STEMI: fibrinolytic therapy
|
General information
Fibrinolytic therapy is indicated if there is prolonged ischaemic chest pain that has begun within the previous 12 hours, in the presence of significant ST segment elevation or left bundle branch block (that is presumed new). Whether or not fibrinolytic therapy should be given to patients who give a history of pain starting between 12 and 24 hours is a matter of clinical judgment. It should be considered if there is evidence of ongoing ischaemia (ongoing chest pain with ST segment elevation) or recurrence of pain with ST elevation, or if there is a stuttering onset of pain.
Contraindications to fibrinolytic therapy for patients with
STEMI (see
Box 3.8) can be absolute or relative. Patients with an absolute contraindication should be transferred for a percutaneous coronary intervention where possible. With relative contraindications, the risks and benefits of treatment must be weighed.
Use one of the following fibrinolytic drugs:
1 | alteplase (for patients greater than 65 kg) 15 mg bolus IV, followed by an IV infusion of 50 mg over 30 minutes and 35 mg over the next 60 minutes (for patients less than or equal to 65 kg) alteplase 15 mg bolus IV, followed by an IV infusion of 0.75 mg/kg over 30 minutes and 0.5 mg/kg over the next 60 minutes |
|
| OR |
|
1 | reteplase 10 units bolus IV, followed by another 10 units bolus IV 30 minutes later |
|
| OR |
|
1 | |
|
| OR |
|
2 | streptokinase 1.5 x 10 6 international units by IV infusion, over 30 to 60 minutes; if the systolic blood pressure is less than 80 mm Hg, the infusion rate should be halved; if the systolic blood pressure is less than 70 mm Hg, stop the infusion—and once the systolic blood pressure is greater than 70 mm Hg, restart the infusion at half the previous rate.
|
|
Plasminogen activators (alteplase, reteplase and tenecteplase) are superior to streptokinase, but considerably more expensive. The bolus drugs reteplase (double bolus) and tenecteplase (single bolus) have major advantages in terms of convenience and could be used in the pre-hospital setting.
Because of a high incidence of neutralising antibodies, which persist indefinitely, streptokinase should not be used in Aboriginal and Torres Strait Islander patients or those who have received streptokinase more than three days previously.
Hypotension can occur, particularly with streptokinase, and should be treated by giving fluid, raising the foot of the bed and slowing the infusion rate.
Significant arrhythmias including ventricular fibrillation are not uncommon at the time of reperfusion. After the administration of thrombolytic therapy, patients should be closely monitored by staff trained in advanced life support and defibrillation.
Allergic reactions are common with streptokinase; they include bronchospasm, periorbital swelling, angioedema, urticaria, itching, flushing, nausea, headache and musculoskeletal pain. Delayed hypersensitivity reactions such as vasculitis and interstitial nephritis have also been observed. Anaphylactic shock is rare.
For mild or moderate allergic reactions and fever, use:
For severe allergic reactions, immediately discontinue streptokinase and give:
| adrenaline 1 in 10 000 solution 1 mL IV, over 5 minutes. |
|
If no response, increase to:
| adrenaline 1 in 10 000 solution 2 to 5 mL IV, over 5 minutes |
|
| AND |
|
|
| |
|
|
| AND/OR |
|
|
|
|
|
In patients in whom there is a contraindication to fibrinolytic therapy (see
Box 3.8), or who are deemed to be high-risk, and where fibrinolytic therapy is felt unlikely to be effective (eg cardiogenic shock), primary coronary angioplasty is an effective therapy if resources are available or the patient can be promptly transferred to a centre where
PCI is available.
Contraindications to fibrinolytic therapy in ST elevation myocardial infarction (Box 3.8)
Absolute contraindications Risk of bleeding
active bleeding or bleeding diathesis (excluding menses) significant closed head or facial trauma within 3 months suspected aortic dissection (including new neurological symptoms) Risk of intracranial haemorrhage
any prior intracranial haemorrhage ischaemic stroke within 3 months known structural cerebral vascular lesion (eg arteriovenous malformation) known malignant intracranial neoplasm (primary or metastatic) Relative contraindications Risk of bleeding
current use of anticoagulants: the higher the international normalised ratio (INR), the higher the risk of bleeding non-compressible vascular punctures recent major surgery (within 3 weeks) traumatic or prolonged (longer than 10 minutes) cardiopulmonary resuscitation recent (within 4 weeks) internal bleeding (eg gastrointestinal or urinary tract haemorrhage) active peptic ulcer Risk of intracranial haemorrhage
history of chronic, severe, poorly controlled hypertension severe uncontrolled hypertension on presentation (>180 mm Hg systolic or >110 mm Hg diastolic) ischaemic stroke more than 3 months ago, dementia, or known intracranial abnormality not covered in absolute contraindications Other
pregnancy |
Acute Coronary Working Group. Management of patients with ST-segment-elevation myocardial infarction. Med J Aust 2006; 184: S13-S22. © 2006. The Medical Journal of Australia—reproduced with permission
|
Adjuvant antithrombin therapy for fibrinolysis
Heparin should be administered with alteplase, reteplase and tenecteplase. The use of heparin with streptokinase is optional. Use:
| unfractionated heparin initially 60 units/kg up to a maximum of 4000 units loading dose IV, followed by an infusion of 12 units/kg/hour (up to a maximum of 1000 units/hour) by IV infusion adjusted according to the APTT. |
|
Enoxaparin is not approved in Australia as an adjunct to fibrinolysis for STEMI. However, a recent clinical trial has demonstrated its efficacy in this situation. The trial protocol used a 30 mg intravenous bolus followed 15 minutes later by 1 mg/kg subcutaneously 12-hourly in patients younger than 75 years. In patients older than 75 years, the intravenous bolus was not given and the subcutaneous dose of enoxaparin was reduced to 0.75 mg/kg 12-hourly.
Fibrinolytic therapy and haemorrhage
Occasionally bleeding may occur following treatment with fibrinolytic therapy and heparin. Intracranial haemorrhages are devastating and life-threatening. Systemic bleeding and gastrointestinal bleeding can occur. If this bleeding does occur:
reverse heparin with protamine (even if a low molecular weight heparin has been used). Protamine dosage depends on the level of anticoagulation. Use 1 mg of protamine for every 100 units of unfractionated heparin
replace fibrinogen using cryoprecipitate (two bags) or fresh frozen plasma (as required)
give blood as necessary.