Failure of surgery in preexcitation. Correlation with pathologic findings.

A 37-year-old man with mitral stenosis and recurrent drug-resistant paroxysmal atrial fibrillation, paroxysmal supraventricular tachycardia, and preexcitation, underwent two surgical attempts to ablate an anomalous pathway (AP). Electrophysiologic study demonstrated a left posterior AP with a short antegrade refractory period. Epicardial mapping at the time of mitral valve replacement (left lateral thoracotomy) suggested a posterior right AP. Mitral valve replacement and incision of the left atrial wall failed to cure preexcitation. Epicardial mapping at a second operation (median sternotomy) demonstrated a subepicardial left posterior AP. Right atrial and atrial septal incisions failed to cure preexcitation. Serial section of the atrioventricular rings and conduction system demonstrated an intact left posterior anomalous atrioventricular muscle bundle with surgical incision placed above the plane of the mitral anulus.