Permanently implanted transvenous pacemakers. Electrical measurements of function

Three patients with complete heart block had a high resistance to electrical stimulation of the endocardium through transvenous pacemaker systems. One patient died; one needed reoperation for implantation of epicardial electrodes; and the third required a generator of higher current. The present enthusiasm for permanent transvenous implantation of pacemakers must be tempered somewhat by the knowledge that high endocardial resistance to pacing represents another cause of failure. Simple and rapid methods of determining the current necessary to stimulate the endocardium are available and should be used prior to permanent implantation of the generator. If a substantial margin of safety does not exist, one should consider substituting a pulse generator with greater output or an epicardial electrode system.