 1.7 ± 0.7 |
| Body mass index (kg/m 2 ) | 26 ± 4 |
| Systolic blood pressure (mm Hg) | 120 ± 8 |
| Diastolic blood pressure (mm Hg) | 78 ± 5 |
| Heart rate (beats/min) | 72 ± 9 |
| New York Heart Association class | 2.9 ± 0.9 |
| Glomerular filtration rate (ml/min/m 2 ) | 63 ± 16 |
| Medical therapy | |
| Angiotensin-converting enzyme inhibitors or angiotensin receptor blockers | 20 (43.7%) |
| β Blockers | 9 (19.6%) |
| Spironolactone | 21 (45.6%) |
| Loop diuretics | 38 (82.6%) |
| Statins | 23 (50.0%) |
| Platelet aggregation inhibitors | 21 (45.6%) |
| Histopathologic data | |
| Atrial fibrosis (%) | 57 ± 39 |
| Atrial endocardial thickness (μm) | 199 ± 100 |
| Variables | Study Population |
|---|---|
| Mitral regurgitant fraction (%) | 70 ± 18 |
| Left atrial area (cm²) | 25 ± 6 |
| Left atrial volume (ml) | 72 ± 15 |
| End-diastolic left ventricular diameter (mm) | 49 ± 6 |
| Left atrial indexed volume (ml/m 2 ) | 35 ± 9 |
| Relative wall thickness | 0.5 ± 0.1 |
| Left ventricular mass index (g/m) | 128 ± 33 |
| Left ventricular ejection fraction (%) | 57 ± 6 |
| Mitral E/A ratio | 0.9 ± 0.7 |
| S′ (cm/s) | 8 ± 2 |
| E′ (cm/s) | 7 ± 2 |
| A′ (cm/s) | 13 ± 3 |
| E/E′ ratio | 11 ± 4 |
| Variable | Study Population |
|---|---|
| Peak atrial longitudinal strain (%) | |
| Global | 21 ± 10 |
| Four-chamber average | 19 ± 10 |
| Two-chamber average | 22 ± 11 |
| Time-to-peak for peak atrial longitudinal strain (ms) | |
| Global | 385 ± 60 |
| Four-chamber average | 381 ± 61 |
| Two-chamber average | 391 ± 58 |
| Peak atrial contraction strain (%) | |
| Global | 10 ± 5 |
| Four-chamber average | 10 ± 4 |
| Two-chamber average | 12 ± 5 |
Of the 782 segments analyzed, the software was able to correctly track 749 (95.9%). A close negative correlation was found between global PALS and the grade of LA myocardial fibrosis (r = −0.82, p <0.0001; Figure 1 ), with poorer correlations for the LA indexed volume (r = 0.51; p = 0.01), LA ejection fraction (r = −0.61; p = 0.005), and E/E′ ratio (0.14; p = NS). Other significant correlations of LA fibrosis were found with New York Heart Association class (r = 0.39; p = 0.01), LV end diastolic diameter (r = 0.23; p = 0.05), and systolic pulmonary pressure (r = 0.29; p = 0.05; Table 4 ). Of these indexes, global PALS showed the best diagnostic accuracy for detecting LA fibrosis (area under the curve 0.89; Figure 2 ). Furthermore, we also demonstrated an inverse correlation between the global PALS and LA endocardial thickness (r = −0.66, p = 0.0001; Figure 3 and Table 5 ).
| R | p Value | |
|---|---|---|
| Clinical parameters | ||
| Age | 0.15 | NS |
| Gender (% female) | −0.09 | NS |
| Body surface area | −0.04 | NS |
| Heart rate | 0.09 | NS |
| Systolic blood pressure | 0.13 | NS |
| Diastolic blood pressure | 0.11 | NS |
| New York Heart Association class | 0.39 | 0.01 |
| Echocardiographic parameters | ||
| Left ventricular ejection fraction | −0.07 | NS |
| Left ventricular end diastolic diameter | 0.23 | 0.05 |
| E/A ratio | −0.08 | NS |
| E/E′ ratio | 0.14 | NS |
| S′ | −0.12 | NS |
| Mitral annular plane systolic excursion | −0.13 | NS |
| Effective regurgitant orifice area | 0.09 | NS |
| Systolic pulmonary artery pressure | 0.29 | 0.05 |
| Left atrial diameter | 0.31 | 0.05 |
| Left atrial area | 0.43 | 0.01 |
| Left atrial indexed volume | 0.51 | 0.01 |
| Left atrial ejection fraction | −0.61 | 0.001 |
| Global peak atrial longitudinal strain | −0.82 | <0.0001 |
