Approach to Percutaneous Coronary Intervention in Myocardial Infarction

Femoral

Retrograde puncture of the femoral artery ( Figure 17-1 ) is required for femoral access during diagnostic coronary angiography and PCI. The common femoral artery is used because of its larger size and its ability to compress against the femoral head during manual compression. Patients should receive sedation and a local anesthetic before arterial cannulation. Because of the variability in body habitus, several landmarks should be noted before choosing an arteriotomy site. A line drawn between the anterior superior iliac spine and pubis demarcates the inguinal ligament. The inguinal crease should not be used to approximate the inguinal ligament, especially in obese patients. Fluoroscopy should be used to mark the femoral head. The common femoral should be entered at a 30- to 45-degree angle approximately 1 to 2 cm below the inguinal ligament, which is typically at the center of the femoral head. A “low stick” can result in cannulation of the superficial femoral artery, which increases the risk of hematoma, dissection, arterial occlusion, or formation of a pseudoaneurysm or arteriovenous fistula. Conversely, a “high stick” above the inguinal ligament or above the inferior epigastric artery on angiography does not allow for effective manual compression against the femoral head, and significantly increases the risk for retroperitoneal hemorrhage. Before administering therapeutic anticoagulation for PCI, limited angiography through the femoral sheath at an oblique ipsilateral angle should be performed to determine the arteriotomy site in relationship to the femoral head, inferior epigastric artery, and femoral bifurcation, which could modify the timing of PCI and/or choice to use a vascular access closure device.

Two commonly used techniques to reduce vascular complications during femoral access include use of a micropuncture needle (Cook Medical, Bloomington, Ind.) or guidance using ultrasound. Traditionally, an 18-gauge wide open-bore needle has been used for arterial cannulation. A smaller micropuncture 21-gauge needle can be used to access the common femoral artery. After placement of a 0.018-inch wire into the artery, limited angiography can be used to localize the site of cannulation through the needle or inner dilator, and if acceptable, the 4F micropuncture sheath can be advanced over the wire. If the arteriotomy site is too low or high, then femoral access at an alternative site can be reattempted, and the needle or inner dilator removed, with minimal risks of bleeding. Real-time ultrasound guidance has also been used for femoral access and allows for visualization of needle entrance into the femoral artery. It can also determine the femoral bifurcation to facilitate cannulation of the common femoral artery above the bifurcation.

Radial

The learning curve for radial access is typically longer compared with femoral access. It should not be used in patients with forearm arteriovenous fistulas. Assessment for collateral ulnar circulation via the ulno-palmar arterial arch is advocated. However, failure to demonstrate dual circulation to the hand (i.e., incomplete palmar arch) is not an absolute contraindication. Assessment is performed using either the modified Allen’s or plethysmo-oxymetric test, the latter of which has a higher specificity. Any abnormal Allen’s test should be confirmed by plethysmo-oxymetric testing. When attempting radial access, a smaller amount of lidocaine (1 to 2 mL) should be administered to minimize the risk of local vasospasm or obscuring the radial pulse. A micropuncture needle is used to access the radial artery and for placement of a hydrophilic radial arterial sheath over a 0.021- to 0.025-inch guidewire ( Video 17-1, Video 17-2, Video 17-3 ). Ultrasound can also be used to minimize the number of attempts needed for arterial cannulation. Vasospasm can be a significant limitation in radial access. Intra-arterial administration of an antispasmolytic drug (e.g., nitrogylcerin, diltiazem, verapamil) is mandatory. A number of single agents or “cocktail” regimens have been used to prevent vasospasm. Most operators use verapamil (2.5 to 5 mg) and/or nitroglycerin (100 to 200 μg). Anticoagulation should be initiated after radial artery cannulation to minimize the risk for radial artery occlusion. Low-dose unfractionated heparin (e.g., 2000 to 3000 IU or 50 IU/kg) can be administered and converted to therapeutic dosing upon placement of the guide catheters in the ascending aorta or with coronary cannulation. Access via the left radial may be advantageous over the right radial because of the higher prevalence of right-handed individuals; the aortic path approximates a transfemoral approach, which allows for easier coronary cannulation with standard Judkin’s guide catheters and easier access to the left internal mammary artery in coronary artery bypass graft (CABG) patients.

Considerations for Radial Approach in ST-Elevation Myocardial Infarction

Despite evidence that the radial approach reduces vascular complications, major bleeding, and mortality in STEMI patients, its use is paradoxically lower in this population than in patients with NSTEMI. One concern is that the increased time required for the radial approach may prolong the time-to-treatment goal in STEMI. However, a door-to-device delay of 83 minutes would be required to offset the mortality benefit of radial PCI over femoral PCI in STEMI. Because of the higher risk for cardiogenic shock, the groin of a patient with STEMI should always be prepped for immediate venous access or additional arterial access for hemodynamic support.

When to Preload with Oral Adenosine Diphosphate P2Y ₁₂ Inhibitors

When possible, pretreatment with a loading dose of an oral ADP P2Y ₁₂ inhibitor in patients with acute MI is recommended, with administration as early as possible after a diagnosis of STEMI. In a meta-analysis, clopidogrel pretreatment reduced mortality in STEMI and major coronary events in both STEMI and NSTE-ACS compared with no pretreatment. The PLATO (Study of Platelet Inhibition and Patient Outcomes Clopidogrel) trial led to the approval of ticagrelor for patients with ACS. All the patients in PLATO were pretreated with ticagrelor before PCI. Delayed administration of ticagrelor has not been formally tested against pretreatment in NSTEMI. Prasugrel is not currently recommended for use as upstream therapy in NSTEMI. In the TRITON-TIMI 38 (Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis in MI) trial, prasugrel was administered at the time of PCI after coronary angiography. However, current ACC/AHA guidelines do advocate for prasugrel pretreatment when possible in STEMI.

Practical Aspects of Monitoring Anticoagulation

ACTs are the standard method used to monitor the therapeutic effect of anticoagulation during PCI. In the balloon angioplasty era, higher levels of ACTs were associated with lower rates of periprocedural ischemic events, but also increased the risk of bleeding. However, this association has not been consistent in coronary stent trials. ACTs are routinely checked throughout the PCI procedure after administration of unfractionated heparin. A bolus of unfractionated heparin (70 to 100 U/kg) is administered, and the ACT is checked approximately 5 minutes later. Traditionally, a minimum therapeutic ACT level is more than 250 seconds without a glycoprotein IIb/IIIa inhibitor (GPI). If a GPI is also administered, an ACT level should be more than 200 seconds. The range of ACT levels may vary based on the complexity of the PCI, but typically should not exceed 350 seconds. If bivalirudin (0.75 mg/kg followed by a 1.75 mg/kg per hour IV infusion) is used, monitoring of ACT levels is not required. However, most operators will check one ACT level to determine that bivalirudin has been administered through a “working” peripheral IV line. In addition, low-molecular-weight heparin does not require any monitoring during PCI. Fondaparinux requires co-administration of heparin during PCI, for which an ACT can be checked to ensure therapeutic levels of anti-IIa activity.

Current Evidence: Bivalirudin versus Heparin in ST-Elevation Myocardial Infarction

Significant controversy has arisen about the safety and efficacy of bivalirudin in primary PCI during STEMI. The HORIZONS-AMI (Harmonizing Outcomes with Revascularization and Stents in Acute MI) trial showed that bivalirudin lowered mortality (all-cause and cardiac) in STEMI compared with heparin plus a GPI. Bivalirudin was associated with a significantly higher rate of acute (i.e., <24 hours of primary PCI) stent thrombosis in the HORIZONS-AMI trial. It was theorized that the risk of stent thrombosis surrounding PCI may be caused by discontinuation of bivalirudin after PCI, with clopidogrel (i.e., a less potent and slower onset ADP P2Y ₁₂ agent) as the predominant antiplatelet therapy.

In the EUROMAX (European Ambulance ACS Angiography) trial, bivalirudin lowered net adverse events and major bleeding compared with unfractionated or low-molecular-weight heparin plus provisional GPI at 30 days. This trial was designed to overcome the limitations of HORIZONS-AMI by using more potent oral ADP P2Y ₁₂ inhibitors (i.e., prasugrel and ticagrelor). In addition, a reduced dose of bivalirudin (0.25 mg/kg per hour) was continued for several hours after PCI. Despite these differences, a higher rate of acute stent thrombosis was still observed in EUROMAX with bivalirudin. A subsequent open-label trial in consecutive STEMI patients who underwent primary PCI (HEAT-PPCI [How Effective are Antithrombotic Therapies in Primary PCI]) demonstrated that heparin with the use of bailout GPIs reduced all-cause mortality, stroke, reinfarction, or unplanned revascularization and stent thrombosis without any differences in the rates of major bleeding compared with bivalirudin.

The BRIGHT (Bivalirudin in Acute Myocardial Infarction vs. Heparin and GPI Plus Heparin Trial) study was designed to overcome the limitations of HORIZONS-AMI by continuing bivalirudin at the standard dose (1.75 mg/kg per hour) for a median of 3 hours after PCI in acute MI patients, of whom 88% presented with STEMI. In BRIGHT, a significant reduction in bleeding was seen in patients treated with clopidogrel and bivalirudin compared with heparin, with and without a GPI. No differences were observed between the groups in the rates of major adverse cardiac or cerebral events, including acute stent thrombosis. It is postulated that a prolonged infusion of standard dose bivalirudin abrogated the risk of acute stent thrombosis seen in the HORIZONS-AMI and EUROMAX trials. A meta-analysis comparing bivalirudin and heparin confirmed the higher rate of acute stent thrombosis with bivalirudin compared with heparin. Prolonged infusion of bivalirudin may eliminate this risk, but this strategy should be confirmed in additional studies. Bleeding is lower with bivalirudin compared with heparin and GPI; yet, in the absence of routine GPIs and with radial access, the benefit appears to be less striking.