BACKGROUND OF THE STUDY

Acute myocardial infarction (AMI) is the most frequent clinical presentation in older adults (≥75 years). Registry data shows that up to 65% of patients ≥75 years with AMI has multivessel disease, namely at least one lesion beyond the culprit one with diameter stenosis \>50% and located in a coronary artery different from the culprit vessel. Presence of multivessel disease is a marker of worse prognosis. The rate of adverse events, such as death and MI is 3-fold higher in multivessel disease patients if compared to single vessel disease patients. During a 3-5 years follow-up, the number of adverse events related to non-culprit lesions is double than the one related to culprit lesions (data from SWEDEHEART registry and PROSPECT trial). These adverse events are even more frequent in older adults reaching a 15-30% incidence at 1 year. Several studies were focused on older adults with AMI in order to optimize their treatment. The main focus of those studies were: optimal dual antiplatelet therapy (DAPT) duration and type of stent. As for DAPT, data is in favour of a short regimen (1-6 months) as it represents the best balance between ischemic protection and reduction of bleeding events. In both LEADERS FREE and ZEUS trials, age was the main criteria for enrollment and it was considered as a marker of high risk of bleeding event. In the ongoing XIENCE 28 study, age ≥75 years is considered a sufficient criteria to prescribe 28 days of DAPT after stent implantation.

As for stent type, the recent SENIOR trial showed that biodegradable polymer second generation drug eluting stents (DES) are the gold standard in older adults receiving percutaneous coronary interventions (PCI). These stents clearly outperformed bare metal stents with a low event rate in presence of a short DAPT regimen. Thus, at the present time, we have sufficient data to consider biodegradable polymer DES and short DAPT as cornerstones of the treatment in older adults with MI. On the contrary, we have no scientific evidence regarding the best treatment strategy to apply in multivessel disease patients. It is not clear whether to prefer a culprit only strategy or if revascularization of non-culprit lesions is associated to a reduction of adverse events.

Culprit lesion treatment with PCI and stent implantation in MI setting is universally agreed as gold standard since it reduces morbidity and mortality. In the last 10 years, several studies were focused on the treatment of non-culprit lesions. PRAMI, CULPRIT, DANAMI 3 PRIMULTI, COMPARE ACUTE trial tried to assess if a systematic treatment of non-culprit lesions was associated with an improved prognosis if compared to a culprit only strategy. All these studies showed that complete revascularization clearly reduce the risk of repeated revascularizations. However, no study showed a significant impact on death or MI. When pooled in a meta-analysis, we can observe a trend in favour of MI reduction but data cannot be considered as conclusive. In 2019, COMPLETE trial results will be disclosed. In COMPLETE trial, more than 4000 patients were enrolled with consequent power to detect a difference in terms of death and MI. The limits of all the above mentioned studies are that the mean age was around 60 years and that only ST-segment elevated MI (STEMI) patients were included. No study included a relevant portion of patients ≥75 years nor included no-STEMI (NSTEMI) patients. However, a culprit lesion is identifiable in more than 90% of NSTEMI patients and the issue on their management is similar to the one of the STEMI patients. In addiction, in older adults, clinical presentation is as NSTEMI in more than 70% of the cases. Consequently, it is mandatory to generate solid data on the correct treatment strategy in these patients.

In younger adults (\<65 years), in concordance with the solid scientific evidences, it is widespread a complete revascularization strategy. In older adults (≥75 years), also guidelines, in absence of clear data, suggest a case-by-case decision and suggest to consider age as one of the determinants of the final decision (Class IIa level of evidence C, ESC NSTEMI guidelines). Both European and American registry data shows clearly that the most frequently applied strategy is the culprit only one, both in STEMI and NSTEMI patients. Also in the LEADERS FREE trial, patients ≥75 years had multivessel disease in 65% of the cases, but in more than 80% of them, treatment was limited to the culprit lesion. In conclusion, the actual gold standard of treatment in older adults with MI and multivessel disease is the culprit-only strategy. The traditional concept of complete revascularization was based on angiography. Operator visually identified the lesions \>50% and decided to treat or not each one of them. Contemporary data on fractional flow reserve and instantaneous free-wave ratio demonstrated that an angio-guided strategy is similar to a coin toss in terms of detection of lesions causing ischemia. This leads to unnecessary PCIs or avoided necessary PCIs in more than 50% of the cases. Studies on angio-complete revascularization probably failed to show an MI reduction because of this reason. In addition, long-term follow-up data of lesions functionally deferred shows that the rate of death and MI at 5 years is below 3%. As a consequence, functional revascularization should be considered as contemporary strategy to achieve a real complete revascularization.