Circadian rhythm of angina in patients with unstable angina: relationship with extent of coronary disease, coronary reserve and ECG changes during pain

A circadian distribution of ischaemic events has been identifiedin ambulatory patients with stable angina. However, whethera similar distribution occurs in patients with unstable anginawho remain at bed rest is still uncertain. Therefore, we analysedthe possible circadian presentation of episodes of angina atrest (n=1222) in 193 patients hospitalized consecutively. Theinfluence of extent of coronary disease (number of vessels with>70% stenosis, 0, 1 and 2–3), type of ECG changes duringpain on a 12-lead ECG, and coronary reserve, as assessed byischaemic threshold (atrial pacing), were also evaluated. Therewere two peaks of highest incidence: at 0700–1000h andat 1900–2200h (P<0.0001) which were unrelated to theextent of coronary disease, coronary reserve or type of ECGchange. Patients with 1 or 2-3 vessel disease with a reducedischaemic threshold (=<150 beats. min ^–1), however,had a higher incidence of midnight angina (2300–0200h)than those with a normal threshold or with no vessel disease(P<0001). It is concluded that, in spite of being at bed rest, patientswith unstable angina present a definite circadian distributionof angina, with peaks in the early morning and late evening.Patients with a low coronary reserve seem to have a higher incidenceof midnight angina than others.