09. Wide Complex Tachycardia Differentiation Algorithms
The differentiation of Wide Complex Tachycardia (QRS duration $\ge 120\text{ ms}$) between Ventricular Tachycardia (VT, $\sim 80\%$) and SVT with aberrancy or pre-excitation is a critical clinical skill.
1. Classical International Algorithms
BRUGADA 4-STEP ALGORITHM
- Absence of an RS complex in ALL precordial leads (V1-V6)? ├─ YES ──> VENTRICULAR TACHYCARDIA (Concordance) └─ NO ──> Step 2: RS interval > 100 ms in any precordial lead? ├─ YES ──> VENTRICULAR TACHYCARDIA └─ NO ──> Step 3: Atrioventricular (AV) Dissociation present? ├─ YES ──> VENTRICULAR TACHYCARDIA └─ NO ──> Step 4: Morphology criteria met in V1/V2 and V6? ├─ YES ──> VENTRICULAR TACHYCARDIA └─ NO ──> SVT with Aberrancy
2. The Vereckei aVR Algorithm (Simplified & Highly Accurate)
Examines Lead aVR only in four sequential steps:
- Initial R wave in aVR? $\to$ VT.
- Initial r or q wave width $>40\text{ ms}$ in aVR? $\to$ VT.
- Notching on the descending limb of a negative QRS in aVR? $\to$ VT.
- Ventricular Activation Velocity Ratio ($v_i/v_t \le 1$)? $\to$ VT.
- ($v_i$: voltage change in first $40\text{ ms}$; $v_t$: voltage change in last $40\text{ ms}$).
3. Pava / Santos Lead II R-Wave Peak Time (RWPT)
- Measure the duration from the onset of the QRS complex to the peak of the R wave in Lead II.
- RWPT $\ge 50\text{ ms} \implies$ Ventricular Tachycardia (Sensitivity $93\%$, Specificity $99\%$).
4. Pathognomonic Physical & Electrocardiographic Hallmarks
- AV Dissociation: Independent P waves marching through wide QRS complexes.
- Capture Beats: A completely normal, narrow QRS occurring during WCT.
- Fusion Beats (Dressler Beats): Hybrid morphology beat confirming two simultaneous activation wavefronts.
- Josephson Sign: Notching near the nadir of the S wave in precordial leads.
- Brugada Sign: Distance from onset of QRS to nadir of S wave $>100\text{ ms}$.