EM Notes – Ventricular Tachycardia

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General

  1. Usually due to re-entrant circuits or increased automaticity.

Monomorphic

  1. Causes: Mostly structural/IHD, but also in HOCM, MVP, drug toxicity (dig, Class I, sympathomimetics)

Features

  1. Historical risk factors: Age>35, active angina, previous MI
  2. Clinical: Often ↓BP, JVP canon a waves, variable S1 intensity
  3. ECG criteria: ≥3 consecutive ventricular beats at >100bpm (usually >130)
  4. Differentiation from SVT + abe’rrant conduction (BBB) [often difficult].
    1. QRS>140ms (100ms in children)
    2. AV dissociation (P and QRS complexes at different rates)
    3. Absence of typical RBBB or LBBB morphology
    4. Fusion beats (transmitted atrial beat superimposed on ventricular beat)
    5. Capture beats (isolated transmitted atrial complex).
    6. Concordance of chest lead QRS complexes (all pos [R] or all neg [QS] complexes)
    7. Axis constant – often >40° different from SR. Typically -90 to -180° (“northwest”)
    8. Brugada’s sign – time from the onset of R wave to nadir of S-wave is >100ms
    9. Josephson’s sign – Notching near the nadir of the descending limb of the S-wave
    10. V1-2 RSr’ complexes with a taller left rabbit ear (in RBBB the right ear is taller).
    11. No change with adenosine (but not 100% reliable)
  5. Vereckei Criteria – aVR only (VT if any yes answer):
    1. Is there an initial R wave?
    2. Is there a r or q wave > 40 msec (1 small box width)?
    3. Is there a notch on the descending limb of a negative QRS complex?
    4. Measure the voltage change in the first (vi) and last 40 msec (vt). Is vi / vt < 1?

Mx: If in doubt treat as VT (more common and more serious)

  1. If pulseless → Rx as for VF cardiac arrest
  2. If sev CP, ↓BP or APO+ → synch DC cardioversion (100J mono or 50J biphasic) 90% success.
  3. Pharmacological ± cardioversion if unsuccessful
    1. Procainamide 25-50mg/min IV until VT ends, ↓BP, ↑QRS>50%, or 17mg/kg max reached. 75% success. Maint. dose 1-4mg/min. NB: -ve ionotrope so avoid in ACS/CCF & if ↑QTc. OR
    2. Sotalol 1.5mg/kg IV over 5mins if BP & QTc ok. 65% success. OR
    3. Amiodarone 150mg IV over 5-10 min. 30% success. Can repeat.Then 1mg/min for 6h OR
    4. Lignocaine 100mg IV 20% success but least toxic. 30% success if get 2nd bolus 50mg IV
  4. Overdrive pacing

Polymorphic – Beat to beat QRS morphology variations.

Torsade de pointes –

  1. Subclass of polymorphic VT where ↑QTc (usually>500ms), variable axis. More common in F>M, CCF, bradycardia, digoxin.
  2. Causes of ↑QTc
    1. Electrolytes (↓Mg2+, ↓Ca2+, ↓K+),
    2. Heart disease (CM, CCF, IHD, 3° HB, HT),
    3. Drugs (Na channel blockers [e.g. phenothiazines, carbamazepine, class I & III antiarrhythmics], Li+, OP, quinolones, terfenadine, methadone,ondansetron[if ↓Mg2+ or ↓K+]),
    4. Congenital (Romano-Ward [A.Dom], Lange-Jervil-Nielsen [A.Rec, deafness]),
    5. ↑ICP (e.g. SAH),
    6. Hypothermia,
    7. ACS
  3. Mx:
    1. DC cardioversion if unstable,
    2. keep K+ 4.5-5.0,
    3. MgSO4 2g bolus,
    4. Ca2+ if hypoCa,
    5. ↑HR (from Rautaharju’s formula: QT = 656/[1+(HR/100)]) with overdrive pacing or isoprenaline (acquired ↑QTc only),
    6. BB (cong ↑QTc only).
    7. Also atropine if OP toxic, sodium bicarbonate for TCA

Fascicular Tachycardia

  1. Rare.
  2. Orig. from post. fascicle.
  3. Mimics SVT with aberrant conduction QRS 110-140ms, RBBB+LAD(post.fasc) or +RAD (ant.fasc).
  4. Responds to CCB not adenosine.