Acute coronary syndromes—thrombus

20.1

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.

20.2

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.

20.3

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) .

20.4

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.”

20.5

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 .

20.6

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.

20.7

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 .

20.8

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.

20.9

Lesion preparation

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