Download Pacing Concepts

Modes of Pacing
Seoul National University Hospital
Department of Thoracic & Cardiovascular Surgery
Electrophysiology of Pacing
• Stimulation & depolarization of
myocardial tissue
• Sensing of intramyocardial electrical
activity
• Current pacemaker technology
• Pulse generator
Stimulation & Depolarization of
Myocardial Tissue
• The myocardium must be excitable
• The stimulus current density (current per unit
cross-sectional area) must be sufficiently high
& of sufficient duration to depolarize a group
of cells that is large enough to initiate impulse
propagation in the myocardium
• The pacemaker-generated impulse then relies
on the intrinsic properties of cardiac
specialized conduction & myocardial tissue for
depolarization of the entire heart
Factors affecting Sensing
Sensing is the detection of real or
spontaneous cardiac depolarization
• Electrode size
• Configuration of electrode (unipolar,
bipolar)
• Position of the lead tip within the
heart
Pacing Lead Technology
Attachment of electrode
• Active fixation
• Passive fixation
1. Chronic ventricular pacing thresholds
tend to be lower with passive lead, in part
because of tissue injury with active fixation
2. Sensing characteristics are similar between
active & passive leads
3. Epicardial electrodes historically have poorer
performance over long term than endocardial
lead
Pulse Generator
•
•
•
•
Power source
Time circuitry
Sensing circuitry
Output circuitry for channels connected
to the electrodes
• Transceiver for telemetric communication
with programming device
Single Chamber Pacemaker
AOO
AAI
AAT
VOO
VVI
VVT
Single Chamber Pacemaker
AAIR
VVIR
Single Chamber Pacemaker
VVI
I
*
Intrinsic P and R waves
Atrial Sensing / Inhibition
Ventricular Sensing / Inhibition
Pacing Interval / Pacing Rate
• The rate at which the pacemaker
will pace if the patient does not have
their own rhythm
– Expressed in either PPM or ms
Rate Conversion
• Conversion
– Pacing rate in PPM divided into
60,000 = ms
• 60,000 / 60 PPM = 1000 ms
– Interval in ms divided into 60,000
= PPM
• 60,000 / 1000 ms = 60 PPM
Ventricular Sensing / Inhibition
pacing interval
pacing interval
pacing interval
Capture
• Definition
The depolarization and
resultant contraction of the
atria or ventricles in response
to a pacemaker stimulus.
Threshold
• Stimulation Threshold
– Definition :
The minimum amount of electrical
energy that consistently produces a
cardiac depolarization
Atrial Capture
• Atrial Capture
Pacemaker Stimulus
Ventricular Capture
• Ventricular Capture (paced ventricular
beats look like PVC’s or LBBB)
Refractory Period
Refractory Period
Alert Period
• Definition
The portion of timing cycle where
the device senses electrical activity
(e.g. cardiac) & responds in a preset
or programmed manner
Alert Period
Refractory Period
Alert Period
Dual Chamber Pacemaker
VAT
VDD
DOO
DVI
DDI
DDD
Dual Chamber Pacemaker
T/I
I
DDD
*
*
Atrial & Ventricular Pacing
Sense in Atrium &
Pace in Ventricle
Pace & Sense in Atrium
& Pace in Ventricle
Pace Atrium & Sense Ventricle
Pace and Sense in Atrium
Sense in Ventricle
AV / PV Delay
AV Delay
PV Delay
Post Ventricular Atrial Refractory
Period (PVARP)
• Definition
Timeframe the atrial channel is refractory,
initiated when there is either a ventricular
pacer spike or sensed R-wave.
PVARP
Atrial Alert Period
• Definition
Timeframe after PVARP when the sense
amplifier is open and can see P-waves
Atrial Alert Period
Alert Period
PVARP
AV Delay
PV Delay
Ventricular Refractory Period
Ventricular Refractory Period
Ventricular Alert Period
• Definition
Timeframe after the ventricular
refractory period that the sense
amplifier is open looking for R-waves
Ventricular Alert Period
Ventricular Refractory Period
Ventricular Alert Period
Dual Chamber Pacing
• Minimum Rate or Base Rate
– Lowest rate that the pacemaker will
pace in the Atrium
– Maximum length of time the
Pacemaker will wait for intrinsic
activity
Dual Chamber Pacing
• Minimum Rate
Dual Chamber Pacing
• Maximum Rate /
Maximum Tracking Rate
– The fastest rate that the Ventricular
channel can track intrinsic P-waves
Maximum Tracking Rate
Pacemaker Follow-up
• Aim
– Verify appropriate pacemaker operation
– Optimize pacemaker functions
• Interval
– Immediate and POD # 1 day
– Postoperative 3, 6, 12 months
Pediatric Aspects of Cardiac Pacing
• Ventricular epicardial leads
Thoracotomy approach
Transdiaphragmatic approach
Subcostal or subxiphoid incision
• Atrial epicardial leads
Base of left atrial appendage
• Transvenous leads
•
•
All the leads have the problem with child growth and results in high
threshold, exit block, lead fracture.
Even when a loop of lead was left in the pericardium, adhesions
frequently formed that prevented unwinding of the loop.
Interrogation
Assess Current Pacemaker Function
• Compare the surface ECG to markers to determine
appropriate pacing (capture) & sensing
Measured Data
Provides information on:
-Magnet Information, -Lead Status, -Battery Status
Diagnostics
Pacemaker Testing
 Sensing and Capture testing
should be performed to insure
adequate safety margins are
programmed
Ventricular Threshold Test
Sensing and Capture testing should be performed to
insure adequate safety margins are programmed
Loss of Capture
• Definition:
The emitted pacemaker stimulus
does not cause depolarization and
resultant cardiac contraction
Ventricular Loss of Capture
Programmed Rate
Programmed Rate
Loss of Capture Causes
 Dislodged Lead
 Insulation Break
Problem Solving
• Program Voltage higher
• Program Pulse Width higher
• Reposition pacing electrode
Sensing Threshold
• The sensitivity number is increased
until loss of sensing is seen
• Then the sensitivity number is
decreased until sensing is regained
– This is the Sensing Threshold
Ventricular Sensitivity Test
Oversensing
• Definition :
The sensing of events other than P
or R-waves by the pacemaker
circuitry
Ventricular Oversensing
Pacing
interval
Pacing
interval
Pacing
interval
Pacing
interval
Pacing
interval
Causes of Oversensing
•
•
•
•
Insulation Break
Intermittent Lead Fracture
Myopotentials
EMI
Problem Solving
• Program sensitivity to a higher number
• Program the refractory period longer
Undersensing
• Definition :
Failure of the pacemaker circuitry
to sense intrinsic P- or R-waves
Ventricular Undersensing
non-sensed R-waves
Causes of Undersensing
Dislodged Lead
Insulation Break
Problem Solving
Program the sensitivity to a lower number
Testing of Chronic Pacing System
Current
Voltage
Resistance
Threshold Threshold
Dislodgement of electrode from endocardium
Perforation
Exit block (fibrosis around electrode tip)
Pulse generator malfunction
Lead/connector abnormality
Battery depletion
Partial lead fracture
Complete lead fracture
Lead insulation fracture
H; high, N; normal, L; low. F; fluctuating
H
H
H
N
N
N
L to N
F
N
H
H
H
H
N
N
N
H
H
H
N
N
N
N
N
N
H
F
H
L
Follow-up Check
Interrogate
Measure Impedance
Check Diagnostics
Check Sensing
Measure Threshold