Mechanism of Decrease in the Atrial Potential After Implantation of a Single‐Lead VDD Pacemaker:

Abstract

The single-lead VDD pacemaker system (VDDPS) enables atrial synchronous ventricular pacing with only one lead in patients with an atrioventricular block. There are some cases in which the atrial potential decreases after implantation of a VDDPS, making physiological pacing difficult. The mechanism of this decrease has not been elucidated yet. To elucidate the possible relationship between the decrease of the atrial potential after implantation of a VDDPS and histopathological changes of the atrium. We implanted a VDDPS from the jugular vein under anesthesia in 10 adult dogs. The tip of the pacing lead was fixed in the right ventricular apex of the heart under fluoroscopic guidance. Then, the lead was ligated and fixed to the jugular vein at a point where a favorable atrial potential was obtained. The end of the lead was passed from the neck to the back subcutaneously; then pulled outside and fixed there to measure the atrial potential. The atrial potential was measured using a pacing system analyzer under anesthesia on days 3 (n = 9) and 7 (n = 8), as well as on weeks 2 (n = 6), 3 (n = 4), and 4 (n = 3), after the implantation. The heart was removed from the dogs on day 3 (n = 2), day 7 (n = 2), week 2 (n = 2), and week 4 (n = 4) to examine the atrial histological findings. The atrial potential was 2.7 +/- 0.7 mV at the time of the implantation, 1.7 +/- 1.1 mV (P < 0.05) on day 3, and 1.7 +/- 0.7 mV on week 4 after the implantation. Macroscopically, the pacemaker lead was covered with thrombus, and adhered to the atrial wall in 80% of animals. Microscopically, the endocardium was hypertrophic due to fibrous tissue; besides RBC extravasation, inflammatory cells infiltration and degeneration of myocardial cells, were observed under the endocardium. Inflammatory changes developed in the atrial wall after implantation of the VDDPS, and this seemed to be one of the mechanisms for the decrease of the atrial potential of the VDDPS.

Biochemical Evidence of Cardiac Damage Following Transvenous Implantation of a Permanent Antibradycardia Pacemaker Lead

“…Coagulation necrosis of the myocardial tissue around the electrode has been reported in the first hours after both epicardial 11 and endocardial 18 lead implantation, followed by an acute inflammatory response. Coagulation necrosis and myocytolysis have also been reported in the studies performed a few days to several weeks after lead implantation and have been attributed to focal myocardial hypoxia around the implanted leads due to proliferation of endocardial and interstitial connective tissue 1,2,4,11 . However, the kinetics of CTNI levels indicate that troponin release is the result of early histological events following electrode implantation.…”

“…They consist of injury, acute and chronic inflammation, formation of granulation tissue, foreign body reaction, and fibrosis 3 . Myocardium is involved in the inflammatory process with infiltration of the interstitium by inflammatory cells and degeneration of myocardial cells 4 …”

Long-term outcome in patients receiving permanent pacemaker implantation for atrioventricular block

“…Undersensing is partly due to the floating dipole without contact with the atrial wall, which is prone to positional change, as well as local inflammatory changes leading to decreased atrial potential. [17] The prevalence of atrial undersensing varied among different studies. [8] Santini et al [4] reported stable atrial signals over time in every physical activity, while extensive variation of atrial signal amplitude between postures was reported in another study.…”

VDD pacing in dogs: When, why and how to perform single-lead atrial synchronous, ventricular inhibited (VDD) pacing

“…The system must also overcome acute reductions in the atrial potential post pacemaker implant 22 and individual variations in the atrial potential during physical maneuvers 23,24 and following administration of cardioactive drugs. 25 Recommendations in the human literature are to program the atrial sensitivity to 33% of the measured atrial potential to insure tracking through the wide range of P wave amplitudes that will be encountered.…”

“…5). The sensed atrial potential decreases in the days post-pacemaker implantation 22 so it may be better to program the atrial sensitivity to 20% of the measured potential for the first month post-operatively. One month postpacemaker implantation and throughout future evaluations the programming parameters are rechecked and re-optimized using the same strategy.…”