Transcranial doppler detection of circulating cerebral microemboli

Thromboembolic events represent a major complication of cardiovascular dise ases and interventions. Although general risk factors and predictors for th romboembolic events are well known from population-based studies, hardly an y therapeutic consequences for the individual patient can be drawn, e.g. fo r a well-balanced therapy with anticoagulants. A new approach towards an op timised therapy adapted to the individual risk of each patient may be based on the detection of circulating microemboli by transcranial Doppler sonogr aphy. With this technique, gaseous or solid microparticles circulating in t he blood can non-invasively be detected. Due to their small size, they do n ot induce thromboembolic events themselves. However, several studies demons trate that they indicate an increased thromboembolic activity and correlate directly with manifest stroke or emboli. From a transcranial Doppler probe positioned on the temporal plane at the patient's skull, the middle cerebr al artery's blood flow is recorded and is analysed acoustically and optical ly for circulating microemboli. This technique has already been used for ri sk stratification of highrisk patients and therapeutic decision-making in n eurologic routine, e.g. for the indication to anticoagulate the patient or for carotis surgery. Data to evaluate its value in cardiology are limited a nd based on few clinical studies. In this review, the basic principles and the methodological and technical background for the detection of microembol i, as well as current limitations, are discussed. Furthermore, clinical stu dies and their results evaluating this technique in patients with cardiolog ical diseases and during cardiovascular interventions are reviewed.