What is clot dissolving treatment (thrombolysis) for heart attack?

What is clot dissolving treatment (thrombolysis) for heart attack?

Clot dissolving treatment used to be an important mode of early treatment of a heart attack. Though it has been largely superseded by mechanical clot removing treatment, clot dissolving treatment may be useful in certain situations. It is still an important form of treatment in resource limited locations.

Heart attack is usually due to sudden blockage of a blood vessel supplying oxygenated blood to the heart known as coronary artery. Sudden blocks are usually due to the formation of a blood clot within the coronary artery. Clots could form over a pre-existing partial block due to fat deposition. Dissolving the clot soon after the occurrence of a heart attack can salvage a lot of heart muscle from damage due to loss of blood supply. This clot dissolving treatment is known as thrombolytic therapy for myocardial infarction. Myocardial infarction is the technical term for a heart attack.

Clot dissolving medications are most effective when given within the initial 3 hours of onset of symptoms. Beyond that, effectiveness decreases as the clot becomes more firm and difficult to dissolve by clot dissolving medications. 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 the blocks in coronary artery using balloon catheters introduced through the blood vessels of wrist or groin. Balloon catheters are small tubes with sturdy balloons at the tip which can be inflated from outside using a syringe like mechanism with a pressure gauge. Balloon catheters are guided to the blood vessels of the heart through larger tubes known as guide catheters, under continuous X-ray imaging. The procedure has to be done soon after arrival in the hospital. If there is a technical delay, clot dissolving treatment may be considered as an initial treatment to buy time.

Clot dissolving treatment or thrombolytic therapy cannot be considered for all type of heart attacks. 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 clot suitable for dissolution with clot dissolving medication. As clot dissolving medications have a potential to cause minor or major bleeds, it is avoided in those at risk for significant bleeding. This would include those on medications which prevent clot formation and in those who have known bleeding disorders.

Please note that these medications are different from the medications which are usually given to prevent formation of blocks in the blood vessels known as anti-platelet agents. Medications to prevent blood clots known as anticoagulants are used in those with artificial heart valves, in those who had clots in leg veins and some of those who have abnormal rhythm from upper chambers known as atrial fibrillation.