Do daily threshold trend fluctuations of epicardial leads correlate with pacing and sensing characteristics in paediatric patients?

AIMS: To evaluate whether the magnitude of daily ventricular pacing threshold fluctuations (Deltafluctuation) in trend graphs of stored diagrams correlate with ventricular threshold and sensing changes over time.

METHODS AND RESULTS: A total of 56 children received AutoCapture devices (St. Jude Medical, Sylmar, CA, USA) connected to steroid-eluting epicardial leads. Maximum lead age at study closure was 12.2 years (median 4.0). Telemetry data and daily Deltafluctuation were obtained every 6 months. Regression slope coefficients and mean values of repeated measurements were calculated for each patient's course. High daily Deltafluctuation correlated with higher pacing thresholds (rho = 0.68, P < 0.001), lower impedances (rho = -0.38, P = 0.004), and a Deltafluctuation-incline (rho = 0.34, P = 0.01) over time. Furthermore, a Deltafluctuation-incline correlated with a pacing threshold-incline (rho = 0.34, P = 0.01). No correlation was observed for ventricular sensing. Higher daily Deltafluctuation were observed if lead age was > 5 years compared with <or= 5 years (0.75 vs. 0.55 V@0.5 ms, P = 0.028).

CONCLUSION: High amplitudes of daily Deltafluctuation correlate with higher and increasing pacing thresholds and lower impedances. Theoretically, this results from electrode microinstability on the epicardial surface. A decrease of the steroid-eluting potency of the electrode can be hypothesized to cause higher daily Deltafluctuation beyond a lead age of 5 years. Potential implications of marked daily Deltafluctuation are short-term follow-up and lead replacement in the presence of high pacing thresholds.