WHAT ARE THEY?
VOL: 100, ISSUE: 26, PAGE NO: 31
WHAT ARE THEY?
- Thrombolytic drugs are used to break down (lyse) occluding clots and fibrin meshes (thrombi) in blood vessels by dissolving them.
- They do this by converting inactive plasminogen (a blood protein) into active plasmin.
- These drugs are also known as ‘clot busters’.
- Alteplase (r-tPA).
- Myocardial infarction is a life-threatening condition.
- It occurs when there is an abrupt cessation of blood flow within the coronary arteries leading to an area of irreversible cell death (necrosis) within the myocardium.
- This is often triggered by the rupture/fissuring of a fatty atheromatous plaque.
- Myocardial infarction is often diagnosed from patient presentation, which is often pale, cold, sweaty and clammy, with crushing chest pain.
TREATMENT BY THROMBOLYSIS
- Emergency percutaneous transmural coronary angioplasty to unblock the affected coronary artery is seldom available 24 hours a day in the UK.
- Thrombolytic therapies are universally available, quickly administered by intravenous injection, and provide a cheap alternative to an expensive trip to the cardiac catheterisation laboratory.
- Thrombolytics are aimed at rapid reperfusion of the myocardium, because every minute wasted correlates with further loss of heart muscle. Their effectiveness at reducing morbidity and mortality if administered rapidly has been proven in a number of studies (ASSENT II, 1999; Gusto III, 1993).
- Administration within one hour of chest pain has maximum benefit.
- Use should certainly be considered within six hours, and even after 12 hours could still have some benefit.
- Success is seen by the reduction of ST elevation by 25 per cent on electrocardiogram (ECG) three hours after administration.
- Aspirin, which has antiplatelet properties, has been shown to complement thrombolytic therapies.
- As thrombolytics are used to lyse clots that have formed over atheromatous clots, they are associated with a high risk of haemorrhage. A checklist of inclusion and exclusion criteria should be used before intravenous administration (see local trust protocols).
- Reperfusion arrythmias like bradycardia and runs of self-terminating ventricular tachycardia are frequently seen one to six hours after administration.
- Haemorrhage is often limited to puncture sites and is usually relieved by the appliance of pressure. On other occasions it can result in gastrointestinal bleeds or more severe haemorrhagic stroke.
- Allergic reaction. As streptokinase is a protein extracted from streptococcal bacteria, antibody production will occur four days after administration. Therefore, some trusts do not advise repeat doses (check hospital protocol).
- On rare occasions readministration may be necessary as unsuccessful reperfusion can lead to increased risk of impaired left ventricular function, further pain, morbidity, and mortality.
- A repeat dose should only be considered once the result from an urgent fibrinogen level test has been received and is more than 1.0. A high fibrinogen level is associated with further arterial thrombosis.