🫀 Mirza's Cardiology Notes

Wide-Complex Tachycardia

3 min read

Approach to WCT

  1. How does the QRS look in V1?
    1. i.e. is the terminal part positive or negative?
  2. Do you have marching QRS complexes in a wide complex rhythm?
    1. If so, that’s artifact.
  3. Look for VA dissociation, i.e. is the V faster than the A?
    1. In other words, do you have more QRS complexes than the P waves? If so, then that’s VT.
  4. If you cannot identify clear P waves, then the next step is to look at QRS morphology to ask the question, “is it physiologically possible to see such a QRS complex?”
    1. axis
      1. aVR with tall R wave (northwest axis)
    2. precordial transition
      1. positive or negative concordance
    3. septal activation (look for unexpected Q waves in V1 if RBBB-like or in V6 if LBBB-like)
      1. if patient has a RBBB-like morphology (terminal QRS is +) and it is aberrancy, the septum should be activated from L → R. ∴ physiologically, you would not expect a Q wave in V1 (or mirror image R wave in V6)
      2. if you have LBBB-like morphology, the septum should be activated from R → L with aberrancy, so it is not physiologically possible to see Q waves in V6
    4. initial versus terminal slope
      1. notch (Josephson’s sign) in predominantly negative QRS (V1 with LBBB-like morphology)
      2. initial slower than terminal → VT
        1. In VT, the initial part is going to be slow and the terminal portion will be fast as as it engages the His-Purkinje system
      3. initial faster than terminal → SVT
        1. with SVT, the unblocked bundle is going to be fast → the initial is fast and the terminal is slow

Differential Diagnosis

  • DDx
    • Ventricular Tachycardia (VT) (in 80% of cases)
      • LV Origin: typically RBBB-like morphology
      • RV Origin: typically LBBB-like morphology
    • pre-excited Supraventricular Tachycardia (SVT)
    • Supraventricular Tachycardia (SVT) with aberrancy (abnormal intraventricular conduction)
      • Dx can confidently be made if a baseline BBB is present and the tachycardia has the same morphology as this baseline block
      • Typically with aberrancy, you will have RBBB-like morphology with QRS width <140 ms or LBBB-like morphology with QRS <160 ms.
    • ventricular paced rhythm
    • drug- and electrolyte-induced QRS widening

  • Steps to evaluate and manage
    • Assess vitals
    • Assess clinical hx: CAD, COPD, etc.
    • If HD stable → 12 lead EKG, vagal maneuvers/adenosine w/ the paper running!
    • If HD unstable → ACLS protocol; Tx reversible causes
      • urgent cardioversion should be done with procedural sedation when feasible
        • fentanyl 50 or 2 of midazolam (usually work well)
    • If WCT terminates w/ adenosine → Tx as SVT
    • If WCT persists w/ adenosine and DDx still unclear → operate as if VT
    • Amio generally most effective Tx for recurrent/refractory WCT, particularly VT
    • If WCT d/t function over pacemaker → apply magnet over ppm → makes the pacemaker asynchronous and terminates ppm-related tachy

AV Dissociation Clues

P waves buried in QRS complexes may cause some QRS complexes to appear “notched.” Also, be on the look out for variable T wave morphology. This can be a hint to the presence of P waves that are dissociated from QRS/T and falling variably over some T waves.

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