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

Differentiating VT from SVT with Aberrancy

Critical First Principle: Assume VT Until Proven Otherwise

When faced with a wide-complex tachycardia (QRS ≥120 ms), treat it as ventricular tachycardia unless you can definitively prove otherwise—administering verapamil or diltiazem for presumed SVT when the rhythm is actually VT can cause hemodynamic collapse or ventricular fibrillation. 1

Immediate Assessment Algorithm

Step 1: Assess Hemodynamic Stability

• Unstable patients (altered mental status, ischemic chest pain, acute heart failure, hypotension, or shock) require immediate synchronized cardioversion—diagnosis comes after stabilization 2
• Stable patients allow time for diagnostic evaluation 1, 2

Step 2: Obtain 12-Lead ECG During Tachycardia

• Record a 12-lead ECG while the patient is in tachycardia—this is essential for accurate diagnosis 1
• Compare with prior ECG in sinus rhythm if available 1

Diagnostic Criteria Favoring VT

High-Specificity Features (When Present, Diagnostic of VT)

AV Dissociation (present in only 30% of VT cases but pathognomonic when found):

• Independent atrial activity with ventricular rate faster than atrial rate 1
• Look for irregular cannon A waves in jugular venous pulse and variable intensity of first heart sound on physical exam 1
• Fusion or capture beats are pathognomonic for VT 1

QRS Width Criteria:

• QRS >140 ms with RBBB morphology strongly suggests VT 1
• QRS >160 ms with LBBB morphology strongly suggests VT 1
• Note: These criteria don't apply if patient has pre-existing bundle branch block or accessory pathway conduction 1

Concordance in Precordial Leads:

• All positive or all negative QRS deflections across V1-V6 indicates VT 1

Clinical History (High Positive Predictive Value)

History of myocardial infarction has >95% positive predictive value for VT 3

• History of congestive heart failure: >95% positive predictive value for VT 3
• Recent angina pectoris: >95% positive predictive value for VT 3
• Age >35 years: 85% positive predictive value for VT (92% sensitivity) 3

Features Suggesting SVT with Aberrancy

Lower Likelihood of VT When:

• Age ≤35 years (70% positive predictive value for SVT) 3
• No history of structural heart disease 3, 4
• QRS morphology identical to known pre-existing bundle branch block 1
• Response to vagal maneuvers or adenosine (see below) 1

Special Consideration: Pre-excitation

• In young adults/children, check for overt pre-excitation on sinus rhythm ECG 4
• Pre-excited tachycardias (antidromic AVRT, AF with WPW) show QRS generally wider than in sinus rhythm 1
• Never use AV nodal blocking agents (adenosine, calcium channel blockers, beta-blockers) in pre-excited atrial fibrillation—this can accelerate ventricular rate and cause ventricular fibrillation 1, 2

Diagnostic Maneuvers in Stable Patients

Adenosine as Diagnostic Tool

• Can be used for both diagnosis and treatment of regular monomorphic wide-complex tachycardia of uncertain origin 2
• Caution: Adenosine may precipitate VF in patients with coronary artery disease and can accelerate ventricular rate in pre-excited tachycardias 1
• Do not use adenosine for irregular or polymorphic wide-complex tachycardia 2
• Record 12-lead ECG during adenosine administration to capture response 1

Vagal Maneuvers

• Perform Valsalva maneuver (bearing down for 10-30 seconds at 30-40 mmHg pressure) or carotid sinus massage 1
• Effective only if AV node is part of reentrant circuit (will not terminate VT) 1
• Demonstration that P waves are not necessary for tachycardia maintenance strongly suggests VT 1

Management Based on Diagnosis

If VT Confirmed or Suspected:

• Amiodarone 150 mg IV over 10 minutes for stable VT 1, 2
• Avoid sotalol if QT interval is prolonged 2
• Immediate cardioversion for unstable patients 1, 2

If SVT with Aberrancy Confirmed:

• Adenosine 6 mg rapid IV push, followed by 12 mg if needed 1, 2
• Alternative: Non-dihydropyridine calcium channel blockers or beta-blockers 1

Critical Pitfalls to Avoid

• Never delay cardioversion in unstable patients while obtaining 12-lead ECG 2
• Never use verapamil or diltiazem for wide-complex tachycardia of uncertain origin—this is the most dangerous error 1
• Do not use multiple AV nodal blocking agents with overlapping half-lives (risk of profound bradycardia) 2
• Remember that stable vital signs do not distinguish SVT from VT—patients with VT can be hemodynamically stable 1
• In adults with structural heart disease, >80% of wide-complex tachycardias are VT—when in doubt, treat as VT 4