Patent foramen ovale (PFO) is associated with numerous clinical conditions, such as cryptogenic stroke, paradoxical embolism, migraine headaches, decompression illness, and shunt-related hypoxemia. As a result, transcatheter closure of PFO has become relatively common, driven by the apparent ease of the procedure, patient and clinician preference over medical therapy, and numerous retrospective analyses demonstrating clinical benefit. The procedure is performed under conscious sedation and, in experienced hands, can been done routinely in under 30 min. The fact that there have been no large prospective randomized trials to prove the efficacy of PFO closure has done little to dissuade the enthusiastic use of closure devices.
See page 561The immediate and long term goal of transcatheter PFO closure is elimination of right-to-left shunt (RLS) through the interatrial septum. When detected, RLS is generally secondary to an atrial level shunt (i.e., PFO), but noncardiac RLS (primarily intrapulmonary) has also been implicated in the pathophysiology of clinical conditions resulting from paradoxical embolism (1). Intrapulmonary RLS can coexist with PFO and in some cases can be mistaken as a source of RLS in a patient presumed to have a PFO. For instance, in the MIST (Migraine Intervention With STARFlex Technology) trial, 5 of the 74 patients with RLS randomized to PFO closure actually had no PFO found at the time of the procedure. The cause of the RLS in these patients was presumably due to an intrapulmonary shunt (2). The presence of coexisting intrapulmonary shunting would clearly have major implications when designing trials to assess the efficacy of PFO closure to eliminate RLS. Methods to identify these confounding patients have not been welldescribed in published reports to date.Jesurum et al. (3), in this issue of JACC: Cardiovascular Interventions, describe a novel method to assess the prevalence of secondary (intrapulmonary) RLS in patients undergoing transcatheter closure of PFO. During sizing-balloon inflation within the PFO (and presumed occlusion of the PFO due to lack of color flow seen with intracardiac echocardiography [ICE] around the balloon), agitated saline was injected into the inferior vena cava with calibrated respiratory strain, followed by assessment of RLS via transcranial Doppler (TCD). If Ͼ10 embolic tracks were detected, this was defined as a "secondary RLS." After PFO closure, residual RLS was assessed immediately with agitated saline and TCD and in late follow-up with TCD and transthoracic echocardiography. This study demonstrated that those subjects with RLS during balloon inflation (secondary RLS) were significantly more likely to have RLS during immediate and late follow-up when compared with those patients without RLS during balloon inflation. Patients with secondary RLS also had more atrial septal aneurysms (p ϭ NS) and significantly larger PFO waist diameters than those without secondary RLS (p ϭ 0.013). With these data, the authors concluded that ICE, TCD, and balloon occlusion can be...