Even though sensing ventricular and atrial signals for arrhythmia detection have been widely used in patients, there are issues that need to be resolved to optimize sensing. One of these issues is the detection of the far field R wave (EFRW) signal in the atria which can result in the delivery of inappropriate therapies. In the experimental setting, variables that affect near field atrial signal (P wave) and FFRW are difficult to separate. Few investigators have analyzed the issue of optimal bipolar electrode spacing for P/FFRW differentiation. A better understanding of the variables that effect P/FlFRW ratio is important for optimizing lead design and placement. In this paper, a theoretical model (see Weimin Sun and Xiaoyi Min, IEEE Trans. Biomed. Eng., vol. BME-44, p. 1237-42, 1997) of the sensed signal was utilized. This study focuses on the effect of bipolar electrode tip to ring spacing on P wave and FFRW amplitude and derivative as well as the P/FFRW ratio. Comparison between bipolar and unipolar sensing is also investigated. The model results show that the peak amplitude of P wave varies with the orientation of a bipolar electrode respect to the propagation direction of a wavefront and becomes plateau at tip to ring spacing of 10 mm or greater. However, the far field R wave amplitude increases with greater bipole spacing. Better acute signal to noise can be achieved with smaller bipole spacing. Bipolar signals have higher slew rate and comparable peak amplitude compared with unipolar signals.
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