Shortening of the AV delay during exercicse

Tracing N° 1
Medtronic Devices: PM Field: Programming for exercise

This 72-year-old male recipient of a pacemaker for complete AV block due to degenerative conduction system disease suffered from coronary artery disease treated with a beta-adrenergic blocker. The device was programmed to the DDDR mode, with a backup rate at 60 bpm, upper rate response at 120 bpm, and an adaptive paced AV delay between 200 and 120 ms; the tracings were recorded at various stages of effort, consisting of repetitive flexing of the legs performed with a telemetry head held over the pacemaker.

Graph and trace

Tracing 1a: the first channel is lead I of the surface ECG with the event markers superimposed, the second channel shows the time intervals, the third is lead III and the fourth channel is lead II;

  1. after 30 sec of repetitive flexing of the legs, the heart rate is 80 bpm and the paced AV delay is 200 ms;

Tracing 1b: slightly greater effort;

  1. the heart rate is 90 bpm and the paced AV delay is 187 ms.

Tracing 1c: moderate exercise;

  1. the heart rate is 100 bpm and the paced AV delay is 162 ms.

Tracing 1d: vigorous effort;

  1. the heart rate is 110 bpm and the paced AV delay is 147 ms.

Tracing 1e: maximum effort;

  1. the heart rate is 120 bpm and the paced AV delay is 120 ms.

This tracing illustrates the functions of the adaptive AV delay and the 3 programmable parameters which govern the means by which the AV delay is adapted to increasing heart rates: in this patient, the backup rate was programmed at 60 bpm with a paced AV delay programmed at 200 ms. The first parameter is the heart rate at onset of shortening of the AV delay, which, in this case, is programmed at 80 bpm. Shortening of the AV delay, whether sensed or paced, begins at that rate (start rate) and the adaptive function adapts the AV delay linearly as the heart rate increases up to the stop rate, programmed in this case at 120 bpm. The shortest sensed and paced AV delays develop from this rate up to the maximum programmed rate response (which can be identical or different). The third parameter is the maximum variation, which corresponds to the range of variations of AV delays, between start and stop rate. In this case, the widest variation was programmed at 80 ms, explaining the difference between an AV delay at 200 ms at the start rate and an AV delay at 120 ms at the stop rate.
The programming of the adaptive AV delay has 2 main objectives:
1) emulation of the physiologic response, by which the PR interval shortens during exercise from the effects conferred by catecholamines, and
2) the spontaneous shortening of the AV delay during an increase in heart rate optimizes the sensing window of rapid atrial events by shortening the total atrial refractory period and by increasing the rate of onset of 2:1 block.

Theoritical features / Basic concepts

Atrioventricular synchronization during exercise The 2:1 block point Synchronous upper rate and pseudo-Wenckebach operation of the pacemaker Specific programming to preseve atrioventricular synchronization during exercise Adaptable atrioventricular delay PVARP auto Maximum synchronous rate Atrial sensitivity Rate responsive pacing Various parameters must be programmed and optimized to allow the adaptation of pacing to exercise. The main objectives of a specific programming dedicated to exercise are to ensure a proper contribution of atrial systole to the cardiac output at high rates while preserving AV synchrony, and allow an adapted increase in heart rate, which represents the main adaptive factor of the cardiac output to exercise. The performance of an exercise test is an important...