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Rejection diagnosis was exclusively handled with noninvasive techniques in 16 children (mean age, 8.6 +/- 5.7 years; range, 0.9 to 15.2 years) over a total follow-up period of 18.3 patient years. No endomyocardial biopsies were performed. Intramyocardial electrogram recordings and echocardiographic investigations were used as two noninvasive techniques for rejection diagnosis. Daily noninvasive telemetric monitoring of the overnight intramyocardial electrogram was the major diagnostic guideline. The intramyocardial electrogram signal of the sleeping child was transmitted to a bedside receiver by an implanted telemetric pacemaker. The QRS amplitude was automatically analyzed and transferred to the in-hospital computer via a telephone modem connection. Rejection was diagnosed when QRS amplitude fell more than 8% below average baseline levels for 3 successive days, which was the indication for hospital admission. Medical antirejection treatment was instituted only if echocardiography showed impaired early diastolic left ventricular relaxation concomitant with a QRS-amplitude loss. The echocardiographic criterion was a prolongation of the parameter Te (Te is defined as the time span between onset of diastole and peak relaxation velocity of left ventricular wall) by more than 10 milliseconds compared to previous intraindividual values. Survival after a mean follow-up time of 13.7 months (range, 2 to 57 months) is 100%. A total of 22 rejection episodes were treated. During the first 6 postoperative months, the incidence of rejection requiring treatment was 1.4 episodes per patient. In patients at home, distant monitoring detected 13 episodes of a significant QRS-amplitude drop, which led to hospital readmission. In eight children, echocardiography was likewise positive, and rejection treatment was instituted. One child with positive intramyocardial electrography received antirejection treatment because of clinical evidence of rejection, although echocardiography was negative. In three instances, systemic infection was associated with the QRS-voltage loss. In one child a reason for QRS-complex reduction could not be identified. One rejection episode was treated on the grounds of clinical signs and positive echocardiography without a significant QRS-voltage drop. We conclude that distant noninvasive rejection monitoring based on meticulous application of the techniques described is a safe procedure. Daily monitoring of QRS amplitude in patients at home is an excellent safeguard against overlooking significant rejection episodes. This is of special importance in infants and children, in whom routine endomyocardial biopsy cannot be performed. Distant overnight monitoring minimizes psychosocial disturbance during follow-up after heart transplantation.