Transcript basics of pacemaker

BASICS OF PACEMAKER
DN
HISTORY
• 1958 – Senning and Elmqvist
– Asynchronous (VVI) pacemaker implanted by
thoracotomy and functioned for 3 hours
– Arne Larsson
• First pacemaker patient
• Used 23 pulse generators and 5 electrode systems
• Died 2001 at age 86 of cancer
• 1960 – First atrial triggered pacemaker
• 1964 – First on demand pacemaker (DVI)
• 1977 – First atrial and ventricular demand pacing (DDD)
• 1981 – Rate responsive pacing by QT interval, respiration,
and movement
• 1994 – Cardiac resynchronization pacing
What is a Pacemaker?
A Pacemaker System consists of
a Pulse Generator plus Lead (s)
Implantable Pacemaker Systems Contain the Following
Components:
• Pulse generator- power source or
battery
Lead
• Leads
• Cathode (negative electrode)
IPG
• Anode (positive electrode)
Anode
• Body tissue
Cathode
S
The Pulse Generator
• Contains a battery that provides the
energy for sending electrical
impulses to the heart
• Houses the circuitry that controls
pacemaker operations
Circuitry
Battery
Anatomy of a Pacemaker
Resistors
Atrial connector
Connector
Ventricular connector
Defibrillation protection
Output capacitors
Hybrid
Clock
Reed (Magnet) switch
Telemetry antenna
Battery
General Characteristics of Pacemaker
Batteries
• Hermeticity, as defined by the pacing industry,
is an extremely low rate of helium gas leakage
from the sealed pacemaker container
• low rate of self-discharge
• lithium iodine -a long shelf life and high
energy density
• DDD drains a battery more rapidly
Power source
• Longevity in single chamber pacemaker is 7 to
12 years.
• For dual chamber longevity is 6 to 10 years.
• Most pacemakers generate 2.8 v in the
beginning of life which becomes 2.1 to 2.4 v
towards end of life.
9
Leads
• Deliver electrical impulses from
the pulse generator to the heart
• Sense cardiac depolarisation
Lead
Lead Characterization
• Position within the heart
– Endocardial or transvenous leads
– Epicardial leads
• Polarity
– Unipolar
– Bipolar
• Fixation mechanism
– Active/Screw-in
– Passive/Tined
• Shape
– Straight
– J-shaped used in the atrium
• Insulator
– Silicone
– Polyurethane
Lead components
• Conductor
• Connector Pin
• Insulation
• Electrode
Transvenous Leads - Fixation Mechanisms
• Passive fixation
– The tines become lodged in
the trabeculae
• Active Fixation
– The helix (or screw) extends into
the endocardial tissue
– Allows for lead positioning
anywhere in the heart’s chamber
Myocardial and Epicardial Leads
• Leads applied directly to
the heart
– Fixation mechanisms
include:
• Epicardial stab-in
• Myocardial screw-in
• Suture-on
Active Fixation
Passive Fixation
Advantages
Easy fixation
Less expensive & simple
Easy to reposition
Minimal trauma to patient
Lower rate of dislodgement Lower thresholds
Removability
Disadvantages
More expensive
>Complicated implantation
Higher rate of
dislodgement (>a/c)
Difficult to remove chronic
lead
• Cathode:-An electrode that is
in contact with the heart
• Negatively charged
• Anode:-receives the
electrical impulse after
depolarization of cardiac
tissue
• Positively charged when
electrical current is flowing
Anode
Cathode
A Unipolar Pacing System
Contains a lead with an electrode in the heart
• Flows through the
tip electrode
(cathode)
• Stimulates the heart
• Returns through
body fluid and tissue
to the PG (anode)
+
Anode
Cathode
A Bipolar Pacing System
Contains a lead with 2 electrodes in the heart
• Flows through the
tip electrode
located at the end
of the lead wire
• Stimulates the
heart
• Returns to the ring
electrode above
the lead tip
Anode
Cathode
Unipolar leads
• One electrode on the tip & one conductor coil
• Conductor coil may consist of multiple strands - (multifilar leads)
• Unipolar leads have a smaller diameter than bipolar leads
• Unipolar leads exhibit larger pacing artifacts on the surface ECG
Bipolar leads
•
Circuit is tip electrode to ring electrode
•
Two conductor coils (one inside the other)
•
Inner layer of insulation
•
Bipolar leads are typically thicker than unipolar leads
•
Bipolar leads are less susceptible to oversensing noncardiac
signals (myopotentials and EMI)
Coaxial Lead Design
Advantages
Unipolar
Bipolar
Smaller diameter
Easier to implant
Large spike
No pocket stimulation
Less susceptible to EMI
Programming flexibility
Disadvantages Pocket stimulation
Far-field oversensing
No programming flexibility
Larger diameter
Stiffer lead body
Small spike
Higher impedance
Voltage threshold is 30%
higher
Electrodes
• Leads have 1/> electrically active surfaces
referred to as the electrodes
• Deliver an electrical stimulus, detect intrinsic
cardiac electrical activity, or both
• Electrode performance can be affected by
–
–
–
–
–
Materials
Polarization
Impedance
Pacing thresholds
Steroids
Electrode Materials
• The ideal material for an electrode
– Porous (allows tissue ingrowth)
– Should not corrode or degrade
– Small in size but have large surface area
– Common materials
• Platinum and alloys (titanium-coated platinum iridium)
• Vitreous carbon (pyrolytic carbon)
• Stainless steel alloys such as Elgiloy
Voltage
• Voltage is the force that causes electrons to
move through a circuit
• In a pacing system, voltage is:
– Measured in volts
– Represented by the letter “V”
– Provided by the pacemaker battery
– Referred to as amplitude
Current
• The flow of electrons in a completed circuit
• In a pacing system, current is:
– Measured in mA (milliamps)
– Represented by the letter “I”
– Determined by the amount of electrons that move
through a circuit
• Constant-Voltage and Constant-Current Pacing
• Most permanent pacemakers are constantvoltage pacemakers
• Voltage and Current Threshold
• Voltage threshold is the most commonly used
measurement of pacing threshold
Pacing Thresholds
• Defined as the minimum amount of electrical energy required to
consistently cause a cardiac depolarization
• “Consistently” refers to at least ‘5’ consecutive beats
• Low thresholds require less battery energy
Capture
Non-Capture
• The strength-duration
curve illustrates the
relationship of
amplitude and pulse
width
– Values on or above
the curve will result
in capture
Stimulation Threshold (Volts)
The Strength-Duration Curve
2.0
1.5
1.0
Capture
.50
.25
0.5
1.0
Duration
Pulse Width (ms)
1.5
• Rheobase- (the lowest point on the curve) by definition is the
lowest voltage that results in myocardial depolarization at
infinitely long pulse duration
• Chronaxie(pulse duration time ) by definition, the chronaxie is the
threshold pulse duration at twice the rheobase voltage
Lessons from SDC
• The ideal pulse duration should be greater than the chronaxie
time
• Cannot overcome high threshold exit block by increasing the
pulse duration, If the voltage output remains less than the
rheobase
• Energy (μJ) = Voltage (V) × Current (mA) × Pulse Duration (PD
in ms).
• Charge (μC) = Current (mA) × Pulse Duration (ms).
• At very low pulse width thresholds, the charge is low, but the energy
requirements are high because of elevated current and voltage
stimulation thresholds.
• At pulse durations of 0.4–0.6 ms, all threshold parameters - ideal
• At high pulse durations, the voltage and current requirements may be low,
but the energy and charge values are unacceptable
-Safety margins
-When a threshold is determined by decrementing the pulse
width at a fixed voltage
•At a given voltage where the pulse width value is < .30 ms:
Tripling the pulse width will provide a two-time voltage
safety margin.
– Daily fluctuations in threshold that can occur due to eating,
sleeping, exercise, or other factors
- a/c pacing system - higher safety margin, due to the lead
maturation process- occur within the first 6-8 weeks following
implant.
Changes in stimulation threshold (voltage or current) following implantation
of a standard nonsteroid-eluting electrode
Impedance
• The opposition to current flow
• In a pacing system, impedance is
– Measured in ohms
– Represented by the letter “R” (W for numerical values)
• The measurement of the sum of all resistance to the flow of
current
Resistance is a term used to refer to simple electric circuits without
capacitors and with constant voltage and current
Impedance is a term used to describe more complex circuits with
capacitors and with varying voltage and current
Impedance
• Pacing lead impedance typically stated in broad ranges, i.e.
300 to 1500 Ω
• Factors that can influence impedance
–
–
–
–
–
Resistance of the conductor coils
Tissue between anode and cathode
The electrode/myocardial interface
Size of the electrode’s surface area
Size and shape of the tip electrode
Ohm’s Law is a Fundamental Principle
of Pacing That:
• Describes the relationship between voltage,
current, and resistance
V
V=IXR
I=V/R
R=V/I
I
x
R
Impedance and Electrodes
• Large electrode tip
– Threshold ↑
– Impedance ↓
– Polarization ↓
• Small electrode tip
– Threshold ↓
– Impedance ↑
– Polarization ↑
Polarization
• After an output pulse, positively charged particles gather near
the electrode.
• The amount of positive charge is
– Directly proportional to pulse duration
– Inversely proportional to the functional electrode size
(i.e. smaller electrodes offer higher polarization)
Polarization effect can represent 30–40% of the total pacing impedance
As high as 70% for smooth surface, small surface area electrodes
Within the electrode, current flow is due to movement of electrons (e−).
At the electrode–tissue interface, the current flow becomes ionic &
(-) vely charged ions (Cl−, OH−) flow into the tissues toward the anode leaving
behind oppositely charged particles attracted by the emerging electrons.
It is this capacitance effect at the electrode tissue interface, that is the basis
of polarization
Lead Maturation Process
• Fibrotic “capsule” develops around the electrode following lead
implantation
• 3 phases
1. A/c phase, where thresholds immediately following implant
are low
2. Peaking phase- thresholds rise and reach their highest
point(1wk) ,followed by a ↓ in the threshold over the next 6
to 8 wks as the tissue reaction subsides
3. C/c phase- thresholds at a level higher than that at
implantation but less than the peak threshold
•
Trauma to cells surrounding the electrode→ edema and
subsequent development of a fibrotic capsule.
•
Inexcitable capsule ↓ the current at the electrode interface,
requiring more energy to capture the heart.
Lead Maturation Process
• Effect of Steroid on Stimulation Thresholds
5
Volts
4
Smooth Metal Electrode
3
Textured Metal Electrode
2
1
Steroid-Eluting Electrode
0
0
1
2
3
4 5 6
7
8
Implant Time (Weeks)
Pulse Width = 0.5 msec
9
10 11 12
Sensing
• Sensing is the ability of the pacemaker to
detect an intrinsic depolarization
– Pacemakers sense cardiac depolarization by
measuring changes in electrical potential of
myocardial cells between the anode and cathode
An Electrogram (EGM) is the Recording of Cardiac
Waveforms Taken From Within the Heart
• Intrinsic deflection on
an EGM occurs when
a depolarization wave
passes directly under
the electrodes
• Two characteristics of
the EGM are:
– Signal amplitude(mv)
– Slew rate(v/sec)
Intrinsic R wave Amplitude
• Typical intrinsic R wave amplitude
measured from pacing leads in the Right
Ventricle are more than 5 mV in amplitude
Intrinsic R wave in EGM
The Intrinsic R wave amplitude is usually much greater than the T wave amplitude
Slew Rate of the EGM Signal Measures the Change in
Voltage with Respect to the Change in Time
• The longer the signal takes to
move from peak to peak:
– The lower the slew rate
– The flatter the signal
• Higher slew rates translate to
greater sensing
Change in voltage
Time duration of
voltage change
Slope
– Measured in volts per second
Voltage
Slew rate=
Time
Slew rate measurements at implant should exceed .5 volts per second
for P waves; .75 volts per second for R wave measurements
Factors That May Affect Sensing Are:
• Lead polarity (unipolar vs. bipolar)
• Lead integrity
– Insulation break
– Wire fracture
• EMI – Electromagnetic Interference
Undersensing . . .
• Pacemaker does not “see” the intrinsic beat,
and therefore does not respond appropriately
Intrinsic beat
not sensed
Scheduled pace
delivered
VVI / 60
Oversensing
Marker channel
shows intrinsic
activity...
...though no
activity is present
VVI / 60
• An electrical signal other than the intended
P or R wave is detected
Pacemaker Implantation
Signal Amplitude / Slew Rate
Signal
Acute Atrial EGM
Chronic Atrial EGM
Acute Ventricular EGM
Chronic Ventricular EGM
Amplitude Range
(mV)
Slew Rate
(v/sec)
1.5 - 4.0
1.0 - 3.0
0.6 - 1.7
0.5 - 1.5
7 - 15
5 - 12
0.8 - 2.0
0.6 - 1.5
NASPE/ BPEG Generic (NBG)
Pacemaker Code
I
Chamber
Paced
II
Chamber
Sensed
III
Response
to Sensing
IV
Programmable
Functions/Rate
Modulation
V: Ventricle
V: Ventricle
T: Triggered P: Simple
programmable
A: Atrium
A: Atrium
I: Inhibited
M: Multiprogrammable
D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating
O: None
O: None
S: Single
S: Single
(A or V)
(A or V)
O: None
V
Antitachy
Function(s)
P: Pace
S: Shock
D: Dual (P+S)
R: Rate modulating O: None
O: None
Pacemaker Timing
• Pacing Cycle : Time between two consecutive
events in the ventricles (ventricular only
pacing) or the atria (dual chamber pacing)
• Timing Interval : Any portion of the Pacing
Cycle that is significant to pacemaker
operation e.g. AV Interval, Ventricular
Refractory period
Single-Chamber Timing
Single Chamber Timing Terminology
•
•
•
•
Lower rate
Refractory period
Blanking period
Upper rate
Lower Rate Interval
• Defines the lowest rate the pacemaker will pace
Lower Rate Interval
VP
VP
VVI / 60
Refractory Period
• Interval initiated by a paced or sensed event
• Designed to prevent inhibition by cardiac or non-cardiac
events
• Events sensed in the refractory period do not affect the
Lower Rate Interval but start their own Refractory Periods
Lower Rate Interval
VP
Refractory Period
VP
VVI / 60
Blanking Period
• The first portion of the refractory period
• Pacemaker is “blind” to any activity
• Designed to prevent oversensing of pacing
stimulus/depolarisation
Lower Rate Interval
VP
Blanking Period
Refractory Period
VP
VVI / 60
Physiologic Classification of Sensors- rate adaptive
Primary
• Physiologic factors that modulate sinus function
Catecholamine level, Autonomic nervous system activity
Secondary
• Physiologic parameters that are the consequence of
exercise
QT, respiratory rate
Minute ventilation,temperature
pH, stroke volume, Preejection interval, SVO2
Peak endocardial acceleration
Tertiary
• External changes that result from exercise
Vibration
Acceleration
Upper Sensor Rate Interval
• Defines the shortest interval (highest rate) the
pacemaker can pace as dictated by the sensor (AAIR,
VVIR modes)
• Limit at which sensor-driven pacing can occur
Lower Rate Interval
Upper Sensor Rate
Interval
VP
Blanking Period
Refractory Period
VP
VVIR / 60 / 120
Hysteresis
• Allows the rate to fall below the programmed
lower rate following an intrinsic beat
• lower rate limit is initiated by a paced event, while
the hysteresis rate is initiated by a non-refractory
sensed event.
Lower Rate Interval-60 ppm
VP
VP
Hysteresis Rate-50 ppm
VS
VP
Noise Reversion
• Continuous refractory sensing will cause pacing at the
lower rate
Lower Rate Interval
Noise Sensed
VP
VVI/60
SR
SR
SR
SR
VP
Modes-SINGLE CHAMBER
AOO & VOO-asynchronous modes
• By application of magnet
• Useful in diagnosing pacemaker dysfunction
• During surgery to prevent interference from
electrocautery
VOO Mode
• Asynchronous pacing delivers output regardless of
intrinsic activity
Lower Rate Interval
VP
Blanking Period
VOO / 60
VP
VOO TIMING
V
VP
VP
VP
VP
VP
VVI Mode
• Pacing inhibited with intrinsic activity
Lower Rate Interval
{
VP
Blanking/Refractory
VVI / 60
VS
VP
VVI TIMING
V
VP
VP
VP
VS
VP
VVIR
• Pacing at the sensor-indicated rate
Lower Rate
Upper Rate Interval
(Maximum Sensor Rate)
VP
VP
Refractory/Blanking
VVIR / 60/120
Rate Responsive Pacing at the Upper Sensor Rate
AAI
•
•
•
•
•
•
•
Useful for SSS with N- AV conduction
Should be capable of 1:1 AV to rates 120-140 b/m
Atrial tachyarrhythmias should not be present
Atria should not be “silent”
If no A activity, atria paced at LOWER RATE limit (LR)
If A activity occurs before LR,- “resetting”
Caution- far-field sensing of V activity
AAIR
• Atrial-based pacing allows the normal A-V activation
sequence to occur
Lower Rate Interval
Upper Rate Interval
(maximum sensor rate)
AP
Refractory/Blanking
AAIR / 60 / 120
(No Activity)
AP
Single-Chamber Triggered-Mode
•
•
•
•
Output pulse every time a native event sensed
↑current drain
Deforms native signal
Prevent inappropriate inhibition from
oversensing when pt does not have a stable
native escape rhythm
Benefits of Dual Chamber Pacing
• Provides AV synchrony
• Lower incidence of atrial fibrillation
• Lower risk of systemic embolism and stroke
• Lower incidence of new congestive heart
failure
• Lower mortality and higher survival rates
Dual Chamber Timing Parameters
•
•
•
•
•
Lower rate
AV and VA intervals
Upper rate intervals
Refractory periods
Blanking periods
Lower Rate
• The lowest rate the pacemaker will pace the atrium in
the absence of intrinsic atrial events
Lower Rate Interval
AP
DDD 60 / 120
VP
AP
VP
AV Delay
• The AV delay in the pacemaker timing cycle is
designed to simulate that natural pause
between the atrial and ventricular events by
mimicking the PR interval
• Benefits of a properly timed AV delay
– Allows optimal time for ventricular filling, which
may contribute to improved cardiac output
– Allows sufficient time for proper mitral valve
closure- minimize MR
AV Intervals
• Initiated by a paced or non-refractory sensed atrial
event
– Separately programmable AV intervals – SAV /PAV
•
Two things can happen with the AV delay
– AV delay times out (and ventricular pacing spike is delivered)
– AV delay is interrupted by a sensed ventricular event (and ventricular pacing spike is
inhibited)
Lower Rate Interval
SAV
PAV
200 ms
AP
DDD 60 / 120
VP
170 ms
AS
VP
Paced AV Delay
Sensed AV Delay
• The time period between
the paced atrial event and
the next paced ventricular
event
• The pacemaker spike
initiates the paced AV delay
timing cycle
• Programmable value
• The time period between
the sensed atrial event and
the next paced ventricular
event
• The pacemaker has to sense
the atrial event before the
timing cycle is initiated—
there is usually a slight time
lag
• Program the sensed AV
delay to a value slightly
shorter than the paced AV
delay (~ 25 ms)
Atrial Escape Interval (V-A Interval)
Lower rate interval- AV interval
=V-A interval
The V-A interval is the longest period that may elapse after a ventricular event before the
atrium must be paced in the absence of atrial activity.
The V-A interval is also commonly referred to as the atrial escape interval
Atrial Escape Interval (V-A Interval)
• The interval initiated by a paced or sensed ventricular
event to the next atrial event
Lower Rate Interval
200 ms
AV Interval
AP
DDD 60 / 120
PAV 200 ms; V-A 800 ms
VP
800 ms
VA Interval
AP
VP
Upper Activity (Sensor) Rate
• In rate responsive modes, the Upper Activity Rate
provides the limit for sensor-indicated pacing
Lower Rate Limit
Upper Activity Rate Limit
PAV
DDDR 60 / 120
A-A = 500 ms
AP
V-A
VP
PAV
AP
VP
V-A
Upper Tracking Rate
• The maximum rate the ventricle can be paced in
response to sensed atrial events
• Prevents rapid ventricular pacing rates in response to
rapid atrial rates
Lower Rate Interval
{
Upper Tracking Rate Limit
SAV
AS
VA
VP
DDDR 60 / 100 (upper tracking rate)
Sinus rate: 100 bpm
SAV
AS
VP
VA
Refractory Periods
• VRP and PVARP are initiated by sensed or paced
ventricular events
– The VRP is intended to prevent self-inhibition such as
sensing of T-waves
– The PVARP is intended primarily to prevent sensing of
retrograde P waves
A-V Interval
(Atrial Refractory)
Ventricular Refractory Period
(VRP)
AP
Post Ventricular Atrial
Refractory Period (PVARP)
VP
Post-Ventricular Atrial Refractory
Period
• PVARP is initiated by a ventricular
event(sensed/paced), but it makes the atrial
channel refractory
• PVARP is programmable (typical settings
around 250-275 ms)
• Benefits of PVARP
– Prevents atrial channel from responding to
premature atrial contractions, retrograde P-waves,
and far-field ventricular signals
– Can be programmed to help minimize risk of
pacemaker-mediated tachycardias
PVARP and PVAB
• The PVAB is the post-ventricular atrial
blanking period during which time no signals
are “seen” by the pacemaker’s atrial channel
• It is followed by the PVARP, during which time
the pacemaker might “see” and even count
atrial events but will not respond to them
• PVAB-independently programmable
– Typical value around 100 ms
PVAB and PVARP
Blanking Periods
• First portion of the refractory period-sensing is disabled
AP
AP
VP
Atrial Blanking
(Nonprogrammable)
Post Ventricular Atrial
Blanking (PVAB)
Post Atrial Ventricular
Blanking
Ventricular Blanking
(Nonprogrammable)
Total Atrial Refractory Period (TARP)
• TARP is the timing cycle on the atrial channel during which the
pacemaker will not respond to incoming signals
• TARP consists of the AV delay plus the PVARP
TARP = AV delay + PVARP
• TARP is not programmable directly -can program the AV delay
and PVARP and thus indirectly control TARP
• TARP is important for controlling upper-rate behavior of the
pacemaker
Total Atrial Refractory Period (TARP)
• Sum of the AV Interval and PVARP
• defines the highest rate that the pacemaker will
track atrial events before 2:1 block occurs
Lower Rate Interval
Upper Tracking Rate
SAV = 200 ms
PVARP = 300 ms
Thus TARP = 500 ms (120 ppm)
DDD
LR = 60 ppm (1000 ms)
UTR = 100 bpm (600 ms)
AS
AS
VP
SAV PVARP
VP
SAV
{
TARP
No SAV started for events sensed in the TARP
PVARP
Wenckebach
• Occurs when the intrinsic atrial rate lies
between the UTR and the TARP rate
• Results in gradual prolonging of the AV
interval until one atrial intrinsic event occurs
during the TARP and is not tracked
Wenckebach Operation
• Prolongs the SAV until upper rate limit expires
– Produces gradual change in tracking rate ratio
Lower Rate Interval
{
Upper Tracking Rate
P Wave Blocked (unsensed or unused)
AS
AS
AR
VP
VP
PVARP
SAV PVARP SAV
TARP
TARP
AP
VP
PAV PVARP
TARP
Wenckebach Operation
DDD / 60 / 120 / 310
Fixed Block or 2:1 Block
• Occurs whenever the intrinsic atrial rate
exceeds the TARP rate
• Every other atrial event falls in the TARP when
the atrial rate exceeds the TARP rate
• Results in block of atrial intrinsic events in
fixed ratios
2:1 Block
• Every other P wave falls into refractory and does not restart the
timing interval
Lower Rate Interval
{
Upper Tracking Limit
AS
AR
VP
{
Sinus rate = 133 bpm (450 ms)
PVARP = 300 ms SAV = 200 ms
TARP=500 ms
AV PVARP
TARP
P Wave Blocked
AS
AR
VP
AV PVARP
TARP
2:1 Block
DDD / 60 / 120 / 310
Summary-upper rate behaviours
– 1:1 tracking occurs whenever the patient’s atrial rate is
below the upper tracking rate limit
– Wenckebach will occur when the atrial rate exceeds the
upper tracking rate limit
– Atrial rates greater than TARP cause 2:1 block
Ventricular Safety Pacing
• Crosstalk is the sensing of a pacing stimulus delivered in the opposite
chamber, which results in undesirable pacemaker response, e.g., false
inhibition
• Following an atrial paced event, a ventricular safety pace interval is
initiated
– If a ventricular sense occurs during the safety pace window, a pacing pulse is delivered
at an abbreviated interval (110 ms)
PAV Interval
Post Atrial Ventricular
Blanking
Ventricular Safety Pace
Window
Ventricular Safety Pace
DDD 60 / 120
VDD Mode
•
•
•
•
Atrial Synchronous pacing or Atrial Tracking Mode
A sensed intrinsic atrial event starts an SAV
The Lower Rate Interval is measured between Vs to Vp or Vp to Vp
If no atrial event occurs at the end of the Lower Rate Interval a Ventricular
pace occurs
• Paces in the VVI mode in the absence of atrial sensing
• AV block with intact sinus node function (esp useful in congenital AV
block)
VDD
• Provides atrial synchronous pacing
– System utilizes a single lead
Lower Rate Interval
{
Upper Tracking Limit
AS
AS
VP
VDD
LR = 60 ppm
UTR = 120 ppm
Spontaneous A activity = 700 ms (85 ppm)
VP
VP
DDD Mode
• Chamber paced: Atrium & ventricle
• Chamber sensed: Atrium & ventricle
• Response to sensing: Triggered & inhibited
– An atrial sense:
• Inhibits the next scheduled atrial pace
• Re-starts the lower rate timer
• Triggers an AV interval (called a Sensed AV Interval or SAV)
– An atrial pace:
• Re-starts the lower rate timer
• Triggers an AV delay timer (the Paced AV or PAV)
– A ventricular sense:
• Inhibits the next scheduled ventricular pace
Four “Faces” of Dual Chamber Pacing
• Atrial Sense, Ventricular Sense (AS/VS)
AV
AS
V-A
VS
Rate (sinus driven) = 70 bpm / 857 ms
Spontaneous conduction at 150 ms
A-A = 857 ms
AV
AS
V-A
VS
Four “Faces” of Dual Chamber Pacing
• Atrial Pace, Ventricular Pace (AP/VP)
AV
AP
V-A
VP
Rate = 60 bpm / 1000 ms
A-A = 1000 ms
AV
AP
VP
V-A
Four “Faces” of Dual Chamber Pacing
• Atrial Pace, Ventricular Sense (AP/VS)
AV
AP
V-A
VS
Rate = 60 ppm / 1000 ms
A-A = 1000 ms
AV
AP
V-A
VS
Four “Faces” of Dual Chamber Pacing
• Atrial Sense, Ventricular Pace (AS/ VP)
AV
AS
V-A
VP
Rate (sinus driven) = 70 bpm / 857 ms
A-A = 857 ms
V-A
AV
AS
VP
Mode Selection
DDIR
Symptomatic
bradycardia
DDDR
Y
Are atrial
tachyarrhythmias
present?
Is AV conduction
intact?
N
N
Y
Are they
chronic?
Is AV conduction
intact?
Y
N
Is SA node function
presently adequate?
AAIR
DDDR
(SSS)
Y
VVI
VVIR
Is SA node function
presently adequate?
Y
N
N
N
N
DDDR, DDIR
DDD, VDD
DDDR
DDDR
Optimal Pacing Mode (BPEG)
•
•
•
•
Sinus Node Disease
AVB
SND + AVB
Chronic AF + AVB
-
AAI (R)
DDD
DDDR + DDIR
VVI
Thank u
Mode Selection Decision Tree
DDIR with
SV PVARP
Symptomatic
bradycardia
DDDR with
MS
Y
Are atrial
tachyarrhythmias
present?
Is AV conduction
intact?
N
N
Y
Are they
chronic?
Is AV conduction
intact?
Y
N
Is SA node function
presently adequate?
AAIR
DDDR
(SSS)
N (CSS,
VVS)
DDD, DDI
with RDR
Y
VVI
VVIR
Is SA node function
presently adequate?
Y
N
N
DDD, VDD
DDDR
N
DDDR
Pacing Modes
Stuart Allen 06
Ventricular Demand
VVI
AMP
Output circuit
Programmed lower rate
VVI
50 mm/s
Ventricular Demand
VVIR
Sensor
AMP
Output circuit
Programmed lower rate
Sensor indicated
rate
50 mm/s
Stuart Allen 06
Atrial Demand
AAI
AMP
Output circuit
Programmed lower rate
50 mm/s
AAI
Stuart Allen 06
Pacing Modes - Summary
Ventricular Demand
VVI
Atrial Demand
AAI
AMP
Output circuit
AMP
Output circuit
Atrial Synchronised
VAT
Atrial synchronised
Ventricular Inhibited
AMP
VDD
AMP
AMP
Output circuit
Output circuit
A-V Sequential
DVI
Output circuit
A-V Universal
DDD
Output circuit
AMP
Timing & Control
AMP
Output circuit
AMP
Output circuit
Stuart Allen 06