Initial experience with dual-sensor rate-responsive pacemakers in children

The efficacy of a new single-chamber, rate-responsive pacemaker that utilizes information from two sensors, activity and stimulus to T wave, was evaluated in 15 children during a mean follow-up period of 10.3 +/- 3.3 months (range 5-16 months). There were 10 males and five females, with a mean age of 5.9 +/- 3.8 years (range 9 months-16 years). The indication for pacing was high grade atrioventricular block in 10 (eight postoperative, two congenital), and sinus node dysfunction in five patients. In endocardial implants the mean T wave amplitude was 2.48 +/- 0.7 mV, and mean T wave sensing 91 +/- 6.3%, whereas in epicardial implants T wave amplitude and sensing were inadequate. Each patient underwent 24-h Holter monitoring and 10 performed a graded treadmill test in three sensor-blending modes (Stimulus-T = Activity, Stimulus-T > Activity, Stimulus-T < Activity), using the chronotropic assessment exercise protocol. Sensor cross-checking was analysed by continuous tapping over the pacemaker. Holter monitoring demonstrated that pacing rate variations were closely related to daily activity. At the initial phases of exercise testing, the mean percentage of increase in pacing rate was significantly lower in Stimulus-T > Activity mode, when compared to Stimulus-T = Activity (P < 0.01); however, the initial disparity among the three modes disappeared halfway through the exercise and similar heart rate changes were observed thereafter. Continuous tapping over the pacemaker in Stimulus-T = Activity mode caused an initial increase in pacing rate, and inappropriate responses were quickly corrected by sensor cross-checking. Rate modulation with a single-chamber, dual-sensor pacemaker is adequate and safe in children, and may offer significant advantages over single-sensor devices in endocardial implants.