Monday, August 14, 2006

Transient Global Amnesia and PFO

Right-to-left shunts in the heart are associated with low arterial oxygen, TIA, decompression illness, migraine with aura and transient global amnesia. The most frequent cause of a right-to-left shunt is a large persistent (or patent) foramen ovTransient global amnesia ale (PFO).

is a condition that seems to be associated with PFO and has been reported in divers. See this thread on our Scuba Clinic forum with discussion by DocVikingo.

Usually, the diver relates normal diving activity with little or no current, surge or wave action. The dives are usually relatively shallow and leisurely, with little in the way of exertion. Occasionally, there is the history of some difficulty clearing with excessive valsalva maneuvers. The problem is that the diver cannot remember any activities after leaving the water for variable periods of time, usually only a couple of hours. There may or may not be associated decompression illness symptoms.

Valsalva-like activities often precede the occurrence of attacks of transient global amnesia (TGA) and abnormalities consistent with hypoperfusion (decreased blood flow) of deep limbic (brain) structures have been reported during a typical TGA episode. The search for an increased frequency of PFO in TGA patients has yielded conflicting results. In the first study, PFO was found in 55% of TGA patients, in 26% of stroke patients and in 26% of controls (Kloetzsch et al., 1966). Another study was unable to replicate this finding in a cohort of 46 consecutive patients in whom the prevalence of PFO (19.5%) was no higher than that found in 33 age-matched control subjects ( 19,6 %) and nonsignificantly lower than in 31 TIA patients (33.3%) (Anzola et al., 2000).

A study in the Archives of Neurology, "Arch Neurol. 1996 Jun;53(6):504-8.
showed an increased frequency of patent foramen ovale in patients with transient global amnesia. Fifty-three consecutive patients with TGA were evaluated by the 2 centers between 1988 and 1995. Using contrast transcranial Doppler sonography they have observed a PFO in 55% of the patients with TGA, compared with 27% of a control group of 100 patients. This difference was statistically significant (P < .01). Twenty-five patients with TGA (47%), 15 of them with a proven PFO, reported a precipitating activity, such as the lifting of heavy weights, immediately before the TGA occurred.

So, here we have another symptom complex from patent foramen ovale in divers that we need to be aware of - the diver who has a temporary but complete loss of memory coming on immediately after a dive and often associated with valsalva-like exertions, such as lifting or climbing right after a dive.

Should the defect be closed? Probably so in the working diver who cannot call his shots; possibly not in sport divers who can control their dives (and consequently the venous bubble load).