Energy-conserving programming of VVI pacemakers: a telemetry-supported, long-term, follow-up study

Long-term experience with AutoCapture-controlled epicardial pacing in children

AIMS

To examine the feasibility and safety of AutoCapture (AC)-controlled pacing with epicardial leads in children, and study the effects on device longevity.

METHODS

A total of 62 children were prospectively enrolled. Pre-discharge testing precluded AC function in six children. In 56 (90%) children, devices with AC-controlled pacing were followed up to 9years. Calculated battery life in AC-controlled pacing was compared with theoretical calculations, using a two-fold stimulation output of measured thresholds.

RESULTS

In 53 of 56 children, no differences were observed for evoked response signals (13.3 vs. 11.5mV, P = 0.20) or lead polarization safety margins (5.5 vs. 4.1, P = 0.25) at 6-month and 4-year follow-up. A crossover to conventional pacing was required in 3 of 56 children. AC-controlled pacing prolonged the calculated battery life up to 15% for the identity and integrity devices with 0.95A h capacity, compared with theoretical conventional settings (P = 0.008). In patients with ventricular pacing thresholds >1.5V at 0.5ms, battery life was increased by 30% compared with theoretical conventional settings (P < 0.001).

CONCLUSION

AC-controlled pacing with epicardial leads is feasible and safe in children during long-term follow-up. An adequate lead polarization safety margin persists in most patients. Calculated battery life was prolonged up to 15% with AC-controlled pacing. Patients with high or fluctuating pacing thresholds benefit the most.

Automatic adjustment of pacing output in the clinical setting

BACKGROUND

AutoCapture (AC) is a programmable feature that enables the pacemaker to both track the capture threshold and automatically adjust the output on a beat-by-beat basis. Although AC safely and significantly reduces the current drainage, some authors have argued that the longevity benefit of such a system is overstated. This study aims to estimate the longevity extension that can be obtained, in the clinical routine, by turning the AC on in comparison to pacemakers programmed to operate at the shipped and manually optimized output.

METHODS

We selected 83 consecutive patients who received implanted St Jude's Affinity pacemakers >6 months earlier. Eight patients died or were lost to follow-up and in 9 subjects the AC could not be turned on. In the remaining 66 patients, current drain and estimated longevity were compared in 3 situations: (1) AC on; (2) AC off, optimized programming (100%-150% voltage threshold); (3) AC off, shipped output (3.5 V).

RESULTS

Five patients had large variations (>1 V) of the AC threshold. Current drainage was 8.0 +/- 0.9 mA in the AC group, 8.7 +/- 1.8 mA with AC off and optimized programming, and 11.3 +/- 2.3 mA at shipped output (P <.01). Estimated longevity was significantly extended (P <.01) by AC (12.1 +/- 1.0 years) when compared to shipped (8.9 +/- 1.7 years) and optimized programming (11.3 +/- 1.4 years).

CONCLUSION

Reprogramming the pacemaker output significantly enhanced its estimated longevity; AC added a moderate but significant extension over manual reprogramming and was associated with increased safety in patients with large ventricular threshold variations.

Telemetry guided pacemaker programming: impact of output amplitude and the use of low threshold leads on projected pacemaker longevity

In a prospective study, a low threshold screw-in electrode (Medtronic 5078, group I, n = 9) was compared to a conventional active fixation lead (Biotronik Y60BP, group II, n = 9) to investigate whether lower pacing thresholds really translate into longer projected service life of the pacemaker. The leads were implanted in the atrium and were connected to a dual chamber pacing system which included the same ventricular lead (Medtronic 5024) and the same pulse generator model (Intermedics 294-03) in both groups. Eighteen months after implantation, atrial and ventricular pacing thresholds were measured as the charge delivered per pulse [microC] at 0.5, 1.0, 1.5, 2.0, and 3.5 V, respectively. For chronic output programming in both channels, patients capturing at 0.5 V were set to 1.0 V, those capturing at 1.5 V were permanently programmed to 2.0 V with the double of the charge threshold as the safety margin for pacing ("safety charge"). A combination of atrial and ventricular output settings was optimal, if it resulted in minimum battery current drain (microA] as measured by pacemaker telemetry. In both groups, current consumption [microA] decreased significantly as output amplitude was decreased, exhibiting its lowest value at 1.0 V in either channel. All ventricular leads could be programmed to the optimum output amplitude of 1.0 V in groups 1 and 2. As the 2:1 "safety charge" values were almost identical, the ventricular channel essential contributes the same amount to the battery drain of the pacing system in both groups. In the atrium, all patients of group 1 could be programmed to the optimum output amplitude of 1.0 V with an average pulse duration of 0.42 +/- 0.15 ms. In group 2, however, all patients had to be programmed to 2.0 V with a mean pulse width of 0.52 +/- 0.15 ms. With the atrial and ventricular output being optimized, the average battery drain of the whole pacing system was 12.19 +/- 0.63 microA in group 1 versus 14.42 +/- 0.32 microA in group 2 (P < 0.001). As patients were chronically programmed to these output settings, this difference translates into a clinically relevant gain in projected pacemaker longevity of 17 months or 18.3% (121 +/- 4 vs. 104 +/- 2 months; P < 0.001). Thus, programming a 2:1 safety margin in terms of charge and optimizing the output parameters by real-time telemetry of the battery current is a useful approach to reduce battery current drain. Making the most of modern lead technology with a different performance in only one channel of an otherwise identical DDD pacing system translates into a significant prolongation of projected pacemaker service life which is of great importance with the increasing awareness of health care expenditures. The gain in projected longevity is mainly due to the option of reducing the output amplitude which is still significantly beneficial well below the nominal voltage of the power source.

Influence of internal current and pacing current on pacemaker longevity

The effects of lower pulse amplitude on battery current and pacemaker longevity were studied comparing the new, small-sized VVI pacemaker, Minix 8341, with the former model, Pasys 8329. Battery current was telemetrically measured at 0.8, 1.6, 2.5, and 5.0 V pulse amplitude and 0.05, 0.25, 0.5, and 1.0 msec pulse duration. Internal current was assumed to be equal to the battery current at 0.8 V and 0.05 msec. Pacing current was calculated subtracting internal current from battery current. The Minix pacemaker had a significantly lower battery current because of a lower internal current (Minix: 4.1 +/- 0.1 microA; Pasys: 16.1 +/- 0.1 microA); pacing current of both units was similar. At 0.5 msec pulse duration, the programming from 5.0-2.5 V pulse amplitude resulted in a greater relative reduction of battery current in the newer pacemaker (51% vs 25%). Projected longevity of each pacemaker was 7.9 years at 5.0 V and 0.5 msec. The programming from 5.0-2.5 V extended the projected longevity by 2.3 years (Pasys) and by 7.1 years (Minix). The longevity was negligibly longer after programming to 1.6 V.

CONCLUSION

extension of pacemaker longevity can be achieved with the programming to 2.5 V or less if the connected pacemakers need a low internal current for their circuitry.