Nocturnal angina in patients with fixed coronary stenosis. Increased coronary vasoconstrictive sensitivity with independence of pacing ischaemic threshold

Atrial pacing and ergonovine tests were performed in 18 consecutivepatients with unstable angina at rest and significant coronaryartery stenosis ( 90% in one vessel in 16 patients). 13 ofthem also had exertional angina. 14 patients presented at leastone positive response (1.0 mm ST-segment shift) to pacing, witha heart rate (144±11 vs 75±13 beats min^–1,P<0.001) and double product (195±26 vs 108±32x 10^–2 P<0.001) significantly higher than during anginaat rest. In the ten patients who presented nocturnal angina,the incidence of positive response to pacing and the pacingischaemic threshold, tested on three different days, were similarto those seen in the remaining patients. In contrast, the ergonovinetest was positive in all patients with nocturnal angina (100%),who required a low dose (0.28±0.2 mg), but it was positivein only four (50%) of those without nocturnal angina, who neededa higher dose (0.55±0.12 mg, P<0.005). Therefore, in patients with severe coronary stenosis and exertionalangina, spontaneous episodes, including nocturnal angina, arenot related to increases in heart rate. The increased coronaryvasoconstrictive sensitivity found in these patients, particularlythose with nocturnal angina, was not dependent on the statusof the coronary reserve, which strongly suggests that changesin coronary tone, focal or diffuse, are involved in the mechanismsof these ischaemic events.