The Interdependence Between Electrogram, Total Electrode Impedance and Pacemaker Input Impedance Necessary to Obtain Adequate Functioning of Demand Pacemakers

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Abstract
Electrogram maximum derivatives (DMAX, SMAX) and electro‐gram amplitudes (AMAX, UMAX) (Figure 2), were studied in 71 cases during permanent pacemaker treatment. During the acute phase, (at first implantation), 29 patients were studied, and during the chronic phase, (at pulse generator replacement), 42 patients were studied. Of these patients, 27 (acute phase) and 36 (chronic phase) were studied for tissue impedance (Ry) and interface impedance (Faraday resistance Rp and Helmholtz capacitych)‐ DMAX and SMAX changed from 3.47 ± 0.33 V/s (mean ± SEM) to 2.48 ± 0.23 V/s and 1.93 ± 0.20 V/s to 1.32 ±0.12 V/s; p < 0.02; p < 0.01. AMAX and UMAX remained nearly unchanged from acute to chronic phase. A paired comparison in 13 patients showed almost identical results.Electrograms recorded in patients with bundle branch block showed no statistical difference in DMAX, SMAX, AMAX, and UMAX compared with electrograms recorded in patients with QRS‐complexes of normal duration.No correlation was found between rise in myocardial threshold and fall in DMAX and SMAX from acute to chronic phase; p > O.8, p > 0.5.Patients with coronary heart disease were found to have significantly higher AMAX than patients classified as having rhythm disturbances of primary cause; p < 0.01. Extremely low values of amplitudes and maximum derivatives were found in some patients with myocardial infarctions and cardiomyopathies. No difference existed in DMAX, SMAX, AMAX, and UMAX recorded from electrodes with a 8 mm2area compared with a 12 mm2area (p > 0.5).rtwas statistically significantly higher on the smaller compared with the larger surface electrodes (p < 0.005). There was a slight but not statistically significant fall inrtfrom acute to chronic phase (p > 0.2). Rp ranged from 2.0–94.6 Kohms. There was no statistically significant differences between the 8 mm2compared with the 12 mm2electrodes (p > 0.2).chvaried between 0.7 and 37.0 microfarads, with significantly lower values for the smallest electrodes (p < 0.05), In patients with electro‐grams of borderline amplitudes and maximum derivatives for being sensed, the lowchfound with the small tip electrodes, will give a higher risk of demand failure if the input impedance in the sensing circuit of a demand pacemaker is too low.