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Clinical Applications - Right to Left Shunts - PFO


Right to left Shunts- Patent foramen ovale (PFO)

One of the most popular and common functional test for transcranial Doppler today is the right to left shunt (RLS)- PFO test for diagnosis the existence of patent foramen ovale (PFO), and follow up after closure device implantation in order to evaluate residual RLS and completeness of closure.

Patent Foramen Ovale (PFO) is a congenital heart defect. It is a persistent opening between right and left atrium of the heart which did not close completely after birth. PFO opening can cause a shunt of blood from right to left (RLS) or from left to right side of the heart. Ordinarily, the left to right shunt will cause no problem; the right to left shunt can cause many problems (as low arterial O2 tension – hypoxia, severely limited exercise capacity, stroke, and migraine).

One of the effects of the PFO is emboli or clots from the venous system that can pass through the hole to the arterial system. In this case lung filtration process is bypassed and the emboli can reach the cerebral circulation. PFO is a recognized cause of cryptogenic stroke (stroke with undetermined causes) in young adults. PFO is quite common and found in all ages. The prevalence of PFO in the population is estimated to be about 30%.

Besides of cryptogenic stroke which is a well-known condition associated with PFO, especially in young adults, there are several more conditions associated with PFO. Studies show that prevalence of PFO in migraine with aura patients is from 50% to 75%, or more than twice what would be expected in the general population. Deep Vein Thrombosis (DVT) is caused by disease or lack of activity, it is especially related to long flights travelers, and Known also as “Economy-Class Syndrome”. Decompression sickness (DCS) is a disorder seen especially in deep-sea divers, astronauts and high altitude aviators and it is also associated with PFO, usually patients who have PFO are not allowed to dive.

           PFO associated conditions            

Figure 1: PFO associated conditions

Digi-Lite TCD is an efficient tool to test PFO thanks to its various and many advantages like non-invasive test, safe, cost-effective, high sensitivity and specificity, simple, comfortable, easily repeatable, and no need of any sedation. In order to perform the PFO test you need to do the following:

  • Inject saline containing air bubbles or echo-contrast enhancing agents.
  • Ask the patient to perform the Valsalva maneuver.
  • If RLS is existing identify signals of air bubbles in the MCA (Middle Cerebral Artery) on the Doppler spectrum window.