In ST-segment elevation myocardial infarction (STEMI), restoring normal coronary flow and, most importantly, normal myocardial perfusion, are the ultimate goals for the interventional cardiologist. Primary percutaneous coronary intervention (PCI) has become the cornerstone of this management, surrounded by a powerful pharmacological environment. Many refinements have been proposed during past decades, particularly in terms of antiplatelet therapy . Angioplasty has also evolved, with the development of new devices (e.g. drug-eluting stents, bioresorbable vascular scaffolds, expandable stents, thrombus-aspiration catheters) and new strategies, such as the minimalist immediate mechanical intervention (MIMI), widely called “deferred stenting” . Indeed, an important feature of primary PCI relies on the optimal timing of stenting, with the operator facing two opposing challenges, the first being the fear of re-occlusion, and the second being distal embolization and no-reflow. Isaaz et al. was the first to describe the MIMI strategy, based on:
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patency restoration by mechanical means (at that time a small balloon inflation, but preferably now, thrombus aspiration);
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and deferred stenting after a few days in a more favorable pharmacological environment.
Such a strategy has a strong pathophysiological rationale since it allows for decreasing thrombus burden and relieving vasoconstriction, both of which are highly prevalent during STEMI. Since this first report by Isaaz et al. , several studies have confirmed the safety of deferred stenting , with a limited risk of re-occlusion.
But what are the real benefits of this strategy?
They can be several:
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a decrease in distal embolization and overall periprocedural complications;
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better sizing of the lesion and of the artery, leading to an optimized stent selection;
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better appraisal of the revascularization strategy, including avoiding unnecessary stenting when the residual stenosis is not deemed significant;
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better location and length assessment of the culprit lesion, avoiding complex or bifurcation stenting;
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an opportunity to implant a bioresorbable vascular scaffold, which requires pre-dilatation and post-dilatation and is sometimes hardly feasible or prejudicial in the acute phase;
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finally, and above all, a better clinical outcome for the patient.
Several reports have suggested that deferred stenting was indeed associated with a lower risk of embolization and no/slow flow. Yet, most of these studies were not randomized and the majority were observational . It has been suggested, albeit not definitively proven, that deferred stenting led to intervene on a larger vessel and thus to select a larger prosthesis, with potential advantages represented by reduced malapposition and thrombosis . Some patients do not require stent implantation if sufficient time is allowed for the thrombus to regress: in our series, almost 20% of the patients did not receive a stent . In terms of outcome, very few data were available, until the recent publication of the MIMI trial by Belle et al. . Their multicenter study randomized 140 patients to two arms: an immediate stenting arm and a delayed stenting arm. The primary objective was the size of the myocardial scar, evaluated by magnetic resonance imaging within the first week. The study was correctly powered to test its primary objective. The authors showed that the strategy of deferred stenting was not superior to the standard strategy. This result differs from the previous DEFER-STEMI trial, in which Carrick et al. demonstrated, in high-risk STEMI patients, that deferred stenting reduced no-reflow and increased myocardial salvage. Despite the fact that DEFER-STEMI was a single-center proof-of-concept study, the population characteristics were substantially different from those in the MIMI trial, as only patients at high risk of no-reflow were included. A few days ago, the results of the largest trial on deferred stenting to date – the DANAMI 3-DEFER trial – were published . This study included more than 1200 STEMI patients who were again randomized to a strategy of deferred stenting or standard PCI. While the study sample size was large, the rate of exclusion was high, including 894 patients with a “lesion unsuitable for deferred strategy (at the discretion of invasive cardiologist)”. This study did not report any benefit of deferred stenting compared to the standard of immediate stent implantation on “hard outcome” including death, heart failure, or reinfarction.
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