Reliability and variability of impedance measured by real-time telemetry

With the aim to detect dysfunction of pacing leads, most present-day pacemakers measure pacing impedance by means of real-time telemetry. The recommended setting for impedance measurement is 5.0 V for pulse amplitude and 0.5 ms for pulse duration. Availability of reliable settings would facilitate impedance measurements during follow-up. The purpose of the present study was twofold: (1) to assess whether telemetrically measured impedance of the studied pacemaker is similar to impedance measured at implantation; and (2) to evaluate whether the pacemaker setting influences telemetrically measured impedance. Sixty-five consecutive patients receiving VVI(R) pacemakers were studied; in all patients, impedance measured at implantation by a pacing system analyzer was 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 measurement, pulse amplitude was programmed to 0.8, 1.6, 2.5, 5.0, and 8.0 V, and pulse duration to 0.05, 0.25, 0.50, and 1.00 ms. Impedance at implantation (606 +/- 113 ohms) did not differ from the data obtained with telemetry (629 +/- 113 ohms; P = NS). Different pacing rates, repeat measurements, and follow-up time failed to show any influence on impedance. Measurement tolerance was < 10% for 15 of 19 studied settings other than 5.0 V and 0.5 ms.

The studied pacemakers provide reliable data for telemetrically measured impedance. Telemetrical impedance does not necessarily have to be measured at 5.0 V and 0.5 ms. These findings should be considered for measurement and interpretation of real-time telemetry impedance during follow-up.