EKG GATING THE PITFALLS AND THE SUCCESSES

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EKG GATINGTHE PITFALLS AND THE SUCCESSES

• Bronwyn Medley
• Advanced Cardiac Applications Specialist

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THE KEYS TO SUCCESS

• Proper patient preparation

• Correct equipment

• Gating Know-How

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Patient Preparation
4 steps

• Use an abrasive gel when prepping the patient

• Use non-metallic, pre-gelled electrodes

• Use an anterior lead placement if possible

• If available, check the contact impedance with an
  impedance meter.

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Patient Preparation
Nu-Prep ECAT Number E8819RA
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Patient Preparation

• Shave the area if necessary

• Rub area where electrodes go with Nu-Prep

• Apply gel to gauze, and rub skin lightly

• Remove excess gel

• Apply patches

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Patient Preparation
Vermed Patches ECAT Number E8819RF
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Patient Preparation
Impedance Meter Readings in Kilo Ohms
WITHOUT NU-PREP
WITH NU-PREP
GE
79K
20K
46K
7.6K
VERMED
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How the EKG Works

• Measures a voltage difference between two points.

• Electrical impulses cause the heart to contract

BASE
LV
RV
APEX
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Electrode Placement

• Left Arm Black lead

• Right Arm White lead

• Left Leg Red lead

• Right Leg Green lead

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How the EKG Works
Measures a voltage difference between two points.

• Lead II is often the best choice in a healthy
  volunteer.

• Disease can cause the orientation of the heart
  within the thorax to change.

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How Signa Measures The EKG

• Signa measure the signal from Leads II and III

• The signal for Lead I is then calculated
  mathematically by performing a sum of the
  averages.

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How Signa Measures The EKG

• Remember, Signa only measures the signal from
  Leads II and III

• If Lead III comes loose during a scan, Signa
  swaps automatically to Lead II

• If Lead II comes loose during a scan, Signa swaps
  automatically to Lead III

Lead II
Lead III
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The EKG Waveform

• An electrocardiogram (ECG or EKG) is a map of the
  electrical activity of the heart

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The EKG Waveform
R
The R-Wave
P
T
Q
S
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The EKG Waveform
The number of R-R Intervals in one minute is the
patients heart rate or BPM
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Signa has 2 Gating Algorithms
Advanced EKG gating on
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Signa has 2 Gating Algorithms
Advanced EKG gating off
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Standard EKG Gating Algorithm

• It assumes a positive amplitude

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Standard EKG Gating Algorithm

• Has a lockout window of 45 of the estimated R-R
  interval, where it wont look for another trigger.

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Standard EKG Gating Algorithm

• If you have a patient with a bigeminy waveform or
  couplets, it will estimate a normal BPM

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Standard EKG Gating Algorithm

• 45 lockout ignores the abnormal R-Wave

R-R
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Advanced EKG Gating

• Standard Gating Algorithm triggers from each
  R-Wave

• Advanced Gating Algorithm triggers from the slope
  of each R-Wave

• Advanced Gating Algorithm is the default gating
  mode

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Advanced EKG Gating

• Assumes a positive slope

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Advanced EKG Gating

• Has no lockout window

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Advanced EKG Gating

• In patients with a bigeminy or couplet waveform,
  it will incorrectly double the BPM

Turn Advanced EKG gating OFF!
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Starting the Scan

• Instruct the patient to lie very still

• Advanced Gating (the default mode), takes 16
  heartbeats to initialize
• measures the slopes of the R-Waves

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Setting up the Patient

• While Advanced Gating is initializing, a cardiac
  initializing message appears.

• Disappears when initialization is complete.

• Do NOT move the patient into the bore during this
  time.

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Setting up the Patient

• Turn on the cardiac waveform

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Setting up the Patient

• Hit Update, and check the mV reading

2.0

• Should be 1mV or higher

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Setting up the Patient

• EKG waveform? but no reading after Update?

• The PAC isnt communicating with the computer.

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Setting up the Patient

• Check for tic marks. These indicate that the
  trace is triggering.

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Setting up the Patient
The tic mark
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Setting up the Patient
Cycle thru the leads until you find the cleanest
trace
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Setting up the Patient
Dont rely on AUTO
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Setting up the Patient

• AUTO measures the strongest signal.

• Strongest signal may be from noise, rather than a
  good EKG trace.

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Have a noisy trace?
Turn on the Noise Filter
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Have a noisy trace?

• Noise Filter adds a greater delay (approx 18ms)
  between when the QRS complex is generated, and
  when Signa detects it.

• Can often improve gating results.

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No Tic Marks?

• If you have a good trace, but no tic marks, try
  turning Advanced EKG Gating OFF

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Gating Reset

• Gating reset is your friend!!

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Gating Reset

• When all else fails.

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Still have a noisy trace?

• At this point, you may need to consider
  re-positioning the patches and/or lead placement.

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Some common issues...
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Scans Taking Longer Than Expected?
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No Tic Marks?

• Take off AUTO and reduce the trigger level

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Trigger Level

• AUTO default is 65

• Try reducing to 50 confirm you are getting tic
  marks.

• Range is 30 - 90

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Trigger Level
Trigger Level reduces the threshold that Signa
uses to detect the R-Wave
R
Trigger level
P
T
Q
S
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T-Swell
A blood dipole caused by the main magnetic field
being perpendicular to the flowing blood
R
T
P
Q
S
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T-Swell
With T-Swell, reducing trigger level can cause
the BPM to double.
R
Trigger level
T
P
Q
S
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T-Swell

• Increase the trigger level

R
Trigger level
T

• Often to a value higher than default of 65

P
Q
S
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Inverted R-Wave

• Signa triggers from positive slopes

• Tends to trigger from the T-Wave

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Inverted R-Wave

• EKG measures a voltage

• Reversing the right arm and left leg leads will
  make the R-Wave go upright again.

Lead II
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The 8.2.5 Gating Control is Master
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The 8.2.5 Gating Control is Master

• Scan screen controls the lead selection until a
  sequence is downloaded.

• Scan, and the lead that was selected will be the
  one Signa scans from.

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The 8.2.5 Gating Control is Master

• Once a sequence is downloaded, Gating Control
  becomes the master

• Changing the lead on Gating Control on a
  downloaded sequence will change the lead Signa
  scans with.

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AND FINALLY.
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