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Tex Heart Inst J. 2006; 33(3): 399–401.
PMCID: PMC1592274

Left Ventricular Outflow Tract Obstruction after Bioprosthetic Mitral Valve Replacement with Posterior Mitral Leaflet Preservation

Abstract

We present a case of transient left ventricular outflow tract obstruction after mitral valve replacement with a high-profile bioprosthesis; only the posterior native mitral valve leaflet was preserved.

A 76-year-old woman was admitted to our institution with pulmonary edema. Two weeks earlier, she had undergone mitral valve replacement at our hospital due to severe mitral stenosis and 2+ mitral regurgitation complicated by cardiac failure and atrial fibrillation. The patient was taking digoxin, furosemide, and warfarin at the time of readmission. Echocardiography showed a narrowed left ventricular outflow tract. Doppler echocardiography revealed a peak 64-mmHg gradient between the septum and the strut of the bioprosthesis. The patient was successfully treated medically.

This case indicates that the risk of left ventricular outflow tract obstruction after bioprosthetic mitral valve replacement is not always eliminated by removal of the anterior mitral valve leaflet when the posterior mitral leaflet is preserved.

Key words: Bioprosthesis/adverse effects, echocardiography, heart valve prosthesis implantation/adverse effects/methods, mitral valve insufficiency/surgery, postoperative complications, ventricularfunction, left, ventricular outflow obstruction

In patients who undergo mitral valve replacement (MVR) with a high- or low-profile prosthesis, left ventricular outflow tract (LVOT) obstruction is a well-recognized postoperative complication.1–3 Herein, we present a case of transient LVOT obstruction after MVR with a high-profile prosthesis and preservation of the posterior native mitral valve leaflet.

Case Report

In February 2005, a 76-year-old woman was admitted to our hospital for MVR due to severe mitral stenosis and 2+ mitral regurgitation complicated by cardiac failure and atrial fibrillation. Preoperative echocardiography showed a normally functioning aortic valve with no LVOT gradient. She underwent implantation of a 29-mm porcine mitral valve bioprosthesis (Edwards Lifesciences, S.A.; Horw, Switzerland) with preservation of the native posterior mitral valve leaflet and its subvalvular apparatus. The postoperative course was smooth, and the patient was discharged on medical therapy on the 9th postoperative day.

One week later, the patient was readmitted with pulmonary edema. She was taking digoxin, furosemide, and warfarin sodium. Physical examination revealed a blood pressure of 100/60 mmHg, a heart rate of 128 beats/min, a diminished A 2 sound, normal prosthetic valve sounds, and bibasilar inspiratory rales. A grade 4/6, late-peaking, systolic ejection murmur was best heard in the 2nd intercostal space, with radiation to the neck. Electrocardiography showed atrial fibrillation with a rapid rate response. Transthoracic echocardiography revealed normal left ventricular (LV) dimensions and thickness, a LV ejection fraction of 0.67, and a normal mitral valve prosthesis. On Doppler echocardiography, the mean gradient across the mitral prosthesis was 4 mmHg, with an estimated area of 3.0 cm2. Systolic narrowing of the LVOT was observed between the septum and the strut of the bioprosthesis (Fig. 1). Acceleration of the color flow was observed in the same region (Fig. 2). The peak gradient across the LVOT was 64 mmHg (mean, 33 mmHg). Aortic valve insufficiency was not seen.

figure 28FF1
Fig. 1 Echocardiography shows obstruction between the struts of the bioprosthesis and the septum. The thin arrow indicates the left ventricular outflow tract; the thick arrow indicates the strut of the bioprosthesis.
figure 28FF2
Fig. 2 Color-flow Doppler echocardiography shows flow acceleration due to left ventricular outflow tract obstruction by the bioprosthesis.

On the basis of the echocardiographic findings and the patient's preference, surgery was postponed. Digoxin was discontinued, and the patient received 200 mg of metoprolol twice daily. Follow-up Doppler echocardiography performed after 1 week of medical therapy showed a substantial decrease in LVOT obstruction, and a mild peak gradient (35 mmHg) was measured between the left ventricle and the aorta. The patient remains under our observation and is checked in our clinic every 6 months; she has had no complaints for 18 months.

Discussion

In most cases of postoperative LVOT obstruction in patients such as ours, such obstruction results from the protrusion of a high-profile prosthetic valve into the LVOT or from abnormal subvalvular positioning of the prosthesis. If the prosthesis is not oriented properly, a strut may obstruct the outflow tract.

In addition to the fixed type of LVOT obstruction, transient or dynamic obstruction may occur after MVR. If there is a narrowed mitral–aortic angle after MVR, transient LVOT obstruction may occur due to a thickened interventricular septum, systolic anterior motion of the anterior mitral leaflet, the reduction of LV dimensions, a hypercontractile left ventricle, or atrial fibrillation.4–6 In our patient, in the setting of a mild LVOT obstruction due to the prosthesis and its abnormal position, the obstruction might have been worsened by preload reduction secondary to atrial fibrillation and diuretics or by hypercontractile cardiac function as a result of digoxin therapy.

This case illustrates the pharmacologic attenuation of dynamic LVOT obstruction after bioprosthetic MVR. If the obstruction first occurs postoperatively, as happened with our patient, appropriate medication may improve the cardiac status, and reoperation may be avoided. Our patient was successfully treated with a β-blocker after discontinuation of the digoxin.

Our patient had undergone MVR with a high-profile bioprosthesis and preservation of the posterior subvalvular apparatus. Preservation of the subvalvular apparatus during MVR preserves LV function and reduces the risk of LV rupture.7–9 However, previous reports have shown that complete preservation of the anterior leaflet after prosthetic MVR harbors the potential for LVOT obstruction, which most frequently occurs after the insertion of a high-profile bioprosthesis.1,3,10 In patients who have isolated mitral stenosis and a small LV cavity, low-profile prostheses are recommended to avoid myocardial impingement and LVOT obstruction that can result from use of a high-profile valve. In our patient, however, echocardiography revealed neither septal hypertrophy nor a small LV cavity. The posterior leaflet was retained at MVR, and LVOT obstruction developed.

Regardless of whether the native leaflets are removed, mitral valve replacement with a high-profile valve frequently causes LVOT obstruction. In addition, correct orientation of high-profile bioprostheses is mandatory.

Footnotes

Address for reprints: Niyazi Guler, MD, Yuzuncu Yil University, Arastirma Hastanesi, Kardiologi Servisi, 65200 Van, Turkey E-mail: moc.liamtoh@relugizayin

References

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