Tracing 21a: manual measurement of the right atrial threshold

1. pacing in the AAI mode with capture verification by the presence of ventricular conduction; 0.1 V step over 2 cycles; effective capture;
2. loss of capture at 0.3 V (threshold measured at 0.4 V);

Tracing 21b: automatic measurement of the right atrial threshold

1. the threshold measurement is carried out in DDI mode (no ventricular trigger of spontaneous atrial activities and therefore no risk of PMT) at a rate 20% higher than the spontaneous rate (in order to favor atrial pacing) with a short AV delay of 50 ms and a post-ventricular atrial blanking of 150 ms (compromise in order to avoid crosstalk and to favor atrial sensing indicating loss of atrial capture); for each tested value, 5 pulses are delivered; the starting value is programmable (in this instance 3 V, nominal value); in the absence of atrial sensing, diagnosis of effective atrial capture;
2. reduction of pacing amplitude in decremental 0.6 V steps (in each instance, 5 pulse tests);
3. for an amplitude of 0.6 V, persistence of the capture (absence of sensing of spontaneous atrial activity);
4. prior to decreasing the amplitude, atrial synchronous pacing delivered at the end of each series of 5 pulses; this atrial pacing is of an amplitude greater than 0.5 V relative to the previous tested amplitude;
5. reduction of amplitude in decremental 0.1 V steps with capture at 0.3 V;
6. new atrial synchronous pacing;
7. loss of capture diagnosed upon the presence of spontaneous atrial activity (traced line on the atrial markers line);
8. after 2 consecutive losses of capture, synchronous pacing;
9. to verify this threshold measurement: first step, 5 pulses at an amplitude above 0.3 V relative to the threshold value; in this instance, 0.7 V since threshold measured at 0.4 V (last effective value); with this margin, capture is effective;
10. second step, 5 pulses at an amplitude under 0.3 V relative to the threshold value; in this instance, 0.1 V since threshold measured at 0.4 V (last effective value); with this margin, the absence of capture is verified;