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Effect of beta blockade with and without sympathomimetic activity (ISA) on sympathovagal balance and baroreflex
C Haberthür1, H Schächinger, W Langewitz
1Department of Internal Medicine, University Hospital Basle, Switzerland.
Insights
Beta blockers without intrinsic sympathomimetic activity (ISA) increase heart rate variability (HRV), while those with ISA do not improve autonomic balance. Pindolol with ISA exaggerates sympathetic responses to passive tilt, unlike propranolol.
Area of Science:
- Cardiology
- Autonomic Nervous System Physiology
Background:
- Beta blockers are known to increase heart rate variability (HRV) and improve survival in coronary artery disease (CAD).
- The efficacy of beta blockers with intrinsic sympathomimetic activity (ISA) in CAD remains debated, and their impact on HRV is not well-established.
Purpose of the Study:
- To investigate the effects of propranolol (without ISA) and pindolol (with potent ISA) on HRV, blood pressure variability (BPV), and baroreflex sensitivity (BRS) in healthy subjects.
- To compare the autonomic effects of beta blockers with and without ISA.
Main Methods:
- Thirty healthy subjects (aged 21-39 years) participated in the study.
- Measurements of HRV, BPV, and BRS were taken under controlled frequency breathing in supine and tilt positions.
- Subjects received propranolol (160 mg q.d.), pindolol (15 mg q.d.), or placebo (q.d.).
Main Results:
- Propranolol increased high-frequency HRV, decreased low-frequency BPV (Mayer waves), and enhanced BRS in the supine position.
- Propranolol decreased low-frequency HRV and Mayer waves after passive tilt.
- Pindolol increased the low-frequency HRV response to passive tilt, unlike propranolol and placebo.
Conclusions:
- Beta-adrenergic blockade with potent ISA (pindolol) does not increase HRV and offers no benefit to autonomic balance.
- Beta blockers with ISA may even amplify sympathetic responses during physiological stress like passive tilt.
- These findings suggest that beta blockers without ISA may be more beneficial for autonomic regulation.
Abstract:
Beta blockers increase heart rate variability (HRV) and improve survival in coronary artery disease (CAD). The benefit of beta blockers with intrinsic sympathomimetic activity (ISA) in CAD still remains a matter of debate, and their effect on HRV has not yet been investigated. Therefore, we measured HRV, systolic blood pressure variability (BPV) and baroreflex sensitivity (BRS) under propranolol (PROP, without ISA, 160 mg q.d.), pindolol (PIN, with potent ISA, 15 mg q.d.) and placebo (PLA, q.d.) in 30 healthy subjects, aged 21-39 years, during controlled frequency breathing (0.30 Hz) in supine and tilt positions. PROP increased HRV in the high-frequency (0.15-0.40 Hz) band (PROP 7.4 +/- 1.0; PLA 6.9 +/- 1.4; PIN 6.8 +/- 1.0 ln MI2; P = 0.003), decreased BPV in the low-frequency band (at 0.1 Hz, Mayer waves) (PROP 0.6 +/- 0.7; PLA 1.3 +/- 1.1; PIN 1.2 +/- 1.2 ln mmHg2; P = 0.001) and enhanced BRS (PROP 14.6 +/- 9.5; PLA 8.0 +/- 6.8; PIN 8.7 +/- 6.8 ms mmHg-1; P = 0.001) in the supine position. After passive tilt, PROP decreased HRV in the low-frequency band (PROP 6.1 +/- 0.9; PLA 6.5 +/- 1.1; PIN 6.9 +/- 0.7 ln MI2; P < 0.001) and decreased Mayer waves (PROP 1.8 +/- 0.8; PLA 2.4 +/- 1.0; PIN 2.7 +/- 0.8 ln mm Hg2; P < 0.001). PIN increased the low-frequency HRV response, which is induced by passive tilt (PIN + 0.9 +/- 1.0; PLA + 0.3 +/- 1.3, PROP + 0.3 +/- 1.0 ln MI2; P = 0.026). Our results prove that beta-adrenergic blockade with potent ISA does not increase HRV, has no beneficial effect on autonomic balance and even exaggerates sympathetic responses to passive tilt.