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Figure 3 Representative data for a patient with a typical microvolt alternans of the T wave during exercise testing. Alternans analysis for leads VM, X, Y, Z, and V4 is shown. The dark shaded areas for each lead indicate regions for which the Valt has a Ralt 
3 SD above the level of noise. Dark shaded areas, which also have %Bad, RPM, Resp and HR Delta indices in the acceptable range, are indicated by a black line along the time axis. In this representative patient, the Valt is 8.8 µV and the Ralt is 759 for lead Z. The alternans increased as the heart rate increased. HR, heart rate trend; %Bad, percentage of beats more than 10% premature; Noise, mean noise in lead VM; eVM, eX, eY, eZ, eV4, enhanced VM, X, Y, Z, and V4 leads; RPM, bicycle ergometer pedaling rate during exercise; Resp, respiratory frequency (0.25 cycles/beat); HR Delta, the difference between the highest and lowest instantaneous heart rates for a 128-consecutive beat interval; RR Alternans, the amplitude of RR interval alternans.