Stenting for Acute Myocardial Infarction —Can We Do Better?

In this issue of the Journal, Muramatsu et al. write of their experience using angioplasty guided by physiological assessment as an alternative to stenting in treating acute myocardial infarction. The potential See Muramatsu et al. on pages 657–662 value of this approach lies in the consideration of the benefits and potential problems with today’s accepted standard: the use of stents for this clinical condition. Several large randomized trials have already demonstrated the value of stenting compared to angiographically guided balloon angioplasty in patients presenting with acute myocardial infarction.1–5 However, even those trials might be examined more closely for possible flaws with routine stenting for acute myocardial infarction. Stent thrombosis remains a devastating problem when it occurs. In the early days of stenting, the observation was made that substituting stent thrombosis for restenosis was not a fair trade, and the Stent-PAMI investigators noted a trend toward increased mortality in the patients receiving a heparin-coated stent compared with balloon angioplasty alone.5 The incidence of stent thrombosis today is low enough that it fares comparably to the incidence of acute closure in the cardiac catheterization laboratory, or shortly after the procedure, a complication largely prevented by the use of stents. However, one might still question whether there are problems arising from stents which do not represent a “fair trade”. In clinical trials, all cases of restenosis fall under the same categorization. Yet not all restenosis is alike: a mild focal restenosis is easily treated, whereas diffuse in-stent restenosis can be not only a vexing problem, but one associated with the more serious presentation of acute myocardial infarction rather than the typical restenosis complaint of recurrent angina. Diffuse restenosis additionally is more associated with multiple recurrences. Clinical trials to date are unable to provide a differentiation between the different types of restenosis, due to limitations of definition and precision in the descriptions of the restenosis process. Hence, it is possible that in trials comparing two types of intervention strategies, such as stenting versus balloon angioplasty, restenosis overall is reduced using one strategy. However, “bad” restenosis might be increased with that strategy, which we might not recognize using current definitions and descriptions.6 “Bad” in-stent restenosis may be due to specific reactions to the metallic foreign body, a process which will always be present when the metal is present, although perhaps attenuated by anti-proliferative or anti-inflammatory medications.7 The awareness that this might be occurring may lead some thoughtful clinicians to consider alternative strategies, such as facilitated angioplasty. There have been trials of facilitated angioplasty compared with stenting, but none have convincingly demonstrated that the extra time and effort involved are rewarded with improved outcomes compared with the much simpler strategy of placing a stent at the outset. In the DESTINI trial, using coronary flow reserve via a Doppler-tipped guidewire, those lesions with excellent angiographic and physiological results were associated with lower restenosis, but not lower than the use of stents.8 Other techniques of facilitated angioplasty include using intravascular ultrasound or fractional flow-reserve using a pressure-tipped guidewire. Neither has yet been subjected to adequately powered randomized trials. The authors in this issue of the Journal describe a small study examing FFR-guided angioplasty for acute myocardial infarction and compare it to an earlier cohort of routine stenting. There are many limitations in their study, including small numbers, lack of randomization, and a 14-day restenosis endpoint, rather than 6 or 9 months. Furthermore, there is actually an increased event rate in the group with FFR guidance, which although not statistically significant, certainly suggests that routine stenting is more likely to be associated with improved short-term outcomes. Observational studies such as this, although not definitive or, as in this case, even highly suggestive, nonetheless are valuable for gathering information for hypothesis generation and initial insight into potential strategies. For example, the investigators provide an assessment of the potential for achieving near normal FFR after balloon angioplasty for acute myocardial infarction, which occurred approximately 50% of the time (at least when they were able to obtain acceptable data). They note that the achievement of such an excellent FFR does not always protect against subacute restenosis — a process which may be due to early recoil, thrombosis or other mechanism. Improvement in the quality of the product, or perhaps in technique, would be important, as adequate FFR information could not be achieved in a high percentage of cases. Each of these issues could be addressed in future studies, perhaps culminating in an appropriately powered randomized study comparing the strategy of physiological guidance of balloon angioplasty (using stents only when necessary) to that of routine stenting. Now, if only we could more clearly define what is “bad” restenosis, and carefully document it when it occurs, perhaps we might be able to appreciate when it might be particularly valuable to avoid placing stents.

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