What's Wobble in EP Study

In electrophysiology (EP) study), the term "wobble" usually refers to:

👉 Variation in the cycle length of a tachycardia from beat to beat — especially during AV nodal reentrant tachycardia (AVNRT) or other reentrant arrhythmias.

In reentrant circuits, the conduction time around the circuit may fluctuate slightly due to changes in refractoriness or conduction velocity.

This produces small irregularity in the tachycardia cycle length (not perfectly fixed as in atrial flutter).

On intracardiac recordings, this is seen as beat-to-beat variation in interval timing (wobbling).

🔹 Clinical importance:

Helps differentiate reentrant tachycardias (which may “wobble”) from automatic tachycardias (which are usually more regular).

In AV nodal physiology, wobble of the AH interval or tachycardia cycle length during induction/termination gives clues to mechanism.

🔹 Example 1: AH interval wobble in AVNRT

During AV nodal reentrant tachycardia, the conduction through the AV node (AH interval) can vary slightly beat-to-beat.

Suppose AH = 120 ms on one beat, then 130 ms, then 125 ms → this variation is wobble.

On the intracardiac recording:

A → H interval doesn’t stay flat.

But H → V interval remains constant.

This supports reentry via AV node rather than automatic focus.

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🔹 Example 2: Tachycardia cycle length wobble

A patient has SVT at ~350 ms cycle length.

You measure: 348 ms → 354 ms → 349 ms → 352 ms.

That small, irregular “breathing” of cycle length = wobble.

It suggests a reentrant mechanism (AVNRT or accessory pathway) rather than atrial tachycardia (which tends to be more stable if automatic).

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🔹 Example 3: Why flutter is “fixed” and doesn’t wobble

Atrial flutter circuit is large and anatomical (cavo-tricuspid isthmus).

Cycle length stays very regular (e.g., exactly 240 ms each beat).

No wobble → favors macroreentry like flutter.

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✅ Take-home pearl:

Wobble = small beat-to-beat variability in conduction intervals or tachycardia cycle length on EP tracings.

Supports reentry as mechanism.

Absent wobble (very fixed cycle length) → favors automatic tachycardia or atrial flutter.

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