- Usually due to re-entrant circuits or increased automaticity.
- Causes: Mostly structural/IHD, but also in HOCM, MVP, drug toxicity (dig, Class I, sympathomimetics)
- Historical risk factors: Age>35, active angina, previous MI
- Clinical: Often ↓BP, JVP canon a waves, variable S1 intensity
- ECG criteria: ≥3 consecutive ventricular beats at >100bpm (usually >130)
- Differentiation from SVT + abe’rrant conduction (BBB) [often difficult].
- QRS>140ms (100ms in children)
- AV dissociation (P and QRS complexes at different rates)
- Absence of typical RBBB or LBBB morphology
- Fusion beats (transmitted atrial beat superimposed on ventricular beat)
- Capture beats (isolated transmitted atrial complex).
- Concordance of chest lead QRS complexes (all pos [R] or all neg [QS] complexes)
- Axis constant – often >40° different from SR. Typically -90 to -180° (“northwest”)
- Brugada’s sign – time from the onset of R wave to nadir of S-wave is >100ms
- Josephson’s sign – Notching near the nadir of the descending limb of the S-wave
- V1-2 RSr’ complexes with a taller left rabbit ear (in RBBB the right ear is taller).
- No change with adenosine (but not 100% reliable)
- Vereckei Criteria – aVR only (VT if any yes answer):
- Is there an initial R wave?
- Is there a r or q wave > 40 msec (1 small box width)?
- Is there a notch on the descending limb of a negative QRS complex?
- 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)
- If pulseless → Rx as for VF cardiac arrest
- If sev CP, ↓BP or APO+ → synch DC cardioversion (100J mono or 50J biphasic) 90% success.
- Pharmacological ± cardioversion if unsuccessful
- 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
- Sotalol 1.5mg/kg IV over 5mins if BP & QTc ok. 65% success. OR
- Amiodarone 150mg IV over 5-10 min. 30% success. Can repeat.Then 1mg/min for 6h OR
- Lignocaine 100mg IV 20% success but least toxic. 30% success if get 2nd bolus 50mg IV
- Overdrive pacing
Polymorphic – Beat to beat QRS morphology variations.
Torsade de pointes –
- Subclass of polymorphic VT where ↑QTc (usually>500ms), variable axis. More common in F>M, CCF, bradycardia, digoxin.
- Causes of ↑QTc
- Electrolytes (↓Mg2+, ↓Ca2+, ↓K+),
- Heart disease (CM, CCF, IHD, 3° HB, HT),
- Drugs (Na channel blockers [e.g. phenothiazines, carbamazepine, class I & III antiarrhythmics], Li+, OP, quinolones, terfenadine, methadone,ondansetron[if ↓Mg2+ or ↓K+]),
- Congenital (Romano-Ward [A.Dom], Lange-Jervil-Nielsen [A.Rec, deafness]),
- ↑ICP (e.g. SAH),
- DC cardioversion if unstable,
- keep K+ 4.5-5.0,
- MgSO4 2g bolus,
- Ca2+ if hypoCa,
- ↑HR (from Rautaharju’s formula: QT = 656/[1+(HR/100)]) with overdrive pacing or isoprenaline (acquired ↑QTc only),
- BB (cong ↑QTc only).
- Also atropine if OP toxic, sodium bicarbonate for TCA
- Orig. from post. fascicle.
- Mimics SVT with aberrant conduction QRS 110-140ms, RBBB+LAD(post.fasc) or +RAD (ant.fasc).
- Responds to CCB not adenosine.
VN:F [1.9.22_1171]EM Notes - Ventricular Tachycardia,