Background
The aim of this retrospective study was to explore whether different tethering patterns in chronic ischemic mitral regurgitation have different distributions of left ventricular (LV) systolic longitudinal, circumferential, and radial strain before and after mitral valve repair.
Methods
Sixty-one patients with chronic ischemic mitral regurgitation who underwent mitral repair were divided on the basis of the preoperative anterior/posterior tethering angle ratio (cutoff value, 0.76). There were 29 patients with symmetric (group 1) and 32 with asymmetric (group 2) preoperative tethering patterns. Assessment of longitudinal peak systolic strain was performed offline by applying speckle-tracking imaging to the apical two-chamber, three-chamber, and four-chamber views of the left ventricle. Peak systolic radial and circumferential strain was obtained from short-axis views at the basal, middle, and apical levels. Twenty healthy subjects served as controls.
Results
In group 1, baseline LV strain was impaired in all LV segments, with the worst values in the anterolateral, anterior, and inferolateral segments at the midventricular and basal levels. In contrast, asymmetric patients showed higher values in the inferior and inferoseptal walls and values closer to normal in the other segments. After surgery, all strain measurements showed significant improvements in all LV segments in group 2, whereas in Group 1, strain worsened in the inferoseptal, inferior, and anteroseptal walls and did not change in the other segments.
Conclusions
Patients with baseline symmetric tethering patterns showed more extensive abnormal strain, which was observed in all LV segments and was not reverted by surgery. These findings require confirmation in additional larger studies.
Myocardial strain echocardiography has been introduced as a clinical index of regional and global left ventricular (LV) function. Two-dimensional speckle-tracking echocardiography measures strain by tracing tissue scatter in grayscale images and enables the angle-independent assessment of myocardial deformation indices. As it is noninvasive and reproducible, strain might be well suited for follow-up and to guide the timing of surgical intervention.
In our previous experiences, measures of leaflet tethering resulted in fundamental findings to identify patients with chronic ischemic mitral regurgitation (CIMR) who can benefit from restrictive annuloplasty. Specifically, preoperative symmetric tethering with anterior mitral leaflet predominance was strongly associated with recurrence of mitral regurgitation (MR) and lack of reverse remodeling.
In the present study, we tested the hypothesis that different tethering patterns in CIMR exhibit different distributions of LV systolic longitudinal, circumferential, and radial strain before and after mitral valve repair.
Methods
Subjects
Patients with CIMR who survived combined coronary artery bypass grafting and undersized mitral ring annuloplasty performed at our institution (Academic Hospital, Maastricht, The Netherlands) between May 2010 and March 2012 were retrospectively included in the study. Inclusion and exclusion criteria are shown in Figure 1 . The final study population consisted of 61 patients who were divided on the basis of the preoperative anterior/posterior tethering angle ratio (α/β). A cutoff value of 0.76 was chosen on the basis of our previous experience. There were 29 patients with symmetric (group 1; mean α/β, 0.83 ± 0.5) and 32 with asymmetric (group 2; mean α/β, 0.63 ± 0.3) preoperative tethering patterns.
Finally, strain data of patients with CIMR were compared with data obtained from 20 healthy controls. The group of healthy controls comprised individuals matched for age, gender, body surface area, and body mass index who were volunteers recruited through general practitioners or subjects referred for echocardiography as part of a routine checkup during the study period. Those individuals who showed LV dilatation, had known hypertension, or were referred for echocardiographic evaluation of known valvular disease, murmur, or heart failure were excluded. Accordingly, all individuals included in the control group had normal echocardiographic results.
Surgery
All patients underwent complete revascularization. The ring size was determined by standard measurements of the intertrigonal distance and anterior leaflet height. Downsizing by two ring sizes was performed in all patients. A successful repair was assessed as leaflet coaptation ≥ 0.8 cm, MR grade ≤ 1, and diastolic mitral valve area > 2 cm 2 on intraoperative transesophageal echocardiography.
Echocardiography
Transthoracic echocardiography was carried out according to a standard protocol before surgery (<1 week before), at 1-year follow-up, and yearly thereafter. Echocardiographic examinations were performed using a commercially available ultrasound system (iE33; Philips Medical Systems, Best, The Netherlands). All patients reached 1-year follow-up. The median follow-up duration was 16.6 months (interquartile range [IQR], 14.1–20.5 months).
Images were acquired by experienced echocardiographers (F.L. and C.M.R.) blinded to the aims of the study, stored in Digital Imaging and Communications in Medicine format, and transferred to a workstation for further offline analysis (TomTec Imaging Systems, Unterschleissheim, Germany).
Standard Echocardiography
Quantitation of MR was carried out as previously described, and the thresholds for mild, moderate, and severe MR followed American Society of Echocardiography recommendations. Recurrent MR at latest follow-up was defined as insufficiency ≥ 2+ in patients with no or trivial MR at discharge.
The anterior mitral leaflet tethering angle, α (between the annular plane and the basal part of the anterior mitral leaflet), and the posterior mitral leaflet tethering angle, β (between the annular plane and the basal part of the posterior mitral leaflet), were directly measured using specific software (Philips DICOM Viewer; Philips Medical Systems).
The ratio of α to β was a quantitative measurement of tethering: the closer the ratio to 1, the more symmetric the tethering.
Tenting area was measured as the area enclosed between the annular plane and mitral leaflets from the parasternal long-axis view at midsystole. Coaptation height was measured as the perpendicular distance between the coaptation point of the mitral leaflets and the line connecting the annular hinge points in the long-axis view at end-systole.
LV volumes and LV ejection fraction were assessed using the apical biplane method of disks. The wall motion score index (WMSI) was calculated according to a 16-segment model. In addition, the WMSI of the basal and midposterior and inferior segments for the posteromedial papillary muscle (PMPM-WMSI) and basal, mid, lateral, and anterior segments for the anterolateral papillary muscle (ALPM-WMSI) were also calculated.
Two-Dimensional Speckle-Tracking Echocardiography
The assessment of longitudinal peak systolic strain was performed offline by applying two-dimensional speckle-tracking echocardiography to the apical two-chamber, three-chamber, and four-chamber views of the left ventricle using commercially available software (TomTec Imaging Systems).
With the beginning of the QRS complex and the aortic valve closure time as reference points, peak longitudinal strain was the maximal negative strain value during the ejection phase. Basal, midventricular, and apical longitudinal strain values were obtained from each LV wall (inferoseptum, anterolateral, inferior, anterior, inferolateral, and anteroseptal).
In addition, peak systolic radial and circumferential strain values were obtained from short-axis views at the basal, middle, and apical levels.
Statistical Analysis
Data are presented as mean ± SD or as median (IQR) after being assessed for normality of distribution by the Kolmogorov-Smirnov test. Data were compared for statistical significance using t tests, Mann-Whitney rank-sum tests, and χ 2 or Fisher’s exact test as appropriate. Multiple comparisons were carried out by analysis of variance with Tukey’s post hoc test.
Two-way analysis of variance for repeated measures was used for comparison between baseline and postoperative echocardiographic data. Intraobserver and interobserver reproducibility of strain measurements by two-dimensional speckle-tracking echocardiography was determined by interclass correlation coefficients and Bland-Altman analysis. Intraobserver reproducibility was determined by repeating strain measurements by one experienced reader in 10 randomly selected patients. A second, blinded experienced reader performed the strain analysis in the same 10 patients, providing interobserver reproducibility data.
Statistical analysis was performed using SPSS version 15.0 (SPSS, Inc., Chicago, IL). The requirement for ethics committee approval was waived because of the retrospective analysis of the study, according to national laws regulating observational retrospective studies (the Dutch WMO law). However, all patients gave their informed consent to access their data for scientific purposes.
Results
Patient Characteristics and Clinical Results
Patient characteristics are shown in Table 1 . No differences were found between the groups in baseline demographics. Four patients (13.7%) in the symmetric group and two (6.25%) in the asymmetric group experienced postoperative complications ( P = .33). These were low-output syndrome ( n = 1), bleeding ( n = 2), respiratory failure ( n = 1), infection ( n = 1), and pericardial effusion ( n = 1). The mean lengths of stay in the intensive care unit (20 hours [IQR, 11–30 hours] in the symmetric group vs 23 hours [IQR, 15–33 hours] in the asymmetric group; P = .29) and the mean in-hospital stay (7 days [IQR, 5–8 days] in the symmetric group vs 6 days [IQR, 4–7 days] in the asymmetric group; P = .82) were comparable between the two groups. At follow-up, recurrence of mitral valve regurgitation (MR ≥ 2+) was 68.9% ( n = 20) in group 1 and 18.7% ( n = 6) in group 2 ( P < .001). Among patients showing recurrent MR, 20 patients (15 in the symmetric group and five in the asymmetric group) were medically treated, whereas six (five in the symmetric group and one in the asymmetric group) underwent reoperation (mitral valve replacement). Neither endocarditis nor other adverse cardiovascular events occurred during follow-up in the two groups.
| Variable | Controls | Symmetric | Asymmetric | P |
|---|---|---|---|---|
| ( n = 20) | ( n = 29) | ( n = 32) | ||
| Baseline | ||||
| Age (y) | 66.0 ± 4.4 | 66.3 ± 5.9 | 67.2 ± 7.2 | .81 |
| Men/women | 14 (70%)/6 (30%) | 19 (65.5%)/10 (34.5%) | 21 (65.6%)/11 (34.4%) | >.90 |
| BSA (m 2 ) | 1.85 ± 1.6 | 1.86 ± 1.8 | 1.88 ± 1.7 | .90 |
| BMI (kg/m 2 ) | 23.3 ± 1.2 | 24.7 ± 1.3 | 25.6 ± 1.7 | .87 |
| NYHA class | 1 (1–2) | 3 (3–4) | 3 (3–4) | >.90 |
| CCS angina class | 1 (1–2) | 2 (1–3) | 2 (1–3) | >.90 |
| EuroSCORE | – | 15.5 (11–18) | 15.7 (10–19) | .84 |
| Hypertension | – | 13 (44.8%) | 16 (50.0%) | .69 |
| Diabetes | – | 6 (20.6%) | 10 (31.2%) | .36 |
| COPD | – | 3 (10.3%) | 7 (21.8%) | .25 |
| Chronic renal disease | – | 4 (13.7%) | 9 (28.1%) | .19 |
| Cerebral vascular disease | – | 1 (3.4%) | 1 (3.1%) | .84 |
| Peripheral vascular disease | – | 3 (10.3%) | 4 (12.5%) | .81 |
| Preoperative IABP | – | 2 (6.8%) | 3 (9.3%) | .75 |
| Myocardial infarction | – | |||
| Inferior/posterior | – | 12 (41.4%) | 15 (46.9%) | .67 |
| Anterior/septal | – | 2 (6.9%) | 3 (9.4%) | .75 |
| Lateral | – | 5 (17.2%) | 4 (12.5%) | .21 |
| Combined | – | 10 (34.5%) | 10 (31.2) | .61 |
| Coronary vessel disease | – | 2 (1–3) | 2 (1–3) | >.90 |
| Left main coronary artery | – | 6 (20.6%) | 7 (21.8%) | >.90 |
| Surgery | – | |||
| CPB time (min) | – | 111 (95–130) | 107 (98–119) | .10 |
| CCL time (min) | – | 99 (79–115) | 93 (80–107) | .23 |
| Mitral ring size (mm) | – | 28 (26–30) | 28 (26–30) | .90 |
| CABG | – | |||
| Anastomoses/patient | – | 2 (1–3) | 2 (1–3) | >.90 |
| Arterial graft/patient | – | 1 (1–2) | 1 (1–2) | >.90 |
| Follow-up | ||||
| NYHA class | – | 2 (2–3) | 1 (1–2) | <.001 |
| NYHA class III or IV | – | 21(72.4%) | 8 (25.0%) | <.001 |
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