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

The 12-lead electrocardiograms of 50 patients with 1 anterogradely con ducting accessory pathway were analyzed to obtain characteristics of e lectrocardiographic findings in the midseptal, anteroseptal, true post eroseptal and right free wall accessory pathway locations. Locations w ere confirmed by surgery (33 patients) or radiofrequency catheter abla tion (17 patients). This study analyzed (1) QRS in the frontal plane, (2) delta wave axis in the frontal plane, (3) the angle between QRS an d delta wave axes, (4) the R/S ratio in lead III, (5) negativity of de lta 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 posterosep tal pathways - range from +30 to -60 (-38 +/- 22-degrees); midseptal p athways range from +15 to +60-degrees (+49 +/- 11-degrees); anterosept al pathways range from 0 to +75 (+46 +/- 22-degrees); (2) delta wave a xis in the right free wall -0 to -60-degrees (-32 +/- 22-degrees); tru e posteroseptal -0 to -60-degrees (-43 +/- 18-degrees); midseptal -0 t o +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-degre es; (p = 0.006); (4) the R/S ratio lead III was < 1 in true posterosep tal and right free wall, > 1 in anteroseptal and equal to 1 in midsept al accessory pathways; (5) delta negativity in > 2 inferior leads was observed in the right free wall -90%; in true posteroseptal -90%, in m idseptal -0%, and anteroseptal accessory pathways -0% (p < 0.0001); (6 ) the R/S ratio > 1 in lead V2 was right free wall -20%, true posteros eptal -10%, midseptal -12%, anteroseptal -0% (p < 0.0001). It is concl uded that midseptal and anteroseptal accessory pathways r-an be differ entiated from a right free wall and true posteroseptal location by the QRS axis and delta wave polarity in inferior leads. Midseptal pathway s can be distinguished from anteroseptal pathways by the difference, b etween the QRS and delta wave axes and the R/S ratio in lead III. A QR S/delta wave axis angle of > 20-degrees and an R/S ratio equal to 1 in lead III favor a midseptal accessory pathway location.