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aVR Algorithm (Vereckei)

Vereckei aVR algorithm (ventricular tachycardia vs. SVT with aberrant conduction)

aVR Algorithm

• Differs between wide-complex tachycardia
• Distinguishes between ventricular tachycardia and Aberrant Supraventricular Tachycardia (SVT)
• Does not differentiate Preexcitation SVT (Antidromic AVRT)
• It is very simple and quick
• Because you only assess the aVR lead on the ECG
• If the QRS (in aVR) is positive, it indicates ventricular tachycardia

Wide-Complex Tachycardia

• aVR algorithm differentiates the mechanism of wide-complex tachycardia
• Distinguishes between ventricular tachycardia and Aberrant SVT (but not from Preexcitation SVT)
• The only algorithm that differentiates between VT and Preexcitation SVT is the Brugada-Stuerer algorithm

aVR Algorithm (Evaluates only the aVR Lead)

• 1. Initial R wave?
• If the initial R wave is dominant in aVR, it indicates ventricular tachycardia
• Ectopic focus is in the apex region, and the vector points toward the aVR lead
• 2. Initial r(q) > 40ms
• If the ventricles are depolarized through the conduction system (in SVT)
• Then they are depolarized rapidly and the initial part of the QRS complex r(q) will be narrow < 40ms
• If the ventricles are depolarized through the myocardium from an ectopic focus (in VT)
• Then they are depolarized slowly and the initial part of the QRS complex r(q) will be wide > 40ms
• 3. Notches in the descending part?
• If the ectopic focus is in the base region, then the vector points away from aVR (QRS in aVR is negative)
• VT almost always occurs in a structurally altered heart
• and the impulse gets "caught" during depolarization (e.g., bypasses a scar from a myocardial infarction)
• Therefore, notches occur in the initial part of the QRS complex (during depolarization) (Josephson's sign)
• 4. V_i/V_t ≤ 1
• Evaluates the propagation speed of the impulse at the beginning and end of the QRS
• In VT, the impulse spreads slowly at the beginning of the QRS
• because it spreads through the myocardium and not through the conduction system as in SVT

Wide-Complex Tachycardia

• The ectopic focus is located in the base, and the resulting vector points away from the aVR lead
• aVR Algorithm
• 1. Initial R wave (aVR) - NO
• If VT is not diagnosed in the 1st step, the subsequent steps of the algorithm become more complex
• 2. Initial r(q) > 40ms - YES
• This indicates ventricular tachycardia (VT)

Depolarization in Aberrant SVT

• In SVT, the ventricles are depolarized
• Through the conduction system, not through the myocardium
• Depolarization through the conduction system is fast
• Therefore, the beginning of the QRS is steeper
• Compared to depolarization through the myocardium in VT
• The beginning of the QRS is steep even in SVT with bundle branch block
• Because one ventricle is depolarized quickly
• Through the intact bundle branch

• V_i = 1mm (A: the height of the curve in 40ms is 1mm)
• V_t = 3mm (B: the height of the curve in 40ms is 3mm)
• V_i/V_t (1/3 = 0.33) ≤ 1, indicating ventricular tachycardia
  
  
• According to the given ECG curve, using the aVR algorithm
• You would diagnose VT already in the 2nd step - initial Q width is > 40ms (80ms)

Wide-Complex Tachycardia

• QRS Duration: 0.2s
• Heart Rate 160/min.
• aVR Algorithm
• Condition 1: Is there an initial R (aVR) - YES
• It is ventricular tachycardia

Wide-Complex Tachycardia

• QRS Duration: 0.14s
• Heart Rate 212/min.
• aVR Algorithm
• Condition 1: Is there an initial R (aVR) - NO
• Condition 2: Initial r(q) > 40ms - NO
• Condition 3: Notches on the descending limb? - NO
• Condition 4: V_i/V_t ≤ 1 - NO
• It is SVT with RBBB (Specifically, AVNRT with RBBB)
• Typical Image of RBBB (In V1, rsR' - right bunny ear is larger)