Background: The drop in T wave amplitude of the ventricular pace-evoked response (VER) is a well-recognized and reliable mean of detecting localized conditions of myocardial hypoxia. In patients who undergo pacemaker implantation, the post-implant change at the electrode-tissue interface consists of an early inflammatory reaction. The aim of this study was to establish whether the extent of the inflammatory reaction following an endocardial lead can be assessed by the changes in the T wave amplitude of VER.
Methods: Modifications in VER amplitude and the correlation between these changes and pacing threshold time-course were evaluated in 30 patients receiving an endocardial catheter. Telemetered endocardial recordings of T wave amplitude and pacing thresholds were measured at the time of implant and after 1, 2, 3, 7, 14 and 30 days.
Results: A biphasic time-course was observed for T wave, characterized by reduction in amplitude of 48% (p < 0.005) from baseline at day 3 and subsequent increment up to 84% (p = ns) of the baseline value at day 30. By using a linear regression analysis, a significant correlation between T wave changes and increment in pacing threshold was found (r = 0.81; p < 0.002). A higher pacing threshold increment was observed in patients having a decrease in VER amplitude > or = 1 mV at 3rd in comparison with patients with a decrease in VER amplitude < 1 mV (1.1 +/- 0.4 vs 0.2 +/- 0.2 V; p < 0.001).
Conclusions: VER recordings during the first days after endocardial lead implantation may be a valuable means of assessing the extent of the inflammatory reaction developing at the electrode-tissue interface. This method may be useful for early identification of patients at risk of increases in pacing threshold and for evaluation of the biocompatibility of different leads.