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Ever wonder why a "STEMI" causes ST elevation on EKG?
The answer is mind-bending.
#medthread #tweetorial #medtwitter
Ever wonder why a "STEMI" causes ST elevation on EKG?
The answer is mind-bending.
#medthread #tweetorial #medtwitter
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We need to review a few basic EKG facts.
First:
💡 If electrical signals travel away from an EKG lead they appear as negative deflections
💡 If electrical signals travel toward an EKG lead they appear as positive deflections
bit.ly/2PIRGWw
We need to review a few basic EKG facts.
First:
💡 If electrical signals travel away from an EKG lead they appear as negative deflections
💡 If electrical signals travel toward an EKG lead they appear as positive deflections
bit.ly/2PIRGWw
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Second:
Recall that the ST segment represents electroneutrality in the cardiac cycle, between depolarization and repolarization, w/ no voltage gradient.
That's why the ST and TP baseline segments are normally flat on EKG (aka isoelectric).
bit.ly/2PGiLJZ
Second:
Recall that the ST segment represents electroneutrality in the cardiac cycle, between depolarization and repolarization, w/ no voltage gradient.
That's why the ST and TP baseline segments are normally flat on EKG (aka isoelectric).
bit.ly/2PGiLJZ
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There are many channels that contribute to ventricular repolarization.
An important one is K-ATP, a potassium exporter channel that needs adequate ATP to remain closed.
Less ATP available = more potassium export from the myocardial cell.
ncbi.nlm.nih.gov/pubmed/9349389…
There are many channels that contribute to ventricular repolarization.
An important one is K-ATP, a potassium exporter channel that needs adequate ATP to remain closed.
Less ATP available = more potassium export from the myocardial cell.
ncbi.nlm.nih.gov/pubmed/9349389…
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Not surprisingly, during ischemia mitochondrial ATP production goes down.
physiology.org/doi/full/10.11…
Not surprisingly, during ischemia mitochondrial ATP production goes down.
physiology.org/doi/full/10.11…
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This decrease in ATP production leads to more potassium export through K-ATP ➡️ faster ventricular depolarization of ischemic cells relative to healthy ones➡️a shorter cardiac cycle.
physiology.org/doi/full/10.11…
This decrease in ATP production leads to more potassium export through K-ATP ➡️ faster ventricular depolarization of ischemic cells relative to healthy ones➡️a shorter cardiac cycle.
physiology.org/doi/full/10.11…
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Here's another way to view the shorter ischemic electrical cycle. 👇
physiology.org/doi/full/10.11…
Here's another way to view the shorter ischemic electrical cycle. 👇
physiology.org/doi/full/10.11…
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This difference in cycle speeds between ischemic and non-ischemic cells causes a relative current during repolarization:
Ischemic➡️non-ischemic, away from overlying EKG leads
This shifts the EKG baseline down, for reasons we discussed above.
bit.ly/2s99b9l
This difference in cycle speeds between ischemic and non-ischemic cells causes a relative current during repolarization:
Ischemic➡️non-ischemic, away from overlying EKG leads
This shifts the EKG baseline down, for reasons we discussed above.
bit.ly/2s99b9l
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Conversely, there is little difference between ischemic/non-ischemic depolarization speeds.
Thus the voltage gradient disappears during the QRS complex and the EKG returns to isoelectric baseline in the ST segment (aka zero voltage).
bit.ly/2s99b9l
Conversely, there is little difference between ischemic/non-ischemic depolarization speeds.
Thus the voltage gradient disappears during the QRS complex and the EKG returns to isoelectric baseline in the ST segment (aka zero voltage).
bit.ly/2s99b9l
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The ischemic ST segment therefore appears elevated on EKG, but only because the baseline has been shifted down.
bit.ly/2s99b9l
👇
The ischemic ST segment therefore appears elevated on EKG, but only because the baseline has been shifted down.
bit.ly/2s99b9l
👇
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Let's summarize:
💡Ischemia➡️decrease in ATP production
💡This➡️K export and faster depolarization
💡An ischemic➡️non-ischemic current is created, lowering the EKG baseline
💡W/ depolarization, the gradient stops➡️ST segment = isoelectric
💡This = appearance of ST elevation
Let's summarize:
💡Ischemia➡️decrease in ATP production
💡This➡️K export and faster depolarization
💡An ischemic➡️non-ischemic current is created, lowering the EKG baseline
💡W/ depolarization, the gradient stops➡️ST segment = isoelectric
💡This = appearance of ST elevation
