Resumen

GUTIERREZ SOTELO, Oswaldo. Variación crónica del umbral de estimulación en pacientes portadores de marcapasos cardiacos. Rev. costarric. cardiol [online]. 2006, vol.8, n.2, pp.19-23. ISSN 1409-4142.

Introduction: The chronic threshold (CT) in patients (Ps) with cardiac pacemakers (PM) is usually measured every 6 to 12 months. Nevertheless CT could have variations that imply clinical consequences related to "loss of capture". This study evaluated CT by mean of automatic measurements performed by the PM software. The main objective was to assess intra and interindividual variations of CT. Materials and methods: We prospectively included Ps with implanted PM with an automatic capture detection algorithm available in the device. It automatically measures CT every 8 hours and averages those values every 2 days. After the follow-up period, we calculated the difference between max CT and min CT, between mean max CT and mean min CT and the individual U slope, reflecting intraindividual variations, and the mean CT x 2, the mean CTx2 - CT max and 2,5 V - CT max that compares our results with routine programming double CT or 2,5 V as output. Results: We collected 1569 mean CT measurements, max CT and min CT values in 11 Ps (21 - 92 y/o) during a 8-19 weeks follow-up period. The difference between max CT and min CT was > 1 V in 5 Ps, 1,6 in 2 and > 3 in 3 Ps. In the other 6 it was < 0,76 V. The differences between mean max CT and mean min CT were similar. Individual CT slope curves had minimal variations in 7 Ps and exhibited significant variations in 4. Mean CT x 2 was > 2,5 in only 2 Ps (4,1 and 2,7). The other 9 had CT <1 V. Mean CT x 2 - max CT was negative in 4 Ps and 2,5 - max CT was negative in the other 4, indicating that programming double CT or 2,5 V as output is not so safe all the time. Conclusion: There are important intra and interindividual differences in CT and doubling the threshold or to program the output at 2,5 V as a safety margin may not be enough.

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