What are Echo-Doppler examinations for?
Doppler ultrasound is used for patients with stroke antecedents, and for patients without such antecedents but presenting with cardiovascular risk factors such as hypertension or high cholesterol, diabetes and sleep apnœa, or whose family members have a history of stroke or cardio-vascular problems.
Patients with no such antecedent or risk factor but who are aged over 55 may also be examined.
Carotid-vertebral and trans-cranial Doppler play a major role in primary prevention by enabling early detection of a potential narrowing of a blood vessel in the neck or a branch of the vessel concerned, even before the patient suffers a stroke. Monitoring the development of such a constriction using Doppler ultrasound and controlling it with suitable treatment makes it possible to significantly reduce the risk of the occurrence of a stroke. Clearly, the aim is to act before it is too late.
Immediately following a stroke, a Doppler ultrasound scan is performed:
on patients with symptoms of a stroke or of a transient ischaemic attack, in addition to the vascular examination already described. The object is to identify significant shrinkage of a blood vessel (stenosis) or a thrombus in the vascular area concerned, associated with the symptoms presented by the patient or with dissection, or signs of a "halo" that could be indicative of Horton’s disease (Giant-cell arteritis (GCA or temporal arteritis or cranial arteritis) which is present in only 60% of cases).
on patients with or without significant narrowing of the blood vessels, for whom regular monitoring by Doppler ultrasound (every 3, 6 or 12 months) makes it possible to significantly reduce the risk of the recurrence of a stroke or arterio-arterial origin (i.e. due to a significantly narrowed blood vessel).
on patients with a history of carotid or vertebral dissection. In this case, there are sound reasons for monitoring at 3 and 6 months at least, then annually for two years, then once every two years, and thereafter depending upon the presence or otherwise of residual stenosis. These regular checks make it possible to adapt the treatment, depending upon how the dissection progresses.
IMT (intima media thickness)
In patients with or without a history of stroke and presenting with arterial hypertension or suspected arterial hypertension, a carotid-vertebral Doppler ultrasound makes it possible to establish the IMT, an index which reflects the repercussion of possible hypertension on the vascular walls.
In practice, this index corresponds to the measurement of the intima media at three different points on the blood vessels (i.e. on the primitive carotid artery, the carotid bifurcation and the internal carotid artery). The normal values depend upon age and the number of cardiovascular risk factors. A higher-than-average IMT will therefore indicate whether or not there is arterial hypertension and how well it is controlled, thereby resulting in anti-hypertensive treatment or an additional treatment of this kind. It should be noted that an abnormal IMT is the most indicative sign of arterial hypertension, even before any other symptoms appear on the target organs.
TRANSCRANIAL DOPPLER ultrasound with Microbubbles
In certain patients, a stroke or transient ischaemic attack may indicate the need to perform a Transcranial Doppler ultrasound with microbubbles in order to detect a Permeable Foramen Ovale (PFO), a small hole, present from birth, in the wall separating the two upper cavities of the heart (auricles). This is done by lying the patient face upwards on the examination table and placing a helmet over his/her head that will enable a Doppler probe to be applied and maintained against one of his/her temples. The examination requires a venflon or cannula to be inserted in the crook of the elbow thus making it possible to inject microbubbles obtained by mixing air (1cc) and NaCl 0.9% (8cc), using two interconnected syringes. If the Doppler probe records the sound of bubbles making a characteristically high-pitched sound in the sylvian artery, recorded by the Doppler ultrasound, this indicates the presence of a PFO (hole in the heart). The examination consists of two parts, one conducted "at rest", in which the microbubbles are simply injected and their potential presence is determined by audio scanning, and the other involving the performance of the "the Valsalva manœvre", during which the patient makes a thrusting effort shortly after the injection of microbubbles. A PFO may be present when the patient is at rest and/or during exertion. This examination is mainly performed on young patients who have suffered a stroke or a transient ischaemic attack, and on older patients who do not present any risk factors or whose risk factors are extremely well controlled. This is an additional examination for the detection of a trans-thoracic and trans-oesophageal PFO using ultrasound. The investigation itself, excluding preparation, takes about 15 minutes.
Detection of Embolisms by TRANSCRANIAL DOPPLER
This investigation is performed solely on patients with significant carotid or sylvian stenosis, with an ulcerated carotid plaque or carotid dissection for the purposes of assessing the effectiveness of treatment (most frequently double anti-aggregation or anti-coagulation medication). The presence of a single embolism is evidence of continued embolic risk and consequently requires the optimisation of current treatment. Again, this examination requires the patient to wear the helmet needed for the purposes of application, and the Doppler probe is attached to both temples. The recording lasts for a total of one hour excluding the time taken to prepare the equipment for the patient. If the examination is to be performed correctly, the patient needs to be calm and remains recumbent, moving as little as possible on the examination table. Good temporal fenestrae are absolutely essential for helping the ultrasound to pass through the skull. No injection is required.