Distinguishing septal and free wall original sites based on: 1) R wave on DII, DIII, aVF was narrower, symmetrical and lacked "notching" with Se 83, 78%, Sp 82, 14%, PPV 92, 54% and NPV 65, 71%, and 2) QRS duration on DI ≤ 140 msec with Se 86, 49%, Sp 98, 86%, PPV 72, 22% and NPV 96, 97%.