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Pacing in tachycardia

HIS synchronous VPB / Zipes

What is ZIpes?

  • Zipes involves adding a paced VPB during tachycardia when the HIS is refractory.

  • This means that it is impossible for the VPB to have retrograde conduction up the AV node due to refractoriness.

  • If there is any change is the following A-A interval this demonstrated an extra circuit is present in the heart (accessory pathway)

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How to perform

  • Sensed extra with Ventricular stimulus faster rate than TCL

  • Cease when tachy terminates or V appears to be HIS synchronous

Confirming beat is HIS synchronous

  1. Ensure ventricular capture

  2. Measure H-H interval on beat prior to paced beat

  3. Drag caliper onset to His – prior to stimulus and lock in

  4. Measure how early pacing artefact is compared to caliper offset

  5. See if there is any effect in timing for the following atrial event

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Responses to Zipes

No change in A-A

  • consistent with AVNRT

  • AVRT is not ruled out

​

Tachycardia termination with no A

  • active AVRT pathway

​

Delay in A-A interval

  • active decremental AVRT pathway

​

A-A advancement

  • could be an active pathway or

  • a bystander pathway

*ventricular advancement/delay proves active pathway

​

Ventricular entrainment

How to perform

  • Paced 20-30ms faster than TCL in the ventricle until ~10 capture beats

-Pacing for too long or too fast may terminate tachycardia

-Pacing too slow will not capture the ventricle

Confirming entrainment

  1. Ensure there is ventricular capture

  2. Ensure the same tachycardia continues when coming off pacing

  3. Measure A-A interval on the last few beats to ensure A is entrained

  4. View response immediately after

  5. Measure the 1st return atrial event to ensure there is no pseudo VAAV response

  6. Measure PPI-TCL by measuring stimulus artefact to return signal on paced catheter

  7. Measure Stim-A – VA by measuring stimulus-entrained A   & compare to tachycardia VA

  8. Look at the start of the entrainment and choose the 1st fully capture ventricular event

  9. Measure forward the A-A intervals until you see a AA interval that equals the ventricular entrainment rate

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Responses to Entrainment

Immediate response

  • VAV: nodal involvement (AVRT/AVNRT)

  • VAAV: atrial tachycardia (ensure is not pseudo VAAV)

​

Post pacing interval - tachcardia cylce length (PPI-TCL)

  • >115ms AVNRT

  • <115ms septal pathway

​

Stim A interval - VA interval

  • >85ms AVNRT

  • <85ms AVRT

​

Number of beats to entrain the atrium

  • 1 AVRT

  • >1 AVNRT

​

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Late & Early APBs

How to perform

  • Sensed extra with Atrial stimulus faster rate than TCL

  • Cease when tachy terminates, A appears to be HIS synchronous or risk of AF

Confirming late APBs

  1. Confirm there is atrial capture

  2. Measure H-H / V-V interval on beat prior to paced beat

  3. Ensure the immediate beat is not effected

  4. Measure the following H-H / V-V to see if there is any change in interval compared to the TCL

  5. If there is a change in VV, measure the VA interval and compare to Tc VA

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Confirming early APBs

  1. Confirm there is atrial capture

  2. Measure H-H interval on beat prior to paced beat

  3. Ensure the immediate beat is effected

  4. Observe the response after

  5. If tach continues, compare immediate VA to Tc VA

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Responses to APBs

Late APB

  • HV advanced

-consistent with AVNRT (if unchanged VA)​

-consistent with atrial tachycardia (if VA is unlinked)

-could still be junctional tc if slow pathway is present (not rules out)

​

  • HV delayed

-consistent with AVNRT (linked VA)​

consistent with atrial tachycardia (unlinked VA)

​

  • Tachycardia terminated

-consistent with AVNRT

​

  • No change

-consistent with junctional tachycardia​

​

Early APB

  • Tachycardia continues​

-consistent with junctional tachycardia​

-consistent with atrial tachycardia (if VA is not linked)

​

  • Tachycardia terminates

-consistent with AVNRT
(fast pathway interrupted for short VA tc, slow pathway interrupted for long VA tc)​

Atrial entrainment

How to perform

  • Paced 20-30ms faster than TCL in the atrium until ~10 capture beats

-Pacing for too long or too fast may terminate tachycardia

-Pacing too slow will not capture the atrium

Confirming entrainment

  1. Ensure there is atrial capture

  2. Ensure the same tachycardia continues when coming off pacing

  3. Measure V-V interval on the last few beats to ensure V is entrained

  4. View the morphology of the entrained V beats

  5. View response immediately after

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Responses to atrial entrainment

SVT

  • AVA response

  • No change in ventricular morphology

​

VT

  • AVVA​​

  • change in ventricular morphology

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