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Figure 5 The P waves in sinus rhythm and atrial ectopy for the high crista and right superior pulmonary vein. Foci at the right superior pulmonary vein show a change in configuration in lead V1 from biphasic in sinus rhythm to upright in tachycardia, a change not observed for right-sided tachycardias. SR = sinus rhythm; other abbreviations as in Figure 1.