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Figure 6 Left anterior descending coronary artery flow velocity recording in a patient from Group I during atrial pacing. (A): at baseline under pacing at 100 beats/min; (B): during maximal hyperemia under pacing at 100 beats/min; (C): during maximal hyperemia under pacing at 140 beats/min. The reduction in cycle length at the higher pacing rate is at the expense of the diastolic flow, indicating that pacing-induced tachycardia leads to a reduction in time-averaged peak flow velocity (as early diastolic flow did not increase significantly) and hence a reduction in coronary flow reserve.