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Figure 5 Discordance With Ectopics
Discordant alternans initiated by ectopic beats in 1 patient. The top tracing shows unipolar ventricular electrograms from epicardial electrode (Epi) 1 during atrial pacing at cycle length 600 ms. Note the 2 spontaneous ectopic beats. The bottom 3 tracings show the corresponding beat-to-beat voltages (at identical time points in the JT interval) for epicardial electrodes 1 to 3. The odd and even beats are indicated by open circles and filled circles, respectively. The ectopic beat and the preceding beat are replaced with an average of the other beats and are indicated by a filled square. After the second ectopic beat (square), discordant alternans develops between electrode 1 and electrodes 2 to 3.
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