DISCUSSION
We need to take into account that advances in AMI management, including potent antithrombotic drugs, rapid interventional reperfusion strategies and advancements in coronary stent designs have rendered ST a rare complication after DES implantation. The incidence of ST at 30 days after PCI is <1%, whereas late and very late ST rates are 0.5-1% and 0.2-2% per year, respectively.[3]
Established factors concurring to ST include: first, stent under-expansion and malapposition, which are especially common in calcified and tortuous vessels; second, stent placement in small vessels (vessel diameter < 2.5 mm) and/or a long lesion may also be related to impaired and turbulent coronary flow; third, edge dissections compromising coronary flow; finally, hypercoagulability or inappropriate platelet inhibition (e.g. non-response to clopidogrel).[4] According to the timing of the event, the ST is labeled as early (within one month of initial placement), late (between 1 and 12 months), and very late (after 12 months).
In this report, we are focusing on ST due to stent under-expansion and describe how we addressed this issue in the three patients presented above.
Current guidelines recommend intravascular imaging to elucidate the mechanism of ST. Due to the higher spatial resolution, OCT might provide more detailed information about stent apposition, stent expansion and the presence of relevant edge dissections. But performing OCT imaging during acute STEMI is challenging due to the presence of large amounts of thrombus making visualization of relevant portions of the stent impossible. Additionally, vessel size is likely to be underestimated in the acute setting due to high levels of circulating vasoconstrictive hormones, namely catecholamines and vasopressin.
In acute ST with AMI, it is crucial to achieve TIMI 3 flow as soon as possible without going through a phase of flow-deterioration, which is usually the consequence of distal embolization of clot, microvascular spasm, thrombosis and friable atheromatous plaques.[5] The “burden” of thrombus in patients with STEMI undergoing primary PCI has been identified as a major determinant of outcomes, having been associated with reduced procedural success and worse early and late event-free survival.[6]
Moreover, it is crucial to correct mechanical factors (particularly stent under-expansion) in order to correct the cause of ST and prevent repeat target lesion failure. In this context, aggressive mechanical expansion is a known risk factor for distal embolization and microvascular injuries, especially for patients with AMI.[7]