Week 8 CIED Follow-Up - EGM Analysis

Tachy EGMs

• Stored in device or printed using programmer

• Abnormal rhythms: sustained and nonsustained

• Determine if the device got it right

  • Inappropriate therapy inhibition/delivery

  • May require programming changes

  • Sensitivity must be 100%

  • Specificity should be as close to 100% as possible

Tachy EGM Analysis: Step 1

Orient yourself to the strip

• Channels:

  • Surface

  • Nearfield

  • Farfield

  • Markers/annotations

• Company/device

Tachy EGM Analysis: Step 2

Analyze and classify presenting and underlying (non-paced) rhythm as much as possible

• No pacing: normal rhythm analysis

  • Sinus node

  • AV node

  • Arrhythmias

• Pacing: paced rhythm analysis

  • Capture

  • Sensing

Tachy EGM Analysis: Step 3

Classify device activity

• Algorithms (mode switch)

• VT/VF detected

• Clinical or induced

• Discriminators

• Episodal pacing

• Therapy delivery

• Charge delivered/aborted

• EGM stored

Tachy EGM Analysis: Step 4

Conduct detailed left to right analysis of markers and IEGMs

First Component of Tachy Analysis

Evaluate detection

Confirm rhythm detected

Evaluate sensing

Assess discriminator function

Second Component of Tachy Analysis

Evaluate therapy

Determine success for type of therapy delivered

Shock: conversion, energy, charge time, impedance

Third Component of Tachy Analysis

Determine need for reprogramming

Other Tachy Information

• Patient history:

  • Indications

  • Arrhythmias

  • Medications

• Symptoms

• Episode details

Scatter Plots Tachy Analysis

Can tell a basic story

CRT EGMs

• CRT-P: pacing therapy only

• CRT-D: includes tachy therapy

• Goal of CRT: 100% BIV pacing to reverse remodel the heart

• Analyze EGMs to optimize therapy for non-responders

Gather Information CRT

• Patient history

• Tachy indication: CRT-D

• Reduced BIV pacing:

  • AF with RVR

  • Frequent PVCs

• Loss of capture:

  • Electrolyte imbalances

  • Medications

  • Diseases/procedures

• Device/leads

• Parameters/algorithms/diagnostics

CRT Strip

CRT orient yourself to the strip

BIV Capture

• Differentiate true BIV capture, RV only capture, LV only capture, RV anodal capture

• Compare morphologies:

  • Presenting rhythm

  • Underlying rhythm

  • RV only threshold

  • LV only threshold

CRT Capture on the Surface ECG

RV Capture:

Lead I: more positive

Lead III: more negative

LV Capture:

Lead I: more negative

Lead III: more positive

Example CRT Capture on the Surface ECG

• Example: BIV pacing, suspect loss of LV capture

  • Raise LV output

  • Lead I more negative, lead I!! more positive

  • LV was not capturing before

CRT LV EGM

• Loss of LV capture difficult to see on surface ECG

• Nearfield helps to differentiate intrinsic/paced

• Lost capture: delay between pacing and LV signal

  • No capture at all: LBBB

  • Only RV capture: cell to cell activation from RV lead

CRT Threshold Testing

• RV: same as other devices

• LV: additional considerations

  • Many pacing configurations

  • RV anodal capture

  • Phrenic nerve stimulation

CRT Phrenic Nerve Stimulation

• Output must be lower than PNS threshold

  • May require safety margin < 2:1

  • Can test different vectors instead

• PNS is positional

  • Different thresholds when sitting/standing/supine

  • Often discovered after implant

CRT Anodal Stimulation

• Depolarization caused by electrons returning to positively charged anode

• Higher threshold than cathodal capture

• RV leads:

  • Anode has larger surface area: anodal capture less likely

  • Close spacing of anode and cathode: anodal capture less significant

CRT Extended Bipolar Configuration

• LV pacing vector only on LV lead: anodal stimulation not a problem

• Extended bipolar:

  • Anode on RV lead (ring or coil)

  • LV thresholds higher than RV thresholds

  • RV anodal threshold similar to LV cathodal threshold

  • Particularly likely with ring (CRT-P or dedicated bipolar CRT-D)

CRT Problems with Anodal Stimulation

RV anodal threshold lower than LV cathodal threshold:

• Confuse RV anodal capture for LV capture

• Set LV output too low

• Begin at output with RV anodal capture only, decrement until RV anodal capture is lost

• No LV capture: no therapy

CRT Avoiding Anodal Stimulation Errors

• Be wary when testing in extended bipolar configuration

• Start at high enough outputs to ensure LV capture

• Continue until there is true loss of capture

• Include RV and LV nearfield EGMs

• Use surface ECG if available

CRT Electronic Repositioning

• Older devices: limited options

• Quadripolar: many possible vectors

• Choose lowest LV threshold with no PNS

• Be wary of anodal stimulation with extended bipolar

• Vary pulse width if thresholds are high

• High impedance decreases energy use

CRT AV Delay Optimization

• Intrinsic conduction: competition with BIV pacing

  • Inhibition

  • Functional non capture

  • Fusion

  • Pseudofusion

• Program short enough to ensure 100% BIV capture

• Program long enough to maintain AV synchrony

• Fusion is acceptable, sometimes preferable

Upper Rate Behavior

• Atrial rate faster than MTR:

  • CHB: pacemaker Wenckebach and fixed ratio block

  • No CHB: intrinsic rate comes through, lower % BIV pacing

• Common to increase MTR in CRT devices