Convulsive syncope after bidirectional Glenn shunts: physiological implications for a neurological event.

OBJECTIVES: Neurological complications after cavopulmonary connections like bidirectional Glenn shunt and Fontan connection are occasionally encountered in the postoperative period. We discuss such a case of bilateral bidirectional Glenn shunt which developed convulsive syncope postoperatively. CASE: A 5-year-old cyanotic girl diagnosed as tricuspid atresia with pulmonary stenosis without any spell history underwent bilateral bidirectional Glenn shunt on the way to a subsequent Fontan. After an uneventful surgery she developed convulsive syncope on straining for defecation in the postoperative period. A thorough neurological and arrhythmia study failed to elicit any organic lesions. DISCUSSION: The diagnosis of a neurological event after a single ventricle palliation is paramount to its management. Differentiating syncope from a seizure has its own management implications. The etiologies of neurological complications are varied after cardiac surgery. The physiology and etiology of syncope and seizure after a cavopulmonary connection is discussed. The role of physiological factors in a situation of altered physiodynamics like a bidirectional shunt and Fontan has not been dealt with before in a clinical setting. We have discussed this case to understand the effects of these factors. The effects of strain on the systemic venous pressure, the pulmonary artery pressure and the intrathoracic pressure, can lead to a neurological event if balance is not maintained between the driving pressure of the systemic venous pressure and the pulmonary capacitance. We have devised a simple test to identify these subsets preoperatively by a modification of the Valsalva maneuver. CONCLUSION: Although neurological complications crop up occasionally after single ventricle palliation, not much in-depth analysis has been done regarding the physiological factors involved after such an altered physiology. The effects of systemic venous pressure, the pulmonary artery pressure and the intrathoracic pressure must be in harmony for proper functioning of the shunt; thus strain can alter physiodynamics to such an extent to manifest clinically as a neurological event. The modified Valsalva maneuver can be applied clinically as a 'biomarker' to identify a subset of patients prone for neurological complications.