Acute coronary syndromes—thrombus





CTO Manual Online cases: 6 , 19 , 103


PCI Manual Online cases: 4 , 9 , 11 , 14 , 19 , 27 , 31 , 35 , 40 , 41 , 42 , 43 , 44 , 45 , 50 , 54 , 57 , 58 , 61 , 66 , 78 , 83 , 84 , 87 , 94


Acute coronary syndromes encompass ST-segment elevation acute myocardial infarction (STEMI), non-ST-segment elevation acute myocardial infarction, and unstable angina. STEMI patients require immediate reperfusion to minimize the infarct size and decrease mortality.



Planning


Given urgency to restore the patency of the culprit vessel in STEMI patients, there is often limited time for planning. Nevertheless, the key components of planning remain essential, such as knowledge of prior revascularization procedures (e.g., STEMI in a patient with prior stenting could be due to stent thrombosis; knowledge of bypass graft anatomy is particularly important in prior CABG patients as it may expedite diagnostic angiography), cardiac function (risk of developing cardiogenic shock is higher in ACS patients who already have decreased ejection fraction) comorbidities (such as renal failure, diabetes, and need for future surgery), and medications that have been administered.


STEMI in postpartum patients may be due to spontaneous coronary dissection (SCAD, Section 22.1 ). STEMI in women who have recently had a stressful event may be due to stress cardiomyopathy (takotsubo), but coronary angiography often needs to be performed to exclude other possible etiologies.



Monitoring


Monitoring is of critical importance in ACS patients, as they are more likely to develop hemodynamic instability and arrhythmias. Often accelerated idioventricular rhythm and ST-segment normalization are indications of successful reperfusion in STEMI patients.



Medications


Potent antithrombotic medication administration (both anticoagulation and antiplatelet) is critical for treating thrombotic lesions, to minimize the risk of thrombus expansion or new thrombus formation. Antiplatelet treatment may be best achieved with more potent and rapidly acting oral P2Y12 inhibitors (such as prasugrel and ticagrelor), sometimes in combination with an intravenous antiplatelet agent, such as a glycoprotein IIb/IIIa inhibitor or cangrelor (for cases with large thrombus burden or for bailout in case of thrombotic complications). Anticoagulation is most commonly achieved with unfractionated heparin .


If glycoprotein IIb/IIIa (GP IIb/IIIa) receptor antagonists or cangrelor are being used, heparin is given at a dose of 50–70 U/kg IV bolus to achieve an activated clotting time (ACT) of 200–250 seconds (Hemochron device). When GP IIb/IIIa receptor antagonists or cangrelor are not being used, 70–100 U/kg bolus of unfractionated heparin is recommended with an ACT goal of 300–350 seconds (Hemochron device) .



Access


Radial access is generally preferred over femoral access in ACS patients, especially those with STEMI, given multiple prior studies that have shown lower bleeding risk and lower mortality with radial access , although the SAFARI-STEMI trial did not show any difference in clinical outcomes with femoral vs. radial access . Femoral access is preferred in prior CABG patients, in many of whom graft engagement can be challenging using radial access. Moreover, timing is important in STEMI patients: if vessel engagement is challenging through radial access causing delays in reperfusion (such as in patients with arteria lusoria) , prompt conversion to femoral access is indicated, since “time=muscle.”



Engagement


Vessel engagement is performed as outlined in Chapter 5: Coronary and Graft Engagement .


In STEMI patients it is often debated whether angiography of both the suspected culprit and the nonculprit vessels should be performed before performing PCI or whether the target vessel should be immediately engaged with a guide catheter with immediate PCI of the culprit lesion.


Immediate engagement of the suspected culprit vessel can shorten door-to-balloon time by 8–13 minutes . However, if the culprit lesion is in the RCA and PCI is done without knowledge of the left coronary anatomy, outcomes may be suboptimal, as some patients may have significant left main or multivessel CAD and may: (1) require hemodynamic support; or (2) be best served with CABG to improve their long-term outcomes, hence balloon angioplasty only of the culprit lesion may be preferable without stent implantation.


A recommended approach to coronary vessel engagement in STEMI patients is shown in Fig. 20.1 .




Figure 20.1


Recommended vessel engagement sequence in STEMI patients.



Angiography


The goal of diagnostic angiography in ACS patients is to identify the culprit lesion(s), and define the overall coronary anatomy, so that the optimal revascularization strategy can be selected.



Determine target lesion(s)


Identification of the ACS culprit lesion(s) is often easy on diagnostic angiography (vessel occlusion with thrombus), but can sometimes be challenging. The following parameters can help identify the culprit lesion ( PCI Manual Online cases 9 , 11 , 42 , 50 , 56 , 78 , 87 ):



  • 1.

    Electrocardiogram.


  • 2.

    Slow antegrade flow.


  • 3.

    Luminal haziness, suggestive of thrombus.


  • 4.

    Collateral flow.


  • 5.

    Occlusion of distal branches, suggestive of prior coronary embolism.


  • 6.

    Left ventriculography (can reveal area of hypokinesis or suggest alternative diagnoses, such as takotsubo cardiomyopathy).


  • 7.

    Intravascular imaging with optical coherence tomography (OCT), revealing plaque rupture or erosion and thrombus.


  • 8.

    Transthoracic echocardiography that can reveal areas of hypokinesis/akinesis and can also help with diagnosis of mechanical complications, such as ventricular rupture, ventricular septal defect, and papillary muscle rupture.



In some cases a culprit lesion cannot be identified, because the presenting symptoms are not due to ischemia (such as in takotsubo cardiomyopathy).


In other cases, the culprit lesion may not be angiographically apparent. Intravascular imaging with OCT can help determine if a culprit lesion is present.


In cases where it remains unclear what the culprit lesion(s) are, subsequent magnetic resonance imaging can help detect the area of myocardial injury and infer what the culprit lesion(s) and vessel(s) are .


Complete revascularization (either at the time of emergent PCI or staged) is recommended for ST-segment elevation myocardial infarction patients, given the results of the COMPLETE trial . In patients with cardiogenic shock culprit-only PCI is recommended in the acute setting based on the results of the CULPRIT-SHOCK trial .



Wiring


Wiring in ACS patients is performed as described in Chapter 8 : Wiring. A specific challenge for wiring (and also lesion preparation and stenting) is the presence of intracoronary thrombus, in part because the distal vessel may be poorly or not at all visible, since collaterals may not have had enough time to form . Moreover, it may be impossible to determine whether there is angulation within the occluded segment, or whether the guidewire has entered into side branches. In case of guidewire exit from the vessel subsequent advancement of a balloon can result in perforation ( PCI Manual Online case 45 ), further complicating an already high-risk clinical presentation.



Guidewire choice




  • 1.

    Workhorse guidewire


    To minimize the risk of perforation, initial wiring through an acute complete thrombotic occlusion is usually attempted with soft workhorse guidewires without hydrophilic tip coating. Occasionally advancement of the guidewire alone will result in restoration of some antegrade flow, that can facilitate subsequent wiring attempts and management of intracoronary thrombus.


  • 2.

    Hydrophilic coated guidewires


    If a soft workhorse guidewire fails to advance through the occlusion, then a soft guidewire with hydrophilic tip coating can be used (such as the Sion or BMW Universal, see Section 30.7.1 ).


  • 3.

    Polymer-jacketed guidewires.


  • 4.

    Filterwire or Spider ( Section 30.8 ). Although these devices are currently only approved for use in SVGs in the United States, they may capture thrombi liberated during thrombectomy, balloon angioplasty, and stenting) ( PCI Manual Online case 61 , 66 ).



If crossing with workhorse (with or without hydrophilic coating, Section 30.7.1 ) guidewires fails, soft polymer-jacketed guidewires, such as the Fielder FC or Sion black (Asahi Intecc, Nagoya, Japan, Section 30.7.2 ) are often used next. Escalation to stiffer polymer-jacketed guidewires (such as the Pilot 200) should be avoided, if possible, as it increases the risk of perforation, but may be needed in some challenging lesions .



Microcatheter and knuckling


Guidewire advancement over a microcatheter or a small balloon (1.0–1.5 mm in diameter) can also be useful for crossing by increasing support and allowing guidewire exchanges without losing wire position.


Occasionally advancing a knuckled guidewire ( PCI Manual Online case 54 ) may help advance through areas of tortuosity with low (although not zero) risk of perforation, but may require strong guide catheter support, for example, by using a guide catheter extension.



Confirmation of guidewire position


If the location of the guidewire tip is uncertain after advancing it through an occlusion, it may be best to not advance a balloon but attempt to clarify the guidewire position first. If there is absolutely no antegrade flow after wiring, obtaining a second arterial access and performing contralateral injection may help clarify guidewire position through collateral filling of the occluded vessel. Injecting contrast through an over-the-wire balloon or microcatheter should be avoided, as it carries risk of extending a subintimal dissection if the microcatheter or balloon tip is in the subintimal space. Use of intravascular ultrasound can often aid in confirming intraluminal placement of the guidewire. Careful “dottering” of the thrombotic lesion with a low-profile short balloon may also be performed, however it is not a reliable strategy to confirm true lumen guidewire position; sometimes, it may restore enough flow to confirm guidewire location.



Wiring the wrong vessel?


Sometimes, wiring may fail because the lesion being crossed is not the culprit lesion for the acute event (it may be a chronic total occlusion). Alternatively some patients may have more than one culprit lesion. Repeat review of the angiogram (and of prior angiograms if available) and correlation of the electrocardiographic and angiographic findings may be helpful in such cases. Intravascular imaging (especially with OCT, which is the best imaging modality for detecting intracoronary thrombus) can be especially helpful in cases with unclear or multiple potential culprit lesions, as presence of thrombus or ulceration within a lesion strongly suggests it is a culprit. Thrombus aspiration can clarify the anatomy distal to the occlusion, and help clarify if the guidewire is in a side branch or in the main vessel.



Lesion preparation


A unique characteristic of ACS lesions is intracoronary thrombus that can be managed as outlined in Fig. 20.2 .




Figure 20.2


Management of intracoronary thrombus.



Antegrade flow present?


Sometimes guidewire crossing alone will restore some antegrade flow. If not, inflation of a small balloon (usually 2 mm in diameter) at low pressure (6–8 atm) may restore some flow and allow planning of subsequent treatment steps.


Failing to restore antegrade flow after ballooning could be due to large residual thrombus, balloon inflation proximal to the culprit stenosis in vessels with TIMI 0 flow, severe distal vessel disease or failure to be in the distal segment with the guidewire. If large thrombus burden is suspected, aspiration thrombectomy or laser may be beneficial. If wiring into a small branch is suspected, it may be best to leave the original wire in place and attempt wiring with another wire, followed by balloon angioplasty. Wire perforation may have occurred if wiring is very challenging.


Administration of anticoagulant and antiplatelet medications is crucial to prevent thrombus expansion, as described in Chapter 3: Medications .



Wiring through thrombus and balloon angioplasty


Balloon angioplasty can restore antegrade flow and also assist with assessing the lesion length and vessel diameter.



Thrombus size


In patients with large thrombus size balloon angioplasty and stenting may cause severe distal embolization that could be difficulty to treat.



Ongoing ischemia


The presence of ongoing ischemia is critical for making decisions about optimal management of patients with large thrombus burden.



Antithrombotic management only with repeat angiography


If antegrade flow is restored yet large thrombus remains, one treatment option is to defer further intervention by allowing 24–48 hours of intense antithrombotic therapy (including aspirin, oral P2Y12 inhibitor, intravenous platelet inhibitor and/or intravenous antithrombotic therapy). Subsequent angiography frequently shows reduced thrombus burden, allowing balloon angioplasty and stenting with lower risk of distal embolization and no reflow .



Thrombectomy, filter, or laser


In lesions with large thrombus, if a decision is made to proceed with PCI due to ongoing symptoms or high-risk plaque features, consideration should be given to thrombectomy before further balloon angioplasty and stenting. Although thrombectomy in this setting is logical in selected cases, routine use is not supported by randomized controlled trial data.


Use of a filter ( Section 30.8, Section 18.8.1 may capture thrombus and prevent distal embolization during treatment of lesions with large thrombus burden.


Laser ( Section 30.11 ) may “burn” through the thrombus and also inhibits platelet aggregation . The 0.9 mm laser catheter (Philips) is most commonly used in native coronary arteries with the larger size catheters reserved for treating saphenous vein grafts or very large native coronary arteries. However, a 5-minute warm up period is required for the laser to become ready for use.



Thrombectomy


There are multiple ways to perform thrombectomy:



  • 1.

    Aspiration thrombectomy using a dedicated catheter ( Section 30.12.1 ). Larger (such as 7 French) aspiration thrombectomy catheters are more effective than smaller ones (such as 6 French). Delivery of the aspiration catheter can be difficult. Some aspiration thrombectomy catheters have stylets that can facilitate delivery. Alternatively, insertion of a 0.035 in. guidewire into the aspiration lumen can make it stiffer and more deliverable (“armored aspiration catheter” technique) .


  • 2.

    Aspiration using the Penumbra system ( Section 30.12.2 ), which is similar to aspiration thrombectomy but has a pump creating stronger and continuous suction.


  • 3.

    Through a deep-seated guide catheter [that can sometimes be accomplished using the “balloon-assisted deep intubation” (“BADI”) technique] and aspirating through the manifold .


  • 4.

    Through a distally inserted guide catheter extension. However, deep guide seating and use of guide catheter extensions, carries risk of complications, such as distal dissection, ischemia leading to hemodynamic compromise, and stent deformation during delivery attempts.



To minimize the risk of embolization (both distally and in the aorta) suction should be maintained until the thrombectomy catheter is removed from the guide catheter, followed by aspiration of the guide catheter. This minimizes the risk of thrombi remaining within the guide catheter and re-injected into the coronary artery or into the aorta. Occasionally there is limited blood return from the aspiration catheter, which may be due to a large thrombus obstructing the tip of the catheter. Sometimes distal embolic protection devices (filters) ( Section 30.8, Section 18.8.1 ) may be used to capture any liberated thrombi.


Multiple runs of aspiration thrombectomy or laser may be needed in cases with large thrombus burden. The over-the-wire lumen of the aspiration catheter could then be used to administer vasodilators or antiplatelet agents directly within the thrombotic coronary artery.


In cases of large thrombus adherent to the coronary wall, thrombus aspiration may fail, resulting in downstream thrombus embolization after balloon inflation or stent deployment. The embolized thrombus is often easier to aspirate.



How to do aspiration (or Penumbra) thrombectomy



Step 1. Select aspiration thrombectomy catheter


Goals:



  • 1.

    Select the catheter that is likely to provide the best thrombectomy result ( Section 30.12 ).


    How ?



    • 1.

      Consider guide catheter size (7 French thrombectomy catheters provide more effective aspiration but cannot be used through 6 French guide catheters).


    • 2.

      Consider coronary artery size, tortuosity, and calcification (larger thrombectomy catheters may be challenging to deliver through tortuous and calcified coronary segments—thrombectomy catheters with a stylet are more deliverable).



    Challenges



    • 1.

      Local availability (you cannot use thrombectomy catheters you don’t have on the shelf!).




What can go wrong ?



  • 1.

    Selection of a catheter that cannot be delivered due to size mismatch (7 French thrombectomy catheter cannot fit into a 6 French guide; a 6 French aspiration thrombectomy catheter cannot be inserted into the guide if there is a buddy wire) or due to poor deliverability to the thrombotic coronary segment.




Step 2. Prepare the aspiration thrombectomy catheter


Goals :



  • 1.

    Promptly and meticulously prepare the aspiration thrombectomy catheter for use.


    How ?



    • 1.

      The aspiration or Penumbra thrombectomy catheter is flushed.


    • 2.

      For aspiration thrombectomy: the vacuum syringe is attached to the back end of the aspiration catheter, the three-way stopcock is closed, the syringe plunger is pulled back and locked.


    • 3.

      For Penumbra: the catheter is flushed and closed off to the patient.




What can go wrong ?



  • 1.

    Incorrect connection of the aspiration syringe (connecting to aspiration catheter without the connecting segment with the on/off switch).


    Causes:




    • Misunderstanding of thrombectomy catheter design.



    • Being in a hurry to complete the procedure.



    Prevention:




    • Attention to catheter assembly.



    Treatment:




    • Disconnect thrombectomy catheter and reconnect with aspiration syringe in the proper fashion.





Step 3. Load the thrombectomy catheter on the guidewire


Goals :



  • 1.

    Load the thrombectomy catheter on the guidewire before delivering to the target thrombotic lesion.


    How ?



    • 1.

      The thrombectomy catheter monorail lumen is inserted over the coronary guidewire.




What can go wrong ?



  • 1.

    Insertion of the guidewire through the aspiration lumen of the thrombectomy catheter. This will be promptly identified if short (180 cm long) guidewires are being used.


    Causes:




    • Misunderstanding of the thrombectomy catheter design.



    • Urgency and time pressure to recanalize vessel.



    Prevention:




    • Closely observe that the guidewire is inserted through the monorail segment of the thrombectomy catheter.



    Treatment:




    • Remove thrombectomy catheter and reinsert the wire in the monorail segment.





Step 4. Deliver the thrombectomy catheter to the thrombotic lesion


Goals :



  • 1.

    Deliver the thrombectomy catheter to the target thrombotic lesion(s).


    How ?



    • 1.

      Advance the thrombectomy catheter over the guidewire to the target thrombotic lesion.




Challenges



  • 1.

    Failure to advance the thrombectomy catheter.


    Causes:




    • Tortuosity.



    • Calcification.



    • Prior stents.



    • Poor guide catheter support.



    Prevention:




    • Balloon angioplasty of vessel proximal to the thrombus.



    • Obtain strong guide catheter support (as outlined in Sections 9.8.1.1-9.8.1.6).



    Treatment:




    • Modify the proximal vessel, for example, with balloon predilation.



    • Improve guide catheter support, for example, by deep intubation, using a guide extension (however, the thrombectomy catheter may not fit within the extension), or side branch anchor.




What can go wrong?



  • 1.

    Loss of guide catheter and wire position.


    Causes:




    • Tortuosity.



    • Calcification.



    • Prior stents.



    • Poor guide catheter support.



    Prevention:




    • Avoid excessive force while attempting to advance the thrombectomy catheter.



    • Obtain strong guide catheter support (Sections 9.8.1.1-9.8.1.6).



    • Continually monitor the position of the guide catheter and the guidewire.



    Treatment:




    • Modify the proximal vessel, for example, with balloon predilation.



    • Improve guide catheter support. This may be a good time for exchanging guide catheter for a more supportive one.





Step 5. Aspirate thrombus


Goals :




  • Remove ideally all thrombus from the target thrombotic lesion(s).


    How ?



  • The connecting switch is opened transmitting the vacuum to the aspiration lumen of the thrombectomy catheter.



  • The catheter is advanced and withdrawn slowly within the area of thrombus.



Challenges



  • 1.

    Unable to aspirate blood or thrombus.


    Causes:




    • Large thrombus size.



    • Poor preparation of the thrombectomy catheter.



    • Positioning in a small vessel or distal to the thrombus.



    Prevention:




    • Use the largest possible thrombectomy catheter.



    • Excellent preparation of the thrombectomy catheter.



    • Initiate suction prior to reaching the occlusion.



    Treatment:




    • Remove thrombectomy catheter while maintaining suction, (to prevent a thrombus from embolizing into the coronary artery, the aorta, or the guide catheter). Aspiration thrombectomy has been associated with increased risk of stroke , hence every effort should be made to minimize the risk of systemic embolization.




What can go wrong ?



  • 1.

    Distal embolization.


    Prevention:




    • Do not stop aspirating until the thrombectomy catheter is removed from the guide catheter.



    • Back bleed and aspirate the guide catheter after removing the thrombectomy catheter.



    Treatment:




    • Repeat thrombectomy of the embolized thrombus.



    • In case of embolization in small branches, administer intracoronary vasodilators, such as nicardipine and adenosine.





Step 6. Remove thrombectomy catheter


Goals :




  • Remove thrombectomy catheter and all aspirated thrombus, while avoiding embolization.


    How ?




    • Withdraw thrombectomy catheter while maintaining suction.




What can go wrong ?



  • 1.

    Thrombus embolization .


    Causes:




    • Large thrombus size.



    • Losing suction while removing catheter.



    Prevention:




    • Keep suction while withdrawing catheter.



    • Remove while enough volume remains in the aspiration syringe.



    Treatment:




    • Aspirate guide catheter.



    • Change aspiration syringe and resume suction.



    • Repeat thrombectomy of the embolized thrombus.





Step 7. Aspirate guide catheter


Goals :




  • Remove thrombus that may be dislodged inside the guide catheter.


    How ?




    • Aspirate guide catheter and discard the aspirated blood.




What can go wrong ?



  • 1.

    Thrombus embolization.


    Causes:




    • Incomplete clearance of the guide catheter.



    • Reinjection of the aspirated thrombus.



    Prevention:




    • Discard aspirated blood.



    Treatment:




    • Repeat thrombectomy of the embolized thrombus.





Step 8. Examine aspirated blood


Goals :




  • Determine if thrombus has been removed.


    How ?




    • Inject the aspirated blood through the provided capture basket or over a clean gauze and examine what is retrieved.





Step 9. Perform repeat angiography


Goals :




  • Determine if thrombus has been removed and antegrade coronary flow has been restored.




Stenting


Stenting is usually delayed until after thrombectomy in cases with large thrombus burden, but in some cases in which thrombectomy fails, stenting over the thrombus may effectively “trap” the thrombus behind the stent struts and restore antegrade flow. However, stenting can still cause distal embolization, in part due to a “cheese grater” effect of the stent struts. Moreover, thrombus can lead to stent undersizing and malapposition.



No stenting for ACS culprit lesions?


In some cases an excellent angiographic result may be obtained after thrombus aspiration alone; in such cases observation without stent implantation has been advocated, especially when the culprit vessel is small. Escaned et al reported outcomes on 28 STEMI patients in whom thrombus aspiration resulted in: (1) restoration of TIMI flow grade 3; (2) residual TIMI thrombus grade ≤3; (3) absence of a residual significant stenosis; and (4) absence of significant distal thrombus embolization. Despite not performing stenting, the culprit vessel was patent when repeat angiography was performed after 6±2 days .



Closure


Radial access is advantageous for treatment of ACS patients, especially STEMI patients, because potent anticoagulation and antiplatelet regimens are often used, increasing the risk of bleeding.


When femoral access is used, the femoral sheath can sometimes be left in place for a few hours after the procedure in patients with borderline hemodynamics that may subsequently need a hemodynamic support device, however, this carries increased risk of bleeding.



Physiology



Culprit lesions


Coronary physiology should not be performed in the suspected culprit lesion(s) for the acute coronary syndrome, due to possible microcirculation injury from the ACS.



Nonculprit lesions


Nonculprit lesions in ACS patients can undergo physiologic assessment, as measurements do not significantly change over time .



Imaging


Imaging can be of critical importance during PCI for ACS.



Before stenting


Intravascular imaging with OCT remains the gold standard for identifying the ACS culprit lesion, and is of particular importance in patients with unclear culprit lesion(s). Ulceration and thrombus are the hallmarks of the culprit lesion, although some lesions only have erosion.



After stenting


Intravascular imaging can help optimize the stenting result (stent expansion and apposition and potential geographic miss) and detect residual thrombus or dissection.



Hemodynamic support


The likelihood of requiring hemodynamic support ( Chapter 14: Hemodynamic Support ) is higher in ACS as compared with stable angina patients, given myocardial injury and possible hemodynamic compromise.



References

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Feb 4, 2021 | Posted by in CARDIOLOGY | Comments Off on Acute coronary syndromes—thrombus
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