What are the key ECG (electrocardiogram) features that distinguish Ventricular Tachycardia (VT) from Supraventricular Tachycardia (SVT) with aberrancy?

Key ECG Features to Distinguish VT from SVT with Aberrancy

The most reliable ECG features that distinguish Ventricular Tachycardia (VT) from Supraventricular Tachycardia (SVT) with aberrancy include AV dissociation, fusion complexes, and specific QRS morphology criteria such as RS interval >100 ms in any precordial lead. 1

Primary Diagnostic Criteria

AV Dissociation

• Presence of AV dissociation (ventricular rate faster than atrial rate) is pathognomonic for VT 1
• Look for independent P waves that bear no relationship to the QRS complexes
• Fusion complexes (merger between conducted sinus impulses and ventricular depolarization) are also pathognomonic of VT 1

QRS Morphology (Brugada Criteria)

• Lack of any RS complexes in precordial leads (V1-V6) indicates VT 1
• RS interval >100 ms (onset of R wave to nadir of S wave) in any precordial lead strongly suggests VT 1

QRS in Lead aVR (Vereckei Algorithm)

• Initial R wave in aVR suggests VT
• Initial R or Q wave >40 ms in aVR suggests VT
• Notch on descending limb at onset of predominantly negative QRS suggests VT 1

Secondary Diagnostic Features

QRS Concordance

• QRS complexes that are all positive or all negative across precordial leads (concordant pattern) strongly suggest VT 1

R-Wave Peak Time

• R-wave peak time ≥50 ms in lead II suggests VT 1

QRS Width

• QRS width >140 ms with right bundle branch block pattern or >160 ms with left bundle branch block pattern suggests VT 2
• However, QRS width alone is not definitive, as some VTs (especially in infants) may have narrower QRS complexes 1

Clinical Context Considerations

SVT with Aberrancy Features

• QRS in tachycardia identical to sinus rhythm suggests SVT 1
• In SVT with aberrancy, after the first 10-20 beats, the QRS is almost always the same as in sinus rhythm 1
• SVT typically has extremely regular R-R intervals after the first 10-20 beats 1

Rate Considerations

• SVT typically has rates of 260-300 bpm in infants, while sinus tachycardia is almost always <230 bpm 1
• VT can have rates of 200-500 bpm with slight variation over several beats 1

Diagnostic Pitfalls

1. Stable Vital Signs: Do not rely on hemodynamic stability to distinguish SVT from VT, as stable vital signs can occur in both conditions 1, 2

2. Misdiagnosis Risk: When in doubt, treat wide-complex tachycardia as VT, especially before administering calcium channel blockers, which can cause hemodynamic collapse in VT 1, 2

3. Atypical Aberrancy: SVT with atypical aberrancy can mimic both monomorphic and polymorphic VT, sometimes requiring electrophysiology studies for definitive diagnosis 3

4. Pre-existing Bundle Branch Block: SVT with pre-existing bundle branch block can be mistaken for VT 1

Algorithmic Approach to Wide-Complex Tachycardia

1. Assess QRS morphology in V1-V6:

   • If no RS complexes present → VT
   • If RS interval >100 ms → VT

2. Examine lead aVR:

   • Initial R wave or Q wave >40 ms → VT
   • Notch on descending limb → VT

3. Look for AV dissociation:

   • Independent P waves or fusion beats → VT

4. Check precordial concordance:

   • All positive or all negative QRS complexes → VT

5. Compare with sinus rhythm ECG:

   • Identical QRS morphology → likely SVT

By systematically applying these criteria, clinicians can more accurately distinguish VT from SVT with aberrancy, leading to appropriate treatment decisions and improved patient outcomes.