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Figure 2 The PJRT cycle length, measured from serial electrocardiograms, is plotted against age in 9 patients presenting during the first 2 years of life. Two serial electrocardiograms were available in 3 patients, three in 1 patient, six in 1 patient, seven in 1 patient, nine in 1 patient, twenty-one in 1 patient and twenty-seven in 1 patient. The data under 2 years of age were obtained from 4 of the 9 patients. To examine for a trend in the data, the curvilinear line in this figure and in Figures 3 and 4 was created by subjecting the data to a nonparametric smoothing technique (Systat, Inc, Aurora, Colorado). Note the gradual increase in cycle length with increasing age. The patients were on no medications for the initial electrocardiogram; later in their course, digoxin, flecainide and propranolol were used predominantly, with no effect on the tachycardia. No measurements were made in the 2 patients during amiodarone therapy. Although drug effect cannot be fully excluded from the serial observations depicted in this figure as well as in Figures 3 and 4, it is unlikely that marked effects occurred given the persistence of the arrhythmia and the uneven use of and inconsistent compliance with the antiarrhythmic agents.
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