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Figure 1 Representative records of pacing-induced mechanical alternans. The traces represent a lead II electrocardiogram (ECG), left ventricular (LV) pressure, and LV dP/dt at a baseline heart rate (HR) of 66 beats/min (bpm) and at atrial pacing of 120 bpm for a male patient with idiopathic dilated cardiomyopathy. Alternating pressure was 30 mm Hg at the pacing rate of 120 bpm. Both LV dP/dt_max and LV dP/dt_min showed alternating changes with LV pressure. dP/dt = first derivative of left ventricular pressure.