Negative HV Interval in EP study - Differentials

 

⚡ Negative HV Interval in EP Study: Understanding the Differentials

A negative HV interval during an electrophysiology (EP) study is an unusual and clinically important finding. In a normal heart, the His-Purkinje system conducts impulses from the His bundle → ventricles, producing a positive HV interval (typically 35–55 ms).

When the HV interval becomes negative, it means the ventricular electrogram precedes the His bundle signal, suggesting ventricular activation is occurring outside the normal His–Purkinje sequence.

This phenomenon strongly indicates the presence of pre-excitation, accessory pathways, or non-physiological retrograde activation patterns. Correct interpretation is crucial because it helps identify arrhythmia mechanisms, particularly in wide-complex tachycardias.

---

🔍 What Is a Negative HV Interval?

Normal: His deflection → ventricular activation (HV positive).

Negative HV: Ventricular activation occurs before His activation.

This indicates that ventricular activation is not dependent on the His-Purkinje system, but instead uses an accessory pathway or ventricular myocardium to activate early.

---

🩺 Differentials of a Negative HV Interval

Below are the established EP differentials when a negative HV interval is observed.

---

1. Antidromic AV Reentrant Tachycardia (AVRT)

(Using an Accessory Pathway for Anterograde Conduction)

In antidromic AVRT, the electrical impulse travels:

Atria → Accessory Pathway → Ventricles → AV Node/His for retrograde return

Because the ventricle activates before the His bundle is activated retrogradely, the HV interval becomes negative.

When seen?

WPW patients during wide-complex tachycardia

Pre-excited tachycardias with broad QRS

Especially in right-sided accessory pathways

---

2. Pre-Excited Atrial Fibrillation (AF with WPW)

During AF with WPW, extremely rapid atrial impulses conduct directly to the ventricles through the accessory pathway.

This leads to:

Short or negative HV,

Very irregular, rapid, wide QRS complexes,

High risk of degeneration to VF.

Negative HV is due to ventricular activation occurring through the accessory pathway before the His system engages.

---

3. Fasciculoventricular Pathway (FVP)

(Rare benign accessory pathway)

FVPs connect the fascicles (His bundle or bundle branches) to the ventricular myocardium.

They cause:

Short or negative HV,

Minimal pre-excitation on ECG,

No participation in tachycardia circuits.

When pacing, the local ventricular activation may precede His activity → negative HV phenomenon.

---

4. Nodofascicular or Nodoventricular Pathways (NF / NV Pathways)

These “Mahaim-like” pathways arise from:

AV node → ventricle

or

AV node → fascicle.

Because they bypass part (or all) of the His–Purkinje system, ventricular activation may precede His bundle activation.

Seen in:

Mahaim-mediated tachycardia

Wide QRS tachycardias with LBBB-like morphology

Adenosine-sensitive pre-excited tachycardias

---

5. Ventricular Tachycardia with His Activation by Retrograde Conduction

In VT, the ventricle is the arrhythmia source.

If retrograde conduction to the His bundle occurs:

➡ Ventricle activates first,

➡ His activation is delayed and retrograde,

➡ HV becomes negative.

Clues:

AV dissociation

Capture or fusion beats

Broad, stable QRS morphology

His activation follows the QRS, not precedes it

This is a key differential when distinguishing VT from antidromic AVRT.

---

6. His Recording Artifact or Misinterpretation

Technical errors can falsely appear as negative HV:

Far-field His signals mistaken as near-field

Incorrect catheter position

Noise or double potentials

Poor filtering

Always confirm with:

His proximal/distal signals

Catheter repositioning

Fluoroscopy/ICE guidance

---

🧠 How to Approach a Negative HV Interval Clinically

1. Confirm the signal

Ensure His catheter is correctly positioned

Rule out artifact

Compare His local EGM across poles

2. Determine rhythm mechanism

Wide QRS → consider VT or antidromic AVRT

Irregular wide QRS → suspect AF with WPW

LBBB pattern tachycardia → consider Mahaim/NF pathway

3. Map earliest ventricular activation

If earliest activation = accessory pathway site → AVRT

If earliest = ventricular myocardium (not pathway) → VT

4. Use pacing maneuvers

Adenosine: may terminate Mahaim tachycardia

Para-Hisian pacing: helps differentiate AV nodal from extranodal pathways

Decremental conduction: suggests Mahaim-like fibers

---

📌 Summary Table

Differential Key Feature Leading to Negative HV

Antidromic AVRT Ventricle activates first via AP → His retrograde

Pre-excited AF Ventricular activation via AP bypasses His

Fasciculoventricular Pathway Fascicle → ventricle shortcut eliminates HV delay

Nodofascicular/Nodoventricular Pathway AV node/fascicles directly to ventricle

Ventricular Tachycardia Ventricular origin → retrograde His activation

Technical Artifact Misinterpreted His potentials

---

⭐ Key Takeaways

Negative HV interval is never normal and always indicates activation outside the usual His-Purkinje system.

Most common mechanisms: antidromic AVRT, pre-excited AF, and VT with retrograde His activation.

Rare mechanisms include FVP, NF/NV pathways, and Mahaim fibers.

Always rule out signal artifact before concluding pathology.

Accurate interpretation prevents misdiagnosis of VT vs AVRT, which is critical for management.