Abstract
A 67-year-old woman with exertional dyspnea was referred to our hospital. Transthoracic echocardiography revealed severe mitral regurgitation and significant left ventricular (LV) outflow tract obstruction due to prominent systolic anterior motion (SAM) of the mitral valve without LV hypertrophy. Oral bisoprolol remarkably attenuated SAM. Two- or three-dimensional echocardiographic analysis demonstrated the elongation of anterior and posterior mitral leaflets and interventricular septum (IVS) bulging due to narrow aorto-mitral angle. In the present case, elongation of mitral leaflet and hyperkinetic motion of left ventricle, and IVS bulging due to narrow aorto-mitral angle possibly play important roles in the development of SAM.
<Learning objective: Mitral regurgitation due to systolic anterior motion (SAM) can be dramatically improved by beta-blocker therapy. Although the precise mechanism of SAM has not been fully elucidated, structural changes of mitral apparatus (elongation of mitral leaflet and papillary muscle displacement), and structural or functional features of left ventricle (hyperkinetic motion, small ventricle, interventricular septum bulging, narrow aorto-mitral angle) possibly play important roles in the development of SAM.>
Keywords: Mitral regurgitation, Systolic anterior motion, Left ventricular outflow tract obstruction, Beta-blocker
Introduction
Systolic anterior motion (SAM) of the mitral valve was first reported as a feature of hypertrophic cardiomyopathy (HCM), and it had previously been considered as a specific finding to HCM [1]. However, SAM may be detected in the absence of left ventricular outflow tract (LVOT) obstruction, and even seen without typical echocardiographic findings of HCM. It has been shown that SAM can be experimentally produced by the administration of dobutamine in normal dogs with a high success rate [2]. A possible role of structural changes of mitral valve during the development of SAM has also been reported such as leaflet elongation and papillary muscle displacement [3], [4], [5], [6]. Herein, we present a clinical case of severe mitral regurgitation (MR) and SAM, which was dramatically attenuated by beta-blocker therapy. The findings in this case seem to be informative with respect to the mechanisms of SAM and consequent MR.
Case report
A 67-year-old woman was referred to our hospital due to a 2-month history of dyspnea on mild exertion. Physical examination and laboratory test revealed no obvious triggers for left ventricular (LV) hyperkinetic motion such as infection, dehydration, anemia, and hyperthyroidism. The 12-lead electrocardiogram results were normal. Transthoracic echocardiography revealed severe mitral regurgitation and significant LV outflow tract obstruction (peak velocity was 5.8 m/s) due to prominent systolic anterior motion (SAM) of the mitral valve without LV hypertrophy. LV wall motion was hyperkinetic, with an ejection fraction of 74%, and interventricular septum (IVS) bulging due to narrow aorto-mitral angle was observed. Anterior mitral leaflet bended at its mid-portion, resulting in loss of coaptation (Fig. 1a and b; Additional movie files show this in more detail (see Additional files 1 and 2)].
Fig. 1.
Two-dimensional transthoracic echocardiography and color flow imaging before initiation of a beta-blocker. (a) Apical long-axis view. Prominent systolic anterior motion of the mitral valve with septal contact can be seen, and the mitral leaflets bended at the mid-portion, resulting in loss of coaptation. Left ventricular wall motion is hyperkinetic, and there is no concentric or asymmetric left ventricular hypertrophy. (b) Color flow imaging shows severe mitral regurgitation with the jet directed posteriorly, and significant left ventricular outflow tract obstruction (peak velocity was 5.8 m/s).
Four days after the initiation of bisoprolol treatment (2.5 mg daily), the LV wall motion was normalized, and SAM of the mitral leaflet was significantly reduced. IVS bulging due to narrow aortic mitral angle was still observed, but MR and LVOT obstruction almost completely disappeared (Fig. 2a and b, and Additional files 3–5). Measurement of the mitral leaflet lengths using three-dimensional reconstruction by transesophageal echocardiography indicated elongation of the leaflets with an anterior leaflet length of 2.2 cm and a posterior leaflet length of 1.7 cm, respectively (normal ranges, 1.8 ± 0.3 cm for anterior leaflet, 1.1 ± 0.2 cm for posterior leaflet [4]). The narrowest LVOT diameter during systole was 1.4 cm (see Additional file 5). Cardiac magnetic resonance imaging revealed no structural abnormalities including displacement of papillary muscles. Bisoprolol was increased to 5 mg daily, and was well tolerated by her. After that, she has never complained of dyspnea on exertion.
Fig. 2.
Two-dimensional transthoracic echocardiography and color flow imaging after initiation of a beta-blocker. (a) Left ventricular wall motion was normokinetic, and systolic anterior motion of the mitral leaflet was significantly reduced. (b) Color flow imaging. Mitral regurgitation and left ventricular outflow obstruction almost completely disappeared.
Discussion
As the main mechanism of SAM, the Venturi theory has been widely accepted. Venturi effect is created by high velocity flow caused by LVOT obstruction, and lifts the mitral valve toward the septum. However, several studies demonstrated that SAM began before the start of LV ejection in patients with HCM, which cannot be explained by the Venturi theory [7]. Thus, structural changes may play a primary role in the development of SAM in HCM patients. Klues et al. analyzed the structure of mitral valves pathologically in HCM patients and showed that 62 (66%) of 94 mitral valves had a constellation of structural malformations, including increased leaflet area and elongation of the leaflets [4]. Increases in mitral leaflet area and papillary muscle displacement were also shown in patients with HCM using real-time 3-dimensional echocardiography [6]. Levine et al. showed in normal dogs that experimental anterior papillary muscle displacement displaced mitral valve anteriorly, shifted the coaptation point toward the insertion of the leaflets, and created longer distal residual leaflets that moved anteriorly [5]. In patients after mitral valve plasty, an excess of valvular tissue and an undersized annuloplasty were considered as major factors that contribute to the development of SAM. A narrow aorto-mitral angle, a hyperkinetic small ventricle, an IVS bulging, and an abnormal configuration of the anterior leaflet were also considered as additional potential contributing factors [8]. In the present case, elongation of mitral leaflet and hyperkinetic motion of left ventricle, and IVS bulging due to narrow aorto-mitral angle possibly play important roles in the development of SAM. Henein et al. reported that in 80% of the patients with exertional dyspnea and negative exercise test, SAM of the mitral valve and high velocity flow in the LVOT appeared during dobutamine stress echocardiography, which were associated with basal septal hypertrophy [9]. In contrast, the present patient did not have any obvious triggers which cause hyperkinetic LV motion. Although there are several previous reports regarding SAM of the mitral valve without LV hypertrophy [10], [11], the present case is rare, because the attenuation of SAM by oral beta-blocker therapy was dramatic, and severe MR and LVOT obstruction completely disappeared. Once severe MR occurred, LV hyperkinetic motion might be enhanced, leading to a vicious circle that progressively exacerbated SAM, LVOT obstruction, and MR. Beta-blocker therapy might terminate the vicious circle, eliminating SAM, LVOT obstruction, and MR. Further studies are necessary to clarify the precise mechanism of SAM in the absence of LV hypertrophy.
Conflict of interest
All authors declare that they have no conflict of interest regarding this manuscript.
Disclosures
None.
Footnotes
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jccase.2015.08.005.
Appendix A. Supplementary data
Two-dimensional transthoracic echocardiography before initiation of a beta-blocker. Apical long-axis view. Prominent systolic anterior motion of the mitral valve with septal contact can be seen, and the mitral leaflets bended in the mid portion, resulting in loss of coaptation. Left ventricular wall motion is hyperkinetic, and there is no concentric or asymmetric left ventricular hypertrophy.
Two-dimensional transthoracic echocardiography and color flow imaging before initiation of a beta-blocker. Color flow imaging shows severe mitral regurgitation with the jet directed posteriorly, and significant left ventricular outflow tract obstruction (peak velocity was 5.8 m/s).
Two-dimensional transthoracic echocardiography after initiation of a beta-blocker. Left ventricular wall motion was normokinetic, and systolic anterior motion of the mitral leaflet was significantly reduced.
Two-dimensional transthoracic echocardiography and color flow imaging after initiation of a beta-blocker. Color flow imaging. Mitral regurgitation and left ventricular outflow obstruction almost completely disappeared.
Three-dimensional transesophageal echocardiography of the mitral valve. Measurement of the mitral leaflet lengths using reconstructed three-dimensional images indicated elongation of the leaflets with an anterior leaflet length of 2.2 cm and a posterior leaflet length of 1.7 cm, respectively. The narrowest left ventricular outflow tract obstruction diameter during systole was 1.4 cm.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Two-dimensional transthoracic echocardiography before initiation of a beta-blocker. Apical long-axis view. Prominent systolic anterior motion of the mitral valve with septal contact can be seen, and the mitral leaflets bended in the mid portion, resulting in loss of coaptation. Left ventricular wall motion is hyperkinetic, and there is no concentric or asymmetric left ventricular hypertrophy.
Two-dimensional transthoracic echocardiography and color flow imaging before initiation of a beta-blocker. Color flow imaging shows severe mitral regurgitation with the jet directed posteriorly, and significant left ventricular outflow tract obstruction (peak velocity was 5.8 m/s).
Two-dimensional transthoracic echocardiography after initiation of a beta-blocker. Left ventricular wall motion was normokinetic, and systolic anterior motion of the mitral leaflet was significantly reduced.
Two-dimensional transthoracic echocardiography and color flow imaging after initiation of a beta-blocker. Color flow imaging. Mitral regurgitation and left ventricular outflow obstruction almost completely disappeared.
Three-dimensional transesophageal echocardiography of the mitral valve. Measurement of the mitral leaflet lengths using reconstructed three-dimensional images indicated elongation of the leaflets with an anterior leaflet length of 2.2 cm and a posterior leaflet length of 1.7 cm, respectively. The narrowest left ventricular outflow tract obstruction diameter during systole was 1.4 cm.