Saturday, October 12, 2013

Polymorphic Ventricular Tachycardia

A woman in her 40's presented with multiple "spells" in the past week, with increasing frequency.  She feels lightheaded, then becomes unresponsive.  It usually lasts about one minute then resolves.  She has had no chest pain.  She has a history of seizures as a child but there is no seizure activity during these spells.

The monitor shows this:
Ventricular Tachycardia, rate approximately 220 beats per minute

During this rhythm she was awake, protecting her airway, with pallor, diaphoresis and cool extremities.  Pulses were present.  There was no respiratory distress.

A 12-lead ECG was recorded:
VT, and it is "Polymorphic" VT because there are multiple morphologies to the complexes.  Rate again approximately 220.  Polymorphic VT is either torsade (associated with a long QT interval)  or not torsade (QT not long, often due to ischemia)


On the monitor, she spontaneously converted to a different rhythm, and another 12-lead was obtained:
There is bigeminy.  Narrow complexes are preceded by P-waves.  The QRS associated with the sinus beats has right bundle branch block (RBBB), and do not appear to have very long QT intervals (I calculated 400ms QT divided by the square root of the preceding R-R interval = 460ms).  The intervening Ventricular complexes (PVC's) look very bizarre with a long QT.  The PVCs have large ST elevation (II, III, aVF) with reciprocal ST depression (aVL, precordial), suggesting inferoposterior STEMI, but this is clearly a mimic because the intervening sinus complexes have no ST elevation.

She went back into tachycardia:

Polymorphic VT again.
What should be done?

First, what kind of VT is this?  Polymorphic VT.  PMVT is defined as a wide complex ventricular rhythm at rate over 100 with rapidly changing QRS axis and/or morphology.


Polymorphic VT

Etiology
Polymorphic VT is either torsades de pointe (associated with a long QT on the baseline 12-lead ECG) or non-torsades (usually associated with ischemia or other organic heart disease).  The presence of QT lengthening on the baseline 12-lead ECG is not always obvious.  Torsade de pointes means "twisting of the points" and refers to the changing axis around an isoelectric line. 

Morphology of the PMVT (i.e., presence of twisting of the points) alone cannot distinguish PMVT due to long QT (torsades) from that due to other etiologies (non-torsades).  It is virtually impossible to distinguish pulseless PMVT from ventricular fibrillation, and studies have shown that the majority of pulseless rhythms that appear to be torsade (with "twisting of the points") are really ventricular fibrillation.  This distinction has no implications for immediate management (defibrillation) but it does have important implications for preventing further dysrhythmias.

Torsades Etiologies of PMVT
1. Acquired: due usually to drugs.  The list is long.  Also due to electrolyte abnormalities, especially hypoK and hypoMg.   Corrected QT interval (Bazett correction = QT divided by the square root of the preceding R-R interval in milliseconds) is usually great than 600 ms.  Torsades in acquired long QT is much more likely in bradycardia because the QT interval following a long pause is longer still.  Thus, torsades in acquired long QT is called "pause dependent": if there is a sinus beat after a long pause (which creates a longer QT interval), then an early PVC ("early afterdepolarization," EAD) is much more likely to occur during repolarization and to initiate torsades.  The usual sequence is: sinus beat, then early PVC, then a long pause because the PVC was early, which then results in a particularly long QT, then another PVC with "R on T" that initiates torsades.

2. Congenital, especially Congenital Long QT Syndrome.   Unstable PMVT due to congenital long QT is much more rare.  (In 26 years of EM and 125,000 patients, I have never seen a case of torsade PMVT due to congenital long QT).  Congenital causes of torsade include "catecholaminergic PMVT," in which there is no visible QT lengthening on the 12-lead, but it is believed to have a similar etiology.   Preventive therapy of Congenital long QT includes use of beta blockers (same with catecholaminergic PMVT, as in both of these, beta stimulation provokes torsade); this is in distinction to acquired long QT, which may be treated with beta stimulation (isopreterenol)

I have not found any recommendations to use beta blockers for acute management of torsade in this group, but it is certain that, in contrast to acquired long QT, isoproterenol should never be used.  It seems that most symptomatic patients with congenital long QT present after syncope, or resuscitated v fib, and rarely present with continuing torsade or instability.  Thus, the management of these patients is primarily recognition and prevention of future syncope and sudden cardiac death, usually with an implantable debribrillator in addition to beta blockers.  Torsades from Congenital long QT can be induced by use of QT prolonging drugs.


Non-Torsade Etiologies of PMVT
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
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
3. Correction of hypoK, even to slightly supranormal levels
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)
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 torsade 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 QTJust 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.  Propranolol and Nadolol are the best long term beta blockers for congenital long QT and the beta 1 selective metoprolol is not very effective.  Whether this is due to the beta selectivity is not clear to me.

Here is a fascinating case of congenital Long QT with Torsade. There is a great discussion of the role and function of beta blockade in congenital long QT.

Therapy of Acute Non-Torsade PMVT: Similar to Monomorphic VT
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

Back to our Case
Cardioversion is indicated only when the patient is in torsade, and will only work temporarily, as the patient goes in and out of the rhythm. Prevention of further episodes is essential.

In this case, we only see a long QT on the PVCs, but not in the native RBBB beats.   Often the torsades is "pause-dependent" and can only be seen in a complex that follows a long pause.  There is no chest pain, and we do not have evidence of ischemia on the sinus ECG complexes.  For polymorphic VT to be due to ischemia, there is usually some unequivocal ECG findings of ischemia.  So all this is suggestive of torsades, but not diagnostic.   The patient was not on any known medication that lengthens the QT interval.  She has only a history of Graves disease and reports that she has been off all medications.

When not in VT, her BP is elevated at 190/80 with a palpable pulse of 90 and oxygen saturations of 99.

An initial K returned normal.   Mg level was unknown at this point.

At t = 12, 2 grams of IV Magnesium were given.
At t = 13 minutes, 150 mg of amiodarone was given
At t = 15 minutes, 100 mg of lidocaine was given

At t = 30 minutes, there was no improvement and esmolol bolus and drip were given.  [This would in fact be contraindicated for Torsades, but reasonable if this were ischemic PMVT.  Although a bedside cardiac ultrasound had poor contractility, suggesting Non-torsades PMVT, Torsades is much more likely without clear ischemia on the ECG.]   Isoproterenol should be given.

The cath lab was activated. Another 2 grams of IV Magnesium was given.

t = 64 minutes: K returns at 2.4 mEq/L (initial value was mistaken).   This suggests Torsade even more strongly.  KCl given in central line.  Amiodarone drip started.  Rectal aspirin given.

t = 79 minutes: Procainamide 1500 mg over 2 minutes given.  (Procainamide may be useful in Non-torsade PMVT, but is likely to lengthen the QT and make Torsades more unstable.  It also is a strong negative inotrope and could be hazardous with poor LV function.)

t = 97 minutes: patient taken to cath lab:

The patient was taken to the cath lab and a pacer was placed.  The rhythm was captured with overdrive pacing and then slowed.  There was diffuse coronary disease, but no culprit lesion (no acute coronary syndrome).  Troponin was negative.

It was found that the patient was on methadone and was methadone toxic.  It is one of the many medications that causes a long QT.  This was Torsade de Pointes due to long QT due to methadone and hypokalemia.

Here is the 12-lead during pacing:
During Pacing

Here is another with the pacer turned off, the next day:
Sinus with RBBB and very long QT

And then on the fourth day:

T-wave inversions, QT still long

Because of the extraordinarily long half life of methadone, it took days for the QT to shorten.  Ultimately, the patient did well.

6 comments:

  1. Thanks for the interesting case and the recommendations on what to do in this difficult scenario.

    Two questions for you:

    1) I am confused about this from the post:
    "An initial K returned normal. This suggests Torsade even more strongly."

    Since hypokalemia is one cause of acquired long QT and therefore torsades, shouldn't a normal K be a piece of information against torsade? The true K value (2.4) which returned later would be the value that is suggestive of torsade. Or am I confused about something?

    2) When you have a patient with PMVT and it is not immediately obvious whether it is torsades or non-torsades, do you think it would be wise to go ahead and give say 2 grams of Mg even without having a Mg level back yet?

    ReplyDelete
    Replies
    1. Pendell,

      1) Ouch. That was a misprint that was left over from editing and I didn't catch it. I will fix it. It is the K of 2.4 that "suggests Torsades even more strongly."
      2) Yes, Mg no matter what. and correction of K no matter what.

      Steve

      Delete
  2. Very interesting case.

    In ecg no 3 from top there is 2-3mm st depression in leads v2-v4. For me it suggests IHD and points towards ischemic origin VT!!

    ReplyDelete
    Replies
    1. It is a good observation. However, this is RBBB, and one expects some proportionally discordant ST depression in right precordial leads. Since the R' wave in V2 and V3 is so large, I don't think the ST depression is excessive.

      Delete
  3. Great case! I think it looks very suggestive of IHD with ischaemia present in numerous leads. It also looks like Torsades from the 12 lead by the distinctive twisting of the points seen in the first 12 lead.

    ReplyDelete
    Replies
    1. Yes, it is tricky because it was not due to IHD, rather to methadone long QT!

      Delete

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