Role of thromboxanes in vasotonic versus vaso-occlusive angina

Abstract

We used a validated radioimmunoassay to examine plasma thromboxane B2 (TxB2) levels in 6 consecutive vasotonic angina (VA) patients, 14 patients with fixed, occlusive coronary artery (VO) disease and 9 healthy volunteers. In the latter groups, basal TxB2 release was absent. However, all 6 VA patients showed basal release. In one, sustained levels of up to 12 pmol/ml over 2 months of clinical instability were found. Daily aspirin rendered TxB2 undetectable with clinical improvement. In a second patient, angina coincided with up to 14 pmol/ml of TxB2 in peripheral blood, and myocardial infarction produced still further increases. The 14 VO patients were then studied by rapid atrial pacing to detect TxB2 release coinciding with pacing-induced angina and myocardial lactate production. All demonstrated significant occlusive disease (2.5 critical lesions per patient). Blood was taken simultaneously from coronary sinus (CS) and brachial artery (BA) catheters for lactate and TxB2 analysis before, immediately after and 10 min after pacing-induced ischemia. Lactate extraction fell from 29.3 +/- 3.7 per cent to -21.1 +/- 12.8 per cent to -74.3 +/- 20.3 per cent during pacing (all p less than 0.01) but was normal in 10 min (25.1 +/- 3.55). CS TxB2 rose from 18 per cent to 204 per cent of control during pacing but was absent after 10 min. BA TxB2 rose from 40 per cent to 132 per cent of control during and after pacing, but was absent after 10 min (p less than 0.05). In VA, TxB2 is uniquely, continuously present in peripheral blood and levels rise further during symptomatic intervals and myocardial infarction. In VO, even CS TxB2 is absent at rest, and rises less rapidly than in VA, even during pacing-induced ischemia. Although antiplatelet agent will block all TxB2 release even in VO, their clinical potential seems greatest in VA.