ACCURACY OF TELEMETRY SIGNALS IN THE POSTIMPLANTATION MONITORING OF ELECTROGRAMS SENSED BY PACEMAKERS

Monitoring of electrograms (EGMs) sensed by pacemakers (PMs) during th eir lifetime is of the utmost importance, since changes of these signa ls, due to modifications of the electrode-myocardial interface may occ ur compromizing the proper functioning of the PM. Since after implanta tion these intracardiac signals are accessible only by means of a tele metry system, it is necessary to ascertain how faithfully the telemetr ic signals reproduce the direct ones. To this aim we devised an accura te method based on linear system theory, which allows the estimation o f the transfer function of the PM-telemetry system and the comparison of a set of time and frequency domain parameters (wave amplitude, slew rate frequency at the spectrum peak and bandwidth) computed on both d irect and telemetric signals. To overcome the problem that these two s ignals cannot be recorded simultaneously, an appropriate model of the input and output signals of the PM-telemetry system and of their inter relationship was identified. This model relies on a set of reasonable assumptions about the nature of the direct signal (supposed to have a fixed morphology within a predefined analysis window) and of noise sou rces corrupting both the direct and telemetric signals. Owing to the i nvolvement of deterministic and stochastic signals, the theory of quas i-stationary signals was employed to obtain the system transfer functi on. To test ou, method, direct and telemetric recordings were performe d on 12 patients with atrial sensing carrying Medtronic Pacemakers (Mo d Elite 7077/7086, programmer Mod 9760) with unipolar steroid eluting leads' (Medtronic Capsure 4523). The results we obtained demonstrate t hat the specific system considered acts as a low-pass filter with a -3 dB frequency at about 90 Hz: this ensures that the telemetric signal contains almost all the information of the direct one and can be used to monitor the changes of the signals sensed by the PIM.