ABNORMAL FOREARM VASCULAR-RESPONSES DURING DYNAMIC LEG EXERCISE IN PATIENTS WITH VASOVAGAL SYNCOPE

Background We have reported previously that in some patients with norm al hearts who present with exercise syncope, abnormal forearm vasodila tion is seen during leg exercise and tilt table tests are positive. Th is suggests that exercise syncope may be a variant of vasovagal syncop e. In this study we tested the hypothesis that there is loss of the no rmal forearm vasoconstrictor response during dynamic leg exercise in a n unselected population of patients with classic vasovagal syncope. Me thods and Results We evaluated forearm vascular responses during maxim al semierect cycle exercise in 28 consecutive patients with vasovagal syncope and compared them with 30 age-matched control subjects. We als o evaluated blood pressure responses during erect treadmill exercise ( Bruce protocol), While forearm vascular resistance at rest was similar in the patients with vasovagal syncope and the control group, forearm vascular resistance was markedly lower in the patients than in contro l subjects at peak exercise (85+/-54 versus 149+/-94 units. P=.002). F orearm vascular resistance fell by 3+/-48% during exercise in patients versus an increase of 135+/-103% in control subjects (P<.0001). Systo lic blood pressure during erect exercise was lower in patients versus control subjects (155+/-32 versus 188+/-17 mm Hg, P<.0001). Six of the vasovagal patients complained of exercise syncope or presyncope on sp ecific inquiry, and 4 of these 6 exhibited exercise hypotension during erect treadmill exercise testing. Conclusions Patients with vasovagal syncope exhibit a failure of the normal vasoconstrictor response in t he forearm during dynamic leg exercise. Exercise syncope and presyncop e are not uncommon in unselected patients with classic vasovagal synco pe, as is exercise hypotension.