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Pacemaker timing & advanced dual chamber concepts
1. Pacemaker Timing & Advanced
Dual Chamber Concepts
Dr D Sunil Reddy
Consultant Cardiologist
KIMS Hospital
2. Topics
• Single Chamber Timing
• The NBG Code
• Dual Chamber Timing
• Dual Chamber Pacing Modes
• Upper Rate Behaviour
• Timings in Rate-responsive Pacemakers
3. Single Chamber Timing Terminology
• Lower rate & Lower Rate Interval
• Refractory period
• Blanking period
• Upper Sensor Rate & Upper Sensor Rate
Interval
4. VP VP VS VP
Lower Rate Interval
• Interval corresponding to the programmed Lower Rate
• Defines the lowest rate the pacemaker will pace
• Starts after every paced or sensed event
• Ends at the next paced or sensed event
• Vp-Vp or Vs-Vp in a VVI pacemaker
• Ap-Ap or As-Ap in an AAI pacemaker
LRI
LRI
Lower Rate = 60, LRI = 1000 ms
5. Voltage Deflections of theVoltage Deflections of the
Sensed EGM in a PacemakerSensed EGM in a Pacemaker
Pacemaker
Stimulus
Paced R wave
Post-pace T wave
Intrinsic R wave
T wave corresponding to
intrinsic R wave
2.5 mV
7. Refractory Period
Lower Rate Interval
VP VP
VVI / 60
• Interval initiated by a paced or sensed event
• Designed to prevent inhibition by cardiac or non-cardiac events e.g.
stimulus evoked R wave, repeated sensing of the same intrinsic R
wave, T waves, noise
• Events sensed in the refractory period do not affect the Lower Rate
Interval but start their own Refractory Periods
8. Refractory Period
Lower Rate Interval
• Interval initiated by a paced or sensed event
• Designed to prevent inhibition by cardiac or non-cardiac events e.g.
stimulus evoked R wave, repeated sensing of the same intrinsic R
wave, T waves, noise
• Events sensed in the refractory period do not affect the Lower Rate
Interval but start their own Refractory Periods
VP VP VR VP
LRI LRI
10. Blanking Period
Lower Rate Interval
VP VP
VVI / 60
• The first portion of every refractory period
• Pacemaker is “blind” to any activity and no events can be sensed
• Designed to prevent oversensing of pacing stimulus & after-
potential
Blanking Period
Refractory Period
11. Sensor-Indicated Rate
• The basic pacing rate in all rate responsive
modes
• Determined by the pacemaker based on the
sensor-detected level of patient activity
• Lower Rate <= Sensor Indicated Rate<= Upper
Activity Rate
13. Accelerometer Based Activity Sensor
• Located on the IC of the
pacemaker
• Does not respond to pressure or
vibrations
• Responds to motion
– Primarily in the anterior-posterior axis
Body
Movement
14. Upper Sensor Rate Interval
Lower Rate Interval
VP VP
VVIR / 60 / 120
• Defines the shortest interval (highest rate) the pacemaker can pace as
dictated by the sensor (AAIR, VVIR modes)
• A paced event can never occur before the UARI expires
Blanking Period
Refractory Period
Upper Sensor Rate
Interval
Sensor Indicated Rate
77. Noise Reversion
VPVP
SRSR SR SR
Noise Sensed
Lower Rate Interval
VVI/60
• Continuous refractory sensing will cause pacing at the lower or
sensor driven rate
78. VVIR
VP VP
Refractory/Blanking
Lower Rate
Upper Rate Interval
(Maximum Sensor Rate)
VVIR / 60/120
Rate Responsive Pacing at the Upper Sensor Rate
• Pacing at the sensor-indicated rate (= Upper Rate Interval)
79. AAIR
Lower Rate Interval
AP AP
Refractory/Blanking
Upper Rate Interval
(maximum sensor rate)
AAIR / 60 / 120
(No Activity)
• Atrial-based pacing allows the normal A-V activation sequence to
occur
Sensor Indicated Interval
80. VP VP VS VP
Lower Rate Interval-60 ppm
Hysteresis
• Allows the rate to fall below the programmed lower rate
following an intrinsic beat
Hysteresis Rate-50 ppm
82. NBG Code Review
I
Chamber
Paced
II
Chamber
Sensed
III
Response
to Sensing
IV
Programmable
Functions/Rate
Modulation
V
Antitachy
Function(s)
V: Ventricle V: Ventricle T: Triggered P: Simple
programmable
P: Pace
A: Atrium A: Atrium I: Inhibited
M: Multi-
programmable
S: Shock
D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating D: Dual (P+S)
O: None O: None O: None R: Rate modulating O: None
S: Single
(A or V)
S: Single
(A or V)
O: None
83. NBG Code Revised - 2002
I
Chamber
Paced
II
Chamber
Sensed
III
Response
to Sensing
IV
Programmable
Functions/Rate
Modulation
V
Multi Site
Pacing
V: Ventricle V: Ventricle T: Triggered V: Ventricle
A: Atrium A: Atrium I: Inhibited
D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) D: Dual (A+V)
O: None O: None O: None R: Rate modulating O: None
S: Single
(A or V)
S: Single
(A or V)
O: None
A: Atrium
84. Rate = 60 bpm / 1000 ms
A-A = 1000 ms
AP
VP
AP
VP
V-AAV V-AAV
• Atrial Pace, Ventricular Pace (AP/VP)
Four “Faces” of DDD Pacing
85. Rate = 60 ppm / 1000 ms
A-A = 1000 ms
AP
VS
AP
VS
V-AAV V-AAV
• Atrial Pace, Ventricular Sense (AP/VS)
Four “Faces” of DDD Pacing
86. AS
VP
AS
VP
Rate (sinus driven) = 70 bpm / 857 ms
A-A = 857 ms
• Atrial Sense, Ventricular Pace (AS/ VP)
V-AAV AV V-A
Four “Faces” of DDD Pacing
87. Rate (sinus driven) = 70 bpm / 857 ms
Spontaneous conduction at 150 ms
A-A = 857 ms
AS
VS
AS
VS
V-AAV AV V-A
• Atrial Sense, Ventricular Sense (AS/VS)
Four “Faces” of DDD Pacing
88. DDD Timing Parameters
• Lower rate & Lower Rate Interval
• AV and VA intervals
• Upper Tracking Rate & Interval
• Refractory periods
• Blanking periods
89. Lower Rate Interval
AP
VP
AP
VP
Lower Rate
• The lowest rate the pacemaker will pace the ATRIUM in
the absence of intrinsic atrial events
• Ap-Ap or As-Ap
• Starts with every atrial event and ends with the next
atrial event
DDD 60 / 120
90. AP
VP
AS
VP
AVI AVI
Lower Rate Interval
AV Intervals
• Electric analog of the PR Interval – allows for AV Synchrony or
atrial kick
• Initiated by a paced or non-refractory sensed atrial event
• The Atrial Channel is refractory during the AV interval
DDD 60 / 120
92. Lower Rate Interval
AP
VP
AP
VP
AV Interval VA Interval
Atrial Escape Interval (V-A Interval)
• The interval between a paced or sensed ventricular event to the
next atrial event
• Starts with a Vs or Vp
• Ends with Ap or (prematurely) with As
DDD 60 / 120
PAV 200 ms; V-A 800 ms
200 ms 800 ms
1000 ms
93. Atrial Escape Interval (VA
Interval)
• Not programmable
• A (non-refractory) ventricular event not
preceded by an atrial event (e.g. PVC, lack of
atrial sensing, no sinus activity) starts a new
VA interval
Lower rate interval – AV interval = VA interval
94. Lower Rate Interval
AP
VP
AP
VP
VA Interval
Atrial Escape Interval (V-A Interval)
DDD 60 / 120
PAV 200 ms; V-A 800 ms
200 ms 800 ms
1000 ms
PV C
95. AS
VP
AS
VP
DDDR 60 / 100 (upper tracking rate)
Sinus rate: 100 bpm
Lower Rate Interval {
Upper Tracking Rate Limit
Upper Tracking Rate
SAV
SAV
VA VA
• Prevents rapid ventricular pacing rates in response to rapid atrial
rates
• The maximum rate the ventricle can be paced in response to
sensed (intrinsic)atrial events
• Starts with every ventricular sensed or paced event
• No Vp can occur before the UTRI expires
SAV
600 ms
96. Programing Upper Tracking
Rate
• Typically programmed to 120 bpm
• Young, active patients – 150 to 180 bpm
• Patients with angina – 100 to 110 bpm
97. Refractory Periods
• Ventricular Refractory Period (VRP)
• Post-ventricular Atrial Refractory Period
(PVARP)
• Total Atrial Refractory Period (TARP)
Separate Amplifiers
• Atrial Channel
• Ventricular Channel
98. Ventricular Refractory Period
• Same as for VVI mode
• Starts with every ventricular event, including refractory
sensed events
• Events in the VRP do not affect the VA interval
AP
VPVentricular Refractory Period
(VRP)
99. Retrograde P waves
• If the AV node is not refractory during a ventricular
event, the ventricular excitation can be conducted
back into the atrium – Retrograde P wave
• Possible in both CHB & SSS patients
• Retrograde P waves may be sensed by the pacemaker
and result in initiation of an AV interval followed by a
Vp
• The Vp can in turn result in another retrograde sensed
P wave causing another Vp
• Pacemaker Mediated Endless Loop Tachycardia
100. Post Ventricular Atrial
Refractory Period (PVARP)
Post-Ventricular Atrial
Refractory Period
• PVARP starts with every sensed or paced ventricular event,
including refractory sensed events
• It renders the ATRIAL CHANNEL refractory and has no effect on
ventricular sensing
• The PVARP is intended primarily to prevent sensing of retrograde P
waves by the atrial channel
• Atrial events sensed in the PVARP do not start an SAV and are
marked Ar
AP
VPVentricular Refractory Period
(VRP)
Retrograde P wave
Lower Rate Interval
AR
101. PVARP
Upper Tracking Rate
Lower Rate Interval
{
No SAV started for events sensed in the TARP
AS AS
VPVP
SAV = 200 ms
PVARP = 300 ms
Thus TARP = 500 ms (120 ppm)
DDD
LR = 60 ppm (1000 ms)
UTR = 100 bpm (600 ms)
Sinus rate = 66 bpm (900 ms)
SAV
TARP
PVARP
Total Atrial Refractory Period (TARP)
• Sum of the AV Interval and PVARP
SAV
103. Issue: Crosstalk
• Crosstalk is the sensing of a pacing stimulus
delivered in the opposite chamber, which
results in undesirable pacemaker response,
e.g., false inhibition
DDD / 70 / 120
104. Blanking Periods
• First portion of the refractory period-sensing when sensing is
completely disabled
• To prevent sensing of the pacemaker stimulus, after potential,
repeated sensing of the same intrinsic wave and cross-talk
AP
VP
AP
Post Ventricular Atrial
Blanking (PVAB) (Programmable)
Post Atrial Ventricular
Blanking (Programmable)
Ventricular Blanking
(Nonprogrammable)
Atrial Blanking
(Nonprogrammable)
106. DDD Mode- Universal Mode
• Atrial Tracking – provides AV Synchrony and
preserves Heart Rate reserves
• Atrial intrinsic events start an SAV
• Sensed Intrinsic events in a given chamber
inhibit pacing in that chamber
107. DDD Mode
• ApVp – AV Sequential Pacing
• Sinus Rate below programmed Lower Rate
• AV conduction absent or PAV interval
programmed shorter than intrinsic AV
conduction time
136. VS VS
AP AP AP
VS
AP
A
V
DDD TIMINGDDD TIMING
137. VS VS
AP AP AP
VS
AP
A
V
DDD TIMINGDDD TIMING
VS
138. VS VS VS
AP AP AP
VS
AP
A
V
DDD TIMINGDDD TIMING
139. VS VS VS VS
AP AP AP AP
A
V
DDD TIMINGDDD TIMING
Atrial Pacing - Ventricular inhibition
140. DDD Mode
• AsVp – Atrial Tracking
• Sinus Rate greater than programmed Lower
Rate
• No intrinsic conduction or programmed SAV
is shorter than intrinsic AV conduction time
149. DDI Mode
• A-V sequential pacing WITHOUT atrial
tracking
• Atrial sensed events do not begin an SAV
• Atrial Sensed events inhibit atrial pacing
• Ventricular pacing rate cannot increase
beyond the programmed lower rate
DDI mode is used during Mode Switch due to
atrial tachycardias
155. AP
A
V
VP VS
VRPVRP
ARP PVARPPVARP ARP PVARPPVARP
ARP
AS
VP
PVARPPVARPARPARP
AS
DDI TIMINGDDI TIMING
AV RPAV RP PVARPPVARP
A-VInterval
V-A
Interval
V-A
Interval
156. AP
A
V
VP VS
VRPVRP
ARP PVARPPVARP ARP PVARPPVARP
ARP
AS
VP
PVARPPVARPARPARP
AS
DDI TIMINGDDI TIMING
AV RPAV RP PVARPPVARP
A-VInterval
V-A
Interval
V-A
Interval
166. DDI/R
Lower Rate Interval
DDI 60
PAV = 200 ms
PVARP = 300 ms
VPVP VP
AS AS APAS
PVARP PVARP
• A non-tracking mode
– Provides AV sequential pacing at lower or sensor indicated rate
VA Interval VA Interval
LR LR
VA Interval
167. 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
or if programmed lower rate > atrial intrinsic rate
169. MVP Basic Operation
AAI(R) Mode
Atrial based pacing allowing
intrinsic AV conduction
PR Intervals are only restricted by the underlying atrial rate or sensor rate;
VS events simply need to occur prior to the next AS or AP.
173. Issue: Crosstalk
• Crosstalk is the sensing of a pacing stimulus
delivered in the opposite chamber, which
results in undesirable pacemaker response,
e.g., false inhibition
DDD / 70 / 120
174. Solution: Ventricular Safety Pacing
• 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)
Post Atrial Ventricular
Blanking
PAV Interval
Ventricular Safety Pace
Window
187. Ventricular Safety Pacing
• Often seen during atrial undersensing in
patients with intact AV conduction
• Atrial undersensing results in Ap despite
intrinsic event and starts an AV interval with a
VSP window
• If the intrinsic event is conducted through the
AV Node and and the Ventricular intrinsic
event occurs during the VSP window, a
ventricular pace is delivered at the end of the
VSP window
188. Other Methods for Managing Crosstalk
• Reduce atrial output (amplitude and/or pulse width)
• Decrease (increase value) ventricular sensitivity
• Program bipolar (if possible)
• Increase the post -atrial ventricular blanking period
190. Upper Rate Behaviour
• Pacemaker operation and timings when the
atrial intrinsic rate is at or above the Upper
Tracking Rate
• Governed by two rates`
– UTR
– TARP rate
191. The Upper Tracking Rate
• Prevents the ventricles from being paced at
high rates in response to atrial tachycardias
• The ventricle can never be paced faster than
the Upper Tracking Rate in response to
sensed atrial activity
• The Upper Rate Interval is given priority over
other timing intervals
192. PVARP
Upper Tracking Rate
Lower Rate Interval
{
P Waves Blocked
AS AS
VPVP
SAV = 200 ms
PVARP = 300 ms
Thus TARP = 500 ms (120 ppm)
DDD
LR = 60 ppm (1000 ms)
UTR = 100 bpm (600 ms)
Sinus rate = 66 bpm (900 ms)
SAV
TARP
PVARP
Total Atrial Refractory Period (TARP)
• Sum of the AV Interval and PVARP
SAV
193. TARP
• The atrial channel is refractory to sensed
events that occur during the TARP
• Any atrial intrinsic event occurring in the
TARP does not start an AV interval
• Any atrial intrinsic event occurring in the
TARP is not tracked by the pacemaker and
does not result in ventricular pacing
194. TARP Rate
• TARP = SAV + PVARP (during atrial sensed rhythms)
• If SAV = 150 ms and PVARP = 350 ms,
TARP = 500 ms
TARP Rate = 120 bpm
• Atrial rates with cycle length’s less than 500 ms (or
rates greater than 120 bpm) will result in at least every
other intrinsic atrial wave falling in the TARP
• Only intrinsic events falling outside the TARP will
generate an SAV and a resultant ventricular pace
195. Fixed Block or 2:1 Block
• Occurs whenever the intrinsic atrial rate
exceeds the TARP rate
• At least 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
196. • Every other P wave falls into refractory and does not restart
the timing interval
Upper Tracking Limit
Lower Rate Interval {
{
P Wave Blocked
AS AS
VPVP
ARAR
Sinus rate = 133 bpm (450 ms)
PVARP = 300 ms SAV = 200 ms
Tracked rate = 66 bpm (900 ms)
AV PVARP AV PVARP
TARP TARP
2:1 Block
214. Wenckebach Operation
• 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
• Cycle repeats
215. PVARP
Wenckebach Operation
Upper Tracking Rate
Lower Rate Interval {
AS AS AR AP
VPVP VP
TARP
SAV PAV PVARPSAV PVARP
P Wave Blocked (unsensed or unused)
DDD Sinus rate = 109 bpm (550 ms) LR = 60 bpm (1000 ms) UTR = 100 ppm (600 ms)
SAV = 200 ms PAV = 230 ms PVARP = 300 ms
• Prolongs the SAV until upper rate limit expires
– Produces gradual change in tracking rate ratio
TARP TARP
232. Wenckebach or 2:1 block rate
during exercise/activity?
• 2:1 block –
– Atrial Rates > TARP rate
• Wenckebach
– Upper Tracking Rate < Atrial Rate < Tarp Rate
• Wenckebach is preferred
– Fewer symptoms
– Warning to patient
233. Wenckebach vs. 2:1 Block –
What Will Happen First?
What will the upper rate behavior of this pacemaker be?
Lower rate = 60 ppm
Upper tracking rate = 120 ppm
PAV = 230 ms
SAV = 250 ms
PVARP = 350 ms
234. Wenckebach vs. 2:1 Block – Solution
Upper tracking rate = 120 ppm
PVARP = 350 ms
SAV = 250 ms
• 2:1 block interval = TARP = SAV + PVARP
(250 ms + 350 ms = 600 ms)
• TARP Rate = 100 bpm
• TARP rate is less than the upper tracking rate
interval
Thus, 2:1 block will occur as soon as atrial rate
exceeds 100 bpm
235. Wenckebach vs. 2:1 Block –
What Will Happen First?
What will the upper rate behavior of this pacemaker be?
Lower rate = 60 ppm
Upper tracking rate = 100 ppm
PAV = 150 ms
SAV = 150 ms
PVARP = 350 ms
236. Wenckebach vs. 2:1 Block – Solution
Upper tracking rate = 100 ppm
PVARP = 250 ms
SAV = 150 ms
• 2:1 block interval = TARP = SAV + PVARP
(150 ms + 350 ms = 500 ms)
• TARP rate is 120 bpm
Thus, Wenckebach will begin as soon as atrial rate
exceeds 100 bpm
Wenckebach behaviour will persist until atrial rate
exceeds 120 (TARP rate), after which 2:1 block
will commence
237. What Can We Do to Make
Wenckebach Occur First?
• Shorten or reduce the TARP by:
– Shortening the PVARP
– Shortening the SAV
– Automatic PVARP
238. DDDR 60 / 120
A-A = 500 ms
AP
VP
AP
VP
Upper Activity Rate Limit
Lower Rate Limit
V-APAV V-APAV
Upper Sensor Rate
• In rate responsive modes, the Upper Sensor Rate provides the
limit for sensor-indicated pacing
• It can be programmed independently of the UTR
• Typically programmed to 120 bpm
• For younger, active patients with chronotropic incompetence –
150 bpm
239. UAR versus UTR
UTR
The ventricle can never be
paced at a rate higher than
the UTR during sensed
atrial activity
e.g. 120 bpm
All atrial rates above 120
bpm will not be tracked 1:1
by the ventricles
UAR
Maximum Sensor Indicated
Rate
The atrium can never be
paced at a rate higher than the
UAR
e.g. 140 bpm
Both atrium and subsequently
the ventricle may be paced up
to 140 bpm
241. Pacemaker Mediated
Tachycardias
• Any tachycardia that occurs due to the
presence of a dual chamber pacemaker
– Rapid ventricular pacing during tracking of rapid atrial
rates
– Sensing of EMI or EMG on the atrial channel resulting in
rapid ventricular pacing
– Tachycardia resulting from stimulation by pacemaker
during myocardial vulnerable periods
– Sensing of Retrograde P waves – Endless Loop
Tachycardia
242. Pacemaker Mediated Tachycardia
(PMT)
• PMT is a paced rhythm, usually rapid, which is
sustained by ventricular events conducted
retrogradely (i.e., backwards) to the atria
244. PMT
• Loss of AV synchrony may be caused by:
– PVC
– Very early PAC
– Atrial non-capture
– Atrial undersensing
– Atrial oversensing
• Long AV intervals can cause the AV node to
recover from refractoriness and result in
retrograde conduction
245. PMT Prevention
• Prevent Retrograde conduction
– Maintain normal AV intervals at all rates
– Good atrial sensing at implant
– Good atrial thresholds at implant
• Prevent sensing of retrograde P wave if it
occurs
246. Rate of PMT
• The rate of the PMT can never exceed the
UTR
• Depends on the programmed parameters and
the Vp to retrograde P wave interval
• Very often exactly equal to the UTR
Good afternoon ladies and gentlemen. It was with great pleasure that I accepted this invitation to discuss heart rate management in the pacing population. I have enjoyed participating in the evolution of rate-adaptive pacing for the past twleve years, and I am truly excited about Kappa’s contribution to clinical practice.
To fully appreciate Kappa’s rate response features, it is important to first understand normal daily submaximal heart rate behavior.
Single chamber timing has three components:
Lower rate interval
Refractory period
Blanking period
Single chamber devices that are programmed to a rate responsive mode add a fourth component, the upper rate interval.
During refractory periods, the pacemaker “sees” but is unresponsive to any signals. This is designed to avoid restarting the lower rate interval in the event of oversensing. T-wave oversensing in VVI and AAI modes will occur if refractory periods are too short. In the AAI mode, the pacemaker may even sense the QRS complex (“far-field R wave”) if the refractory period is not long enough.
Events that fall into the refractory period are sensed by the pacemaker (the marker channel will display a “SR” denoting ventricular refractory or atrial refractory in single chamber systems) but the timing interval will remain unaffected by the sensed event.
A refractory period is started by a paced, non-refractory, or refractory sensed event.
During refractory periods, the pacemaker “sees” but is unresponsive to any signals. This is designed to avoid restarting the lower rate interval in the event of oversensing. T-wave oversensing in VVI and AAI modes will occur if refractory periods are too short. In the AAI mode, the pacemaker may even sense the QRS complex (“far-field R wave”) if the refractory period is not long enough.
Events that fall into the refractory period are sensed by the pacemaker (the marker channel will display a “SR” denoting ventricular refractory or atrial refractory in single chamber systems) but the timing interval will remain unaffected by the sensed event.
A refractory period is started by a paced, non-refractory, or refractory sensed event.
A paced or sensed event will initiate a blanking period. Blanking is a method to prevent multiple detection of a single paced or sensed event by the sense amplifier (e.g., the pacemaker detecting its own pacing stimuli or depolarization, either intrinsic or as a result of capture). During this period, the pacemaker is &quot;blind&quot; to any electrical activity. A typical blanking period duration in a single-chamber mode is 100 msec*.
Note: In Thera and Kappa devices, nonprogrammable blanking parameters are dynamic (ranging from 50-100 ms) depending on the strength/duration of the paced or sensed signal.
Accelerometers are used with the Sigma and Kappa 700 family of pacemakers. It does not respond to pressure waves like the piezoelectric crystal, however, it interprets the data the same way.
The upper sensor rate interval in single chamber pacing is available only in rate-responsive modes. The upper rate defines the limit at which sensor-driven pacing can occur.
VOO mode paces in the ventricle but will not sense and, therefore, has no response to cardiac events. Pacemakers programmed to the VVI, VVIR, and VDD modes will revert to VOO mode upon magnet application.
In this example, an intrinsic beat occurs, but it has no effect on the timing interval and another ventricular pace is delivered at the programmed rate. No sensing occurs, thus, the entire lower rate interval is unresponsive to intrinsic activity.
In inhibited modes (VVI/AAI), intrinsic events that occur before the lower rate interval expires will reset the lower rate interval, as shown in the example above. As with paced events, sensed events will also initiate blanking and refractory periods.
The portion of the refractory period after the blanking period ends is commonly called the &quot;noise sampling period.&quot; This is because a sensed event in the noise sampling period will initiate a new refractory period and blanking period. If events continue to be sensed within the noise sampling period causing a new refractory period each time, the pacemaker will asynchronously pace at the lower rate since the lower rate timer is not reset by events sensed during the refractory period. This behavior is known as &quot;noise reversion.&quot;
Note: In rate-responsive modes, noise reversion will cause pacing to occur at the sensor-driven rate.
Single chamber rate-responsive pacing is identical to non-rate responsive pacing operation, with the exception that the pacing rate is driven by a sensor. The sensor determines whether or not a rate increase is indicated, and adjusts the rate accordingly. The highest rate that the pacemaker is allowed to pace is the upper rate limit or interval.
In this example, the pacemaker is pacing at the maximum sensor indicated rate of 120 ppm.
Although this mode is seldom used (particularly in the USA) , AAI/R pacing is a mode which, unlike VVI/R, allows for normal AV conduction to occur. AAI/R is not often used because of the risk of development of AV block which can occur over time.
In this example, the patient received a single chamber device programmed to the AAIR pacemaker mode due to sick sinus syndrome and chronotropic incompetence. Presently the patient is at rest, so the sensor is at the programmed lower rate. An atrial event (paced or sensed) will initiate a refractory period including a blanking period.
As previously stated, in AAI/R, the refractory period must be long enough so that the far-field R and T waves are ignored. Therefore, the refractory period must be longer in the AAI/R mode than in the VVI/R mode—typically 400 msec. Atrial events sensed during the refractory period in AAI/R are marked with an &quot;SR&quot; on the marker channel.
Hysteresis allows the sensed intrinsic rate to decrease to a value below the programmed lower rate before pacing resumes. Hysteresis provides the capability to maintain the patient&apos;s own heart rhythm as long as possible, while pacing at a faster rate if the intrinsic rhythm falls below the hysteresis rate.
The hysteresis rate is always &lt; the lower rate limit. The lower rate limit is initiated by a paced event, while the hysteresis rate is initiated by a non-refractory sensed event.
In the example above, the lower rate limit is 60 ppm (1000 ms), while the hysteresis rate is 50 ppm (1200 ms). The patient is paced at 60 ppm until an intrinsic event occurs, and an interval of 1200 ms is started. This patient did not have another sensed event, so a ventricular pace was delivered. However, if another sensed event had occurred, the pacemaker would again have extended the interval to 1200 ms.
Knowing the basic A-V and V-A intervals will help in understanding the four modes or “faces” of dual chamber pacing. In the first example, the pacemaker is pacing in both the atrium and the ventricle–most likely a patient with sinus node dysfunction and AV block.
In this example, the atrium is being paced, but AV conduction is intact, so the ventricular output is inhibited by a sensed ventricular event.
In this example, the atrial rate is driving the ventricular rate–also called atrial tracking. This patient has adequate sinus node function with AV block.
In this example, the patient has adequate sinus node function and intact AV conduction, but may experience little to no increase in sinus rate with activity and/or AV block that occurs at increased rates. At appropriate rates, it is best to try and utilize the patient’s intrinsic rhythm when possible.
Dual-chamber pacing requires attention to these parameters:
Lower rate
AV and V-A intervals
Upper rates
Refractory periods
Blanking periods
In order to provide optimal hemodynamic benefit to the patient, dual-chamber pacemakers strive to mimic the normal heart rhythm. In dual-chamber pacemakers, the lower rate is the rate at which the pacemaker will pace the atrium in the absence of intrinsic atrial activity. Similar to single-chamber timing, the lower rate can be converted to a lower rate interval (A-A interval), or the longest period of time allowed between atrial events.
The SAV is usually programmed to a shorter duration than the PAV to allow for the difference in interatrial conduction time between intrinsic and paced atrial events. Think of the difference in the activation sequence between a cycle initiated with an intrinsic atrial event versus a paced atrial event. The cycle starting with the intrinsic atrial event will use the normal conduction pathways between the right atrium and the left atrium. The cycle starting with the paced atrial beat will not use the normal interatrial conduction pathways but will instead use muscle tissue, which takes a little longer to reach the left atrium and causing it to contract.
If the AV interval is timed to allow the appropriate amount of time for left ventricular filling when the cycle is initiated with a sensed atrial event, the same duration for the PAV may not be the appropriate amount of time to allow for left ventricular filling when the cycle is initiated by a paced atrial event. Proper LA-LV timing promotes left ventricular filling (&quot;atrial kick&quot;) and prevents regurgitant flow through an open mitral valve. Therefore, it is beneficial to have separately programmable PAV and SAV intervals.
In this example, the lower rate interval is terminated by a sensed atrial event, which initiates a SAV interval (and restarts the the lower rate interval).
Knowing the lower rate interval and the PAV interval (A-V interval after a paced atrial event), the V-A interval can be found:
V-A interval = lower rate interval minus the AV 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.
The A-V interval is employed to allow the appropriate amount of time to optimize ventricular filling and mimic the activation sequence of the normal heart. Knowing the lower rate interval and the PAV interval (A-V interval after a paced atrial event), the V-A interval can be found:
V-A interval = lower rate interval minus PAV 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.
Knowing the lower rate interval and the PAV interval (A-V interval after a paced atrial event), the V-A interval can be found:
V-A interval = lower rate interval minus the AV 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.
The sequence of an atrial intrinsic event being sensed, starting an SAV interval, timing out the SAV interval, and pacing in the ventricle can be referred to as &quot;tracking.&quot; If the atrial rate begins to increase and continues to increase, is it desirable to let the ventricle &quot;track&quot; to extremely high rates? No. It is desirable to limit the rate at which the ventricle can pace in the presence of high atrial rates. This limit is called the upper tracking rate.
The Post-Ventricular Atrial Refractory Period (PVARP) is the period of time after a ventricular pace or sense when the atrial channel is in refractory. In other words, atrial senses outside of blanking that occur during this period are &quot;seen&quot; (and marked “AR) on the marker channel), but do not initiate an AV interval.
The purpose of PVARP is to avoid allowing retrograde P waves, far-field R waves, or premature atrial contractions to start an AV interval which would cause the pacemaker to pace in the ventricle at a high rate.
The refractory period after a ventricular event (paced or sensed) is designed to avoid restarting of the V-A interval due to a T wave. Ventricular sensed events occurring in the noise sampling portion of the ventricular refractory period are &quot;seen&quot; (and marked “VR” on the marker channel) but will not restart the V-A interval.
The atrial channel is refractory following a paced or sensed event during the AV interval. This allows atrial senses occurring in the AV interval to be &quot;seen&quot; but not restart another AV interval .
The Post-Ventricular Atrial Refractory Period (PVARP) is the period of time after a ventricular pace or sense when the atrial channel is in refractory. In other words, atrial senses outside of blanking that occur during this period are &quot;seen&quot; (and marked “AR) on the marker channel), but do not initiate an AV interval.
The purpose of PVARP is to avoid allowing retrograde P waves, far-field R waves, or premature atrial contractions to start an AV interval which would cause the pacemaker to pace in the ventricle at a high rate.
The refractory period after a ventricular event (paced or sensed) is designed to avoid restarting of the V-A interval due to a T wave. Ventricular sensed events occurring in the noise sampling portion of the ventricular refractory period are &quot;seen&quot; (and marked “VR” on the marker channel) but will not restart the V-A interval.
The atrial channel is refractory following a paced or sensed event during the AV interval. This allows atrial senses occurring in the AV interval to be &quot;seen&quot; but not restart another AV interval .
The total time that the atrial chamber of the pacemaker is in refractory is during the AV interval and during the PVARP. The Total Atrial Refractory Period (TARP) is equal to the SAV interval plus the PVARP. The TARP is important to understand as it defines the highest rate that the pacemaker will track atrial events before 2:1 block occurs.
Crosstalk is a phenomenon that occurs when one chamber senses the output pulse of the other chamber. Crosstalk can become a problem when one chamber senses the output of the other chamber and is inhibited.
If the ventricular chamber is inhibited by the atrial pacing pulse, as seen in the third complex above, the ventricular output is withheld. In this particular example, crosstalk inhibition is intermittent but the outcome could be disastrous if it occurred with every paced atrial beat. If the ventricular lead is &quot;blanked&quot; for an adequate period of time after the atrial pacing pulse to avoid seeing the atrial pacing pulse, crosstalk inhibition will not occur. Programmable ventricular blanking after an atrial pace is one method used to address the problem of crosstalk. Another solution is ventricular safety pacing.
Crosstalk is a phenomenon that occurs when one chamber senses the output pulse of the other chamber. Crosstalk can become a problem when one chamber senses the output of the other chamber and is inhibited.
If the ventricular chamber is inhibited by the atrial pacing pulse, as seen in the third complex above, the ventricular output is withheld. In this particular example, crosstalk inhibition is intermittent but the outcome could be disastrous if it occurred with every paced atrial beat. If the ventricular lead is &quot;blanked&quot; for an adequate period of time after the atrial pacing pulse to avoid seeing the atrial pacing pulse, crosstalk inhibition will not occur. Programmable ventricular blanking after an atrial pace is one method used to address the problem of crosstalk. Another solution is ventricular safety pacing.
DDD/R modes have four types of blanking periods:
A non-programmable atrial blanking period (varies from 50-100 msec) is initiated each time the atrium paces or senses. This is to avoid the atrial lead sensing its own pacing pulse or P wave (intrinsic or captured). In Thera and Kappa devices, this blanking period is dynamic, depending on the strength of the paced/sensed signal.
The PVAB-(Post-Ventricular Atrial Blanking Period) is initiated by a ventricular pace or sensed event (nominally set at 220 msec) to avoid the atrial lead sensing the far-field ventricular output pulse or R wave.
In dual-chamber timing, a non-programmable ventricular blanking period occurs after a ventricular paced or sensed event to avoid sensing the ventricular pacing pulse or the R wave (intrinsic or captured). This period is 50-100 msec in duration and is dynamic, based on signal strength.
There also is a ventricular blanking period after an atrial pacing pulse in order to avoid sensing the far-field atrial stimulus (crosstalk). This period is programmable (nominally set at 28 msec). This blanking period is relatively short because it is important not to miss ventricular events (e.g., PVCs) that occur early in the AV interval. Ventricular blanking does not occur coincident with an atrial sensed event. This is because the intrinsic P wave is relatively small and will not be far-field sensed by the ventricular lead.
The issue of ventricular safety pacing and cross-talk will be addressed later on in the presentation.
A note of caution in programming long ventricular blanking periods after an atrial pace should be mentioned. If the ventricular blanking period after an atrial pace is excessively long, conducted ventricular events may go unsensed and cause the pacemaker to pace in the ventricle after the AV interval expires. This pace could occur before the ventricle has recovered from depolarization and may induce a ventricular arrhythmia (R on T phenomena).
This is an example of normal DDI/R operation. In the DDI/R mode, the pacemaker will pace in both chambers and sense in both chambers. In response to sensing, the pacemaker will inhibit, but a sensed P wave will not trigger an AV Interval (therefore, there is no SAV Interval in the DDI/R mode). DDI/R pacing can be thought of as AAI/R with VVI/R backup.
In DDI mode the device is not tracking the atrial events, so pacing in V and A is always at lower rate.
In the case of faster AS, the unit can not control the faster atrial rate, but it will not increase the pacing rate in Ventricle and hence continue to pace at lower rate in V. (As a result you see changing AV delays).
DDIR works identical like DDI, but the sensor controls the Lower Rate and can make it pace faster and slower than programmed Lower Rate, following the sensor.
The following three slides graphically depict the three main phases of operation of the MVP pacing mode.
Primarily, MVP looks like AAI(R) mode, EXCEPT that it allows for prolonged A-V. It is an atrial-based pacing mode that looks for any consecutive A-A intervals without associated ventricular events.
AAI(R) Figure: If your patient has AV conduction, the device will operate in AAI(R) mode. The device will allow prolonged AV intervals and occasional, single, non-conducted normal atrial contractions.
Programming Recommendation – For patients with long PR intervals, the device will remain in AAI(R) mode. Permanent DDDR or DDD modes may be more appropriate if the patient is symptomatic with first degree block.
The next slide shows operation for transient loss of conduction (backup V-pacing).
Ventricular Backup Figure: For occasional, single, non-conducted normal atrial contractions, the device will provide backup ventricular pacing to ensure ventricular support.
The backup VP occurs at 80 ms post the AP event (or inhibited AP if an AS occurs prior to it).
DDD(R) Switch Figure: If your patient develops persistent loss of conduction, the device will automatically switch to DDD(R) operation, but continue to periodically look for restored conduction. Persistent loss of conduction is detected whenever 2 out of the previous 4 A-A intervals have no conducted VS event.
Note: Backup V-pacing will occur after each of the dropped beat intervals. Once the transition to DDD(R) occurs, the PAV and SAV values will operate at their permanently programmed settings. To avoid pacing the ventricle at long AV delays (upon loss of conduction), it is recommended that PAV and SAV remain at their nominal/shipped settings.
Crosstalk is a phenomenon that occurs when one chamber senses the output pulse of the other chamber. Crosstalk can become a problem when one chamber senses the output of the other chamber and is inhibited.
If the ventricular chamber is inhibited by the atrial pacing pulse, as seen in the third complex above, the ventricular output is withheld. In this particular example, crosstalk inhibition is intermittent but the outcome could be disastrous if it occurred with every paced atrial beat. If the ventricular lead is &quot;blanked&quot; for an adequate period of time after the atrial pacing pulse to avoid seeing the atrial pacing pulse, crosstalk inhibition will not occur. Programmable ventricular blanking after an atrial pace is one method used to address the problem of crosstalk. Another solution is ventricular safety pacing.
One method to manage crosstalk is to program Ventricular Safety Pacing (VSP) ON. If VSP is programmed ON, a ventricular safety pace window opens up for 110 msec after an atrial pace. The first portion of this window (about 28 msec) is blanked. After the blanking period ends, if a ventricular event is sensed within 110 msec after the atrial pace, the pacemaker will pace at the end of the 110 msec window. The logic here is that it is assumed that if a sensed event happens within 110 msec of an atrial pace, it may not have happened as a result of conduction to the ventricle (i.e., it is not physiologic), and it may be crosstalk or noise. Rather than inhibit the ventricular pace and risk having no ventricular support, the pacemaker will pace. By pacing at the end of 110 msec, if the event was truly physiologic, the pace will fall into the absolute refractory period of the ventricular muscle tissue.
Ventricular Safety Pacing is characterized by short (110 msec) AV intervals. On the marker channel, the VSP will be marked by two downward spikes–one for the ventricular sense and one for the ventricular pace. Ventricular Safety Pacing is designed to minimize the effects of cross-talk, but it can also occur under other circumstances. If a ventricular sensed event (e.g., a PVC or a conducted ventricular event) falls within the first 110 msec after an atrial pace, the pacemaker may Ventricular Safety Pace.
Also, if there is an atrial undersensing problem, ventricular safety pacing may be seen. This happens if a scheduled atrial pace is delivered shortly after this unsensed P wave. The scheduled atrial pace initiates a PAV. If the unsensed P wave conducts to the ventricle within the Ventricular Safety Pace window, a Ventricular Safety Pace will occur.
Other names for Ventricular Safety Pacing are &quot;non-physiologic AV delay&quot; or &quot;110-msec phenomenon&quot;. When in effect, the AV interval will always be shortened.
Programmed parameters for this strip are: DDD; lower rate 60; upper rate 120; PAV 150ms; SAV 150 ms. Ventricular Safety Pace (VSP) ON. VSP occurred due to a PVC falling in the AV interval.
Other methods to manage crosstalk include reducing the atrial output (while maintaining an appropriate stimulation safety margin), decreasing ventricular sensitivity (while maintaining an appropriate sensing safety margin), and programming the polarity to bipolar (if a bipolar lead is implanted).
The total time that the atrial chamber of the pacemaker is in refractory is during the AV interval and during the PVARP. The Total Atrial Refractory Period (TARP) is equal to the SAV interval plus the PVARP. The TARP is important to understand as it defines the highest rate that the pacemaker will track atrial events before 2:1 block occurs.
Pacemaker 2:1 block is characterized by two sensed P waves per paced QRS complex. This pattern develops because every other P wave falls into PVARP.
Starting on the left side of this ECG, the sequence begins with a sensed P wave. This P wave initiates a SAV, followed by a paced ventricular event. The next P wave falls into the PVARP, started by the ventricular pace, so no SAV is initiated. The following P wave is sensed outside of the PVARP, so a SAV is started. Again, no ventricular event occurs during the SAV, so the pacemaker paces in the ventricle. In this manner, a 2:1 block pattern is created.
The rate at which the pacemaker will exhibit a 2:1 block pattern is determined by the SAV and the PVARP (or the TARP). Atrial rates with a P-P coupling interval shorter than the TARP will result in 2:1 block. To determine at what rate the pacemaker will go into 2:1 block, the TARP is simply converted from an interval to a rate. Therefore, the rate the pacemaker will go into 2:1 block is: 60,000/TARP.
Pacemaker Wenckebach has the characteristic Wenckebach pattern of the PR (AV) interval gradually extending beat-to-beat until an atrial event falls into the PVARP and cannot restart an AV interval. In effect, a ventricular beat is “dropped”.
In this graphic, starting from the left side of the ECG, the pacemaker senses an atrial beat and starts an SAV. Because no ventricular event occurs by the end of the SAV, a ventricular pace is delivered. Now the pacemaker is looking for a sensed atrial beat. An atrial beat is sensed outside of the PVARP and starts an SAV. This time, when the SAV times out, the upper rate interval has not yet expired. Since the pacemaker can never violate the upper tracking rate, the ventricular pace has to be delayed until the end of the upper rate interval, at which time a ventricular pace is delivered.
This pattern of sensing a P wave, starting an SAV, waiting for the upper rate interval to time out, and pacing in the ventricle repeats until a P wave falls into the PVARP and does not start an SAV. The amount of delay created by the time from the sensed P wave until the upper rate interval expires is a little longer each time, producing the gradually lengthening of the P wave to ventricular pace intervals.
Once a P wave falls into the PVARP and does not initiate an SAV, the pacemaker looks for the next sensed P wave and the pattern starts all over again. This is how the classic Wenckebach pattern develops.
The rate at which the pacemaker will exhibit Wenckebach behavior is at the upper tracking rate (or upper rate if the pacemaker does not have a separate upper tracking rate and upper activity rate).
This ECG depicts Wenckebach operation.
Compare the P-P interval at which the pacemaker will exhibit Wenckebach to the P-P interval at which the pacemaker will go into 2:1 block.
Upper tracking interval = 60,000/120 = 500 msec
2:1 block interval = TARP = 200 msec + 350 msec = 550 msec
As the P-P interval shortens from the lower rate interval, the 2:1 block interval (550 msec) will be met before the upper tracking interval (500 msec). Therefore, the pacemaker will go into 2:1 block as the atrial rate increases and will never exhibit Wenckebach behavior.
In this example, the TARP is shorter than the upper tracking rate interval. Therefore, the pacemaker will exhibit Wenckebach operation as the P-P interval exceeds the upper tracking rate interval.
Going to 2:1 block first without a Wenckebach period may not be the optimal situation because many patients do not tolerate a precipitous drop in ventricular rate well. What can we do to make Wenckebach occur first?
Shorten PVARP (Note: Sensor varied PVARP will be addressed later on in the module with mode switching, but it can be discussed as a solution briefly)
Shorten SAV
Turn on RA-AV
This upper rate is defined as the upper activity rate, also known as the upper sensor rate or maximum sensor rate.
Before mode switching was available, pacemakers utilized a separate activity/sensor rate and upper tracking rate to limit the rate to which the patient could track (e.g., in the presence of SVTs), but allow the patient to pace to higher rates if they were exercising.
Even patients who have complete antegrade block may have the ability to conduct retrograde. But having the ability to conduct retrograde is not enough. There must be a situation in which the conduction pathways have had a chance to recover when a ventricular contraction occurs. Basically, anything that causes a loss of AV synchrony may promote retrograde conduction and potentially a PMT. All of the above conditions (PVC, atrial non-capture, atrial undersensing, and atrial oversensing) cause a loss of AV synchrony and may promote a PMT.
This diagram shows the initiation of a PMT by a PVC. A retrograde P wave occurs as a result of the PVC. This retrograde P wave is sensed outside of the PVARP and starts an SAV Interval. When the SAV Interval times out, if the Upper Tracking Rate has not yet expired so the SAV Interval is extended. A ventricular pace is delivered at the end of the upper tracking rate. The AV conduction pathways have recovered and the ventricular pace causes another retrograde P wave.
The sequence continues resulting in a sustained Pacemaker Mediated Tachycardia (PMT).
