LDH, / LDH2 in acute MI is –
Lactate dehydrogenase (LDH) has different isoenzymes. In acute myocardial infarction (MI), certain isoenzymes are elevated. I remember that LDH1 is typically higher than LDH2 in MI, leading to a flipped ratio. So the correct answer would involve LDH1 being elevated compared to LDH2, or a specific ratio like LDH1/LDH2 >1.
For the core concept, I need to explain that LDH isoenzymes are diagnostic markers for tissue damage. The heart has higher LDH1, so when there's MI, LDH1 levels rise more than LDH2, causing the ratio to flip from the normal LDH2 > LDH1 to LDH1 > LDH2.
Why the correct answer is right: In MI, myocardial cells release LDH1 and LDH2. Normally, LDH2 is higher in the heart, but during infarction, the release pattern changes. The LDH1/LDH2 ratio becomes greater than 1, which is a key diagnostic clue. The peak occurs in 24-48 hours and returns to normal in 7-10 days.
Wrong options would include other enzymes like CK-MB, troponin, or maybe incorrect ratios. For example, if an option says LDH2 is higher in MI, that's wrong because the ratio flips. Another wrong option might be about other isoenzymes like LDH3 or LDH4 being elevated, which are more associated with other tissues like liver or lungs.
Clinical pearl: Remember the "flipped LDH ratio" in MI. The LDH1/LDH2 ratio >1 is a hallmark. Also, troponins are now preferred over LDH for MI diagnosis, but understanding the LDH pattern is still important for historical context or when other markers aren't available.
Putting it all together, the correct answer is about the LDH1/LDH2 ratio being greater than 1. The explanation should highlight the isoenzyme distribution in the heart versus other tissues and how MI causes a shift in the ratio. The wrong options can be addressed by explaining which isoenzymes are associated with other conditions or why other enzymes are more specific.
**Core Concept**
Lactate dehydrogenase (LDH) isoenzymes are tissue-specific enzymes. In acute myocardial infarction (MI), **LDH1** (predominant in myocardium) rises disproportionately compared to **LDH2** (mainly in red blood cells), creating a "flipped" **LDH1/LDH2 ratio >1**. This is a classic biochemical marker of cardiac injury.
**Why the Correct Answer is Right**
In acute MI, myocardial cell necrosis releases **LDH1** into circulation. Normally, **LDH2** levels are higher than LDH1 in serum (LDH2 > LDH1). Post-MI, the **LDH1/LDH2 ratio inverts**, peaking 24–48 hours after infarction.