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Optimal atrioventricular delay at rest and during exercise in patients with dual chamber pacemakers: a non-invasive
1Department of Cardiological Sciences, St George's Hospital Medical School, London.
Insights
Determining the optimal atrioventricular delay for dual chamber pacemakers is crucial. A longer delay benefits resting cardiac output, while a shorter delay enhances performance during exercise in patients with heart block.
Area of Science:
- Cardiology
- Biomedical Engineering
Background:
- Dual chamber pacemakers are essential for managing heart block.
- Optimizing atrioventricular (AV) delay is critical for hemodynamic efficiency.
Purpose of the Study:
- To investigate the optimal atrioventricular delay for cardiac output at rest and during exercise in patients with heart block and dual chamber pacemakers.
Main Methods:
- Nine patients with heart block and pacemakers were studied.
- Cardiac output was measured using Doppler echocardiography at rest (supine and erect) and during exercise.
- Pacemakers were programmed with varying AV delays (75-200 ms) in DDD mode.
Main Results:
- Resting cardiac output was highest with an AV delay of 140-150 ms.
- During exercise, cardiac output was significantly greater with a shorter AV delay of 75-80 ms.
- 1:1 AV conduction was maintained across all tested AV delays during exercise.
Conclusions:
- The optimal atrioventricular delay differs between rest and exercise.
- A shorter AV delay is preferable during exercise for improved cardiac output.
- Rate modulation of AV intervals may enhance hemodynamic response and exercise tolerance.
Abstract:
The optimal atrioventricular delay at rest and during exercise was investigated in nine patients with heart block and implanted dual chamber pacemakers. All patients studied had normal left ventricular function and a normal sinus node rate response to exercise. Cardiac output was measured by continuous wave Doppler and was calculated as the product of stroke distance measured by Doppler at the left ventricular outflow, aortic root area measured by M mode echocardiography, and heart rate. Pacemakers were programmed in the DDD mode. Cardiac output was measured with the patient at rest while supine and while erect and at the peak of submaximal exercise (the end of stage 1 of the Bruce protocol) with the pacemakers programmed to the following atrioventricular intervals: 75-80 ms, 100-110 ms, 140-150 ms, and 200 ms. During exercise the basic pacing rate was programmed to 70 beats/min. Cardiac output at rest while supine and erect was greatest with an atrioventricular delay of 140-150 ms and it was significantly higher than that with an atrioventricular delay of 75-80 ms. On average there was a 31% decrease in cardiac output when patients stood up. During treadmill exercise, however, cardiac output was greatest when the atrioventricular delay was 75-80 ms, and this was significantly higher than the cardiac output with atrioventricular delays of 150 and 200 ms. During exercise 1:1 atrioventricular relations were maintained in patients at all atrioventricular intervals. In patients with atrioventricular sequential pacemakers cardiac output at rest is greatest with an atrioventricular delay of 140-150 ms but during exercise the optimal atrioventricular delay is shorter. Rate modulation of the atrioventricular interval may improve the haemodynamic response and possibly exercise tolerance in patients with dual chamber pacemakers.