Transcript pacemaker basics

PACEMAKER BASICS
Frijo jose a
• Cathode: negative
– Electrode on the tip of a
pacing lead
• Anode: positive
– The “ring” electrode on
a bipolar lead
– The PG case on a
unipolar system
Anode
Cathode
Implantable Pacemaker Circuit
• Pulse generator (PG):
– Battery
– Circuitry
– Connector(s)
Lead
• Leads
– Cathode
– Anode
IPG
• Body tissue
Anode
Cathode
The Pulse Generator
• Battery - provide energy
• Circuitry - controls
pacemaker operations
• Connector- join the PG to
the lead(s)
Connector
Block
Circuitry
Battery
Lead Characterization
• Position within the heart
– Endocardial/transvenous leads
– Epicardial leads
• Fixation mechanism
– Active/Screw-in
– Passive/Tined
• Shape
– Straight
– J-shaped used in the atrium
• Polarity
– Unipolar
– Bipolar
• Insulator
– Silicone
– Polyurethane
Endocardial Passive Fixation Leads
• The tines become lodged
in the trabeculae,
a fibrous meshwork, of the
heart
Tines
Transvenous Active Fixation Leads
• The helix, or screw,
extends into the
endocardial tissue
– Allows for lead positioning
anywhere in the heart’s
chamber
– The helix is extended
using an included tool
Epicardial Leads
• Leads applied directly to the
surface of the heart
– Fixation mechanisms include:
• Epicardial stab-in
• Myocardial screw-in
• Suture-on
– Applied via sternotomy or
laproscopy
Lead Polarity
• Unipolar leads
– Smaller diameter lead body
than bipolar leads
– Usually larger pacing artifacts
on ECG
Unipolar lead
To tip (cathode)
• Bipolar leads
– Usually less susceptible to
oversensing of non-cardiac
signals
Bipolar coaxial lead
Unipolar Pacing System
• Lead has only one electrode –
cathode – at the tip
• PG can - anode
• When pacing, the impulse:
– Flows through the tip electrode
(cathode)
– Stimulates the heart
– Returns through body fluid and
tissue to PG can (anode)
•more interference (myopotentials)
• Big spike on ECG
• Pectoral (pocket) stimulation possible
Anode
+
Cathode -
Bipolar Pacing System
• The lead has both an anode
and cathode
• The pacing impulse:
– Flows through the tip
electrode located at the end
of the lead wire
– Stimulates the heart
– Returns to the ring electrode,
the anode, above the lead tip
•less interference
Anode +
Anode
Cathode -
• Spike difficult to see on ECG
• No pectoral (pocket) stimulation
Cathode
STIMULATION THRESHOLD
• The minimum stimulus intensity & duration
necessary to reliably initiate a propagated
depolarising wavefront from an electrode
• For a pacing stimulus to “capture”, the
stimulus must exceed a critical amplitude &
must be applied for a sufficient duration
• Stimulus amplitude & duration interactminimal amplitude required to capture
depends on the pulse duration
Strength–Duration Relation
Stimulus amplitude for endocardial stimulation
has an exponential relation to duration of the
pulse- rapidly rising strength–duration curve at
pulse durations <0.25 ms and a relatively flat
curve at pulse durations > 1.0 ms
• Chronaxie pulse duration ~ point of min
threshold energy on strength–duration curve
• With pulse durations > chronaxie- relatively
little ↓ in threshold V
• Wider pulse dur→wasting of energy without
providing a substantial ↑ in safety margin
• When threshold determined by ↓ amplitude,
stimulus V set twice the threshold value
• PG that determine threshold by automatically
↓pulse duration-at least 3times threshold
• Wedensky effect
Hyperacute phase of threshold evolution- active fixation electrodes
may produce,immediately following implantation,an ↑
stimulation threshold that ↓over the next 20-30 min- transient
high threshold – a/c injury at myocardial–electrode interface
Proper programming of the stimulus amplitude
• The strength–duration relation must be
appreciated
• The safety margin that is chosen for a particular
pt must be based on the degree of pacemaker
dependency
• An appreciation of the effect of stimulus
amplitude & duration on battery longevity
• The overall metabolic & pharmacologic history of
the pt must be considered
• Pacing threshold varies inversely with surface
area of the stimulating electrode
Strength–Interval Relation
• The stimulation threshold is influenced by the
coupling interval of electrical stimuli and
frequency of stimulation
• ICD- greater stimulus intensity during ATP than
during antibradycardia pacing
(Ztotal) = Zc Ze Zp
Zp - related to movmnt
of charged ionmyo
toward the s in
cathode
Zp -directly related to
pulse duration & can
be ↓ by use of
relatively ↓ pulse
durations
Polarization is inversely
related to SA of
electrode- to ↓ Zp
but ↑ Ze, SA of
electrode can be
made large but
radius small by use
of a porous coating
Afterpotential of opposite charge
is induced in the myocardium at the interface of
the stimulating electrode
The slope of
intrinsic deflectn
(dV/dt)
expressed in V/s
-referred to as
slew rate
For an EKG to be
sensed, the
amplitude &
slew rate must
exceed the
sensing
threshold
• For a battery,the decay characteristics should be
predictable. The ideal battery should have a
predictable fall in V near the end of life, yet provide
sufficient service life after initial voltage decay to allow
time for the elective replacement indicator to be
detected and for replacement to be performed
RATE-ADAPTIVE SENSORS
• Activity Sensors and Accelerometers
• Minute Ventilation Sensors
•
•
•
•
•
•
•
•
•
P- Native atrial depolarization
A- Atrial paced event
R- Native ventricular depolarization
V- Ventricular paced event
AV- Sequential pacing in the atrium and ventricle
AVI- Programmed AV pacing interval
AR- Atrial paced event foll by intrinsic ventricular
ARP- Atrial refractory period
PV- Native atrial foll by paced ventricular, Psynchronous
• AEI- Interval from a ventricular sensed/paced to
atrial paced event, the VA interval
NASPE/ BPEG Generic (NBG) Pacemaker
Code
I. Chamber
Paced
II. Chamber
Sensed
III. Response to
Sensing
O= none
A=atrium
V= ventricle
D= dual
(A+V)
O= none
O= none
A= atrium
T= triggered
V= ventricle
I= inhibited
D= dual
D= dual
(A+V)
(T+I)
Manufacturers’ Designation only:
S= single
(A or V)
S= single
(A or V)
IV. Programmability
V. Antitachy
Rate Modulation arrhythmia funct.
O= none
P= simple
M= multi
C= communication
R= Rate Modulation
O= none
P= pacing
S= shock
D= dual
PACING MODES
AOO & VOO
• By application of magnet
• Useful in diagnosing pacemaker dysfunction
• During surgery to prevent interference from
electrocautery
Ventricular asynchronous (VOO) pacing
• Neither sensing nor mode of response
• Irrespective of any other events, V pacing
artifacts occur at programmed rate. Timing
cycle cannot be reset by any intrinsic event
Atrial asynchronous (AOO)
AV sequential asynchronous (DOO)
• AVI & VAI or AEI are both fixed- intervals never
change, as is insensitive to any atrial or
ventricular activity, and timers never reset
Ventricular demand inhibited (VVI)
• Sensing on V channel- output inhibited by
sensed V event
• Refractory after V/R- VRP- any V event in VRPnot sensed & doesn’t reset V timer
• LRL
VVI MODE
• Automatic interval starts from a paced
complex (to the next paced complex)
Automatic Interval
• Escape interval starts from a sensed
complex (to the next paced complex)
If the intervals are equal:
Escape Interval
•No hysteresis
If the escape interval > automatic interval:
•Hysteresis
VVI MODE (with hysteresis)
1000 ms
850 ms
Escape interval = 1000 ms (60 ppm)
Automatic interval = 850 ms (70 ppm)
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”
An A activity too early may not cause depolarisation & better
not sensed- ARP
• Caution- far-field sensing of V activity
Atrial inhibited (AAI) pacing
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
• Can be used for noninvasive EPS,with already
implanted PPI tracking chest wall stimuli created
by a programmable stimulator
Single-Chamber Rate-Modulated Pacing
AV sequential-V Inhibited Pacing (DVI)
• PPI is inhibited & reset by sensed V activity
but ignores all intrinsic A complexes
• Native R during AVI sensed – V output
inhibited & AEI reset
• For both A&V stimuli to be inhibited, sensed R
must occur during AEI
• Modified or partially committed version-physiologic AVI
AV Sequential, Non–P-Synchronous
Pacing with D-Chamber Sensing (DDI)
• AAI + VVI
• Difference btw DVI & DDI- DDI incorporates A
sensing as well as V sensing- prevents
competitive A pacing
• Mode of response is inhibition only- no
tracking of P waves - paced V rate cannot be >
programmed LRL
• Goes by LR for each
• Timing cycles- LRL, AVI, PVARP & VRP
A Synchronous (P-Tracking) Pacing (VDD)
•
•
•
•
•
•
VAT + VVI
Timing cycle- LRL,AVI,PVARP,VRP,& URL
Concept of AV interval (AVI)
A sensed atrial event initiates AVI
Goes by LR
If no A event occurs, PPI escapes with a V pace
at LRL- VVI
• AV block with intact sinus node function (esp
useful in congenital AV block)
DDD
•
•
•
•
VAT + AAI + VVI
AV interval & VA interval
VA interval replaces the LR
Concept of PVARP (to prevent endless loop or PMT)
• Indications
• 1. The combination of AV block and SSS
• 2. Patients with LV dysfunction & LV hypertrophy
who need coordination of atrial & ventricular
contractions to maintain adequate CO
DDD
DDD Examples
The Four Faces of DDD
• Atrial and ventricular pacing
A
P
V
P
A
P
V
P
– Atrial pace re-starts the lower rate timer and
triggers an AV delay timer (PAV)
• The PAV expires without being inhibited by a ventricular sense, resulting
in a ventricular pace
DDD Examples
The Four Faces of DDD
• Atrial pacing and ventricular sensing
A
P
V
S
A
P
V
S
– Atrial pace restarts the lower rate timer and
triggers an AV delay timer (PAV)
• Before the PAV can expire, it is inhibited by an intrinsic ventricular event
(R-wave)
DDD Examples
The Four Faces of DDD
• Atrial sensing, ventricular pacing
A
S
V
P
A
S
V
P
– The intrinsic atrial event (P-wave) inhibits the lower
rate timer and triggers an AV delay timer (SAV)
• The SAV expires without being inhibited by an intrinsic ventricular event,
resulting in a ventricular pace
DDD Examples
The Four Faces of DDD
• Atrial and ventricular sensing
A V
S S
A V
S S
– The intrinsic atrial event (P-wave) inhibits the
lower rate timer and triggers an AV delay timer
(SAV)
• Before the SAV can expire, it is inhibited by an intrinsic ventricular event
(R-wave)
Dual Response to Sensing
DDD
• The pacemaker can:
– Inhibit and trigger
– A P-wave inhibits atrial pacing and triggers an SAV
interval
– An atrial pace triggers a PAV interval
– An R-wave inhibits ventricular pacing
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
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 pacing stimulus
Lower Rate Interval
VP
Blanking Period
Refractory Period
VP
VVI / 60
Upper Sensor Rate Interval
• Defines the shortest interval (highest rate) the
pacemaker can pace as dictated by the sensor (AAIR,
VVIR modes)
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 Interval-60 ppm
VP
VP
Hysteresis Rate-50 ppm
VS
VP
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 Intervals
• Initiated by a paced or non-refractory sensed atrial
event
– Separately programmable AV intervals – SAV /PAV
Lower Rate Interval
SAV
PAV
200 ms
AP
DDD 60 / 120
VP
170 ms
AS
VP
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
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
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)
Dual Chamber Timing
• Atrial Pace (AP) - Ventricular Pace (VP)
example
DDD 60
A-A interval
A-A interval
V-A interval
PAV
V-A interval
PAV
PVAB
ARP
PVAB
PVARP
VRP
ARP
PVARP
VRP
Atrioventricular Interval
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