Why is it important that clopidogrel and aspirin are given as soon as an acute myocardial event has happened?
Summary Show Introduction This means that the most important measure to reduce deaths is to educate people about the symptoms and signs of acute myocardial infarction. Patients must get near a defibrillator as soon as possible. Once the patient is in a situation where sudden death can be prevented, the important issue is reducing the size of the myocardial infarct, and in this, drug therapy has a major role to play. Aetiology Aim of treatment
Restoration of flow The speed at which the flow is restored is important. For every hour of delay, the effect of therapy diminishes and mortality increases. Decreasing myocardial oxygen consumption Initial treatment Aspirin Fibrinolytic therapy Fibrinolytic therapy should be given to all patients with appropriate indications and no contraindications (Table 1). The indications for fibrinolytic therapy are symptoms of myocardial ischaemia, of less than 12 hours' duration, with ECG changes of ST elevation or left bundle branch block. Patients without these ECG changes should not be given fibrinolytic therapy.3
The concern with fibrinolytic therapy is bleeding. The most feared form of bleeding is intracerebral bleeding which is usually fatal. Therefore, patients with contraindications (Table 1) should be considered for acute PTCA. Uncontrolled hypertension is a relative contraindication and attempts should be made to lower the blood pressure below 175 mmHg systolic and 100 mmHg diastolic. A history of an ulcer or recent cardio-pulmonary resuscitation is not an absolute contraindication. Streptokinase An intravenous infusion of 1.5 million units is given over 30-60 minutes. Most patients will develop hypotension if streptokinase is given quickly, but this is usually easily overcome by slowing the infusion and giving fluid. Streptokinase is derived from Streptococci and will produce an antibody reaction. These antibodies appear after 2-3 days and persist for some years. The presence of antibodies reduces the efficacy of subsequent doses of streptokinase and increases the potential for anaphylaxis. The present consensus is that streptokinase should be used only once per patient.5 All patients should be informed about being treated with streptokinase and ideally given a card or other form of record so that this information is available should they have another infarction. Tissue plasminogen activator (tPA) Clot dissolution occurs more promptly with tPA than streptokinase restoring patency at 90 minutes in 55% of patients.4However, by 3 hours and 5-7 days there is no major difference in patency in patients treated with streptokinase or tPA. This improved early patency results in slightly improved mortality (6.3% tPA versus 7.1% streptokinase).6 Compared with streptokinase, tPA appears to cause more bleeding and, in particular, produces a higher incidence of cerebral bleeding. There are 2-3 extra strokes per 1000 patients treated and one of these patients dies from their stroke. Therefore, care should be taken with patients at risk of stroke, the elderly and those with high blood pressure. Despite the increased risk of stroke, the net clinical benefit is greater with tPA in nearly all subgroups of patients. For every 1000 patients treated with tPA, there will be 10 extra survivors at the cost of one patient surviving with disability from a stroke. tPA is not used in all patients because of its cost - approximately $1900 compared with $150 for streptokinase. The current consensus in Australia is that tPA should be utilised in
The treatment regimen is shown in Table 2.
Heparin Heparin and streptokinase Intravenous heparin is given as a 5000 unit bolus followed by 1000 units per hour intravenously, adjusted after 24 hoursaccording to the activated partial thromboplastin time (APTT). (APTT measurements are little use in the first 24 hours as streptokinase also raises the APTT.) Heparin and tPA ACE inhibitors
Most Australian cardiologists give ACE inhibitors only to patients with large infarcts and those with clinical signs of left ventricular failure. Captopril 6.25 mg, or equivalent low doses of another ACE inhibitor, should be used as a first dose and, if tolerated, the dose increased to at least 25 mg twice daily of captopril or the equivalent dose of the alternatives. Current consensus is that they should be given as early as feasible when the patient is haemodynamically stable. Beta blockers Beta blockers can be given if the patient is haemodynamically stable with a heart rate above 50 beats per minute and systolic blood pressure above 100 mmHg. The standard regimen is atenolol 5 mg intravenously over 5 minutes followed 10 minutes later by a further 5 mg. Oral beta blockade is commenced 30 minutes later. Many centres use only oral beta blockade (atenolol 50 mg, metoprolol 50 mg) commenced as soon as possible after admission. Much of the data on beta blockers was obtained before the widespread use of thrombolytic therapy. It is likely that the relative improvement in outcome would be the same in patients treated with thrombolysis, but it is possible that the absolute magnitude of the benefit would be reduced. Glyceryl trinitrate Oral nitrates should not be used routinely as they are of no benefit. Other drugs Pain relief is important and should not be forgotten while administering thrombolytic therapy or other drugs. Intravenous morphine titrated slowly, starting at 2.5 mg until adequate relief is obtained, is the most appropriate drug. Intramuscular injection should be avoided. Oxygen therapy is thought to be beneficial, although there have been no trials to confirm this. Summary Dr Aylward is the National Co-ordinator for the GUSTO group in Australia. Why is aspirin and clopidogrel used together for MI?Aspirin combined with clopidogrel has been shown to decrease the risk of cardiovascular events in patients at higher risk of cardiovascular disease, as well as in those with acute coronary syndrome.
Why is clopidogrel given in myocardial infarction?Clopidogrel reduces the risk of death and cardiovascular complications in patients with symptomatic atherosclerotic disease, in the setting of percutaneous coronary intervention (PCI), and in patients with unstable angina or non-STEMI.
Why is aspirin recommended in the management of acute myocardial infarction?Aspirin is effective in reducing the blood clots that are blocking a coronary artery during an acute heart attack.
Why is aspirin administered as a first line medication in ACS?Aspirin in Acute Coronary Syndrome
1: Aspirin acts to inhibit the activity of the cyclooxygenase enzyme and thus attenuates the production of prostaglandins and thromboxane. 2: The ADP receptor antagonists bind to the P2Y12 receptor to prevent ADP-induced platelet activation.
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