General description of procedure, equipment, technique
Percutaneous coronary intervention (PCI) is a widely-applied invasive procedure meant to treat obstructive lesions in epicardial coronary arteries and their major branches. After the insertion of a vascular sheath in a peripheral artery (radial, brachial, or femoral), specially shaped catheters are advanced to the ostia of coronary arteries and coronary angiography is performed using radio opaque contrast material. After the obstructive lesions have been identified and characterized, adequate anticoagulation is provided and PCI starts.
First, a steerable wire is guided through and distal to the obstruction and over it balloons, aspiration catheters, atherectomy devices, and stents are deployed for treatment. Currently, more than 90% of PCIs involve the implantation of a coronary stent—a metallic scaffold intended to push the intraluminal material (atherosclerotic plaque, thrombus, calcium) to the vessel wall, while promoting vascular healing and restoration of endothelial function. Most of the stents currently used are covered with antirestenotic compounds (drug-eluting stents), such as paclitaxel, sirolimus or its modified related compounds, which prevent to a great extent the natural smooth muscle cell migration and proliferation inherent to vascular injury and healing. Even more novel stents either have bioresorbable polymers that dissolve after drug elution or are made of entirely of bioresorbable polylactic acid scaffolds (without a metallic frame), which disappear in 1-3 years after implantation.
Indications and patient selection
PCI is performed in more than one million patients yearly in the United States alone and in approximately two million people world-wide. Nearly two thirds of these patients present with an acute coronary syndrome (ACS), encompassing clinical presentations as diverse as unstable angina, non-ST-elevation myocardial infarction (NSTEMI) and ST-elevation myocardial infarction (STEMI). The other third are elective patients with stable coronary artery disease (CAD), abnormal stress tests, or symptoms that are unacceptable despite intensive medical therapy.
STEMI patients are a particularly important segment of the overall PCI population. Although it comprises only 350,000 to 400,000 patients yearly in the United States, it is in this group that the maximal benefit of PCI is attained, in terms of reduction in mortality, morbidity, and hospital length of stay.
STEMI patients are those in whom a sudden disruption of the atherosclerotic plaque leads to intense coagulation and formation of a platelet-rich thrombus that evolves into an occlusive fibrin-rich thrombus built around the initial platelet plug. For these patients, immediate reperfusion therapy is crucial in limiting infarct size, promoting favorable remodeling of the involved territory and adjacent segments, and preventing deterioration of hemodynamic status.
Reperfusion can be provided either by administering fibrinolytic agents or by performing emergency (primary—because it is the primary method of reperfusion) PCI. More than 25 clinical studies and numerous meta-analyses have demonstrated that, as compared with fibrinolysis, PCI prevents two deaths, six nonfatal myocardial infarctions, 15 episodes of recurrent ischemia, and one stroke (predominantly hemorrhagic stroke) for every 100 patients treated with it. In each of these categories there is a 20 to 75%, highly statistically significant, relative risk reduction and an accompanying reduction in hospital stay of approximately 1 day. Such profound clinical benefit is attributed to the unique features of primary PCI, namely its ability to restore normal antegrade flow (Thrombolysis in Myocardial Infarction [TIMI] 3 flow) in the infarct-related artery in approximately 90% of patients. This compares very favorably with the 40 to 60% success rate seen with fibrinolysis.
But beyond epicardial flow, primary PCI is extremely beneficial in restoring myocardial perfusion or normal blood flow to the infarcting myocardial cells. It is this particular outcome which is highly predictive of reduced infarct size, lack of cardiogenic shock or heart failure, and lower mortality. In contrast, only 25% of patients treated with fibrinolysis achieve successful reperfusion at the myocardial level. The salvage index (myocardium recovering function as proportion of myocardium at risk at beginning of STEMI) associated with fibrinolysis is only approximately 0.25, while it is 0.50 to 0.60 with primary PCI. We can assess this reperfusion success by qualitative and quantitative assessments of myocardial blush grade (MBG), resolution of ST-segment elevation, and restoration of regional wall motion function.
While primary PCI is extremely valuable in most patients with STEMI, certain special scenarios may exist and dictate an alternative strategy.
Some patients are not good candidates for reperfusion therapy in general. Old, debilitated patients with advanced dementia, few symptoms, and hemodynamically insignificant myocardial infarction (MI) may be best treated with appropriate medical therapy. Similarly, those with MI that occurred more than 24 to 36 hours prior to arrival, and who are in extremis from a hemodynamic point of view may be beyond salvage, particularly if they are very old and debilitated. Interventional procedures in these cases may only hasten the inevitable.
Patients with witnessed cardiac arrest and resuscitation in the field should be taken immediately for primary PCI, if STEMI is present, irrespective of neurological status. Consideration should be given, though, to utilization of cooling protocols to improve chances for neurological recovery.
Occasionally, the interventional team cannot be assembled in a timely fashion because of ongoing high-risk cases or circumstances beyond control (extreme weather, traffic, etc.) Then, patients should be quickly evaluated for fibrinolysis and treated with it, if suitable candidates. Definitive mechanical therapy can be provided at a later time, without compromising the potential benefit of timely reperfusion.
Details of how the procedure is performed
Performing primary PCI requires additional skills from the interventional cardiologist beyond those needed during elective PCI. Because time to reperfusion is critical in securing its effectiveness and because performance measures and clinical guidelines recommend timely and rapid intervention, hospitals performing primary PCI need to meet special personnel and equipment requirements.
There needs to exist capability for 24-hour, 7-day a week availability of highly trained interventional cardiologists, nurses, and technicians who can perform primary PCI (first device deployed in the infarct related artery [IRA]) within 90 minutes of first medical contact, according to most recent STEMI and PCI guidelines. Whether the patient arrives via ambulance (preferred) or on his/her own, immediate triage and an electrocardiography (ECG) scan need to be performed within 10 minutes. It is expected that the Emergency Department physician will correctly identify STEMI and alert the STEMI team without the need for a cardiology consultation. This step is crucial in ensuring timely intervention, particularly during off-hours. Rapid cardiac enzymes and basic laboratory tests are obtained (preference is given to point-of-care testing) and a brief history and examination ensures that there are no significant contraindications to primary PCI.
Once the catheterization laboratory (CL) team has been alerted, it is expected that the patient will arrive in the CL within at most 45 minutes from hospital arrival. The CL team needs to work as a team with well-defined tasks assigned to each member—such as hemodynamic monitoring, preparation of access area and sterile covering, as well as opening and preparing the procedure kit. Once the vascular access route is selected, expert and rapid puncture and sheath insertion are important to minimize bleeding risk. Preparations for use of left ventricular assist devices should be made in most patients—such as cleansing of two access sites, adequate monitoring capabilities, etc.
Recently, radial access has gained popularity in STEMI because of the reduced risk of major access site bleeding, and the potential to thus reduce mortality. It is estimated that up to 25% of STEMI primary PCI cases are done via this route, particularly in Europe. Randomized clinical trials have confirmed lower bleeding rates, but no consistent difference in mortality.
Some interventional cardiologists would start the procedure with a left ventricle angiogram to detect unsuspected mechanical complications requiring immediate open-heart surgery and hemodynamic support, and to assess the extent of myocardial damage. This is particularly critical in patients with tenuous hemodynamic status and in those in whom the clinical status is more severe than expected from the suspected MI size.
If hemodynamics are compromised or frank cardiogenic shock is present, one should start with insertion of a left ventricular assist device and even consider endotracheal intubation. The procedure continues with imaging of the non-IRA to establish the overall severity of CAD, identify collaterals which supply perfusion to the infarcting territory, and assess the hemodynamic risk of failure to recanalize the IRA. If ECG suggests anterior MI, a Judkins Right 4.0 (JR4) diagnostic catheter should be appropriate for this purpose in order to cannulate the tight coronary artery (RCA).
If inferior MI is suspected, the operator needs to evaluate the ECG scan for the likelihood that the IRA is the RCA (more ST elevation in leads II or aVF than ST depression in V2–V3) or the left circumflex coronary artery, in order to choose the appropriate starting catheter. Remember that in the overwhelming majority of patients the RCA is dominant and supplies the inferior wall. After the operator is satisfied with imaging of the non-IRA, a guide catheter should be selected to engage the IRA. I prefer a 6F XB 3.5 catheter for the left coronary and a JR4 catheter for the RCA. Changes are made if the size of the aorta appears unusually small or large when the first diagnostic catheter is passed.
I choose these catheters because they have a high rate of success in engaging the IRA in a short time. As few images as are sufficient to allow for PCI planning are taken of the IRA. Further detailed imaging of non-IRA lesions can be done after reperfusion. Most often (70–80% of the cases) the IRA is completely occluded and there is TIMI 0 or 1 flow.
As delineation of the coronary anatomy is performed, the operator needs to ensure that adequate anticoagulation and antiplatelet therapy are ongoing. Because approximately 90% of patients with STEMI undergo PCI, I prefer that suspected STEMI patients be treated with dual antiplatelet therapy (DAPT) and a heparin (unfractionated heparin [UFH], or enoxaparin) bolus in the Emergency Department, according to prewritten protocols. Currently, aspirin (four chewable 81mg tablets), ticagrelor 180mg loading dose and 60U/kg of UFH—maximum 4,000 units comprise our regimen. After the decision to proceed with PCI is made (lesion present as suspected and no pressing indications for surgery present), one can initiate adjunctive glycoprotein IIb/IIIa inhibition with abciximab or eptifibatide or high-dose tirofiban, or switch the antithrombin regimen to bivalirudin. Rapid assessment of bleeding risk (age, gender, baseline hemoglobin, and kidney function) may assist in this decision. Intralesion abciximab delivered via specialized “weeping” balloons may reduce infarct size.
PCI of IRA starts with rapid wiring of the vessel, using one’s favorite work-horse wire. Change it quickly to a different wire if progress is not evident after a few attempts! It is important to try and cross the lesion once to avoid the creation or enlargement of existing dissection planes around the plaque rupture.
Occasionally, a large thrombus burden will impede wire passage. This process rarely takes more than 3 to 5 minutes. Wiring frequently results in restoration of some flow in the IRA. This enables the operator to assess vessel size and lesion length. If an aspiration catheter, such as EXPORT™ (Medtronic) or a similar one is used, it is prepared by flushing first with saline the aspiration port and applying vacuum to it before insertion.
Aspiration should start before the lesion is reached to create a “head start.” It is the first device insertion—aspiration catheter, balloon or stent—which determines door-to-balloon time, which should be more properly named door-to-device time. I usually strain the aspirate in a provided filter to see the thrombus.
In more than 50% of cases, aspiration results in restoration of TIMI 3 flow in the IRA and the patient typically experiences resolution or marked improvement in chest pain and ST elevation. If hemodynamics allow, intracoronary nitroglycerin and adenosine can further improve flow and allow accurate assessment of lesion length and vessel diameter for stent placement. Initial data from the TAPAS study indicated a reduction in mortality with manual thrombus aspiration compared to conventional PCI. Two larger trials—TASTE and TOTAL—performed in nearly 20,000 patients refuted this finding and suggested even that there may be a higher incidence of early stroke in patients treated with aspiration. Because of these recent data, the enthusiasm for routine thrombus aspiration has declined.
The choice of stent type—drug-eluting or bare-metal—is based on our assessment of patient’s ability and willingness to take DAPT for at least a year, plans for noncardiac surgery in the immediate future, compliance with medical therapy in general, and comorbidities, such as diabetes mellitus, chronic kidney disease, or need for chronic anticoagulation. Recent data suggest a benefit to certain second-generation drug eluting stents versus bare metal stents in primary PCI. Stent implantation leads nearly always to an excellent angiographic result. Residual thrombus may be seen in areas of the lesion but as long as flow is brisk and the stent is well apposed, further therapy is not needed.
Interpretation of results
At the end of the IRA PCI, the operator should assess formally, beyond symptom status (complete, incomplete, or no change in pain), the IRA epicardial flow (TIMI grade), and myocardial blush and ST-elevation resolution as markers of myocardial reperfusion. If the angiographic and ECG findings are not satisfactory, additional vasoactive therapy may be considered.
Outcomes (applies only to therapeutic procedures)
Primary PCI is successful in more than 90% of patients. As shown in Figure 1, Figure 2, and Figure 3, the benefit of primary PCI exceeds that of other reperfusion strategies, particularly when patients present beyond 2 hours from symptom onset.
Complications and their management
One should pay special attention to the distal IRA and its branches to identify possible distal embolization that may have occurred after aspiration thrombectomy or stent deployment. If such a complication is detected, wiring of the vessel (if a branch of the IRA) may dislodge the small thrombus and restore flow. Additional useful maneuvers include passage of a balloon without inflation or repeat aspiration thrombectomy, if the vessel size permits it. If these mechanical interventions and aggressive pharmacology are not sufficient, PCI of the area with or without stenting may be necessary, particularly if the subtended area is sufficiently large.
Beyond distal embolization, other important intraprocedural complications should be assessed. Slow flow in the IRA is not uncommon, particularly in an IRA with large thrombus burden. Repeated passes with the aspiration catheter and even mechanical thrombectomy in the case of a large RCA may be necessary.
Aggressive pharmacological intervention may be needed with intracoronary vasoactive substances, such as nitroglycerin, adenosine, verapamil, or nitroprusside. Nicardipine is widely used in Japan for this purpose and some reports indicate that epinephrine, paradoxically, is helpful by stimulating beta-2 adrenoreceptors. Remember to administer these substances into the distal vessel by inserting the aspiration catheter or an over-the-wire balloon and inject through them. Proximal administration in a vessel without brisk flow will not solve the problem and will only lead to proximal dissemination of the injectate and hemodynamic compromise.
Lately, attention is paid to a “new” complication, intraprocedural stent thrombosis (IPST). This is the appearance of new or worse thrombus after its initial resolution or improvement. IPST is not captured in the classical definitions of stent thrombosis, which only assess complications after the procedure is completed. Yet, IPST is associated with a marked increase in subsequent death and stent thrombosis, even when TIMI 3 flow is achieved at the end of the procedure. The most important implication from these observations is that more prolonged or intense antithrombotic therapy may be needed in these patients. A rapid intravenous P2Y12 receptor inhibitor—cangrelor—has recently been approved by the FDA and EMA to specifically decrease IPST and prevent peri-procedural myocardial infarction in patients not previously treated with an oral P2Y12 inhibitor, as is frequently the case with STEMI patients.
What’s the evidence?
Bhatt, DL, Stone, GW, Mahaffey, KW. ” Effect of platelet inhibition with cangrelor during PCI on ischemic events”. N Engl J Med. vol. 368. 2013. pp. 1303-13. (CHAMPION PHOENIX evaluated cangrelor during PCI, including patients with STEMI.)
Brener, SJ, Barr, LA, Burchenal, JE. ” Randomized, placebo-controlled trial of platelet glycoprotein IIb/IIIa blockade with primary angioplasty for acute myocardial infarction. ReoPro and Primary PTCA Organization and Randomized Trial (RAPPORT) investigators”. Circulation. vol. 98. 1998. pp. 734-41. (First randomized trial of abciximab as adjunct to primary PCI.)
De Luca, G, Suryapranata, H, Stone, GW. ” Abciximab as adjunctive therapy to reperfusion in acute ST-segment elevation myocardial infarction: a meta-analysis of randomized trials”. JAMA. vol. 293. 2005. pp. 1759-65. (Contribution of adjunctive abciximab to improved outcomes in patients receiving primary PCI or fibrinolysis.)
Jolly, SS, Cairns, JA, Yusuf, S. ” Randomized trial of primary PCI with or without routine manual thrombectomy”. N Engl J Med. vol. 372. 2015. pp. 1389-98. (TOTAL evaluated routine manual aspiration thrombectomy in STEMI.)
Keeley, EC, Boura, JA, Grines, CL. “Primary angioplasty versus intravenous thrombolytic therapy for acute myocardial infarction: a quantitative review of 23 randomised trials”. Lancet. vol. 361. 2003. pp. 13-20. (Meta-analysis of trials comparing primary PCI with fibrinolysis.)
Kumbhani, DJ, Bavry, AA, Desai, MY. ” Aspiration thrombectomy in patients undergoing primary angioplasty: totality of data to 2013″. Catheter Cardiovasc Interv. vol. 84. 2014. pp. 973-7. (Meta-analysis of trials comparing manual aspiration thrombectomy with routine care in STEMI.)
Lagerqvist, B, Frobert, O, Olivecrona, GK. ” Outcomes 1 year after thrombus aspiration for myocardial infarction”. N Engl J Med. vol. 371. 2014. pp. 1111-20. (TASTE evaluated routine manual aspiration thrombectomy in STEMI.)
Levine, GN, Bates, ER, Blankenship, JC. ” 2011 ACCF/AHA/SCAI guideline for percutaneous coronary intervention: a report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines and the Society for Cardiovascular Angiography and Interventions”. Circulation. vol. 124. 2011. pp. e574-651. (Updated guidelines for PCI, including in the setting of STEMI.)
O’Gara, PT, Kushner, FG, Ascheim, DD. ” 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines”. J Am Coll Cardiol. vol. 61. 2013. pp. 485-510. (Updated guidelines for management of STEMI.)
Schömig, A, Kastrati, A, Dirschinger, J. ” Coronary stenting plus platelet glycoprotein IIb/IIIa blockade compared with tissue plasminogen activator in acute myocardial infarction. Stent versus Thrombolysis for Occluded Coronary Arteries in Patients with Acute Myocardial Infarction Study Investigators”. N Engl J Med. vol. 343. 2000. pp. 385-91. (The Stent versus Thrombolysis for Occluded Coronary Arteries in Patients with Acute Myocardial Infarction study compared myocardial salvage in patients treated with primary PCI or with fibrinolysis.)
Schömig, A, Ndrepepa, G, Mehilli, J. ” Therapy-dependent influence of time-to-treatment interval on myocardial salvage in patients with acute myocardial infarction treated with coronary artery stenting or thrombolysis”. Circulation. vol. 108. 2003. pp. 1084-8. (Influence of door-to-balloon and door-to-needle time on outcome—comparison of primary PCI with fibrinolysis.)
Stone, GW, Witzenbichler, B, Godlewski, J. ” Intralesional abciximab and thrombus aspiration in patients with large anterior myocardial infarction: one-year results from the INFUSE-AMI Trial”. Circ Cardiovasc Interv. vol. 6. 2013. pp. 527-34. (INFUSE AMI evaluated the role of intralesion abciximab in reducing infarct size in large anterior STEMI.)
Stone, GW, Witzenbichler, B, Guagliumi, G. ” Bivalirudin during primary PCI in acute myocardial infarction”. N Engl J Med. vol. 358. 2008. pp. 2218-30. (Bivalirudin compared with heparin and GPI in STEMI.)
Wallentin, L, Becker, RC, Budaj, A. ” Ticagrelor versus clopidogrel in patients with acute coronary syndromes”. N Engl J Med. vol. 361. 2009. pp. 1045-57. (Novel antiplatelet therapy with ticagrelor for STEMI.)
Wiviott, SD, Braunwald, E, McCabe, CH. ” Prasugrel versus clopidogrel in patients with acute coronary syndromes”. N Engl J Med. vol. 357. 2007. pp. 2001-15. (Novel antiplatelet therapy with prasugrel for STEMI.)
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