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 consecutive patients with unstable angina at rest and significant coronary artery stenosis (greater than or equal to 90% in greater than or equal to one vessel in 16 patients). 13 of them also had exertional angina. 14 patients presented at least one positive response (greater than or equal to 1.0 mm ST-segment shift) to pacing, with a heart rate (144 +/- 11 vs 75 +/- 13 beats min-1, P less than 0.001) and double product (195 +/- 26 vs 108 +/- 32 x 10(-2), P less than 0.001) significantly higher than during angina at rest. In the ten patients who presented nocturnal angina, the incidence of positive response to pacing and the pacing ischaemic threshold, tested on three different days, were similar to those seen in the remaining patients. In contrast, the ergonovine test was positive in all patients with nocturnal angina (100%), who required a low dose (0.28 +/- 0.2 mg), but it was positive in only four (50%) of those without nocturnal angina, who needed a higher dose (0.55 +/- 0.12 mg, P less than 0.005). Therefore, in patients with severe coronary stenosis and exertional angina, spontaneous episodes, including nocturnal angina, are not related to increases in heart rate. The increased coronary vasoconstrictive sensitivity found in these patients, particularly those with nocturnal angina, was not dependent on the status of the coronary reserve, which strongly suggests that changes in coronary tone, focal or diffuse, are involved in the mechanisms of these ischaemic events.