This systematic review and meta-analysis first assesses the clinical and angiographic outcomes of post-dilation after coronary stent implantation in patients with ACS, which shows that the post-dilation of stent deployment was associated with an increase of all-cause death but not related to MACE, stent thrombosis, myocardial infarction, and target vessel revascularization of clinical outcomes. In addition, the rate of no reflow and slow reflow in post-dilation group are similar to that in non-post-dilation group.
The ESC guideline recommended that the majority of patients with ACS shouled use the invasive PCI, and primary PCI is the preferred reperfusion strategy for STEMI patients . In the bare metal stents era, the restenosis rate caused by neointimal hyperplasia was between 20% and 30% . With the advancement of stents technology, the drug-eluting stents improve restenosis compared with bare-metal stents . However, complications after stent implantation, such as in-stent thrombosis, no reflow and others still occur. The majority of non-fatal myocardial infarction and 45% of death were included in the clinical sequelae of stent thrombosis . The post-dilation is a treatment strategy with non-compliant balloon of appropriate size , which could improve stent under-expansion and incomplete stent apposition, in turn reducing in-stent restenosis and target vessel revascularization . The POSTIT trial, aiming to evaluate the necessity of post-dilation after coronary stent deployment, manifested that only 29% of patients achieved the optimum stent deployment (minimal stent diameter ≥ 90% of the average reference lumen diameter assessed by intravascular ultrasound), 71% of patients were under-expansion . The CRUISE (Can Routine Ultrasound Influence Stent Expansion) study showed that target vessel revascularization had been reduced by 44% and the final minimum stent area had been increased by 14% after the post-dilation with the guidance of intravascular ultrasound . During the bioresorbable vascular scaffolds and sirolimus-eluting stents implantation, the post-dilation with high-pressure non-compliant balloon and large sizes balloon (balloons > 1 mm larger than the stent nominal size) also demonstrated safe clinical and angiographic results [33, 34]. There were a few studies on the post-dilation at present, the majority of them were observational studies and excluded patients with ACS, only patients with stable coronary artery disease, long lesions or calcification lesions were included. Recently, a meta-analysis (conference abstract) including seven observational studies for patients with coronary artery disease indicated that the post-dilation could not reduce the risk of MACE, all-cause death, myocardial infarction and target vessel revascularization, and recommended that the post-dilation should be performed in selective patients but not in all patients undergoing PCI . However, due to the high pro-inflammatory risk, thrombotic environment and coronary spasm caused by circulating vasoconstrictors in patients with acute myocardial infarction, the conclusions of post-dilation in patients with coronary artery disease can not be extended to patients with ACS. Therefor, it is necessary to explore the benefits of post-dilation in patients with ACS.
This meta-analysis suggested that there were no significant difference in MACE, myocardial infarction and target vessel revascularization between post-dilation group and non-post-dilation group, which was similar to the results of the meta-analysis by Chen et al in 2018 . However, The heterogeneity of MACE, myocardial infarction and target vessel revascularization in this study was obvious. The sensitivity analysis of MACE did not find study producing heterogeneity. Therefore, the result of MACE in this study should be interpreted with caution. The sensitivity analysis of target vessel revascularization found that the heterogeneity came from the study of Gao et al . The target lesions were more complex and immediate TIMI flow was impaired in the post-dilation group in this study, finial TIMI flow was same in two groups due to the use of intracoronary vasodilator agents. However, it may be associated with further adverse clinical outcomes. Meanwhile, the subgroup analysis showed that the target vessel revascularization could be reduced after the post-dilation within 12 months, and patients with any ACS could also benefit from this strategy. The sensitivity analysis of myocardial infarction displayed that the heterogeneity was derived from the study by Imoril et al . The bioabsorbable scaffolds were used in this study, which was different from drug-eluting stents and bare-metal stents used in other studies. The post-dilation increased myocardial infarction after excluding this study, which indicated that the post-diltation was more suitable for bioabsorbable scaffolds. This may be due to the fact that the stent platform materials of bare-metal stent and drug-eluting stent are stainless steel, chrome-cobalt, platinum–chromium, or nickel/titanium alloy, which have a stable structure that provides reliable, compliant struts expansion without the risk of disruption. However, the bioabsorbable scaffolds use polylactic acid and other polymer materials as scaffolds to provide temporary mechanical support for stenotic or occluded coronary arteries. It represents a potential risk for clinical outcomes because of the relatively thick struts and limited expansion. Five-year follow-up from the ABSORB III Trial indiciated that rate of target lesion failure was increased compared with everolimus-eluting stents . The post-dilation after the use of bioabsorbable scaffolds appears to be effective. Meanwhile, this meta-analysis suggested that the post-dilation did not reduce thrombosis, which was consistent with the conclusion of Hong et al in 2017 (HR = 0.39,CI 0.07–2.31, P = 0.279) . The study by Chen et al. also found that the post-dilation did not change all-cause death, which was different from the conclusion that the post-dilation increased all-cause death in this study. This may be related to the inclusion criteria of that study . All patients with coronary artery disease undergoing PCI were included in that meta-analysis, including patients with stable coronary artery disease. The levels of troponin I and highly sensitive creactive protein were elevated after stent expansion, suggesting more myocardial damage and inflammation . The primary lesion in patients with acute coronary syndrome is more unstable due to more necrotic cores and fewer fibrous fatty plaques than in patients with stable coronary artery disease ,the elevation of cardiac troponin occurs in lesions with a large necrotic core area and in lipid-rich lesions [39, 40]. Therefore, patients with ACS may suffer more myocardial damage. This may be the reason for increase of all-cause death rate in ACS patients with stent post-dilation. Interestingly, there was no increase in all-cause death in ACS patients within 12 months after post-dilation. At present, dual antiplatelet therapy is mainly used in ACS patients for 12 months after PCI. After 12 months, aspirin monotherapy or dual antiplatelet therapy regimen should be depended on the specific conditions of patients, which may affect long-term all-cause death. In addition, studies have shown that the levels of plasma B-type natriuretic peptide significantly increase following the post-dilation, which is a biomarker of heart failure . Long-term heart failure can also cause an increase death. Moreover, previous studies lacked a uniform definition of reflow, making no reflow rate and slow reflow rate fluctuate between 1% and 30% , which was difficult to guide clinical practice. Therefore, this study unified the definition of no reflow and slow reflow and coneluded that the post-dilation had no effect on no reflow and slow reflow.
However, these results should be interpreted carefully. Firstly, whether or not to receive the post-dilation strategy after stent deployment mainly depends on the individual situation of patients and the wills of operator. Secondly, different definitions of outcomes and baseline characteristics of studies included will affect clinical outcomes. For example, in the pooled analysis of MACE, the study by Gao et al. defined MACE as hospitalization caused by angina pectoris, dyspnea, ventricular thrombus, which is quite different from other studies. Similarly, for repeat revascularization, the definition was vague and the outcome cannot be evaluated. Furthermore, the complications of PCI are not only related to the stent under-expansion, but also to thrombus aspiration, thrombolytic drugs for intracoronary injection or vasodilator, and antiplatelet drug compliance. Finally, although some studies have shown coronary TIMI flow grade after PCI, only a few studies compared no reflow or slow reflow between two groups. Therefore, further randomized controlled trials are needed to verify the benefits of post-dilation.