[ST segment depression during recovery after treadmill exercise test in stable patients with previous myocardial infarction].

Background: The significance of exercise-induced ST segment depression is well known while limited data are available on the clinical/prognostic power of ST depression occurring only during recovery. Aim of the study was to clarify the clinical/prognostic value of "recovery only" ST depression in stable patients late from myocardial infarction (AMI) and to determine whether the addition of recovery data to exercise parameters improves the interpretation of exercise test.

Methods: From a population of 766 consecutive patients (mean age: 57.2 +/- 8.6 yrs.; male: 89%) who underwent a Bruce Treadmill test at least 1 year after a Q wave AMI and whose exercise data were prospectively entered in the database of our Institution, 4 different Groups were identified: 1) 99 patients with a negative exercise test; 2) 53 patients with "exercise only" ST depression; 3) 140 patients with "exercise and recovery" ST depression; 4) 31 patients with "recovery only" ST depression. The main clinical and exercise data and a cardiac follow-up (average mean length: 1530 +/- 600 day) were evaluated by one-way analysis of variance, Bonferroni T-test, chi-square, relative risk (RR) with 95% confidence intervals (CI), Kaplan-Meler method and log-rank.

Results: Baseline clinical parameters were similar in the 4 Groups except for older age in Group 3 compared to Group 2 (< 0.05) and higher prevalence of anterior AMI in Group 4 compared to others (= 0.004). Patients with exercise and recovery ST depression or with "recovery only" ST depression had significantly less exercise tolerance than patients with negative exercise test or "exercise only" ST depression [exercise duration (< 0.05, Group 1 vs. 3, vs. 4; Group 2 vs. 3), peak rate pressure product (< 0.05), maximal heart rate (< 0.05; Group 1 vs. 2; vs. 3; vs. 4)]. Exercise-induced ST depression was higher and angina was significantly more frequent in patients with exercise and recovery ST depression as well as an high Mark's risk score (< 0.001). Only patients with exercise and recovery ST depression demonstrated significantly higher risk of overall mortality (RR: 1.35, CI: 1.04-1.74), unstable angina (RR: 1.34, CI: 1.09-1.65) or revascularisation procedures (RR: 1.51, CI: 1.25-1.83). Relative risk of patients with "recovery only" ST depression was similar to that of subjects with "exercise only" ST depression.

Conclusions: In stable patients with old Q wave AMI, "recovery only" ST depression is rate, but does represent a true sign of ischemia. It could be associated with indirect indexes of worse ventricular function. The prognostical power of "recovery only" ST depression is mild, although similar to that of "exercise only" ST depression. Moreover the presence of ST depression not only during exercise but also during the recovery phase identifies patients with more severe prognosis. Therefore the inclusion of findings from the recovery phase in the analysis of the exercise test could increase the predictive power of the test itself.