THE 12-LEAD ELECTROCARDIOGRAM IN MIDSEPTAL, ANTEROSEPTAL, POSTEROSEPTAL AND RIGHT FREE-WALL ACCESSORY PATHWAYS

The 12-lead electrocardiograms of 50 patients with 1 anterogradely conducting accessory pathway were analyzed to obtain characteristics of electrocardiographic findings in the midseptal, anteroseptal, true posteroseptal and right free wall accessory pathway locations. Locations were confirmed by surgery (33 patients) or radiofrequency catheter ablation (17 patients). This study analyzed (1) QRS in the frontal plane, (2) delta wave axis in the frontal plane, (3) the angle between QRS and delta wave axes, (4) the R/S ratio in lead III, (5) negativity of delta wave in inferior leads, and (6) the R/S ratio in precordial leads. Results were (1) QRS axis in the frontal plane in the right free wall - range from +15 to -65-degrees (-32 +/- 19-degrees); true posteroseptal pathways - range from +30 to -60 (-38 +/- 22-degrees); midseptal pathways range from +15 to +60-degrees (+49 +/- 11-degrees); anteroseptal pathways range from 0 to +75 (+46 +/- 22-degrees); (2) delta wave axis in the right free wall -0 to -60-degrees (-32 +/- 22-degrees); true posteroseptal -0 to -60-degrees (-43 +/- 18-degrees); midseptal -0 to +45-degrees (+24 +/- 15-degrees), and anteroseptal -0 to +60-degrees (+45 +/- 17-degrees); (3) QRS/delta wave axis angle in the right free wall -7 +/- 6-degrees, true posteroseptal -9 +/- 7-degrees; midseptal -22 +/- 6-degrees, and anteroseptal accessory pathway, -3 +/- 5-degrees; (p = 0.006); (4) the R/S ratio lead III was < 1 in true posteroseptal and right free wall, > 1 in anteroseptal and equal to 1 in midseptal accessory pathways; (5) delta negativity in > 2 inferior leads was observed in the right free wall -90%; in true posteroseptal -90%, in midseptal -0%, and anteroseptal accessory pathways -0% (p < 0.0001); (6) the R/S ratio > 1 in lead V2 was right free wall -20%, true posteroseptal -10%, midseptal -12%, anteroseptal -0% (p < 0.0001). It is concluded that midseptal and anteroseptal accessory pathways r-an be differentiated from a right free wall and true posteroseptal location by the QRS axis and delta wave polarity in inferior leads. Midseptal pathways can be distinguished from anteroseptal pathways by the difference, between the QRS and delta wave axes and the R/S ratio in lead III. A QRS/delta wave axis angle of > 20-degrees and an R/S ratio equal to 1 in lead III favor a midseptal accessory pathway location.