An Unusual Location of the Accessory Pathway on the Anteromedial Side of the Mitral Annulus

Several algorithms have been proposed for the localization of an accessory pathway the pre-excited 12-lead ECG. Some of these algorithms are based on the polarity of the QRS complex, 1-2 as others are based on a combination of QRS and delta-wave polarities. 3–5 However, none of these algorithms is 100% sensitive or specific. Furthermore, there may be considerable variations between algorithms in the predicted site of the accessory pathway, particularly in cases with minimal pre-excitation or pre-excitation in more unusual locations. This brief case report describes a patient with frequent episodes of palpitations and electrocardiographic abnormalities consistent with pre-excitation and multiple episodes of tachyarrhythmia such as atrioventricular reciprocating tachycardia and pre-excited atrial fibrillation, with an unusual location of the accessory pathway. The patient was a 42-year-old female. Her 12-lead ECG showed evidence of pre-excitation with a positive delta wave in V1, and II, III, aVF and a negative delta wave in I, aVL, and aVR. During electrophysiologic study, an orthodromic atrioventricular reciprocating tachycardia was induced and the earliest site of retrograde atrial depolarization was recorded at the proximal site of the coronary sinus. Meticulous mapping via septostomy and during tachycardia showed the local ventriculoatrial fusion in the anteromedial mitral annulus, and radiofrequency application in this area resulted in the termination of the tachycardia and elimination of the accessory pathway.