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Background: The daily activity of pediatric patients with implantable cardiac devices provides behavioral evidence of functional outcomes. Modern devices provide continuous accelerometer data that are sensitive to movement, but normative values have not been published for pediatric activity rates. This study provides the first normative accelerometer data on activity rates in a large sample of pediatric cardiac device patients., Methods: Patients were between 3 and 18 years old (N = 1,905) and implanted with a cardiac device from a single device company, and enrolled in remote monitoring., Results: The median age at implant was 14 years (interquartile range = 12-16); 61.3% were male. Data for 4 weeks were extracted from a company database at 53 weeks postimplant and an average of daily activity was calculated. Daily average activity for all patients was 5.4 hours (standard deviation  =  2.0). In a multivariate analysis, increased level of activity was associated with: being male, having a pacemaker versus implantable cardioverter defibrillator (ICD), epicardial device location, rate response turned off, having experienced a shock, and younger age., Conclusions: These results provide the first baseline data of physical activity in children with implanted cardiac devices and provide a clinical guide to physical activity assessment in this population. Further, our data suggest physical activity in children with implantable cardiac devices may differ based on demographic variables, device type, device location, indication for implantation, and history of ICD shock., (© 2017 Wiley Periodicals, Inc.)

It has been established that the chronic thresholds of cardiac pacing leads vary as a function of the (spherical) electrode's radius or (geometric) surface area and the thickness of fibrotic encapsulation. Where the radius of the electrode is equal to the thickness of the fibrous capsule (about 0.7 to 1 mm for polished surfaces), threshold should be at a minimum. Where the radius of the electrode is larger or smaller than the thickness of the fibrous capsule, then thresholds should increase since the electric field strength required to stimulate decreases as the square of the distance between the electrode's surface and stimulatable tissue. In addition, it has become (incorrectly) accepted that small electrodes do not sense well. About 8-mm electrodes, therefore, became the "standard" surface area, providing the best tradeoffs between pacing and sensing. Analysis of 18 years of canine data in our laboratory, however, suggest that these relationships may be overemphasized for the surface areas of clinical interest. In fact, new small porous and steroid-eluting electrodes do not have high thresholds, are efficient, and their sensing is excellent.