Revisiting Acute Myocardial Infarction: TH+ABC—August 30, 2001

Revisiting Acute Myocardial Infarction: TH+ABC—August 30, 2001

Acute myocardial infarction (AMI) is a common condition with an extremely high mortality rate. In recent years, PTCA (percutaneous transluminal coronary angioplasty) and CAGT (coronary artery bypass grafting) have been employed, providing relief to some patients. However, during the emergency phase, it is essential to carry out appropriate resuscitation to create favorable conditions for surgery. The guiding principle for proper resuscitation is TH+ABC. T stands for Thrombolysis, i.e., thrombolytic therapy. Currently, the commonly used intravenous thrombolytic agents in China include streptokinase (SK), urokinase (UK), and recombinant tissue plasminogen activator (γt-PA). H refers to HepazIn, i.e., heparin or low-molecular-weight heparin. This drug plays an important role in preventing re-thrombosis; typically, the dosage is 100 µg per kg of body weight, meaning a 50 kg adult would receive 5,000 µg, with a maintenance dose of 10 µg per kg. Low-molecular-weight heparin is administered at 0.01 mL per kg, so a 50 kg adult would receive 0.5 mL; the latter does not require monitoring of coagulation time. A represents aspirin, whose purpose is to inhibit cyclooxygenase (COX), thereby suppressing thrombus formation. Low-dose aspirin (40–80 mg) requires several days to achieve antiplatelet aggregation effects; therefore, during AMI, it should be chewed and absorbed through the oral mucosa to accelerate absorption and quickly achieve therapeutic effect. Aspirin solutions are even easier to absorb. Early administration of aspirin in myocardial infarction can significantly reduce mortality, with reductions ranging from 25% to 50%. B denotes beta-blockers, which can limit the extent of infarction, lower heart rate and blood pressure, reduce myocardial oxygen consumption, and alleviate pain. Betaloc is administered intravenously at 5 mg, with a total dose of 15 mg, followed by oral administration of 150 mg daily in three divided doses. C refers to angiotensin-converting enzyme inhibitors (ACEI), with captopril being a typical representative. It is taken at 25 mg three times daily, orally, to correct latent heart failure and reduce myocardial infarction mortality.

Finally, it is important to discuss the indications and related issues of thrombolytic therapy. Indications include ST-segment elevation that does not resolve after nitroglycerin administration; persistent chest pain with ST-segment depression in leads V1–V3, indicating a posterior wall Q-wave type myocardial infarction. It is particularly important to note that the notion that once a Q wave appears on the ECG, thrombolytic therapy should not be performed is incorrect. The appearance of a Q wave indicates an old myocardial infarction, but if there is ST-segment depression or upward bowing, it suggests that a thrombus is forming, so thrombolytic therapy is still appropriate. Urokinase 50,000 µg (UK) is added to glucose and infused over 10 minutes, followed by 60,000 µg per hour for 12 consecutive hours. Streptokinase (after skin testing) 250,000 µg is added to 100 mL of 5% glucose and infused over 30–60 minutes, then continued at 100,000 µg per hour for 12 hours. To prevent fever caused by streptokinase, 25 mg of Phenergan can be administered intramuscularly beforehand.