The Predictive Value of Mitral Leaflet Motion and Thickness Index Scores on Early Restenosis after Mitral Balloon Valvuloplasty

Abstract

The purpose of this study was to investigate whether there is any association between mitral leaflet motion (LMI) and leaflet thickness index (LTI) scores and the rate of restenosis 3 months after successful mitral balloon valvuloplasty.

The study population consisted of 46 patients with symptomatic rheumatic mitral stenosis who underwent balloon valvuloplasty (37 women, 9 men; mean age, 36 ± 9 years). Two-dimensional and Doppler echocardiography were performed in all patients on the day before, immediately after, and 3 months after valvuloplasty. The severity of restriction of leaflet motion and the severity of leaflet thickening were classified into grades of mild (a score of 0), moderate (a score of 1), and severe (a score of 2). Subvalvular disease and commissural involvement were homogeneous in all patients. Before and immediately after mitral balloon valvuloplasty, there were no significant differences in mitral valve area among the groups with different LMI and LTI scores. However, at 3 months after valvuloplasty, reduction in mitral valve area was more significant in patients who had higher pre-procedural LMI and LTI scores (P < 0.05). The rates of early restenosis were 0 with a total score of 0, 14.2% with a total score of 1–2, and 32% with a total score of 3.

In conclusion, quantitative assessment of LMI and LTI scores by 2-dimensional echocardiography may be helpful in predicting early restenosis after mitral balloon valvuloplasty. Early reduction in mitral valve area is significant in patients who have higher total LMI and LTI scores.

Rheumatic mitral stenosis is a common form of acquired heart disease characterized by chronic restriction of diastolic left ventricular filling.¹ Percutaneous mitral balloon valvuloplasty (MBV) has been shown to produce major increases in mitral valve area (MVA) and to relieve symptoms in patients with severe mitral stenosis.^2,3 Previous experience with surgical mitral commissurotomy has shown that the morphology of the mitral valve apparatus influences the results of the procedures.^4–6 The best predictor of immediate results is a pre-procedural echocardiographic score that indicates the severity of mitral valve morphologic abnormalities.^7,8 Two-dimensional echocardiographic total scoring methods have been proposed for the analysis of mitral valve morphology before MBV.^8–10 However, such methods rely on total scores for leaflet motion, leaflet thickness, subvalvular disease, and valvular calcification, without assessing the relative contribution of each variable.²

The relief of symptoms and improvement of hemodynamic parameters produced by MBV persists at mid- and long-term follow-up. It has been suggested that the best long-term results are seen in patients with echocardiographic scores of 8 or less, as described by Abascal and colleagues.⁹ When MBV produces a good immediate outcome in this group of patients, restenosis is unlikely to occur at 3-month follow-up. Although MBV can result in a good outcome in patients with echocardiographic scores greater than 8, hemodynamic and echocardiographic restenosis is frequently observed.^11–13 We performed this study to determine whether the total of mitral leaflet motion index (LMI) and leaflet thickness index (LTI) scores has any effect on the early restenosis rate, after 3 months in patients with successful MBV.

Patients and Methods

Patients

The study group consisted of 46 symptomatic patients with rheumatic mitral stenosis who underwent MBV. There were 9 men and 37 women, with a mean age of 36 ± 9 years (range, 18–70 years). Thirty-one were in sinus rhythm, and 15 had atrial fibrillation. Before the procedure, 15 patients were in New York Heart Association (NYHA) functional class IV, 24 were in class III, and 7 were in class II (Table I).

TABLE I. Patient Characteristics before Mitral Balloon Valvuloplasty

Echocardiographic Study

Two-dimensional and Doppler echocardiography were performed in all patients on the day before MBV, immediately after, and 3 months after, with use of a Hewlett-Packard Sonos 2500 echocardiographic system (Hewlett-Packard Medical, acquired by Philips Medical Systems; Andover, Mass). The images were obtained in all standard views and were recorded on videotape for playback analysis. Measurements of 2-dimensional and Doppler echocardiographic parameters were obtained by taking the average of 3 beats in patients in sinus rhythm and the average of 5 to 10 beats in patients with atrial fibrillation. Mitral valve area was calculated by the pressure half-time method, by evaluating mitral flow from the apical 4-chamber view. The observers who made the echocardiographic determinations were blinded to the initial clinical and hemodynamic results of MBV.

Leaflet Motion Index

To assess leaflet motion, the mitral valve leaflets were imaged in the parasternal, long-axis, 2-dimensional echocardiographic view during maximal doming of the anterior leaflet, upon early diastole. The extent of doming of the anterior leaflet was measured by drawing a line from the junction of the posterior wall of the aortic root and the anterior mitral valve to the tip of the mitral valve leaflet. From this line, a perpendicular line was drawn to the leading edge of the maximal dome of the anterior leaflet of the mitral valve. Leaflet motion was expressed as a slope by dividing the height of the dome by the length (H/L) (Fig. 1). The severity of restriction of leaflet motion was classified as mild when H/L was ≥0.45, moderate when H/L was 0.44 to 0.26, and severe when H/L was ≤0.25 (Table II).²

Fig. 1 In the 2-dimensional, parasternal, long-axis echocardiographic view, maximal doming of the anterior mitral leaflet was measured. Height (H) of doming was divided by length (L) to express slope of leaflet motion (slope = H/L).

AO = aorta; LA = left atrium; LV = left ventricle

TABLE II. Two-Dimensional Echocardiographic Assessment of Mitral Valve Morphology

Leaflet Thickness Index

To assess leaflet thickness, the tip of the anterior leaflet of the mitral valve was measured in the parasternal long-axis view. To minimize the effects of gain settings, mitral valve thickness was normalized to the posterior wall of the aortic root. Leaflet thickness index was then expressed as a ratio by dividing the thickness of the mitral valve by the thickness of the posterior wall of the aortic root (Fig. 2). The severity of leaflet thickening was classified as severe when the resulting figure was > 2.0 (Table II).²

Fig. 2 In the same 2-dimensional, parasternal, long-axis echocardiographic view as in Figure 1, the thickness of the mitral valve's anterior leaflet (A) at the tip and the thickness of the posterior wall of the aorta (B) were measured. Leaflet thickness is expressed as a ratio of the thickness of the mitral valve to that of the aortic wall (thickness ratio = A/B).

Subvalvular Disease and Commissural Calcium

The subvalvular apparatus and commissural calcium were assessed by visual inspection of the echocardiograms. Only those patients who had thin, faintly visible chordae tendineae, no more than minimal thickening below the valve, and no commissural calcium deposits were included in the study, in order to exclude the possible effects of subvalvular disease and commissural calcium upon study results.

Scoring

A score of 0 was assigned to each finding of mild, 1 to each finding of moderate, and 2 to each finding of severe leaflet thickening and restriction of leaflet motion.

Percutaneous Mitral Balloon Valvuloplasty

All patients underwent complete diagnostic right and left heart catheterization before MBV. All patients were given intravenous heparin (100 U/kg) immediately after we achieved left atrial access by means of transseptal left heart catheterization. Mitral balloon valvuloplasty was performed via a transatrial approach using Inoue's single-balloon technique. There were no severe complications after MBV. Hemodynamic calculations were performed with the use of standard formulas.^3,8

Follow-Up Evaluation

Echocardiographic examination was repeated 3 months after the procedure. The mitral valve area and the maximal and mean transmitral gradients were calculated. Restenosis at follow-up was defined as a loss of 50% or more of the initial gain, with a resultant valve area of less than 1.5 cm².^14–16

Statistical Analysis

Measurements of mitral valve area are expressed as mean ± standard deviation. Student's t-test was used to assess differences between the mean MVA of patients in sinus rhythm and those in atrial fibrillation. Analysis of variance was used to assess differences between the mean MVA of patients with mild, moderate, and severe LMI and LTI scores. In all instances, statistical differences in MVA were analyzed before, immediately after, and 3 months after valvuloplasty. Bonferroni correction was applied in order to distinguish between the different groups. A P value < 0.05 was considered statistically significant.

Results

There was no significant difference in MVA and transmitral gradient among patients with different LMI and LTI scores before MBV (Table III). Subvalvular lesions and commissural calcium were homogeneous in all patients. Mitral valve area and mean gradient assessed right after MBV were similar in both groups. Heart rate was not significantly different between patients in sinus rhythm and those in atrial fibrillation. Cardiac rhythm did not influence MVA immediately after or 3 months after MBV (P < 0.05) (Table III).

TABLE III. Mean Mitral Valve Areas before, Immediately after, and 3 Months after Mitral Balloon Valvuloplasty in 46 Patients with Various LMI and LTI Scores and Cardiac Rhythms

New York Heart Association functional class improved in 95% of the patients 3 months after MBV. Thirty patients (65%) were in class I, 13 patients (28%) were in class II, and 3 patients (7%) were in class III. Early reduction in MVA at 3 months after MBV was detected in patients who had elevated LMI and LTI scores (P < 0.05). The percentage of patients with early restenosis was 0 in those with a total LMI plus LTI score of 0, 14.2% in those with a total score of 1–2, and 32% in those with a total score of 3 (Fig. 3).

Fig. 3 The association of total mitral leaflet motion and thickness index scores with the rate of early restenosis (at 3 months) after mitral balloon valvuloplasty.

LMI = leaflet motion index; LTI = leaflet thickness index

Discussion

Rheumatic heart disease results in varying degrees of fusion of the mitral commissures, fibrosis and calcification of the valve leaflets, and fusion and shortening of the chordae tendineae.¹⁷ The consequential morphology of the valve influences the selection of the therapeutic intervention and the result of the procedure applied. Belcher¹⁸ reported that the restenosis rate was very low (<5%) after surgical commissurotomy in which the fused and retracted chordae could be manually separated.

Mitral balloon valvuloplasty increases MVA primarily by splitting the fused commissures. Tears of either the anterior or posterior mitral valve leaflet usually cause mitral regurgitation, but they rarely occur. McKay's¹⁹ and Kaplan's²⁰ groups showed in their postmortem studies that, after successful MBV, improvement of mitral valve area and leaflet mobility were due to fracturing of the commissures, and of the calcific and fibrotic tissues of the leaflets.

Because the mechanism of the increase in mitral valve area by balloon commissurotomy is splitting of the commissures, it may be assumed that the morphology of the mitral valve apparatus influences the results of the procedure. Total echocardiographic scoring systems that have their basis in leaflet morphology have been proposed as a guide to the selection of patients for MBV. Many studies have shown that leaflet thickness and mobility can affect the MVA after MBV. Herrmann and colleagues⁸ showed that echocardiographic evaluation of mitral leaflet thickening and mobility and of subvalvular thickening and calcification may be useful in predicting the immediate hemodynamic effects of MBV. The echocardiographic scoring system of Wilkins and associates⁷ took into consideration leaflet rigidity, leaflet thickening, leaflet calcification, and subvalvular thickening, all of which can affect the early results and the restenosis rate after MBV. Wilkins scored each of these variables from 0 to 4.⁷ Using Wilkins's system, Palacios and coworkers¹¹ reported that MBV produced excellent immediate and follow-up results in patients with total echocardiographic scores of 8 or less; suboptimal results immediately after MBV and hemodynamic restenosis were more likely to occur in patients who had scores of more than 8. However, a wide scattering of data makes the value of these methods questionable for predicting the results of MBV in an individual patient. We propose, rather, that the severity of the individual morphologic variables of the mitral valve be used as a guide.

The characteristic feature of rheumatic mitral stenosis on 2-dimensional echocardiography is doming of the body of the leaflets during diastole due to fused commissures.²¹ Reid and associates²² showed that qualitative assessment of leaflet mobility was the only echocardiographic variable that independently predicted MVA after MBV. Subsequently, Reid's group² showed that quantitative assessment of leaflet mobility was the best echocardiographic morphologic variable for the prediction of MBV results. The presence of calcification limits valve mobility and is associated, after balloon valvuloplasty, with less satisfactory immediate results than after surgical mitral commissurotomy.^23,24

We selected patients without subvalvular disease or calcification to determine whether leaflet motion and thickness index scores influence the early results and early restenosis rate of MBV. Although Reid^2,22 reported that mitral leaflet motion scores had the strongest influence on MVA immediately after balloon valvuloplasty, we did not duplicate that result. We showed that neither mitral leaflet motion nor leaflet thickness index score influenced MVA immediately after balloon valvuloplasty. Reid²² also reported that no 2-dimensional echocardiographic feature predicted which patients would experience an early reduction in MVA 3 months after MBV. However, we found that higher (more severe) leaflet motion index scores were associated with reductions in MVA at 3 months. Clinical variables like cardiac rhythm had no impact on immediate and early results of MBV. Our findings are consistent with previous studies that linked improvement in MVA after MBV with leaflet mobility.

After successful MBV, the incidence of restenosis is usually low, between 10% and 20%. Age, mitral valve area immediately after MBV, and the anatomy of the mitral valve apparatus are considered factors in the prediction of restenosis.¹⁶ Our study consisted of young patients without subvalvular disease or calcification and with variant LMI and LTI scores. Leaflet morphology and clinical variables did not influence the immediate results of MBV. Although no clinical variable—including MVA right after MBV—affected early restenosis, pre-procedural echocardiographic variables of LTI and LMI scores predicted the restenosis rate at 3 months.

The best hemodynamic result after MBV is to be expected in a patient who has a highly mobile mitral valve, without calcification or severe subvalvular disease. We believe that LTI and especially LMI scores reflect leaflet mobility well. These parameters are more practical to apply than is the grading system suggested by Wilkins and colleagues,⁷ in which these variables are defined qualitatively in an observer-dependent fashion. Leaflet motion and commissural calcification should be evaluated carefully in patients who are candidates for MBV.

Limitations of the Study

We did not perform cardiac catheterization 3 months after MBV, because catheterization is an invasive procedure. Whether the early reduction in MVA that we observed will be progressive and will result in a worsened functional class will require longer follow-up studies. Although follow-up cardiac catheterization was not done, a full echocardiographic examination was performed in all patients.

Conclusion

Percutaneous mitral balloon valvuloplasty is an effective treatment for acquired mitral stenosis. Balloon valvuloplasty results in an immediate increase in MVA and improvement in functional class. The restenosis rate is low in patients who have comparatively low LMI scores. Quantitative assessment of leaflet motion index by 2-dimensional echocardiography is helpful in understanding and predicting early restenosis after MBV. Early reduction in MVA (3 months after MBV) is significant in patients who have higher (more severe) total LMI and LTI scores.