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Figure 2 Alternans Predominates in AP Phase II of LV APs
Alternans predominates in AP phase II of left ventricular (LV) APs in this 59-year-old man with coronary artery disease and an LVEF of 21%. (A, B) Action potential duration (APD) does not oscillate during pacing. However, (C) marked AP amplitude alternans in phase II is seen (red/blue separation). (D) AP alternans occurs in phase II (arrows, k-score = 7.9, absolute voltage of alternation [Valt] = 59 µV) but is undetectable in phase III (k-score = –0.38); AP duration variations were also minimal. (E) T-wave alternans (TWA) was positive at this time (arrows) in leads Y, Z, and Vm. Abbreviations as in Figure 1.