Stability of far field R wave signals in different conditions

The presence of far field R wave sensing (FFRS) is usually evaluated in patients with dual chamber pacemakers in supine position. To check if this approach is valid, we tested whether FFRS is consistent both in terms of amplitude threshold and timing characteristics in different daily life conditions. In 42 patients with a DDD pacemaker, the presence, amplitude threshold and timing parameters of FFRS were therefore determined, with patients supine, standing and at peak exercise. Measurements were made of paced and sensed R waves, in unipolar and bipolar sensing configurations (at peak exercise only paced R waves and bipolar sensing). After paced R waves (bipolar sensing) amplitude thresholds/time of FFRS after V pace were 0.32+/-0.18 mV/119-139 ms (supine), 0.32+/-0.16 mV/114-130 ms (upright) and 0.27+/-0.13 mV/121-136 ms (exercise) - with unipolar sensing, this was 0.49+/-0.27 mV/101-150 ms (supine), 0.51+/-0.29 mV/100-144 ms (upright). After sensed R waves (bipolar sensing) amplitude thresholds/time of FFRS after V sense were 0.27+/-0.18 mV/24-42 ms (supine), 0.29+/-0.16 mV/18 to 41 ms (upright) - with unipolar sensing, thresholds were 0.59+/-0.32 mV/3-50 ms (supine), 0.59+/-0.36 mV/2-58 ms (upright). given the lower FFRS thresholds with bipolar sensing, bipolar sensing is superior in avoiding FFRS compared with unipolar sensing. No differences were found in terms of amplitude thresholds and timing characteristics with patients supine, standing and at peak exercise. Thus, measurements made in the supine position are basically sufficient to predict the presence/absence of FFRS under different conditions.