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CARDIOVASCULAR ANESTHESIOLOGY

Thrombotic Occlusion of a Bileaflet, Mechanical Mitral Valve

From the Department of Anaesthesia, St. George Hospital, Kogarah, New South Wales, Australia.

Address correspondence to David A. Pybus, FANZCA, Department of Anaesthesia, St. George Hospital, Belgrave St., Kogarah, NSW 2217, Australia. Address e-mail to dpybus{at}bigpond.net.au.

An 83-yr-old woman was scheduled for repeat mitral valve replacement having undergone implantation of a 29 mm Carbomedics bileaflet prosthesis 18 mo before.

Over the preceding 3 mo, the patient had suffered two separate periods of poor anticoagulant control during which her prothrombin time was documented at an International Normalized Ratio of <2.0. The patient presented in acute pulmonary edema. Cine-fluoroscopy of her mitral prosthesis demonstrated complete immobility of one valve leaflet and virtually complete immobility of the other, and the diagnosis of thrombotic occlusion of the valve was made. The patient was deemed unsuitable for thrombolytic therapy because she had clear evidence of valve obstruction and was dyspnoeic at rest (New York Heart Association Class IV) (1). Accordingly, she was referred for urgent surgical replacement of the prosthesis.

Figure 1 is a composite, continuous wave Doppler analysis of the mitral inflow obtained during the intraoperative, transesophageal examination of the prosthetic valve. The upper tracing was obtained after induction of anesthesia, but before institution of cardiopulmonary bypass. The patient was in sinus rhythm at this time. The features which are consistent with valve occlusion are the absence of an opening and closing "click; " the abnormal elevation of the "E" wave (E_max 3.3 m/s); the fusion of the "E" and "A" waves and the prolongation of the pressure half-time (550 ms). The calculated mean gradient across the valve was markedly elevated at 31 mm Hg and the valve area (calculated from pressure half-time) markedly reduced at 0.4 cm². [However, it should be borne in mind that the pressure half-time formula was derived for native mitral valves and may not accurately reflect the effective orifice area of a prosthetic mitral valve (2).] Moderate mitral regurgitation was also present. For comparison, the normal values of a 29 mm Carbomedics valve in the mitral position are peak gradient 8.78 ± 2.9 mm Hg; mean gradient 3.39 ± 0.97 mm Hg; pressure half-time 88 ± 17 ms; effective orifice area 2.3 ± 0.4 cm² (3).

View larger version (54K): [in this window] [in a new window]   Figure 1. Continuous wave Doppler interrogation of the mitral inflow before and after valve replacement. The early mitral inflow, atrial systolic inflow, and ventricular systolic regurgitant flow are marked as "E," "A," and "V," respectively; the opening and closing clicks of the normal prosthesis are marked as "O" and "C."

The asymmetry of the regurgitant jet profile is also noteworthy. This may represent "V wave cutoff " (4); which is a sign of acute, severe mitral regurgitation, and which occurs when left atrial pressure is high and left atrial compliance is low. At the time, the patient’s pulmonary artery occlusion pressure was 28 mm Hg.

The lower tracing was obtained after replacement of the valve with another 29 mm prosthesis and weaning from cardiopulmonary bypass. The patient was subject to atrioventricular pacing at this time. The features of satisfactory valve function are the presence of an opening and closing "click; " the reduction of the "E" wave (E_max 1.6 m/s), the separation of the "E" and "A" waves and the reduction of the pressure half-time. The mean gradient of 4 mm Hg and the pressure half-time of 90 ms are consistent with normal valvular function (3).

Video 1 (please see video clip available at www.anesthesia-analgesia.org) is a composite two-dimensional sector scan showing the valve before and after replacement. Note the complete immobility of the left-hand leaflet and the virtually complete immobility of the right-hand leaflet before replacement. A small amount of thrombus is apparent at the tip of the right-hand leaflet. The explanted valve (viewed from the ventricular aspect) is shown below the two-dimensional sector scan. Note the large amount of thrombus which almost completely obliterates the hinge line of the valve and which encroaches upon both leaflets. A small amount of nonobstructive pannus is also present on the sewing ring between 5 and 11 o’clock. After replacement, the full range of movement of both leaflets is clearly visible. For comparison, a normal Carbomedics prosthesis is also shown.

Prosthetic valve thrombosis (PVT) is one of the most feared complications of heart valve replacement with a mechanical prosthesis and, for reasons which are not clear, the Carbomedics valve is thought to be at particular risk for this condition in the poorly anticoagulated patient (5).

PVT may either be obstructive or nonobstructive. The incidence of obstructive PVT varies between 0.3% and 1.3% patient years, whereas the incidence of nonobstructive PVT may be as high as 10% patient years in the early years after surgery (6). The differential diagnosis of the condition includes leaflet obstruction by pannus, bacterial endocarditis, and mechanical failure of the valve.

The condition is usually diagnosed using either cine-fluoroscopy or echocardiography. Cine-fluoroscopy is appropriate for the initial diagnosis of obstructive PVT as it can accurately detect even minor degrees of impaired leaflet mobility. However, it cannot be used for the calculation of transvalvular gradients and cannot detect the presence of valvular incompetence. Furthermore, it is of no use in the identification of nonobstructive PVT as it cannot be used to visualize thrombus (or pannus). In the absence of a contraindication, such as the presence of a large amount of thrombus, thrombolytic therapy is usually recommended as the first line of treatment in patients with nonobstructive PVT, whereas surgery is advised in those with obstructive PVT (1).

In conclusion, this case illustrates the central role of transesophageal echocardiography in the evaluation of a patient with suspected obstruction of a prosthetic mitral valve. Interested readers may also wish to refer to the review by Montorsi et al. (7) who have described this role in much greater detail.

Footnotes

Accepted for publication August 17, 2007.

Reprints will not be available from the author.

This article has supplementary material on the Web site: www.anesthesia-analgesia.org.

REFERENCES

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2. Chambers JB. Mitral pressure half-time: is it a valid measure of orifice area in artificial heart valves? J Heart Valve Dis 1993;2:571–7[Medline]
3. Bjornerheim R, Ihlen H, Simonsen S, Sire S, Svennevig J. Hemodynamic characterization of the Carbomedics mitral valve prosthesis. J Heart Valve Dis 1997;6:115–22[Web of Science][Medline]
4. Schiller NB, Foster E, Redberg RF. Transesophageal echocardiography in the evaluation of mitral regurgitation. The twenty-four signs of severe mitral regurgitation. Cardiol Clin 1993; 11:399–408[Medline]
5. Williams MA, Crause L, Van Riet S. A comparison of mechanical valve performance in a poorly anticoagulated community. J Card Surg 2004;19:410–4[Web of Science][Medline]
6. Roudaut R, Serri K, Lafitte S. Thrombosis of prosthetic heart valves: diagnosis and therapeutic considerations. Heart 2007; 93:137–42[Free Full Text]
7. Montorsi P, De Bernardi F, Muratori M, Cavoretto D, Pepi M. Role of cine-fluoroscopy, transthoracic, and transesophageal echocardiography in patients with suspected prosthetic heart valve thrombosis. Am J Cardiol 2000;85:58–64[Web of Science][Medline]

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