This was a retrospective observational study in a contemporary, population-based and unselected cohort of ACS-patients, with a long follow-up period, reporting long-term cardiovascular outcomes after ACS. To our knowledge, there are no comparable studies reporting outcomes in absolute numbers. Almost one out three patients died for cardiovascular reasons or had a recurrent ischemic event during the study period. Over 40% of all events and more than half of all MI´s occurred during the first year. IS events were more evenly distributed, with nearly 1/3 occurring during the first year.
Compared with the Cardiovascular risk in post-myocardial infarction patients: nationwide real-world data demonstrate the importance of a long-term perspective study (6), which was a Swedish nationwide register based study (n = 97254) to assess the incidence and risk factors of subsequent cardiovascular events in the Swedish post MI population, we found a lower event rate both short and long term. That study included AMI-patients surviving the first week after discharge, with a total follow-up of 4 years and a mean follow-up time of 2.5 years. The 1-year rate of the composite of cardiovascular (CV) death, recurrent MI and stroke was estimated to 18.3%, and the risk remained high in patients without an event during the first year, in the subsequent 2 years at about 20%, which is almost twice as high as in our material. The patient data upon which these results are based is comparable with ours in terms of a high median age and a relatively low frequency of revascularization during hospitalization. On the other hand, preexisting heart failure was clearly more prevalent (26.3%) compared with our cohort (5.3%) which might contribute to a higher event rate in general and CV mortality in particular. Moreover, in our study all end-points were adjudicated and we only included type-1 MI´s, which likely contributes to the observed lower event rate. Type-2 MI has been associated with a clearly higher mortality in previous reports and the proportion of type-2 MI in SWEDEHEART has been estimated to 7.1%(11).
In a large study comparing long-term outcomes after MI (3 years) 2002–2011 in nationwide registers from England, France, Sweden and USA in more than 100000 patients > 65 years, the cumulative incidence of the composite of all-cause death, MI and stroke varied between 26% (France) and 36.2% (USA)(12). These numbers are more at level with our results when taking into account that the end-point included all-cause death and that the studied populations had a high burden of comorbidities and a very high mean age of 77.5–78.6 years.
These results indicate that the risk is high during the first year, and remains high also in a longer time perspective, which highlights the importance of adequate secondary prevention and revascularization procedures.
Older age, diabetes mellitus, prior ischemic stroke, heart failure (treatment with diuretics at discharge), established coronary heart disease (prior PCI, CABG or angina) independently predicted increased risk for the primary endpoint in our material, whereas revascularization during index hospitalization and lipid-lowering therapy were associated with favorable outcome.
In accordance with previous publications, older age conferred increased risk for recurrent cardiovascular events in this study(13). An ageing population and increasing proportion of survivors of ACS should urge health care systems to direct their attention regarding secondary prevention not only to younger patients. Diabetes Mellitus has repeatedly been shown to forcefully increase the risk for cardiovascular disease(14). It has also been linked to excess mortality after MI compared with patients without diabetes(15), and ESC guidelines for non-ST-segment elevation acute coronary syndromes (NSTE-ACS) recommend that a multifactorial approach, with treatment targets should be considered in this subset of ACS-patients (grade of recommendation IIa)(16). In our material, diabetes was the comorbidity with the strongest association of elevated long term ischemic risk after ACS, which in conjunction with previous evidence points at the importance of good metabolic control and intensive lipid lowering therapy(17). There is vast evidence from clinical trials that lipid-lowering statin therapy reduces cardiovascular morbidity and mortality in both chronic and acute coronary syndromes(18, 19). In our study, lipid-lowering therapy was strongly associated with a reduced risk for recurrent events in the long term, which confirm the results from clinical trials and contribute to generalizability to a real-world ACS-population.
Ischemic stroke and heart failure have, as in this study, been identified previously as markers of elevated risk for recurrent ischemic events and death(6, 13, 20, 21).
Revascularization during index-hospitalization for ACS, both CABG and PCI, were strongly associated with better outcome in this study. Jernberg et al reported that absence of revascularization was associated with increased cardiovascular risk (6). An early invasive strategy, with coronary angiography followed by PCI if appropriate, has been shown to reduce cardiovascular events long-term after NSTE-ACS, compared with an initial conservative strategy (22, 23). In ST-segment myocardial infarction (STEMI), there is solid evidence that prompt revascularization reduces mortality and subsequent ischemic events (24, 25). Elderly patients are generally considered to have a greater burden of coronary disease and thereby more myocardial ischemia and seem to derive a relatively greater benefit from revascularization (26, 27). Given the high median age in this cohort, this seems to hold true for our patient population and has important implications for the often difficult clinical decision-making regarding revascularization in the care of elderly patients with ACS.
Strengths and limitations
This unselected, single-center cohort, with the aim to study the long-term cardiovascular outcome after hospitalization for ACS, was relatively small, which is a limitation. However, the data collected can be considered to be of high quality as well as the adjudication of clinical endpoints. The outcome measures cardiovascular death, myocardial infarction and ischemic are fairly standardized. We chose to only include type 1 MI´s, because we had the opportunity to evaluate every clinical event, and since a type 1 MI has a different prognostic impact than for example a type 2 MI. This might lead to lower event rates compared with register-based studies, in which it is hard to discriminate between infarction types. Due to the establishment of a PPCI-network in the region, patients received a different reperfusion treatment, with a clear dominance of PPCI from May 2015 until the end of follow-up, compared with a fibrinolysis dominated reperfusion treatment before May 2015, which might has affected outcomes.