Long QT and TdP

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Long QT and TdP

• Morning Report
• Elias Hanna, LSU Cardiology

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(No Transcript)
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• Markedly prolonged QT (QTc700 ms)
• Wide and ample T waves in V2-V4, deep T wave
  inversion in the inferior leads
• T wave alternans

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Arrows of different colors point to the T wave
of alternating morphology every other beat,
called T wave alternans. T wave alternans may be
seen in a subgroup of patients with prolonged QT
and implies a very heterogeneous repolarization
and a more imminent risk of TdP. More typically
seen in congenital long QT syndrome
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How to we define long QT?

• QTgt ½ RR
• Corrected QT (QTc)gt450 ms in M, 460 ms in F

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How to calculate corrected QT?

• Corrected QT means QT corrected for heart rate.
  QT normally decreases at faster heart rate. Thus,
  while QT is normally lt460 ms at a rate of 60
  bpm, a lower cutoff should be used for a rate of
  100 bpm
• How to calculate corrected QT
• 1-QTc QT/vRR ( RR in sec, not msec!!)
• e.g QT of 400 msec at a heart rate of 100
  bpm
• -At a rate of 100 bpm, RR interval is 600
  msec0.6 sec? QTc400/v0.6515 msec

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• 2-Another quick method QTc is the patients QT
  had the heart rate been 60 bpm. Normally, QT ? 20
  ms for every 10 beat ? in rate, and
  ? 20 ms for every 10 beat ? in rate
• ? to calculate QTc, i.e QT at the rate of 60
  for this pt, add 20 ms for every 10 beats above
  60
• ? if QT is 400 ms at a rate of 100, then QTc
  400 (4x20)480 ms
• (the 2 methods may yield slightly different
  results)

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Differential dx of long QT

• Electrolytes (?K, ?Mg, ? Ca) (other
  hypothyroidism)
• Drugs (antiarrhythmics class I, III macrolide or
  quinolone antibiotics antipsychotics)
• Ischemia
• Congenital long QT syndrome (LQT 1,2,3)

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In this case

• The pt had low K (3.0) and Mg (0.7).
• However, the shape of ST segment and T wave,
  particularly the fact that T wave is wide and
  ample T, does not fit with hypokalemia or
  hypocalcemia (see next slide for electrolyte
  shapes)
• In light of the ST/T shape, K and Mg
  abnormalities are not the sole cause of QT
  prolongation but rather an exacerbating factor
• The pt likely has ischemia or congenital long QT
  syndrome as underlying etiology.
• In this case, coronary angio did not show
  any CAD, and QT interval strikingly ? but
  remained prolonged (480 msec) after correction of
  lytes abnormlities? congenital long QT syndrome
  is the underlying cause of his QT prolongation

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Typical ST/T shape in hypokalemia
ST depression with prominent T (actually U) and
prolonged QT when Klt2.5-3
Flat T with K3
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Hypocalcemia Long QT that is due to a long ST
segment, which is different from long QT due to
congenital long QT syndrome, drugs, or
hypokalemia. T wave is not wide, there is no T
wave abnormality.
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Hyperkalemia
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• The ST/T shape in this case is not typical of
  electrolyte abnormalities, but QT prolongation is
  certainly exacerbated by these electrolyte
  abnormalities

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Pt goes into this rhythm
Torsades de pointe (polymorphic VT with changing
QRS polarity,
with a long baseline QTc)
sinus
VF (disorganized and chaotic rhythm, QRS almost
vanishes every now and then)
Defibrillation
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Polymorphic VT vs. TdP

• Polymorphic VT with changing polarity of the QRS
  complexes is not necessarily torsades de point
  (TdP).
• In order to say TdP, you need to have
• (1)polymorphic VT as in the prior slide
• (2) long baseline QT on the ECG obtained
  before or after TdP
• If you have TdP but normal QT, then the rhythm is
  called polymorphic VT not TdP
• The tx of TdP is different from polymorphic VT

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• Polymorphic VT is usually an ischemic rhythm and
  is treated with shock, emergent cath/PCI, and
  amiodarone

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• TdP is given 3 therapies
• 1-Defibrillation
• 2-Magnesium 2 g IV (regardless of Mg level)
  start correcting K
• 3-Temporary pacing after the run of TdP has
  resolved. Temporary pacing prevents TdP from
  recurring
• Usually, TdP occurs in a pt with prolonged
  QT who is also bradycardic. Bradycardia further
  prolongs QT and furthers disperses repolarization
  delays across the myocardium. Bradycardia is a
  major trigger of TdP, particularly TdP in
  patients with acquired long QT. Pacing to a rate
  of 80-100 bpm will prevent TdP recurrence.
• Pacing does not apply to our pt here
  because he is tachycardic. Congenital long QT, as
  opposed to acquired long QT, is often triggered
  by catecholamine surge and may be associated with
  tachycardia

No Amiodarone!!! Amiodarone prolongs QT