In the treatment of STEMI, the widespread use of PCI treatment strategies can reduce mortality, but the choice of treatment should take into account the patient’s condition, the skill level of the medical staff and the equipment of the hospital where the patient is seen. Adequate transport networks should be established in a particular region to improve the “green channel”. PCI is often performed with a combination of drugs and devices or mechanical assisted circulatory devices in order to obtain proper myocardial microcirculatory perfusion.
In August 2010, the Guidelines for the Diagnosis and Treatment of Acute ST-segment Elevation Myocardial Infarction (STEMI) (“the Guidelines”) were published by the Cardiovascular Disease Society of the Chinese Medical Association. The guidelines define, diagnose, and classify myocardial infarction, including early medical and emergency procedures; clinical and laboratory evaluation, risk stratification; initial management and reperfusion therapy after admission; antithrombotic and antimyocardial ischemic therapy; coronary artery bypass grafting (CABG); stem cell therapy;
Special types of STEMI; complications and management; pre-discharge risk assessment; and secondary prevention and rehabilitation are described in detail. The guidelines emphasize that the principles of STEMI diagnosis and treatment must implement the concept of “time is myocardium, time is life”, and that early, continuous and effective opening of infarct-related arteries should be carried out to restore effective myocardial perfusion.
Emphasize the diagnostic significance of biological markers
In the diagnosis of STEMI, the guidelines emphasize the value of troponin, while creatine kinase isoenzyme (CK-MB) remains a specific diagnostic index, while CK alone and aspartate aminotransferase, lactate dehydrogenase and their isoenzymes are poorly specific for the diagnosis of STEMI and are no longer recommended for diagnosis. It is important to note that clinicians should not delay STEMI treatment by waiting for the results of serum biological marker measurements and imaging studies.
Highlighting early medical treatment with shorter time delays
The pathogenesis of STEMI is primarily a complete coronary thrombotic obstruction, and early opening of the infarct-related artery is the key to treatment. The benefit of early pharmacological or mechanical reperfusion therapy is clear in patients within 12 h of onset, with persistent ST-segment elevation or new left bundle branch block. Moreover, the time delay between onset and admission and reperfusion therapy should be minimized.
For hospitals not equipped for emergency PCI, patients with high-risk STEMI suitable for transport, patients at high risk of bleeding with thrombolysis, patients seen 4 h after symptom onset, and patients at low risk but with persistent symptoms after thrombolysis and suspected thrombolytic failure should be transported to a hospital where emergency PCI is feasible as soon as possible after intravenous thrombolysis. Antiplatelet and anticoagulation therapy may be considered prior to transfer to the catheterization laboratory.
Establish close collaboration between the emergency department and cardiovascular specialists with a 24-hour and 7-day-a-week on-call emergency PCI team, aiming to complete the first ECG within 10 min and balloon dilation within 90 min of arrival at the hospital for STEMI patients. By working closely with the receiving hospital, a “green channel” is formed between pre-hospital (ambulance) and in-hospital; a 12-lead ECG is transmitted to the hospital by telephone or by remote wireless transmission system to start STEMI treatment in advance.
Reperfusion therapy: comprehensive assessment and careful implementation are required
Thrombolytic therapy: little benefit from thrombolysis in those with bleeding tendencies
For patients with STEMI, regardless of the choice of thrombolytic agent and regardless of gender, diabetes, blood pressure, heart rate, or history of myocardial infarction, the magnitude of benefit depends primarily on the timing of treatment and the TIMI flow obtained. Thrombolytic therapy within 3 h of onset resulted in increased opening of the infarct-related vessels and significantly lower mortality, with clinical efficacy comparable to direct PCI.
Thrombolysis within 3 to 12 h of onset was less effective than direct PCI, but still beneficial. Within 12 to 24 h of onset, if there are still persistent or intermittent ischemic symptoms and persistent ST-segment elevation, thrombolytic therapy is still effective. Moreover, the survival benefit of thrombolysis can be maintained for up to 5 years. The benefit of thrombolysis is greatest in patients with left bundle branch conduction block and large infarcts.
Prehospital (ambulance) thrombolysis is defined as starting thrombolysis within 30 min of ambulance arrival. Currently, it is difficult to meet these requirements in most areas of China, and thrombolysis is mostly performed in the hospital.
Thrombolysis is preferred in the following cases.
①STEMI patients who are not eligible for 24-h emergency PCI, who are not eligible for rapid transport, and who have no contraindications to thrombolysis;
②Patients who are eligible for 24-h emergency PCI, but who are seen early (≤3 h after onset) and cannot be catheterized in time;
(iii) Patients eligible for 24-h emergency PCI, but the difference between the time from door to balloon dilation (D2B) and the time from consultation to the start of thrombolysis (D2N) was >60 min and the D2B time was >90 min;
④ In patients with reinfarction, if angiography and PCI cannot be performed immediately (within 60 min of symptom onset), thrombolytic therapy is given.
Contraindications to thrombolytic therapy must be noted, especially in those with bleeding tendencies, including severe liver and kidney disease, malignancy, and end-stage tumors. Because of the high incidence of hemorrhagic stroke in the Chinese population, PCI should be preferred in patients ≥75 years of age, and thrombolytic therapy should be chosen with caution and dose reduction should be considered as appropriate.
Direct PCI: first choice for patients with <12 h onset
Patients with STEMI should undergo direct PCI targeting the infarcted vessel within 12 h of symptom onset, with a D2B time of <90 min. stenting should be routinely performed during direct PCI. Patients <75 years of age with cardiogenic shock <36 h after onset should undergo PCI <18 h after shock onset if there is no contraindication to the procedure. Patients with severe cardiac insufficiency and/or pulmonary edema should undergo direct PCI at <12 h of onset.
The following are Class II recommendations for emergency PCI: Coronary angiography and PCI (or emergency CABG) is reasonable in patients ≥75 years of age who have received thrombolytic therapy for cardiogenic shock and are candidates for hemodynamic reconstruction. It is reasonable for patients to undergo PCI if one or more of the following conditions are present: hemodynamic or electrocardiographic instability; persistent ischemic symptoms; the patient has failed thrombolysis (ST-segment elevation in the most significant lead falls back <50% within 90 min of the start of thrombolysis) and has moderate or large areas of myocardium at risk (anterior wall infarction, inferior wall infarction involving the right ventricle, or ST-segment downshift in the anterior thoracic leads).
A strategy of coronary angiography and PCI for moderate-to-high-risk patients who do not have class I and IIa indications may be reasonable, but the benefits and risks are currently unknown. The earlier the onset of ischemic symptoms, the greater the benefit of PCI treatment.
Patients without hemodynamic disturbances should not undergo PCI of noninfarct-related vessels at the time of direct PCI; patients with asymptomatic, hemodynamically and electrically stable STEMI after 12 h of onset should not undergo direct PCI. Coronary angiography and PCI are not recommended for patients already receiving thrombolytic therapy who are contraindicated to PCI or who do not consent to further invasive therapy.
Translational PCI: also consider the translational physician
If a patient with high-risk STEMI is seen in a hospital where direct PCI is not available, the patient can be transported to a hospital where PCI is feasible or to an experienced interventionalist for local care while on thrombolytic or antithrombotic therapy.
Patients undergoing thrombolysis are recommended for coronary angiography and PCI (or emergency CABG) if they have any of the following: persistent symptoms or manifestations of myocardial ischemia 45-60 min after thrombolysis; patients <75 years of age with cardiogenic shock who are suitable for revascularization; severe chronic heart failure and/or pulmonary edema (Killip class III); hemodynamically unstable ventricular arrhythmias.
Antithrombotic therapy: clear benefit and individualization
Antiplatelet therapy: aspirin combined with clopidogrel is essential
Unless contraindicated, all patients with STEMI should receive early chewable aspirin 300 mg followed by a long-term dose of 75-150 mg. An initial loading dose of clopidogrel 300 mg (preferably 600 mg for direct PCI) should be given as soon as possible before or at the time of first or repeat PCI, or prasugrel 60 mg as soon as possible at the time of emergency PCI, with a maintenance dose of 10 mg/day. . If the patient has been thrombolized and is not already taking thienopyridines, a loading dose of clopidogrel 300-600 mg is given.
During hospitalization, all patients continued to receive clopidogrel 75 mg/day. In STEMI patients with a history of stroke and transient ischemia, the use of prasugrel as a dual antiplatelet agent prior to emergency PCI is not recommended. After discharge, clopidogrel 75 mg/day for more than 15 months may be considered in patients with DES placement. Patients preparing for elective CABG who are taking clopidogrel should discontinue the drug at least 5-7 days before the procedure.
Intravenous thrombolysis combined with GP IIb/IIIa receptor antagonists may improve efficacy but increase bleeding complications. In patients >75 years of age, thrombolysis in combination with GP IIb/IIIa receptor antagonists is not recommended because of the significantly increased risk of intracranial hemorrhage. Instead, it is best applied as early as possible before direct PCI (with or without stenting). Intracoronary injection of GP IIb/IIIa receptor antagonists during direct PCI is beneficial to increase myocardial perfusion, reduce infarct size and improve the near-term prognosis.
Anticoagulation: all STEMI patients should be used in the acute phase
Normal heparin has become the most commonly used adjunct to thrombolytic therapy for STEMI. Recombinant tissue-type fibrinogen activator (rt-PA) is a selective thrombolytic agent, so it must be combined with adequate anticoagulant therapy. Urokinase and streptokinase are non-selective thrombolytic agents that have a significant effect on the systemic coagulation system, and therefore do not require adequate anticoagulation during thrombolysis. Low-molecular-weight heparin has the advantages of easy application, no monitoring, and low bleeding complications, so it is recommended to replace regular heparin with low-molecular-weight heparin.
In patients undergoing thrombolysis or no direct PCI, fondaparinux sodium is beneficial in reducing death and reinfarction without increasing bleeding complications. Fondaparinux sodium alone is not recommended for direct PCI for STEMI because it needs to be combined with common heparin therapy to reduce the occurrence of intracatheter thrombosis. Bivalirudin may be considered for direct PCI.
After the acute phase of STEMI, oral warfarin is required for 3-6 months for those with active intra-cardiac thrombus suggested by echocardiography. Those who cannot tolerate aspirin and clopidogrel can take warfarin for a long time with INR maintained at 2~3.
Secondary prevention: pharmacologic and non-pharmacologic interventions are equally important
A thorough evaluation should be completed before the patient is discharged, especially to detect residual myocardial ischemia and to determine myocardial viability. Patients should also be educated about the importance of nonpharmacologic interventions, including smoking cessation, moderate exercise, and weight control. For pharmacologic interventions, aspirin, beta-blockers, angiotensin-converting enzyme inhibitors/angiotensin receptor antagonists, and statins should be maintained.
Patients with STEMI should be discharged from the hospital to control various risk factors and to achieve blood pressure, lipid and glucose standards. Rehabilitation therapy is beneficial in reducing the overall mortality and cardiac death rate and should be advocated.