What is thrombolytic therapy for myocardial infarction? Cardiology Basics

What is thrombolytic therapy for myocardial infarction? Cardiology Basics

Thrombolytic therapy used to be an important mode of early treatment of acute myocardial infarction. Though it has been largely superseded by primary angioplasty, thrombolytic therapy may still be useful in certain situations. It is still an important form of treatment in resource limited locations.

Myocardial infarction is usually due to sudden occlusion of a coronary artery by thrombus formation on a pre-existing partial obstruction by an atherosclerotic plaque. Plaque rupture with local thrombus formation is the usual mechanism.  Dissolving the thrombus soon after the occurrence of a myocardial infarction can salvage a lot of myocardium from ischemic damage. Myocardial infarction due to sudden coronary occlusion is Type 1 as per the universal definition of myocardial infarction.

Thrombolytic therapy is most effective when given within the initial 3 hours of onset of symptoms. Beyond that, effectiveness decreases as the clot becomes firmer and more difficult to dissolve by thrombolytic agents. Still it may be considered as a reasonable option within the first 6-12 hours after onset of symptoms. When recurrent chest pain is present, it may be considered even beyond that, in rare cases. With the availability of coronary angioplasty, first preference is now given for angioplasty rather than clot dissolving treatment.

Coronary angioplasty is the procedure of removing obstructions in coronary artery using balloon catheters introduced through the radial or femoral artery. Balloon catheters are guided to the coronary arteries through larger catheters known as guide catheters, under fluoroscopy. Primary angioplasty for acute myocardial infarction has to done soon after arrival in the hospital, for best results. If there is a technical delay, thrombolytic therapy may be considered as an initial treatment to buy time.

Thrombolytic therapy cannot be considered for all types of myocardial infarction. Use is limited to a specific type known as ST elevation myocardial infarction, with ST segment elevation in the ECG. Reason is that non-ST elevation myocardial infarction is unlikely to have a soft red thrombus suitable for dissolution with thrombolytic therapy. Non-ST elevation myocardial infarction usually has a firmer platelet rich white thrombus.

As thrombolytic therapy has a potential to cause minor or major bleeds, it is avoided in those at risk for significant bleeding. This would include those on anticoagulants and in those who have known bleeding disorders. Thrombolytic therapy is not given in those who had a hemorrhagic stroke. It is also not given in those who had  a recent ischemic stroke beyond the window period for stroke thrombolysis. Those who have severe hypertension on presentation needs control of hypertension before initiation of thrombolysis.