Pacing impedance variability in tined steroid eluting leads

The aim of the study was to investigate pacing impedance (PI) behavior in ambulatory patients. Eighteen atrial and 18 ventricular tined steroid eluting leads with 1.2-mm(2) and 5.6-mm(2) electrodes were implanted in 20 patients. At 9-27 months after implantation PI was measured automatically by means of additional algorithms downloaded via telemetry links into implanted Thera(R) pulse generators. PI was determined based on the voltage drop on the output capacitor during the 5 V-1 ms pacing impulse, at the programmable sampling rates from 1 second to 30 minutes. The study examined in particular: (1) PI trends and variations associated with different breathing patterns, body postures, provocative maneuvers, bike exercise, and during 24 hours; (2) impact of pacing rate and AV-delay on PI; (3) correlation between PI variability and pacing threshold, lead configuration, absolute PI value, age, gender, disease, and cardiac chamber. The most important findings were: (1) large PI variations of up to 450 Ohm were observed in properly functioning leads, (2) PI variability exhibited a weak negative correlation with pacing thresholds as if electrode positional stability was not a major factor underlying PI variations, (3) unipolar and bipolar PI variations were equivalent to each other (correlation factor = 0.93) implying that PI was mostly dependent on the circumstances around the lead tip.