Even though sensing ventricular and atrial signals for arrhythmiadetection have been widely used in patients, there are issues that needto be resolved to optimize sensing. One of these issues is the detectionof the far field R wave (EFRW) signal in the atria which can result inthe delivery of inappropriate therapies. In the experimental setting,variables that affect near field atrial signal (P wave) and FFRW aredifficult to separate. Few investigators have analyzed the issue ofoptimal bipolar electrode spacing for P/FFRW differentiation. A betterunderstanding of the variables that effect P/FlFRW ratio is importantfor optimizing lead design and placement. In this paper, a theoreticalmodel (see Weimin Sun and Xiaoyi Min, IEEE Trans. Biomed. Eng., vol.BME-44, p. 1237-42, 1997) of the sensed signal was utilized. This studyfocuses on the effect of bipolar electrode tip to ring spacing on P waveand 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 theorientation of a bipolar electrode respect to the propagation directionof a wavefront and becomes plateau at tip to ring spacing of 10 mm orgreater. However, the far field R wave amplitude increases with greaterbipole spacing. Better acute signal to noise can be achieved withsmaller bipole spacing. Bipolar signals have higher slew rate andcomparable peak amplitude compared with unipolar signals
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