Low settings of the ventricular pacing output in patients dependent on a pacemaker: are they really safe?
BACKGROUND
It is generally acknowledged that pacemaker output must be adjusted with a 100% voltage safety margin above the pacing threshold to avoid ineffective pacing, especially in patients dependent on pacemakers.


OBJECTIVE
The aim of this prospective crossover study was to assess the beat-to-beat safety of low outputs in patients who are dependent on a pacemaker between 2 follow-up examinations.


METHODS
The study included 12 patients who had received a DDD pacemaker with an automatic beat-to-beat capture verification function. The ventricular output at 0.4 milliseconds pulse duration was programmed independently of the actual pacing threshold in a crossover randomization to 1.0 V, 1.5 V, and 2.5 V for 6 weeks each. At each follow-up, the diagnostic counters were interrogated and the pacing threshold at 0.4 milliseconds was determined in 0.1-V steps. The diagnostic pacemaker counters depict the frequency of back-up pulses delivered because of a loss of capture. During the randomization to 1.0-V output, we evaluated whether the adjustment of the output under consideration of the >100% voltage safety margin reduced the frequency of back-up pulses.


RESULTS
Pacing thresholds at the randomization to 1.0-V, 1.5-V, and 2.5-V output were not significantly different, with 0.7 +/- 0.3 V at 2.5-V output, 0.6 +/- 0.2 V at 1.5-V output, and 0.6 +/- 0.2 V at 1.0-V output. The frequency of back-up pulses was similar at 2.5-V and 1.5-V output, 2.2% +/- 1.9% and 2.0% +/- 2.0%, respectively. The frequency of back-up pulses significantly increased at 1.0-V output to 5.8% +/- 6.4% (P <.05). Back-up pulses >5% of the time between the 2 follow-ups were observed in no patient at 2.5 V, in 1 patient at 1.5 V, and in 5 patients at 1.0 V. At the randomization to the 1.0-V output, 6 patients had pacing thresholds of 0.5 V or less, and 6 patients had pacing thresholds >0.5 V. The frequency of back-up pulses in the 2 groups was not significantly different, 6.4% +/- 8.6% and 5.7% +/- 2.6%.


CONCLUSIONS
The frequency of back-up pulses was significantly higher at 1.0-V output than at 1.5-V and 2.5-V output. This also applied to patients with pacing thresholds of < or =0.5 V. Fixed low outputs seem not to be absolutely safe between 2 follow-ups in patients who are dependent on a pacemaker, even when the output has a 100% voltage safety margin above the pacing threshold. When patients with pacemakers programmed to a low ventricular output have symptoms of ineffective pacing, an intermittent increase of the pacing threshold should be carefully ruled out.
Schuchert
Andreas
A
University-Hospital Hamburg-Eppendorf, Hamburg, Germany. schuchert@uke.uni-hamburg.de
Frese
Jens
J
Stammwitz
Ekkehard
E
Novák
Miroslav
M
Schleich
Arthur
A
Wagner
Stefan M
SM
Meinertz
Thomas
T
D000368:Aged; D002138:Calibration; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects* / Q000379:methods / Q000592:standards; D018592:Cross-Over Studies; D005260:Female; D006327:Heart Block / Q000150:complications / Q000628:therapy*; D006801:Humans; D008297:Male; D010138:Pacemaker, Artificial; D011446:Prospective Studies; D012449:Safety