Effect of beta blockade with and without sympathomimetic activity (ISA) onsympathovagal balance and baroreflex sensitivity

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, an d their effect on HRV has not yet been investigated. Therefore, we measured HRV, systolic blood pressure variability (BPV) and barore-flex sensitivity (BRS) under propranolol (PROP, without ISA 160 mg q.d.), pindolol (PIN, wi th potent ISA 15 mg q.d.) and placebo (PLA, q.d,) in 30 healthy subjects, a ged 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 In 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; PW 1.2 +/- 1.2 ln mmHg(2); P = 0.001) and enha nced BRS (PROP 14.6 +/- 9.5; PLA 8.0 +/- 6.8; PW 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 In MI2; P<0.001) and decreased Mayer waves (PROP 1.8 +/- 0.8; PLA 2.4 +/- 1.0; PIN 2.7 +/- 0.8 In mm Hg-2; 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 In MI2; P = 0.026). Our results prove that be ta-adrenergic blockade with potent ISA does not increase HRV, has no benefi cial effect on autonomic balance and even exaggerates sympathetic responses to passive tilt.