Donald Hopper

Assessment of Pacemaker Chronotropic Response: Implementation of the Wilkoff Mathematical Model

FREEDMAN, R.A., et al.: Assessment of Pacemaker Chronotropic Response: Implementation of the Wilkoff Mathematical Model. There are few practical guidelines for proper adjustment of rate responsive pacemaker sensor parameters. This study describes the application of the chronotropic assessment exercise protocol (CAEP) and the Wilkoff model of chronotropic response to assess the adjustment of pacemaker sensor parameters. In 31 patients implanted 1 month previously with a dual sensor pacemaker, pacemaker sensor parameters were adjusted to yield a peak sensor rate of 100 beats/min on a simple 6‐ minute walk (low intensity treadmill exercise [LITE] protocol); the maximum sensor rate was set to the age predicted maximum heart rate (220‐age). The rate response behavior of the pacemaker was then assessed using the slope of metabolic‐chronotropic relation (MCR) during CAEP exercise. After adjustments based on the LITE protocol, CAEP exercise yielded MCR slopes of 0.92 ± 0.25 for the entire study group, which compares well with the predicted normal slope of 1. However, 7 of the 31 patients had sensor MCR slopes during CAEP exercise that were 2 SD or more below expected. To test the sensitivity of this approach to suboptimal pacemaker programming or suboptimal exercise, simulations were performed with the maximum sensor rate programmed below age‐predicted maximum heart rate or with exercise truncated before maximum exertion; with these conditions, MCR slopes were sharply lower for the entire group. The authors conclude that a simple treadmill walk (LITE) allowed for optimum programming of sensor parameters in most patients, but in a minority the chronotropic behavior was underresponsive. Failure to appropriately adjust pacemaker maximum sensor rate or failure to achieve peak exercise sharply limits the accuracy of this methodology.

Design and Rationale of the Assessment of Proper Physiologic Response with Rate Adaptive Pacing Driven by Minute Ventilation or Accelerometer (APPROPRIATE) Trial

Rate-adaptive sensors are designed to restore a physiologic heart rate response to activity, in particular for patients that have chronotropic incompetence (CI). Limited data exist comparing two primary types of sensors; an accelerometer (XL) sensor which detects activity or motion and a minute ventilation (MV) sensor, which detects the product of respiration rate and tidal volume. The APPROPRIATE study will evaluate the MV sensor compared with the XL sensor for superiority in improving functional capacity (peak VO2) in pacemaker patients that have CI. This study is a double-blind, randomized, two-arm trial that will enroll approximately 1,000 pacemaker patients. Patients will complete a 6-min walk test at the 2-week visit to screen for potential CI. Those projected to have CI will advance to a 1-month visit. At the 1-month visit, final determination of CI will be done by completing a peak exercise treadmill test while the pacemaker is programmed to DDDR with the device sensors set to passive. Patients failing to meet the study criteria for CI will not continue further in the trial. Patients that demonstrate CI will be randomized to program their rate-adaptive sensors to either MV or XL in a 1:1 ratio. The rate-adaptive sensor will be optimized for each patient using a short walk to determine the appropriate response factor. At a 2-month visit, patients will complete a CPX test with the rate-adaptive sensors in their randomized setting.