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We compared the rate responsiveness of an activity-detecting multiprogrammable, single chamber pacemaker (Medtronic Activitrax) to rate responsiveness of the normal sinus node. This pacemaker changes its basic pacing rate in response to physical activity. The rate responsiveness is programmable by selecting one of three activity thresholds, and one of 10 rate response settings. The study included a group of six normal volunteers and 12 patients implanted with Activitrax to examine the similarity of the pacemaker rate to normal sinus rhythm during acceleration and deceleration. The pacemaker was set to Activity mode, at a basic rate of 60 bpm. In volunteers, the device was externally secured on the chest wall and tested at two programmed settings. When programmed at a high threshold of activity and high rate response in volunteers, there was no significant difference in maximum normal sinus rates and pacemaker rates during arm waving, jumping in place, and walking during stress testing. At a medium activity threshold, the only significant difference occurred during submaximal stress testing, when the maximum sinus rate achieved was 141 +/- 19 bpm and the maximum pacing rate was 105 +/- 8 bpm (p less than .02). The pacemaker behaved in a similar manner in patients, successfully simulating the typical fast acceleration and slow deceleration of a normal sinus node in exercise testing. There was no difference in pacer response when implanted in abdominal or infraclavicular locations. The implanted units have functioned normally over a follow-up period of nine to 22 months. Activitrax can be programmed to achieve physiologic pacing rates in response to normal daily activities with appropriate programming.

An esophageal electrode can be employed to provide atrial sensing which then can be used to change from temporary right ventricular (VVI) pacing to P-synchronous (VAT) pacing. Two cases of postoperative aortic valve replacement, each with new complete heart block (CHB) and dopamine dependency, are presented. In both cases, establishment of P-synchronous pacing resulted in improved hemodynamic status characterized by successful weaning from dopamine and maintenance of adequate cardiac output (CO).

In order to evaluate the behavior of lithium-powered cardiac pacemakers, a database of 25,919 lithium-powered pacing systems including 23,517 single and 2,402 dual chambered pacemaker generators were followed in 21,750 patients. Of this group, 11,319 were currently active in addition to 7,560 who died, as well as 2,871 patients who terminated their follow-up service prior to the end-of-life of the pacemaker system. A total of 23,517 single chambered pacemakers were followed for 719,173 months of pacing. The mean time to explant for generator malfunctions was 42 months and for all pacing system malfunctions it was 38 months compared to 31.9 months and 28.6 months, respectively, for the 2,402 dual chambered units that were observed for 38,718 months. In the single chambered units, the most frequent reason for explant was battery exhaustion (37% of explants) followed by lead problems (26%) compared to 49% and 12%, respectively, for the dual chambered units. The incidence rates, defined as a transtelephonic test result, required physician decision for action or clarification of the pacing mode or program parameters and showed a high incidence rate immediately post-implant; thereafter, there was a relatively trouble-free period until the 36th month when capture, sensing, and battery problems began to occur at a steady rate reaching 4% at the end of 48 months. Similarly, for dual chambered units, an 8% incidence rate was seen within the first 3 months, followed by a quiescent period until the 28th month when the incidence rate jumped to 16%.(ABSTRACT TRUNCATED AT 250 WORDS)

Of 1,193 consecutive pediatric (less than 18 years) patients undergoing intracardiac repair from 1975 to 1984, 38 (3.2%) developed surgically induced complete heart block and were treated by permanent pacemaker implantation. Anomalies included complete atrioventricular septal defect = 9 (24%), simple ventricular septal defect = 9 (24%), atrioventricular discordant connection = 8 (212), tetralogy of Fallot = 7 (182), and other complex anomalies = 5 (13%). There were no hospital deaths. follow-up was 100% complete. There were six late deaths = 16%. Actuarial survival was 79 + 9% at 10 years. None of the late deaths were related to disturbance of cardiac rhythm or pacemaker system failure. Twelve patients (32%), required 27 reoperations for various types of pacemaker system failure. Indications for reoperation included: lead failure (44%). Pulse generator failure (44%), and wound sepsis (12%). Actuarial freedom from any pacemaker related reoperation was 50 + 16% at 48 months and 25 + 15% at 96 months. Only first reoperation was found to be an incremental risk factor for subsequent reoperation (p = 0.03). Surgical heart block has been neutralized as a risk factor for hospital death after repair of congenital cardiac defects. The risk of the development of surgical heart block now approaches zero, as indicated by a decreased incidence (1 of 401 = 0.25%) in our institution from 1985 to 1987, as compared to the era 1975 to 1984 (p = 0.001).

A 17-year-old boy with severe sick sinus bradycardia had a doubly redundant pacemaker inserted. With two separate ventricular leads inserted by the epicardial route, the pacemaker is able to compensate for a lead that has developed high threshold by activation of an alternate lead. The two pacing channels of the pulse generator can be programmed independently of one another. In addition, there is a back-up pacing circuit separate from the two primary channels. The pacer can be used with both channels active for continuous automatic redundancy for safety, or with one channel active and the other in reserve.