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

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.

Clinical testing of a new pacemaker function to monitor ventricular capture

Automatic beat-by-beat capture functions are designed to minimize the pacing energy delivered, while maintaining the highest safety by delivering an immediate back-up stimulus in case of loss of capture. The objective of this study was to estimate the lowering of ventricular pacing amplitude allowed by such a function, compared to amplitudes usually set manually in routine practice. An automatic ventricular pacing threshold test is launched every 6 hours to measure the automatic capture threshold (AT). From AT the function calculates: (1) the"capture amplitude"(V(c)) = AT + 0.5 V at a minimum output of 1 V and (2) the"safety amplitude" (V(s)) = twice AT at a minimum output of 2.5 V. The function preferentially uses V(c) and verifies capture after each paced beat. In case of loss of capture, a back-up spike is delivered and V(s) is implemented until the next threshold measurement. We estimated the ventricular amplitude delivered by the pacemaker from data stored in the pacemaker memory. We compared these values with the pacing amplitude typically programmed manually (MPA) by physicians at twice AT and a minimum of 2.5 V. Data from 57 recipients of Talent 3 DR pacemakers were analyzed. Complete data sets were available in 25 patients at 1 day, 28 at 1 month, and 39 between 1 day and 1 month. No loss of capture or ventricular pause was observed on 53 ambulatory electrocardiograms (ECG); and pulse amplitude automatically delivered by the device was significantly lower than the MPA at each of the three time points analyzed. This new beat-by-beat capture function allows a significant lowering of the pacing amplitude compared to manual settings, while preserving a 100% safety.

Effect of modern pacing algorithms on generator longevity: a predictive analysis

Pulse generator (PG) longevity is of major importance to the quality of care of pacemaker patients. A series of automatic algorithms affect PG longevity. This study investigated the individual and combined effects of three algorithms incorporated in the Medtronic Kappa 700 pacemaker series: Capture Management periodically measures the stimulation threshold and adjusts the PG output, Sinus Preference allows the sinus rate to prevail in a specified range below the sensor rate, and Search AV allows an extension of the AV interval if spontaneous conduction is observed. The effects of Capture Management, Sinus Preference, and Search AV on device longevity were studied in 21 consecutive patients treated in the VDD and DDDR modes. Patients were followed for 1 year. The data were analyzed using an equation provided by the manufacturer. Capture Management was activated in 20 patients. For 11 PGs at the basic settings, longevity was extended by 5.2%, whereas reprogrammed PGs had no gain. Sinus Preference was active in four DDDR patients, who gained 12.0 +/- 5.3%atrial sensing from it, with a resultant longevity gain of1.4 +/- 0.45 months(NS). Search AV was active in 19 patients and 8 responders gained 7.8 +/- 4.4 months PG longevity. The overall longevity in this study was 106.3 +/- 8.4 months with all features as programmed, whereas the longevity without Capture Management and Search AV algorithms would be 98.2 +/- 4.9 months, saving 8.1 +/- 5.8 months(range 0-18) of battery life. Thus, two algorithms: Capture Management and Search AV, have clinical relevance in the extension of PG longevity.

Evolution of an active fixation atrial pacing lead

Three bipolar atrial pacing leads from one manufacturer differing in a single electrode design characteristic were compared. Each lead had nonretractable screw and a microporous electrode tip made of activated carbon. Model S84F had a tip surface area of 8 mm2. In model S44F, the tip surface area was reduced to 4 mm2 by insulation of the screw, and in model BS45D, steroid elution was added to the 4 mm2 tip. Ten patients in each group received identical pulse generators. During implantation, atrial potentials (5.4 +/- 2.0, 4.2 +/- 2.0, 4.6 +/- 2.1 mV), pacing thresholds at 0.5 ms (0.47 +/- 0.14, 0.41 +/- 0.15, 0.55 +/- 0.33 V) and lead impedance at 2.5 V/0.5 ms (515 +/- 80, 575 +/- 152, 546 +/- 131 omega) were comparable among groups. The early postoperative threshold peak was significantly lower with the BS45D than with the S84F and S44F lead models. One year after implantation, charge threshold was significantly lower with the BS45D lead than with the S84F and the S44F model (0.34 +/- 0.11 vs. 0.68 +/- 0.20 and 0.56 +/- 0.21 microC; P < 0.05). Lead impedance at 2.5 V/0.5 ms (557 +/- 90, 549 +/- 36, 524 +/- 72 omega) and atrial sensing (4.3 +/- 2.1, 4.7 +/- 1.9, 4.7 +/- 0.9 mV) were not significantly different. One year postimplant, current drain of the pacing system was measured by pacemaker telemetry at chronic output settings in AAI mode/70 beats/min. Battery current measured among the three atrial lead models did not differ significantly (S84F: 11.9 +/- 0.90, S44F: 12.2 +/- 1.8, BS45D: 11.5 +/- 0.26 microA).

IN CONCLUSION

reduction of the tip surface area by insulation of the screw did not improve pacing performance. Addition of steroid elution to the 4 mm2 tip significantly lowered the early threshold peak and the long-term pacing threshold. Lowering of the pacing threshold, however, did not lower the current drain of the pacing system.