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Sympathetic nervous system response to dynamic exercise in complete AV block patients treated with AV synchronous
O Igawa1, A Tomokuni, M Saitoh
1First Department of Internal Medicine, Tottori University, Japan.
Insights
Patients with complete atrioventricular block (CAVB) show heightened sympathetic nervous system (SNS) responses during exercise, even with pacing. Automatic atrioventricular delay (auto-AVD) pacing improves exercise tolerance compared to fixed AV pacing.
Area of Science:
- Cardiology
- Exercise Physiology
- Neurocardiology
Background:
- Complete atrioventricular block (CAVB) significantly impacts cardiac function and exercise capacity.
- Atrioventricular (AV) synchronous pacing aims to restore physiological AV synchrony but may not fully normalize circulatory responses to exercise.
- Sympathetic nervous system (SNS) activity, indicated by plasma norepinephrine (NE), is a key regulator of cardiovascular response during physical exertion.
Purpose of the Study:
- To evaluate sympathetic nervous system (SNS) and circulatory responses to exercise in patients with CAVB managed with AV synchronous pacing.
- To compare the efficacy of fixed AV interval pacing versus automatic AV delay (auto-AVD) pacing during exercise in CAVB patients.
- To assess plasma norepinephrine (NE) as a biomarker for cardiac function adaptation in patients with DDD pacemakers.
Main Methods:
- Eight patients with CAVB underwent symptom-limited treadmill stress tests with fixed AV interval pacing.
- Plasma norepinephrine (NE) levels and circulatory parameters (e.g., systolic blood pressure, heart rate) were measured at rest, peak exercise, and recovery.
- Three patients were further evaluated using three different auto-AVD pacing modes during repeated stress tests.
Main Results:
- CAVB patients exhibited significantly higher plasma NE levels at all measured points compared to healthy controls.
- Patients showed poor heart rate increase during peak exercise and elevated systolic blood pressure post-exercise, suggesting persistent cardiac dysfunction.
- Plasma NE concentrations were lower during exercise with auto-AVD pacing compared to fixed AV interval pacing, indicating better SNS regulation.
Conclusions:
- Even with optimal AV synchronous pacing, latent cardiac dysfunction persists in CAVB patients, reflected by elevated SNS activity.
- AV synchronous pacing with auto-AVD is superior to fixed AV interval pacing in managing SNS and circulatory responses during exercise in CAVB patients.
- Plasma NE response during exercise serves as a valuable indicator for assessing the functional status and adaptation of cardiac function in patients with DDD pacemakers.
Abstract:
To investigate the sympathetic nervous system (SNS) responses and circulatory responses to exercise in eight patients (five male and three female) with complete atrioventricular block (CAVB) treated with atrioventricular (AV) synchronous pacing, a symptom-limited, multistaged treadmill stress test was performed, and plasma norepinephrine (NE) and circulatory parameters were measured at rest, at peak exercise, and in the recovery period. The eight patients were tested using the fixed AV interval (150 or 156 msec). Their exercise tolerance was generally poor. In all measured points, plasma NE levels were significantly higher in the eight study patients than those in the 12 normal subjects (eight male and four female). Systolic blood pressure (SBP) of CAVB patients elevated significantly after exercise compared to that at peak exercise. Heart rate (HR) responses of CAVB patients were characterized by their poor increase at peak exercise. These results suggest that some latent cardiac dysfunction continues in the CAVB patients however satisfactorily the AV synchronous pacing might perform. AV synchronous pacing with three different kinds of auto-atrioventricular delay (auto-AVD) was applied to three of the eight patients. In each AVD mode, a treadmill stress test was performed repeatedly according to the same protocol. Plasma NE concentrations under the condition with fixed AVD at peak exercise increased compared to those under the other two conditions with auto-AVD. These findings suggest that AV synchronous pacing with auto-AVD was better than that with fixed AVD during exercise. Plasma NE response to exercise seems to be a useful indicator for evaluating the condition of patients treated with DDD pacemakers and their adaptation for cardiac function.