How do you differentiate and manage ventricular tachycardia (VT) versus supraventricular tachycardia (SVT) with aberrancy?

Differentiation and Management of VT vs SVT with Aberrancy

When faced with a wide QRS complex tachycardia, always treat as ventricular tachycardia (VT) if the diagnosis cannot be easily and definitively proven to be supraventricular tachycardia (SVT) with aberrancy. 1, 2

Diagnostic Differentiation

Key ECG Findings Suggesting VT:

• AV dissociation: The most diagnostic finding, with ventricular rate faster than atrial rate (visible in only 30% of VTs) 1
• Fusion complexes: Pathognomonic for VT 1
• QRS width: >140 ms with RBBB pattern or >160 ms with LBBB pattern 1, 2
• Concordance: All precordial leads showing either positive or negative deflections 1
• Lead II time to first peak >40 ms and lead aVR time to first peak >40 ms 3

Key Physical Examination Findings Suggesting VT:

• Irregular cannon A waves in jugular venous pulse
• Variability in loudness of first heart sound
• Variability in systolic blood pressure 1

Clinical History Factors Favoring VT:

• History of myocardial infarction (>95% predictive value)
• History of congestive heart failure (>95% predictive value)
• Recent angina pectoris (>95% predictive value)
• Age >35 years (85% predictive value) 4

Key ECG Findings Suggesting SVT with Aberrancy:

• Identifiable P waves preceding QRS complexes
• QRS morphology identical to that seen during sinus rhythm with bundle branch block
• Response to adenosine (termination or transient AV block revealing atrial activity) 1

Management Algorithm

1. Initial Assessment:

• Assess hemodynamic stability
• Obtain 12-lead ECG during tachycardia if possible without delaying treatment
• If hemodynamically unstable: immediate DC cardioversion regardless of diagnosis 1

2. If Hemodynamically Stable:

• If diagnosis is uncertain, treat as VT 1, 2
• Avoid calcium channel blockers (verapamil, diltiazem) in wide-complex tachycardia of uncertain origin as they may precipitate hemodynamic collapse in VT 1, 2

3. For Confirmed or Presumed VT:

• IV amiodarone: 150 mg over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min maintenance 5
• Consider DC cardioversion if medication fails
• For recurrent episodes, evaluate for underlying structural heart disease

4. For Confirmed SVT with Aberrancy:

• Vagal maneuvers (Valsalva, carotid massage)
• Adenosine: 6 mg rapid IV bolus, followed by 12 mg if needed
• Beta-blockers or calcium channel blockers (only if SVT is definitively diagnosed)
• Consider electrophysiology study and catheter ablation for recurrent episodes 6

Important Caveats

1. Diagnostic Pitfall: Stable vital signs do not differentiate between VT and SVT - both can present with hemodynamic stability 1

2. Treatment Risk: Administering calcium channel blockers to patients with VT can cause cardiovascular collapse 1, 2

3. Diagnostic Challenge: Up to 10% of wide-complex tachycardias defy differentiation even with all available criteria 7

4. Invasive Diagnosis: Electrophysiology study should be considered in recurrent cases of wide-complex tachycardia where diagnosis remains uncertain 6

5. Misdiagnosis Consequences: Patients with SVT with aberrancy are sometimes misdiagnosed with VT and unnecessarily receive ICDs; electrophysiology studies can prevent this 6

Remember that when in doubt about the diagnosis of a wide-complex tachycardia, the safest approach is to treat as VT until proven otherwise, as misdiagnosing VT as SVT with aberrancy carries greater risk than the reverse.