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Pacing Reference
Questions included for
Critical Care Competency Day
2010 - 2011
Pacemaker
• Medtronic 5388 Dual
Chamber (DDD)
Temporary Pacing Review
• The following slides are designed to help
you review some aspects of temporary
pacing.
• Other resources available include
– pacing resource book in SICU
– medtronic website: temporary pacing
powerpoints
Indications for Temporary Pacing
Placement of Epicardial Wires
Transvenous Pacing
Insertion Sites
Internal Jugular Vein
External Jugular
Vein
Internal Jugular
Subclavian
Brachial Vein
Femoral
Femoral Vein
Subclavian Vein
Transvenous Pacing Wire
•
Bipolar lead system
– Transvenous wire
is floated into the
right ventricle
– The negative
and positive
electrodes
are in contact with
the heart
Single Chamber Temporary Pacing
Pacer Settings:
• Pacing rate (heart rate)
• Output/stimulation
threshold
• Sensitivity
Model 5388 Dual Chamber Temporary Pacemaker
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Pace/Sense LEDs
Lock/Unlock Key
Lock Indicators
Rate Dial
Atrial Output Dial
Ventricular Output Dial
Menu Parameter Dial
Parameter Selection Key
Menu Selection Key
Pause Key
Power On Key
Power Off Key
Emergency/Asynchronous
Pacing Key
Lower Screen
Ventricular Output Graphics
Atrial Output Graphics
Upper Screen
Rate Graphics
Setup Indicators
DDI Indicator
Low Battery Indicator
Setup Labels
Lower Screen Menus
Menu 1: Pacing
Parameters
Menu 2: Rate-Based
Pacing Parameters
Menu 3: Rapid
Atrial Pacing
Menu M:
Dial-A-Mode
NBG Codes
1st Letter
Chamber(s) Paced
A = atrium
V = ventricle
D = dual (both atrium
and ventricle)
Chamber
paced
2nd Letter
3rd Letter
Chamber(s) Sensed
A = atrium
V = ventricle
D = dual
O = none
Response to Sensing
I = inhibit
(Demand mode)
T = triggered
D = dual
O = none (Asynch)
Chamber sensed
Action or
response to a
sensed event
Set Up Guide
Pacemaker EKG Strips
• Assessing Paced EKG Strips
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–
–
–
–
Identify intrinsic rhythm and clinical condition
Identify pacer spikes
Identify activity following pacer spikes
Assess for Failure to capture
Assess for Failure to sense
• EVERY PACER SPIKE SHOULD HAVE A PWAVE OR QRS COMPLEX FOLLOWING IT.
Capture
Depolarization of cardiac muscle
following an electrical stimulus
Sensitivity
The degree that the pacing system “sees” or senses
signals, controlled by the sensitivity setting which
is graduated in millivolts (mV)
Sensitivity (mV)
5 (mV)
2.5 (mV)
1.25 (mV)
Sensitivity
The lower the setting, the more sensitive
the pacemaker is to intracardial signals
Normal Pacing
• Atrial Pacing
– Atrial pacing spikes followed by P waves
Normal Pacing
• Ventricular pacing
– Ventricular pacing spikes followed by wide, bizarre
QRS complexes
Normal Pacing
• A-V Pacing
– Atrial & Ventricular pacing spikes followed by atrial &
ventricular complexes
Troubleshooting Pacing
• Look for
– Failure to Fire (No Output from Pacer)
– Failure to Capture (pacer not followed by
depolarization)
– Failure to Sense
• Undersensing: pacer not sensing all intrinsic
activity so may misfire at inappropriate times
• Oversensing: pacer sensing artifact as well as
intrinsic activity so may not fire when necessary
Failure to Fire: No Output
Possible Causes
Corrective Measures
•Battery depletion
•Pacemaker OFF
•Faulty cable connections
•Fractured/dislodged lead
•Oversensing
•Replace battery
•Verify pacemaker settings
•Check cable connections
•Replace/reposition lead
•Verify/adjust sensitivity
Failure to Fire
• Indicated by absence of pacer spikes where
they should be
• Possible Causes:
Solution:
– Low battery
– Loose connections
– Oversensing
– Lead dislodged or Fractured
Replace battery
Check and secure
connections
Increase mV to
lower sensitivity
Place skin wire or
reposition transvenous wire
Factors that Affect Capture and
Sensing
Failure to Capture
• Causes
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–
–
–
Insufficient energy delivered by pacer
Low pacemaker battery
Dislodged, loose, fibrotic, or fractured electrode
Electrolyte abnormalities
• Acidosis
• Hypoxemia
• Hypokalemia
• Danger - poor cardiac output
Failure to Capture
• Solutions
–
–
–
–
Check connections
Increase pacer output (↑mA)
Change battery, cables, pacer
Reverse polarity
Atrial/Ventricular Stimulation Thresholds
Capture
Loss of Ventricular Capture
Abnormal Pacing
• Atrial non-capture
– Atrial pacing spikes are not followed by P waves
Abnormal Pacing
• Ventricular non-capture
– Ventricular pacing spikes are not followed by QRS
complexes
Capture Threshold testing
• Capture Stimulation threshold
– Definition: Minimum current necessary to capture &
stimulate the heart
– Testing
•
•
•
•
Set pacer rate 10 ppm faster than patient’s HR
Starting at 0 mA, increase mA until 100% capture is obtained
This is your pacing threshold
Set mA 2-3x greater than the pacing threshold
– Example: Set output at 10-15 mA if 100% capture was at 5mA
Failure to Sense : Undersensing
• Causes
– Pacemaker not sensitive enough to detect patient’s intrinsic
electrical activity (mVset too high)
– Asynchronous pacing
– Insufficient myocardial voltage
– Dislodged, loose, fibrotic, or fractured electrode
– Mechanical failure: wires, bridging cables, pacemaker
– Low battery
• Danger
– Potential (low) for paced ventricular beat to land on T
wave and lead to Vtach
Undersensing
• Solutions
– Check all connections
– Make sure pacer is not set for asynchronous
pacing
– Increase pacemaker sensitivity (↓mV) until
pacer spikes move away from intrinsic beats
– Change battery
Undersensing
Abnormal Pacing
• Atrial undersensing
– Atrial pacing spikes occur irregardless of P waves
– Pacemaker is not “seeing” intrinsic activity
Abnormal Pacing
• Ventricular undersensing
– Ventricular pacing spikes occur regardless of QRS
complexes
– Pacemaker is not “seeing” intrinsic activity
Failure to Sense
• Danger – potential for paced ventricular beat to
land on T wave
Oversensing
• Inhibition of the pacemaker by events
it should ignore such as:
– T waves
– Artifact
Oversensing
• Causes
– Pacemaker inhibited due to sensing of “P” waves &
“QRS” complexes that do not exist
– Pacemaker too sensitive
– Possible wire fracture, loose contact
– Pacemaker failure
• Danger – asystole or heart rate too low to
maintain adequate cardiac output
– If pacer “thinks” intrinsic heart rate is at or above set
rate, then it won’t pace
Oversensing
• Solution
–
–
–
–
–
Check connections
Decrease pacemaker sensitivity (↑mV)
Change cables, battery, pacemaker
Reverse polarity
Check electrolytes
Oversensing
One Last Thing to Consider:
Fusion and Pseudofusion Beats
Pseudofusion
Beat:
Fusion Beat:
When Intrinsic
Depolarization
Initiates at Same
Instant as Pacer
Fires: Beat is
A combination
Of a paced and
Intrinsic beat
This is NOT a
problem with
The pacemaker
Intrinsic Beat
Intrinsic Beat
Fusion Beat
Fusion Beat
Paced Beat
Paced Beat
Pseudofusion Beat
Pseudofusion Beat
Occurs when pacer
fires just after
intrinsic depolarization
begins. Pacer spike will
appear at middle to
end of R wave.
Beat will be intrinsic.
This is also not a
malfunctoning
pacemaker. The
pacemaker has fired
too close to time of
depolarization to be
able to detect it.
If this were
undersensing the pacer
spike would be at the
end of QRS or later.
Pacing Responsibilities
• Check all connections are proper
• Assess and troubleshoot pacing problems
– Failure to fire
– Failure to capture
– Under or over sensing
• Determine pacing threshold and set mA
appropriately
– Document threshold and setting
Pacing Responsibilities
• Determine underlying rhythm and document
– This can be done when you are determining pacing threshold
– By turning down the mA to below the pacing threshold, the
patient’s intrinsic rhythm will become apparent
• Document sensitivity settings
– Atrial is normally < 1 mV
– Ventricular is usually between 2-7 mV
• For patient attached to pacemaker but not actively
pacing, thresholds still need to be checked and
documented
– It is important to know that the pacemaker will work if the patient needs it
• Additionally for transvenous pacing
– Check and document position of pacing wire
Pacing Questions
• Look at each of the following pacing strips
– ?fire
– ?capture
– ?sensing properly
• if not, is it undersensing or oversensing
– ?what would you do if you saw this strip
Practice Strip #1
Practice Strip #2
Pacing Strip #3
Practice Strip #4
Practice Strip #5
Pacing Strip # 6
Pacing Strip # 7