Purpose: Local and remote ischemic preconditioning are cardioprotective mechanisms. We examined the time-dependent impact of pre-infarction angina pectoris and intermittent claudication on short- and long-term mortality following myocardial infarction.
Methods: We conducted a nationwide population-based cohort study using medical registries. We identified all first-time hospitalizations for myocardial infarction in our country between 1996 and 2012. We used Cox regression to compute mortality rate ratios (MRRs) within 30 days, 31-365 days, 1-5 years, and 6-10 years comparing patients with and without previous angina or intermittent claudication. We repeated the analyses according to time between first diagnosis of angina or intermittent claudication and subsequent myocardial infarction (≤7 days, 8-14 days, 15-30 days, 31-90 days, and >90 days). We adjusted for age, sex, calendar period of diagnosis, and comorbidities.
Results: We identified 150,480 patients with first-time myocardial infarction, among whom 23,705 (15.8%) had previously been diagnosed with stable angina, 3,806 (2.5%) with unstable angina, and 3,740 (2.5%) with intermittent claudication. Compared to patients without previous stable or unstable angina, the adjusted 30-day MRR was 0.85 (95% CI: 0.82-0.88) for patients with prior stable angina and 0.67 (95% CI: 0.61-0.74) for patients with prior unstable angina. The mortality reduction was higher the shorter time interval between angina presentation and myocardial infarction and higher for unstable than stable angina. Thus, the 30-day MRR was 0.33 (95% CI: 0.20-0.55) for patients presenting with unstable angina within 7 days before myocardial infarction compared to myocardial infarction patients without previous angina. Beyond 30-days of follow-up, there was no additional survival benefit of pre-infarction angina. Independent of time to myocardial infarction, patients with intermittent claudication had increased short and long-term mortality.
Conclusions: Pre-infarction angina, but not intermittent claudication, improved 30-day mortality following myocardial infarction. The dependency of time and angina type, suggests an effect of endogenous local ischemic preconditioning. The results for intermittent claudication may reflect an absent remote preconditioning effect or the higher comorbidity burden among these patients.