Angiographically, intracoronary thrombus is defined as the presence of a filling defect with reduced contrast density or haziness. Angiographic evidence of thrombus can be seen in 91.6% of patients who present with STEMI(1). Large intracoronary thrombus has an incidence of 16.4% of patients with acute coronary syndrome (ACS).
Thrombus encountered in the setting of ACS has been correlated with acute complications during percutaneous coronary interventions including: 3 times higher MACE - ischemic complications, lower procedural success, higher distal embolization leading to slow/no flow, high mortality, ST elevation and longer hospital stays.
High thrombus burden can be defined using Yip's criteria:
1. Large infarct-related artery (visually estimated reference vessel diameter ≥ 4 mm)
2. Angiographic thrombus with the greatest linear dimension \> 3 times the reference vessel diameter;
3. "Cutoff pattern" (lesion morphology with an abrupt cutoff without taper before the occlusion);
4. Accumulated thrombus (\> 5 mm of linear dimension) proximal to the occlusion;
5. Floating thrombus proximal to the occlusion;
6. Persistent dye stasis distal to the obstruction. IF more than two criteria indicate the presence of very high thrombus burden.
PCI Strategies introduced in HIGH thrombus BURDEN include incorporation of both pharmacological and mechanical thrombus removal.
Immediate stenting of the culprit coronary artery may lead to high chances of the slow-flow/no-reflow phenomenon that leads to periprocedural MI and adverse cardiovascular events. Current studies show that routine deferred stenting has not been found beneficial except when careful patient selection is done where deferral may reduce the final infarct size.
Glycoprotein IIa/IIIb inhibitors have been used in such cases. Current guidelines recommend GPIIa/IIb as bailout therapy following PCI when massive thrombus is found: Class IIa. (6) The rationale in using intracoronary GPIIa/IIIb is that it can be more effective, faster and safer in terms of bleeding.
Deferred stenting is a method of dealing with thigh thrombus burden in STEMI patients. This means to wait 24-48 hour and delay stenting. During this time gap, patient receives intravenous tirofiban. This may be beneficial as the thrombus burden will reduce, minimizing the occurrence of the slow-flow/no-reflow phenomenon.
During coronary angiography the epicardial perfusion can be demonstrated using the TIMI grade flow where:
* TIMI 0 flow (no perfusion) complete blockage - absence of any antegrade flow (forward flow) beyond a coronary occlusion.
* TIMI 1 flow (penetration without perfusion) is faint antegrade coronary flow beyond the occlusion, with incomplete filling of the distal coronary bed.
* TIMI 2 flow (partial reperfusion) is delayed or sluggish antegrade flow with complete filling of the distal territory.
* TIMI 3 is normal flow which fills the distal coronary bed completely. (7) During Primary PCI, If TIMI 0-1 flow is encountered a technique called minimally invasive mechanical intervention (MIMI) can be employed to restore flow. This MIMI entails the use of a guidewire, an undersized balloon or thrombus aspiration to establish distal coronary flow.
