Paraprosthetic regurgitation, defined as abnormal retrograde flow between the sewing ring and the native valve annulus, is a well recognised complication of prosthetic valves. Paraprosthetic jets detectable by the diagnostic methods available until the 1970s were frequently caused by infective endocarditis of the prosthetic valve and were associated with unequivocal clinical signs. The diagnosis was confirmed by angiography, severe haemolysis was generally present, and treatment usually involved reoperation. Paraprosthetic regurgitation was thus a severe and feared complication of prosthetic heart valves.

Now that transoesophageal echocardiography (TOE) is widely available, a different picture is emerging. Small and asymptomatic paraprosthetic jets are often detected incidentally as a result of the high sensitivity of colour flow mapping, mainly when it is used with TOE. However, important clinical issues have not yet been adequately studied, such as the prevalence of these jets, their cause and time course, and their clinical consequences. Answers to these questions are clinically relevant for deciding which (if any) patients with small paraprosthetic jets, detected either incidentally or because of systematic study, need more careful follow up or even a repeat operation.

Intravascular haemolysis is often considered an unavoidable consequence of paraprosthetic regurgitation. This notion dates from the pre-echocardiographic era, when the only paraprosthetic jets that came to medical attention were severe and haemodynamically significant, and it may not apply to small jets detected incidentally by colour flow mapping. Most published studies have relied on measurement of lactate dehydrogenase (LDH) concentration to diagnose haemolysis8 but LDH may be raised from other causes and LDH concentrations may be high preoperatively.

To address these questions we studied prospectively a large cohort of patients undergoing elective valve replacement.