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It is not unusual to find a Doppler derived peak gradient of 40 mm Hg across a Bjork-Shiley valve in the aortic position. However, in the case reported below1 further investigation led to the identification of thrombus, and the patient underwent reoperation despite being asymptomatic. Should this case affect our management of mechanical valves?
Most centres perform routine postoperative echocardiography. This is useful to compare with future studies as a new paraprosthetic leak may be a sign of endocarditis, and a major change in forward flow pattern may support the clinical suspicion of obstruction. However, published guidelines2 ,3 do not recommend further studies unless the patient has symptoms or there is clinical suspicion of valve dysfunction. According to these guidelines, the study ultimately leading to surgery in this patient need not have been performed. We do not know if this would have mattered. The patient might have remained asymptomatic. Alternatively, the thrombosis could have progressed leading to symptomatic severe obstruction, an embolic event or even death.
Thrombosis of mechanical valves in the aortic position is exceptionally rare.4 It is therefore unlikely that many lives would be saved by routine echocardiography in all patients. On the contrary, it is more likely that lives would be endangered as a result of replacing valves unnecessarily on the suspicion of obstruction incorrectly diagnosed from the echocardiogram; surgery based largely or exclusively on gradient alone has occurred anecdotally. In this case report the echocardiogram was clearly abnormal. The disk probably opened incompletely and the peak gradient had doubled compared with previous studies and was well above the published 95% upper limit of 30 mm Hg (Chambers JB, unpublished data, 1990)5 ,6 for a valve of this size and type. However, a peak gradient of 40 mm Hg1 could be normal for a 23 mm or smaller Björk-Shiley valve (Chambers JB, unpublished data, 1990).5 ,6 For a 19 mm St Jude or Carbomedics valve a peak gradient as high as 60 mm Hg could be normal.7 ,8Thus, an apparently high individual velocity or derived gradient requires careful interpretation in relation to the valve type and size, to previous studies in the same patient, and in the context of left ventricular function and symptoms before clinical management is changed.
The risk of mechanical thrombosis is so close to 04 that if a patient is well the valve can usually be assumed to be normal. The present case1 is a rare exception and routine echocardiography of asymptomatic patients with clinically normal mechanical valves is not necessary.