Wednesday, July 8, 2015

Long QT Syndrome with Continuously Recurrent Polymorphic VT: Management

A young woman presented with intermittent shocks from her implantable defibrillator.  She was intermittently unconscious and unable to give history.   The monitor showed intermittent polymorphic ventricular tachycardia.    The physician was presented with this ECG at the same moment he was observing the repeated syncope:

Time zero
It is a bigeminal rhythm with a very bizarre PVC.  The PVC has an incredibly long QT, but the intervening native rhythms do not.  However, when I saw this (it was texted to me), it immediately reminded me of this case, so I knew by sheer recognition that it was long QT and the patient was having Torsades de Pointes.  

The patient was moved to the critical care area.  An ICD was noted on her chest.  Vital signs were normal when the rhythm was normal. 

Another ECG was recorded 8 minutes later:
The computer measures the QT as 435 ms and QTc as 435 ms.  What do you think? 






As I have pointed out many times, the computer is awful at making the diagnosis of long QT.
See these posts:
Do not trust the computerized QT when the QT is long
Altered Mental Status, possible ingestion.  What does the ECG show?


The QT is at least 640 ms, and QTc(Bazett) also = 640 ms (RR interval = 1)


The monitor showed continued bursts of tachycardia, and another 12-lead was recorded, this one at 15 minutes:
Polymorphic VT initiated by R on T


At 22 minutes, 4 continuous ECGs were recorded:

More R on T initiating Torsade

Same. Notice that you can see the R-R interval that precedes the complex that precedes the R on T in 2 places.  In both, the R-R interval is greater than 1 second.

Same



As the patient was repeatedly losing consciousness and not protecting her airway, she was intubated and started on propofol.  She was given 3 grams of magnesium.  Her rhythm stabilized and this ECG was recorded:
Sinus Tach and long QT, but no more Torsades.

And another:
Sinus Tach and Even longer QT; still, no more Torsades

Her heart rate slowed:
Now there is atrial pacing at a rate of 60 and still a very long QT.


Further history revealed a previous history of long QT, presumed congenital, with history of syncope and cardiac arrest.   The patient had also been on Nadolol.  The K returned at 3.3 mEq/L and Mg at 1.7 mEq/L.  IV potassium was given.

The patient remained stable after these interventions.


It was later found that she had not been taking her Nadolol (a non-selective beta blocker).


She was restarted on Nadolol and her pacer rate was increased to 80, making the longest possible R-R interval 750 ms.  When the rate is increased, the R-R intervals are decreased, and thus the preceding R-R interval is decreased.  This shortens the QT, and diminishes the probability of getting an R on T.



But wouldn't beta blockers (BBs) decrease the heart rate and thus increase the R-R interval and therefore lead to lengthened QT and increased risk?  NoBBs work by mitigating the adverse effects of sympathetic stimulation on the membrane ion channel.  Sympathetic stimulation directly affects the QT interval, although this is mainly in LQT1 and LQT2.  LQT3 is different.  Here is a thorough article from UpToDate on the topic, if you have access.

Why did the Torsades stop with intubation and propofol?


This is congenital long QT: Most of these (LQT1 and LQT2, but not LQT3) are made worse by catecholamines, and are treated with beta blockers (As is Catecholaminergic Polymorphic Ventricular Tachycardia, but for different reasons).  By taking away the endogenous catecholamines, intubation and sedation may have been all that was necessary.  Administering Mg and K contributed as well.  This episode was probably initiated by both Nadolol noncompliance and hypokalemia.  


What do beta blockers (BBs) do?  See this article.  It is very confusing because their effect is different for the different types of Long QT, with some at least apparently conflicting evidence (conflicting to me anyway, and I am no expert!).  LQT1 and 2 behave similarly, but LQT3 appears to be opposite (apparently similar to acquired long QT).  For LQT1 and 2, epinephrine infusion lengthens the QT and increases QT dispersion (differing QT intervals throughout the myocardium, which also increases vulnerability to Torsade); conversely, BBs both shorten the QT interval and decrease dispersion, mitigating the risk of Torsade.  Exception: However, in LQT3, beta stimulation does the opposite, and beta blockers may facilitate Torsades.


The data is conflicting, however: whereas, in accordance with the above, observational studies show that BB are most effective in LQT1 and also in LQT2, observational studies of patients with LQT3, which it seems should be opposite LQT1 and 2, have been variable; they do not necessarily show an adverse effect of BBs.  See this article.  And this article.


BBs also decrease the triggering PVCs ("early afterdepolarizations"), mitigating the risk of Torsade. 

Here is another point of confusion: The patient's heart rate was increased with pacing, but held in check with Nadolol.  In fact, this seems to be ideal, as pacing decreases the risk of Torsades if the heart is protected from sympathetic stimulation: see this study.  Although the primary effect of beta blockade is on the ion channels themselves, UpToDate states that: "The goal of beta blocker therapy is to blunt the maximal heart rate achieved during exertion, and is particularly important in patients with LQT1 who are at increased risk during exercise. A theoretical concern is that beta blockers also decrease the sinus rate, a property that may prolong repolarization and potentially predispose to TdP."

Acute management of Torsades specifically due to congenital long QT: I have been unable to find any guidelines or articles specific to the emergency treatment of recurrent Torsades due to congenital long QT (in contrast to acquired long QT) except for the following statement in UpToDate: "In those with congenital long QT syndrome, beta blockers may be used to reduce the frequency of premature ventricular contractions and shorten QT interval."  There is no recommendation as to which beta blocker should be used in this acute situation.  In chronic therapy, Propranolol and Nadolol are best, and metoprolol appears to be ineffective.  Both propranolol and nadolol are nonselective (both Beta-1 and Beta-2) blockers.   Is the absence of selectivity critical to the treatment?  I do not know and could not find out.  Nonselective beta blockade has its adverse effects, including bronchospasm.  Furthermore, my favorite beta blocker in the ED is esmolol because it can be immediately turned off (very short half-life).  However, it is beta-1 selective and I don't know if it would work.


Here is a great review of the chronic management of long QT syndrome.


Management of Polymorphic VT (PMVT)

Non-Torsades Etiologies of PMVT (normal QT)
Most commonly due to ischemia.  These will almost always be overt, severe episodes of ischemia, with chest pain and/or unequivocal ischemic ECG abnormalities. Also due to pre-existing cardiomyopathy.

Management of polymorphic VT (with long QT = Torsades de Pointes)
Most torsade is self-limited.  If it does not spontaneously convert, then it needs defibrillation if the patient is unstable.  If it does convert, then it is likely to recur, and therapy is aimed at preventing recurrence.

Therapy of Acute Episodes of Torsades:
1. Cardioversion or Defibrillation if active, especially if unstable
2. Removal of offending agent in acquired long QT (usually a medication)
3. Correction of hypoK, even to slightly supranormal levels. K helps to prevent the early afterdepolarizations (PVCs) that initiate Torsades with R on T.
4. Administration of 2-4g of MgSO4 even if the Mg level is normal (a drip of 3-10 mg per minute may be useful).  Mg also helps to prevent the early afterdepolarizations (PVCs) that initiate Torsade with R on T.
5. Only if it is acquired long QT: beta-adrenergic stimulation with isoproterenol
6. If these do not work, then overdrive pacing, usually at a rate of about 100 to prevent any pauses, will almost always work (transcutaneous pacing is fine for temporary relief as a bridge to transvenous pacing).
7.  Lidocaine may also be of benefit because it can suppress the PVCs (early afterdepolarizations) which initiate Torsades if they occur on the T-wave. 
8. Amiodarone is of questionable benefit, and possible harm.  By itself, it lengthens the QT interval, though without greatly increasing the risk of Torsades 
9. Do not give beta blockers unless the patient carries a diagnosis of congenital long QT.  Just the opposite: isoproterenol.

10. If it is congenital [congenital long QT, or catecholaminergic PMVT (which has a normal QT interval)], then acute beta blockade may be indicated.  I would try esmolol first, as it can be turned off.  However, it does not have beta-2 blockade and it is unclear to me if this is important and/or necessary.  If esmolol does not work, then IV propranolol should be given.



At the bottom are more specific guidelines for catecholaminergic PMVT.

Therapy of Acute Non-Torsade PMVT: Similar to Monomorphic VT (except for catecholaminergic PMVT, which is outlined below)
1. Cardioversion or Defibrillation if active
2. Correction of electrolyte disorders, especially hypoK or hypoMg
3. Prevention of further episodes with lidocaine or amiodarone, possibly a beta blocker such as esmolol (which you would avoid in any acquired long QT Torsades).
4. Anti-ischemic therapies, up to and including revascularization
5. Implantable Cardioverter-defibrillator may be necessary even with successful revascularization


Catecholaminergic PMVT:

1. Cardioversion or defibrillation (depending on presence of pulses), but with beta blocker pre-treatment (if possible), as the shock itself can cause catecholamine surge, further aggravating the situation and causing early recurrence of VT.

2. Intravenous beta blockers should be administered.  Esmolol is a great choice, as it has a very short half-life and can be turned off if there are complications.  Dose: Esmolol can be given in a bolus of 500 mcg/kg (0.50 mg/kg), followed by a drip of 50 mcg/kg/min (0.05 mg/kg/min).  It can be rebolused repeatedly, as needed, each time increasing the infusion by 50 mcg/kg/min.

3. For recurrent VT in the absence of prolonged QT, amiodarone should be administered by bolus and drip.  Amiodarone has beta-blocking effects.

4. Verapamil is recommended based on studies in which it prevents exercise-induced PMVT (3, 4).  However, I haven't found literature on its use in the acute situation.  Our electrophysiologist wrote that he would try it.  In this case, it appears to have made things worse, but that is the problem with isolated cases without control groups.

4.  Sedation, as in this case, to decrease sympathetic drive?  Or, class IIb in ACC/AHA guidelines for incessant VT is general anesthesia.

Avoid isoproterenol and overdrive pacing.  For polymorphic VT due to acquired long QT (Torsade de Pointe), isoproterenol is indicated to increase the sinus rate and prevent further torsade.  However, this makes CPVT worse.  Fortunately, Torsade is more common, but if you know the patient has CPVT, avoid isoproterenol.

Overdrive Pacing is listed as class IIb for incessant VT in the ACC/AHA guidelines, but this should not to be applied to CPVT.  

Overdrive pacing is used to prevent recurrence of pause-dependent PMVT (Torsade), which is worsened by bradycardia and improved by tachycardia).  The pathophysiology of CPVT is very different from Long QT syndrome.  CPVT, unlike Torsade, is worsened with tachycardia.   See this post for management of Torsade. 

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