The Annals of Thoracic Surgery, Vol 31, 334-338, Copyright © 1981 by The Society of Thoracic Surgeons
Acute and chronic stimulation thresholds of intramyocardial screw-in pacemaker electrodes
DS Starr, GM Lawrie and GC Morris Jr
Two screw-in intramyocardial electrodes were inserted in the left ventricle
of each of 6 mongrel dogs, and the electrical characteristics were studied
over a six-month period. The unipolar lead configuration had consistently
better threshold and sensing values than the bipolar configuration during
this period. Peaking between implantation and 3 weeks later, mean lead
thresholds increased significantly (unipolar, 0.4 to 8.2 mu J; bipolar, 0.6
to 10.2 mu J) while R wave amplitude decreased (unipolar, 16.6 to 8.5 mv;
bipolar, 10.6 to 5.8 mv). Mean chronic values for stimulation thresholds
were as follows: unipolar, 2.6 mu J, and bipolar, 3.1 mu J. Mean values for
the R wave amplitude were as follows: unipolar, 10.6 mv, and bipolar, 7.2
mv. Analysis of the results indicated that with certain exceptions, the
optimum system has 2 intramyocardial electrodes, 1 in unipolar
configuration and 1 "reserve." In general, adequate values at implantation
are a stimulation threshold of 1.4 mu J (e.g., 1.1 v at 500 ohms and 0.6
msec pulse width) and an R wave amplitude of 5 mv.
