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Ever wonder why magnesium (Mg) is used to treat Torsades de Pointes?
The answer is fascinating, elegant, and also explains why Mg treats another clinical entity - eclampsia
#medthread #tweetorial #medtwitter
Ever wonder why magnesium (Mg) is used to treat Torsades de Pointes?
The answer is fascinating, elegant, and also explains why Mg treats another clinical entity - eclampsia
#medthread #tweetorial #medtwitter
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First, let's find how torsades was originally described (and named!):
💡Francois Dessertenne noted "ventricular tachycardia with two variable foci" in a patient in 1966
💡He coined the arrythmia torsades de dointes, connoting "twisting peaks"
bit.ly
First, let's find how torsades was originally described (and named!):
💡Francois Dessertenne noted "ventricular tachycardia with two variable foci" in a patient in 1966
💡He coined the arrythmia torsades de dointes, connoting "twisting peaks"
bit.ly
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To understand how Mg treats torsades we need to understand the pathophys of the arrythmia itself.
▶️Torsades is a ventricular arrythmia of repolarization, occurring in patients with prolonged QT intervals (usually acquired from drugs, ischemia, or⬇️electrolytes)
To understand how Mg treats torsades we need to understand the pathophys of the arrythmia itself.
▶️Torsades is a ventricular arrythmia of repolarization, occurring in patients with prolonged QT intervals (usually acquired from drugs, ischemia, or⬇️electrolytes)
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There are 4 phases of repolarization of cardiac myocytes
1: K efflux
2: Ca influx
3 and 4: K efflux
Calcium influx in phase 2 "stalls" repolarization as in/out charge flow is balanced (more on this later)
bit.ly
There are 4 phases of repolarization of cardiac myocytes
1: K efflux
2: Ca influx
3 and 4: K efflux
Calcium influx in phase 2 "stalls" repolarization as in/out charge flow is balanced (more on this later)
bit.ly
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Torsades arises from a specific sequence of events that disrupts repolarization.
✅Sinus beat
❌Prolonged QT
❌Ventricular ectopic beat during depol (aka an "early after depolarization" or EAD, thought to be calcium-mediated)
❌Re-entrant arrythmia
bit.ly
Torsades arises from a specific sequence of events that disrupts repolarization.
✅Sinus beat
❌Prolonged QT
❌Ventricular ectopic beat during depol (aka an "early after depolarization" or EAD, thought to be calcium-mediated)
❌Re-entrant arrythmia
bit.ly
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It turns out that seeing torsades on the monitor is literally watching a re-entry circuit circulate
💥Terrifying but also striking to see
bit.ly
It turns out that seeing torsades on the monitor is literally watching a re-entry circuit circulate
💥Terrifying but also striking to see
bit.ly
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Now that we understand torsades, how did Mg come to be preferred therapy?
The original description was in 1984 when Mg infusion treated 3 patients w/ torsades who had acquired long QT.
All had normal serum Mg levels, the QT intervals didn't shorten
bit.ly
Now that we understand torsades, how did Mg come to be preferred therapy?
The original description was in 1984 when Mg infusion treated 3 patients w/ torsades who had acquired long QT.
All had normal serum Mg levels, the QT intervals didn't shorten
bit.ly
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It is not totally clear how they figured out that this might work, but they cite a paper from 1968 where 2 patients w/ Vfib from low Mg (which was actually torsades) were treated with overdrive pacing.
It is not totally clear how they figured out that this might work, but they cite a paper from 1968 where 2 patients w/ Vfib from low Mg (which was actually torsades) were treated with overdrive pacing.
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So how does Mg actually work?
💡It turns that Mg, as a cation, is an effective Ca channel blocker.
bit.ly
So how does Mg actually work?
💡It turns that Mg, as a cation, is an effective Ca channel blocker.
bit.ly
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💡Blocking Ca channels suppresses the EADs, allowing the re-entrant arrythmia to terminate. This was first described in dogs who had torsades-like arrythmias induced by cesium infusions with magnesium rescue.
bit.ly
💡Blocking Ca channels suppresses the EADs, allowing the re-entrant arrythmia to terminate. This was first described in dogs who had torsades-like arrythmias induced by cesium infusions with magnesium rescue.
bit.ly
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Calcium channel blockade also explains why Mg treats eclamptic seizures:
💡Eclamptic seizures are driven by dysregulated cerebral vasoconstriction
💡Mg blocks Ca channels and induced vasodilation
✅Seizures stop
bit.ly
Calcium channel blockade also explains why Mg treats eclamptic seizures:
💡Eclamptic seizures are driven by dysregulated cerebral vasoconstriction
💡Mg blocks Ca channels and induced vasodilation
✅Seizures stop
bit.ly
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To sum up:
💡Torsades is a re-entrant ventricular arrythmia in the setting of a prolonged QT interval
💡Early after depolarizations, triggered by Ca influx, lead to torsades
💡Mg blocks Ca channels and ❌the arrythmia
💡Mg treats eclamptic seizures by a similar mechanism
To sum up:
💡Torsades is a re-entrant ventricular arrythmia in the setting of a prolonged QT interval
💡Early after depolarizations, triggered by Ca influx, lead to torsades
💡Mg blocks Ca channels and ❌the arrythmia
💡Mg treats eclamptic seizures by a similar mechanism
What do you think #medtwitter?
CC: @laxswamy @ChrisWorsham @virenkaul @grecoa3 @dina_khateebDO @AdamRodmanMD @tony_breu @ETSshow @cjchiu @gbosslet @aoglasser
CC: @laxswamy @ChrisWorsham @virenkaul @grecoa3 @dina_khateebDO @AdamRodmanMD @tony_breu @ETSshow @cjchiu @gbosslet @aoglasser
Props to @downsjw2000 @ElizaMillerMD and others who pointed out that, in eclampsia, Mg has other effects besides vasodilation including NMDA blockade (also by blocking calcium channels!) and neuromodulatory effects
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