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Figure 1 Measurement of ARI and Maximum Slope of Repolarization Restitution Curve

(A to C) Unipolar electrograms (EGMs) and their first derivatives (dV/dt) of the S2 at S1 to S2 intervals of 250 ms, 280 ms, and 310 ms with a basic drive cycle length (BCL) of 600 ms are shown. The activation recovery interval (ARI) is the interval between the minimum dV/dt of the QRS and minimum dV/dt of the T wave (between the two dashed lines). (D) The ARI restitution curve is constructed by plotting the ARIs of the S2 against the preceding diastolic intervals. The least-squares linear fit to the 40-ms diastolic interval with the maximum slope is shown. A, B, and C of the curve correspond to the ARIs in A, B, and C, respectively.