RELIABILITY AND VARIABILITY OF IMPEDANCE MEASURED BY REAL-TIME TELEMETRY

With the aim to detect dysfunction of pacing leads, most present-day p acemakers measure pacing impedance by means of real-time telemetry. Th e recommended setting for impedance measurement is 5.0 V for pulse amp litude and 0.5 ms for pulse duration. Availability of reliable setting s would facilitate impedance measurements during follow-up. The purpos e of the present study wets twofold: (1) to assess whether telemetrica lly measured impedance of the studied pacemaker is similar to impedanc e measured at implantation; and (2) to evaluate whether the pacemaker setting influences telemetrically measured impedance. Sixty-five conse cutive patients receiving VVI(R) pacemakers were studied; in all patie nts, impedance measured at implantation by a pacing system analyzer wa s compared to measurements obtained telemetrically within 1 day after implantation. In 44 other patients, impedance was determined 3 months after implantation at 60 and 120 ppm (n = 44), twice at 60 ppm (n = 42 ), and 12 months after implantation at 60 ppm (n = 34). For each measu rement, pulse amplitude was programmed to 0.8, 2.6, 2.5, 5.0, and 8.0 V, and pulse duration to 0.05, 0.25, 0.50, and 1.00 ms. Impedance at i mplantation (606 +/- 113 ohms) did not differ from the data obtained w ith telemetry (629 +/- 113 ohms; P = NS). Different pacing rates, repe at measurements, and follow-up time failed to show any influence on im pedance. Measurement tolerance was < 10% for 15 of 19 studied settings other than 5.0 V and 0.5 ms. Conclusion: The studied pacemakers provi de reliable data for telemetrically measured impedance. Telemetrical i mpedance does not necessarily have to be measured at 5.0 V and 0.5 ms. These findings should be considered for measurement and interpretatio n of real-time telemetry impedance during follow-up.