Final answer:
Creatine phosphokinase (CPK), particularly its MB isoenzyme, is the enzyme used to diagnose acute myocardial infarction (MI). It is the first enzyme to increase in the blood plasma following a heart attack, and coupled with lactate dehydrogenase (LDH) and cardiac troponin levels, it aids in confirming the diagnosis.
Step-by-step explanation:
The enzyme used to diagnose acute myocardial infarction (MI), or heart attack, is Creatine phosphokinase (CPK). This enzyme, particularly its MB isoenzyme, serves as a marker for detecting heart damage. CPK levels increase quickly following a cardiac event, often making it the first enzyme to spike in blood plasma. CPK levels can increase up to 10 times after the first heart attack and may rise even further with subsequent attacks. Another key enzyme used in diagnosis is lactate dehydrogenase (LDH), particularly its H4 or LDH₁ isoenzyme form, which peaks in the plasma and remains elevated for about 6 days following a heart attack. In addition, cardiac troponin, a protein involved in muscle contraction, is also commonly tested for and its elevated levels serve as an indicator of cardiac muscle damage. The diagnosis of MI may also involve analysis of the patient's ECG, echocardiography, and cardiac magnetic resonance imaging.