Previous work using a transfer function to estimate central systolic blood pressure (SBP) from the pressure waveform in the radial artery reported that, central SBP was lower in the amlodipine-based regimen compared with the atenolol-based regimen in the Anglo Scandinavian Cardiac Outcomes Trial (ASCOT)¹. However use of a transfer function to estimate central BP has been criticised and more recently Munir et al.,² have proposed that the late systolic shoulder (pSBP₂) may be a direct estimate of central SBP. We compared pSBP₂ between patients randomized to the amlodipine-based and atenolol-based regimens in a substudy of ASCOT.

229 patients participated in the substudy. Applanation tonometry was performed at the right radial artery using a Millar tonometer. Waveforms were ensemble averaged and calibrated to brachial artery pressure. All data are means (SD).

Brachial BP did not differ significantly (137.5 (12.2)/79.6 (7.4) vs. 142.1 (15.3)/80.5 (9.2) mmHg; NS), but pSBP₂ was significantly lower in the amlodipine-based regimen (112.4 (10.4) vs. 119.3 (13.1) ; p< 0.01). pSBP₂ occurred earlier in the amlodipine-based group (415.8 (53.0) vs. 453.5 (51.6) ms; p < 0.01) probably due to the lower heart rate in the atenolol-based regimen.

Lower pSBP₂ in people randomized to the amlodipine-based regimen in ASCOT are in keeping with previous findings using a transfer function applied to the radial pressure waveform and direct measurements in the carotid artery and suggest that pSBP₂ may be a useful indicator of central SBP.