What are the MDN (Monophasic‑Dominant‑No‑RS) criteria for diagnosing ventricular tachycardia and how should ventricular tachycardia be managed?

MDN Criteria for Ventricular Tachycardia

What Are the MDN Criteria?

The MDN criteria do not appear in the provided evidence or established cardiology literature. You may be referring to alternative ECG algorithms for diagnosing ventricular tachycardia (VT), such as the Brugada criteria, Vereckei algorithm, or VT score. 1 The most clinically relevant and validated approaches for distinguishing VT from supraventricular tachycardia (SVT) with aberrancy are outlined below.

Definitive Diagnostic Criteria for VT

When evaluating wide QRS complex tachycardia (>120 ms), treat as VT unless proven otherwise—misdiagnosis can be life-threatening. 2, 3

Pathognomonic Features (100% Specific for VT)

• AV dissociation with ventricular rate faster than atrial rate is diagnostic of VT 1, 2, 3
• Fusion beats (combination of supraventricular and ventricular complexes) confirm VT 3
• Capture beats (intermittent normal QRS during wide complex tachycardia) prove VT 1

Highly Specific Criteria (>90% Specificity)

• Absence of RS complex in all precordial leads (V1-V6) has 92-99% specificity for VT 2, 4, 5
• RS interval >100 ms (onset of R wave to nadir of S wave) in any precordial lead strongly suggests VT 2, 3, 4
• Negative concordance (all QRS complexes negative in precordial leads) is diagnostic for VT 2
• Positive concordance (all QRS complexes positive in precordial leads) suggests VT or pre-excitation 1, 2

Lead-Specific Morphology Criteria

In lead aVR:

• Initial R wave in aVR suggests VT 2, 3
• Initial R or Q wave >40 ms in aVR indicates VT 3, 6

In lead II:

• R-wave peak time ≥50 ms suggests VT 3, 6

In leads V1-V2:

• Initial r wave >40 ms suggests VT 6, 7
• Notched S wave on downstroke in V1 or V2 indicates VT 7
• Duration >60 ms from QRS onset to nadir of S wave in V1/V2 suggests VT 7

QRS Width Criteria

• QRS >140 ms with RBBB pattern or >160 ms with LBBB pattern strongly suggests VT 2, 3
• QRS duration >120 ms is the basic threshold for wide complex tachycardia 1, 3

Simplified Diagnostic Algorithm

Step 1: Check for AV dissociation, fusion beats, or capture beats → If present, diagnose VT 1, 2, 3

Step 2: Look for absence of RS complex in all precordial leads → If absent, diagnose VT 2, 4, 5

Step 3: Measure RS interval in precordial leads → If >100 ms in any lead, diagnose VT 2, 3, 4

Step 4: Assess lead aVR morphology → Initial R wave or R/Q >40 ms suggests VT 3, 6, 8

Step 5: Apply Vereckei algorithm (Vi/Vt ratio) → Vi/Vt ≤1 suggests VT 8, 5

VT Score System (Alternative Approach)

A validated scoring system assigns points as follows 6:

• 1 point each for:

  • Initial dominant R wave in V1
  • Initial r >40 ms in V1 or V2
  • Notched S in V1
  • Initial R wave in aVR
  • Lead II R-wave peak time ≥50 ms
  • Absence of RS in V1-V6

• 2 points for:

  • AV dissociation (including fusion/capture beats)

≥3 points = firm diagnosis of VT 6

Critical Clinical Context

• History of myocardial infarction strongly suggests VT in wide complex tachycardia 2, 3
• QR complexes (indicating myocardial scar) are present in ~40% of post-MI VT 3
• Similar morphology between PVCs during sinus rhythm and tachycardia confirms VT 3

Management Approach

For hemodynamically unstable patients:

• Immediate DC cardioversion is the treatment of choice 2

For stable patients with presumed VT:

• IV procainamide, sotalol, or amiodarone may be used 2
• Adenosine can be used for stable, regular, monomorphic wide-QRS tachycardia for both diagnosis and treatment 2

Critical Safety Warning:

• Never give calcium channel blockers (verapamil/diltiazem) for wide complex tachycardia unless SVT is definitively proven—these agents may precipitate hemodynamic collapse in VT 2, 3
• When diagnosis is uncertain, always treat as VT 2, 3

Post-event management:

• Refer all patients to an arrhythmia specialist after successful termination of wide QRS-complex tachycardia of unknown etiology 2

Common Pitfalls to Avoid

• Hemodynamic stability does not exclude VT—younger patients may tolerate VT well 3, 9
• Pre-existing bundle branch block can complicate interpretation; compare tachycardia QRS to baseline ECG 1, 3
• Electrolyte abnormalities (especially hyperkalemia) can cause QRS widening mimicking VT 2, 3
• WCT algorithms have lower specificity (33-69%) in patients with pre-existing LBBB and heart failure—rely on specific individual criteria rather than complete algorithms in this population 5