Guidance on the use of drugs for early thrombolysis in the treatment of acute myocardial infarction

Acute myocardial infarction (AMI) is caused by blockage of a coronary artery by a thrombus or clot. This is usually the result of rupture of an atherosclerotic plaque within the artery. The heart muscle supplied by that artery is damaged or dies because of lack of oxygen (ischaemia). Patients with AMI may develop heart failure or potentially fatal cardiac arrhythmias as a result of damage to the heart muscle. These and other complications may occur early, within the first few hours of the event, or may develop over the subsequent months or years.

Around 240,000 people experience AMI in England and Wales each year. Up to 50% of people who have an AMI die within 30 days of the event, and over half of these deaths occur before medical assistance arrives or the patient reaches hospital.

Onset of AMI symptoms is usually rapid and the highest risk of death (usually as the result of an acute fatal arrhythmia) is within the first hour of experiencing symptoms – around one-third of all AMI deaths occur within the first hour.

Thrombolytic drugs break down the thrombus so that the blood flow to the heart muscle can be restored to prevent further damage and assist healing. The sooner the blood flow can be restored, the better the chances of avoiding the death of the heart muscle. Along with clinical symptoms (typically but not exclusively chest pain), characteristic changes in the 12-lead electrocardiogram (ST segment elevation) provide the most immediate indication of the diagnosis of AMI for patients requiring thrombolysis for AMI.

Intravenous thrombolytic therapy is an established standard treatment for AMI. It is estimated that around 50,000 patients currently receive thrombolysis in England and Wales each year. However, evidence suggests that thrombolysis continues to be under-used.

Thrombolytic drugs are routinely given in hospital as soon as possible after a confirmed diagnosis of AMI. Additionally, their administration in pre-hospital settings, principally by ambulance paramedics, is becoming more common.

Early primary percutaneous coronary intervention (PCI) may be an alternative to thrombolysis. Despite research evidence of the potential value of early PCI, currently few hospital trusts have the capacity to provide it. Treatment delivering thrombolytics in combination with glycoprotein IIb/IIIa inhibitors is also the subject of research studies. However, these interventions are beyond the scope of this appraisal.