With the increasing use of transesophageal echocardiography during cardiac surgical operations, the presence of incidental patent foramen ovale (PFO) is being detected more frequently. Since it is estimated that the incidence of PFO is 17%–35% in the general population (1,2), this situation is quite common. Unfortunately, there are no randomized clinical trials to guide the decision as to whether PFO closure is appropriate in these patients.
As for all therapeutic decisions, the benefit and risk of a proposed procedure (in this case, incidental PFO closure during cardiac surgery) must be compared with the benefit and risk associated with the alternative (in this case, ignoring the PFO). As is usually the case, this results not in a single answer to the question, “should I close the PFO,” but rather a range of answers, from “absolutely in this patient” to “only if this patient has x risk factors,” to “absolutely not in this patient.”
To understand the relative frequency of these answers, we must look more closely at the benefit versus risk equation. What is the risk of closing a PFO? More accurately, what is the additional risk associated with PFO closure, above and beyond the risk of the planned cardiac surgical procedure? This depends somewhat on the status of the patient and the magnitude of the procedural deviation represented by the addition of PFO closure. For patients undergoing procedures already requiring cardiopulmonary bypass (CPB) and bicaval cannulation (e.g., mitral or tricuspid valve surgery), this deviation is minimal; for those undergoing procedures not requiring bicaval cannulation (e.g., aortic valve replacement, coronary bypass surgery), the deviation is a bit more substantial, involving a change in the cannulation scheme; for procedures otherwise done without CPB (e.g., off-pump coronary artery bypass surgery), the deviation is most significant, requiring institution of extracorporeal support. The incremental risk of closing a PFO in the first two instances is negligible; in the third, in which CPB must be instituted, it is significant, and the magnitude of this significance depends on patient characteristics. There are certainly specific patient populations in whom avoidance of CPB is considered prudent (severe aortic calcification, heparin-induced thrombocytopenia with thrombosis, renal insufficiency, etc.). Excluding this group of high-risk patients (who comprise a small proportion of all patients having cardiac surgery), it is fair to assume that addition of PFO closure in a patient already undergoing cardiac surgery with CPB should result in a very small incremental risk, especially since published series of patients having surgery for PFO alone report very low morbidity and no mortality (3,4).
The assessment of the second half of the equation, the potential benefit of incidental PFO closure, is a bit less straightforward, owing to the substantial controversy surrounding the management of PFO in general. The proposed benefits of incidental PFO closure surgery are prevention of two sequelae of right-to-left interatrial shunting: systemic thromboembolism and hypoxemia. Of the 700,000 strokes that occur in the United States each year, 20% are cryptogenic, and 40%–50% of these patients have PFO (5). The incidence of PFO, and especially large PFO, is significantly higher in patients with cryptogenic stroke than those with strokes of known causation (6), leading to estimates that as many as 60,000 strokes per year are caused by paradoxical embolism through PFO (5). In certain populations with PFO, e.g., those with atrial septal aneurysms and a history of stroke, the incidence of recurrent stroke is as high as 15% (7). Paradoxical embolism through a PFO is also a concern in patients at risk with a history of pulmonary embolism, due to the unfavorable combination of right atrial thrombus and increased right atrial pressure (8). Finally, hypoxemia due to shunting through a PFO has been reported during and after cardiac surgical procedures (9,10), and is of particular concern in the setting of high right atrial pressures (e.g., pulmonary hypertension, right ventricular failure, pneumonia) and/or low left atrial pressures (e.g., left ventricular assist device insertion).
In patients presenting with cryptogenic stroke and PFO but no other indication for surgery, there is substantial controversy about whether to close the PFO, mainly because this involves an otherwise unplanned procedure with its attendant risks. For the patient who is found to have a PFO during an already planned cardiac operation, there is much less controversy. In this situation, the foregoing analysis of the risk/benefit relationship leads me to conclude that the available evidence supports closure of the PFO:
- In all cases in patients whose planned operation already involves CPB, since the small risk of altering the cannulation scheme and slightly prolonging the bypass time is outweighed by the chance that a cryptogenic stroke will be averted perioperatively or thereafter.
- In most cases, even if the originally planned operation does not involve CPB, if the patient has a history of stroke (especially if cryptogenic), pulmonary embolism, pulmonary hypertension, or right ventricular failure, especially if the PFO is large, except in cases in which CPB is contraindicated (e.g., calcified aorta, heparin-induced thrombocytopenia with thrombosis).
Of course, patients, their families, and referring physicians should be involved in decisions leading to modification of planned operations whenever possible. However, in the circumstances outlined above, the available data support the decision to proceed with PFO closure in the vast majority of patients.
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