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Bipolar Ventricular Far‐Field Signals in the Atrium

1999; Wiley; Volume: 22; Issue: 11 Linguagem: Inglês

10.1111/j.1540-8159.1999.tb00379.x

1540-8159

G. Fröhlig, ZARAH HELWANI, Oliver Kusch, MONIKA BERG, H. Schieffer,

ECG Monitoring and Analysis

In an attempt to evaluate the prevalence and predisposing factors of bipolar ventricular far‐field oversensing, 57 patients were studied who had a Medtronic dual chamber pacemaker implanted (models 7940: n = 6; 7960i: n = 41; 401: n = 3; 8968i: n = 7) and bipolar atrial leads with a dipole spacing from 8.6 to 60 mm attached to various parts of the atrial wall (lateral/anterior: n = 30; appendage: n = 10; atrial septum: n = 10; floating: n = 7). Median bipolar sensing threshold for P waves was 4.0 mV (2.8–4.0 mV, lower and upper quartile) with standard leads and 0.35 (0.25–1.4) mV with single pass (VDD) devices. At the highest sensitivity available, 43 of 50 DDD pacemakers but only two of seven VDD systems detected intrinsic R waves in the atrium (P < 0.01). Ventricular far‐field oversensing occurred at 0.5 mV in 28 (56%) and at 1.0 mV in 16 of 50 DDD units (32%), respectively, and there was one observation in a septal implant at a sensitivity of even 2.8 mV. With ventricular pacing, VDD systems were as susceptible to far‐field signals as DDD pacemakers. Outside the postventricular blanking period (100 ms), evoked R waves were detected by 27 of 57 systems (47%) at maximum atrial sensitivity, by 10 (18%) at 0.5 mV, and by 2 (4%) at a setting of 1.0 up to 1.4 mV, respectively. There was no definite superiority of any lead position, there was a trend in favor of the atrial free wall for better intrinsic R wave rejection, but just the opposite was the case for paced ventricular beats. Bipolar signal discrimination tended to be higher with short tip‐to‐ring spacing (17.8 mm) but the difference to larger dipole lengths (30–60 mm) was not significant in terms of the R to P wave ratio and the overall far‐field susceptibility. In summary, bipolar ventricular far‐field oversensing in the atrium is common with short postventricular blanking times and high atrial sensitivity settings that may be warranted for tachyarrhythmia detection and mode switching. A potentially more discriminant effect of shorter dipole lengths (≤ 10 mm) remains to be tested.