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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"
https://bit.ly/2XN9Hp5
First, let's find how torsades was originally described (and named!):
Francois Dessertenne noted "ventricular tachycardia with two variable foci" in a patient in 1966He coined the arrythmia torsades de dointes, connoting "twisting peaks"https://bit.ly/2XN9Hp5
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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, orelectrolytes)
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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)
https://bit.ly/34khj4T
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)
https://bit.ly/34khj4T
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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
https://bit.ly/2ruAj1R
Torsades arises from a specific sequence of events that disrupts repolarization.
Sinus beatProlonged QTVentricular ectopic beat during depol (aka an "early after depolarization" or EAD, thought to be calcium-mediated)Re-entrant arrythmiahttps://bit.ly/2ruAj1R
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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
https://bit.ly/2OKJdjL
It turns out that seeing torsades on the monitor is literally watching a re-entry circuit circulate
Terrifying but also striking to seehttps://bit.ly/2OKJdjL
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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
https://bit.ly/2OhCm2q
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
https://bit.ly/2OhCm2q
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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.
https://bit.ly/2OkFt9H
So how does Mg actually work?
It turns that Mg, as a cation, is an effective Ca channel blocker.https://bit.ly/2OkFt9H
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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.
https://bit.ly/2XKz7DK
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. https://bit.ly/2XKz7DK
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This was described by @PulmCrit as naloxone for torsades (I really like that description)
He also advocates for protocol-driven, continuous Mg infusions to make sure the serum levels stay up (goal 3.5-5 mg/dl) and those Ca channels stay blocked.
https://bit.ly/2OLEJcK
This was described by @PulmCrit as naloxone for torsades (I really like that description)
He also advocates for protocol-driven, continuous Mg infusions to make sure the serum levels stay up (goal 3.5-5 mg/dl) and those Ca channels stay blocked.
https://bit.ly/2OLEJcK
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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
https://bit.ly/2KUupxX
Calcium channel blockade also explains why Mg treats eclamptic seizures:
Eclamptic seizures are driven by dysregulated cerebral vasoconstrictionMg blocks Ca channels and induced vasodilationSeizures stophttps://bit.ly/2KUupxX
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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 intervalEarly after depolarizations, triggered by Ca influx, lead to torsadesMg blocks Ca channels and the arrythmiaMg 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
