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]