▁prior ▁to ▁surg ery . ▁ ▁( If ▁Eisen men ger ' s ▁phys i ology ▁has ▁set ▁in , ▁the ▁right - to - left ▁sh unt ▁must ▁be ▁shown ▁to ▁be ▁revers ible ▁with ▁pul mon ary ▁ar tery ▁vas od il ators ▁prior ▁to ▁surg ery .) ▁ ▁S urg ical ▁mort ality ▁due ▁to ▁closure ▁of ▁an ▁AS D ▁is ▁lowest ▁when ▁the ▁procedure ▁is ▁performed ▁prior ▁to ▁the ▁development ▁of ▁significant ▁pul mon ary ▁hy pert ension . ▁ ▁The ▁lowest ▁mort ality ▁rates ▁are ▁achieved ▁in ▁individuals ▁with ▁a ▁pul mon ary ▁ar tery ▁syst ol ic ▁pressure ▁less ▁than ▁ 4 0 ▁mm H g . ▁If ▁Eisen men ger ' s ▁synd rome ▁has ▁occurred , ▁a ▁significant ▁risk ▁of ▁mort ality ▁exists ▁regardless ▁of ▁the ▁method ▁of ▁closure ▁of ▁the ▁AS D . ▁In ▁individuals ▁who ▁have ▁developed ▁Eisen men ger ' s ▁synd rome , ▁the ▁pressure ▁in ▁the ▁right ▁vent ric le ▁has ▁raised ▁high ▁enough ▁to ▁reverse ▁the ▁sh unt ▁in ▁the ▁at ria . ▁ ▁If ▁the ▁AS D ▁is ▁then ▁closed , ▁the ▁after load ▁that ▁the ▁right ▁vent ric le ▁has ▁to ▁act ▁against ▁has ▁suddenly ▁increased . ▁ ▁This ▁may ▁cause ▁immediate ▁right ▁vent ric ular ▁failure , ▁since ▁it ▁may ▁not ▁be ▁able ▁to ▁p ump ▁the ▁blood ▁against ▁the ▁pul mon ary ▁hy pert ension . ▁ ▁S urg ical ▁closure ▁ ▁S urg ical ▁closure ▁of ▁an ▁AS D ▁involves ▁opening ▁up ▁at ▁least