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The haemodynamic importance of atrioventricular synchrony and rate increase at rest and during exercise
Insights
Atrioventricular synchronous pacing improved cardiac output at rest but not during exercise. Heart rate increase is more critical than atrioventricular synchrony for exercise cardiac output in patients without heart disease.
Area of Science:
- Cardiology
- Physiology
Background:
- Atrioventricular (AV) synchrony is crucial for optimal cardiac function.
- The relative importance of AV synchrony versus heart rate increase for cardiac output during exercise is not fully understood, particularly in patients without myocardial disease.
Purpose of the Study:
- To compare the haemodynamic significance of AV synchrony versus heart rate increase in patients with AV block.
- To evaluate the impact of AV synchronous pacing (VDD) compared to fixed-rate ventricular pacing (VVI) on cardiac output at rest and during exercise.
Main Methods:
- 10 patients with AV block were studied using VDD and VVI pacing modes.
- Haemodynamic data (cardiac output, stroke volume) were collected at rest and during two submaximal exercise intensities.
- VVI pacing rates were adjusted to match those achieved during VDD pacing.
Main Results:
- At rest, VDD pacing significantly increased cardiac output compared to VVI pacing (P < 0.05), due to enhanced atrial contribution to ventricular filling.
- During exercise (50% and 80% of maximal aerobic tolerance), no significant differences in cardiac output or stroke volume were observed between VDD and VVI pacing.
- The capacity for heart rate increase was the primary determinant of cardiac output during exercise.
Conclusions:
- Heart rate increase is the dominant factor for augmenting cardiac output during exercise in patients without myocardial disease.
- Preserved AV synchrony offers limited additional haemodynamic benefit during exercise in this population.
- These findings highlight the importance of rate-responsive pacing algorithms for maintaining adequate cardiac output during physical activity.
Abstract:
To compare the added haemodynamic importance of atrioventricular synchrony to rate increase, we studied 10 patients, healthy except for atrioventricular block, treated with atrioventricular synchronous pacemakers. Haemodynamic data were obtained by brachial and pulmonary arterial catheterisation. Recordings were made at rest and during upright bicycle ergometry at two submaximal work loads (50% and 80% of maximal aerobic exercise tolerance). The investigation was first performed in the atrioventricular synchronous mode of pacing (VDD) and later repeated during fixed-rate ventricular pacing (VVI) at ventricular rates adjusted to the levels achieved during atrioventricular synchronous pacing. At rest (mean rate 74 bpm), preserved atrioventricular synchrony increased cardiac output (5.0 +/- 0.7 l min-1; mean +/- SD) compared with asynchrony (4.5 +/- 1.0; P less than 0.05), owing to a higher stroke volume (70 +/- 19 versus 64 +/- 22 ml; P less than 0.05), illustrating the importance of the atrial contribution to ventricular filling. During exercise at 50% (mean rate 122 bpm) and 80% (mean rate 146 bpm) of maximal aerobic tolerance, there were no significant differences in cardiac output (50%: VVI 10.1 +/- 2.5, VDD 10.5 +/- 1.6 NS; 80%: VVI 12.8 +/- 4.1, VDD 12.3 +/- 3.5, NS) or in stroke volume (50%: VVI 83 +/- 23, VDD 88 +/- 17, NS; 80%: VVI 89 +/- 32, VDD 85 +/- 27, NS). We conclude that the capacity for rate increase is of major importance while preserved atrioventricular synchrony seems to be much less important for the ability of the individual to increase cardiac output during exercise, at least in patients without myocardial disease.
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