The Journal of Thoracic and Cardiovascular Surgery, Vol 78, 281-291, Copyright © 1979 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
The porous-surfaced electrode: a new concept in pacemaker lead design
DC MacGregor, GJ Wilson, W Lixfeld, RM Pilliar, JD Bobyn, MD Silver, S Smardon and SL Miller
Three major problems which may be encountered with endocardial pacemaker
electrodes are a lack of stable position, a chronic increase in stimulation
threshold, and a diminishing magnitude of the sensed endocardial signal.
These problems are particularly manifest in the atrium. Having previously
shown that porous metal surfaces can support stable tissue ingrowth in both
bloodstream and soft tissue environments, we set out todetermine the
performance of porous-surfaced endocardial pacing electrodes in the atrial
position. In two groups of six dogs each, J-shaped atrial leads with
Elgiloy electrode tips (2.3 mm. in diameter, 2.3 mm. in length), having
either conventional smooth surfaces (control) or porous surfaces (20 to 50
micron particle size) produced by powder metallurgy techniques, were
positioned in the right atrial a-pendage. Stimulation thresholds and P-wave
amplitude were repeatedly measured until the dogs were put to death 30
w-eks following implantation. The presence or absence of electrode fixation
was observed and the atrial tissue reaction was examined grossly and by
both light and scanning electron microscopy (SEM). The porous-surfaced
electrodes demonstrated superior long-term stimulation thresholds which, at
30 weeks, averaged less then one third of those in the control group. In
addition, the porous group showed a small but significant improvement in
the amplitude of the sensed P wave. None of the smooth-surfaced electrodes
showed fixation, and the tissue reaction consisted of a thick layer of
granulation and fibrous tissue on the underlying endocardium, widely
separating the electrode from the myocardium. In contrast, all of the
porous-surfaced electrodes were fexed to the endocardium by fibrous tissue
ingrowth into the surface pores. This tissue fixation of the electrode tip
in close proximity to underlying myocytes explains their superior
performance.
