described about pacemaker timing cycle, pacing mode, upper rate behavior

1. Pacemaker timing cycles
Dr Harsh Pandey

2. overview
• Introduction
• Pacing modes
• Timing cycles
• Rate modulated pacing
• Base rate behaviour
• Upper rate behaviour
• Special algorithms

3. Introduction
• Development of implantable pacemaker in 1958
• Become highly complex
• In an attempt to treat different cardiac conditions
• Addition of multiple specialized features

4. Timing cycles
• Based on cardiac events
• Include different blanking periods, refractory periods and intervals
• Number and complexity depends on no. of leads, pacing modes, rate
sensor

5. Pacing nomenclature
• 5 letter code
• First  Chamber pacing  A, V, D
• Second  Sensing  A, V, D
• Third  Response to sensed event  I, T, D
• Fourth  Rate modulation (sensor)
• Fifth  Multisite pacing  A, V, D (BV device)

6. Pacing modes

7. Types of Pacing
• Single Chamber
• Dual Chamber
• Fixed Rate
• Asynchronous
• Demand
• Synchronous

8. PACING MODES
• Single chamber
• Asynchronous pacing
• VOO
• AOO
• Synchronous
• Inhibited - VVI, AAI
• Triggered – VVT, AAT
• Dual Chamber
• Asynchronous
• Both chambers : DOO
• Single chamber : Non P –
synchronous pacing
• Synchronous
• DDD
 Rate Modulated Pacing
 Single or dual chamber
 Synchronous or asynchronous

9. Asynchronous Pacing
VV
AA
AV VA
VOO pacing
AOO pacing
DOO pacing

10. Atrial inhibited pacing (AAI)
Automatic Interval
Ap Ap Ap Ap
As
Escape Interval
AV Conduction disease is an issue

11. Ventricular inhibited pacing (VVI)
Automatic Interval Escape Interval
Vp Vp Vp
Vs
Vp Vp Vp
VRP
Associated with AV dysnchrony – manifest as pacemaker syndrome, higher
incidence of atrial arryhthmias

12. Single chamber triggered mode (w/o inhibition) (AAT OR VVT)
• Deliver pacing output every time a native event is sensed or LRL is
reached
• Deforms native signal, may compromise ECG interpretation
• Historically used to prevent inappropriate inhibition from oversensing
• In contrast to AOO or VOO mode, less likely to induce arrhythmias
• Pace within refractoriness

13. VVT

14. Dual Chamber pacing
• The role of Dual Chamber Pacing is to fill in the blanks for the patient.
• In other words, if the patient doesn’t have a P-wave then the pacemaker will pace in the atrium
• If the patient doesn’t have an R-wave then the pacemaker will pace in the ventricle
Ap Vp Vp
Ap As As
Vs Vs
Complete
inhibition
P wave
synchronous
Atrial
Pacing
AV
sequential

15. DDD
• Pacing & sensing both in Atrium & Ventricle
• Response of Sensing: Triggered & Inhibition
• A- Sense-
• Inhibits the next schedule Ap
• Triggers an AV interval (SAV)
• A- paced
• Triggers an AV interval (PAV)
• V- sense events-Inhibits the next schedule Vp.

16. Dual-chamber Timing
AV Delay
VA Interval
LRL
A-Blanking
PVARP
V-Blanking
MTR
V Ref
Timing Intervals – Dual Chamber (DDD):

17. DDI mode
• Dual chamber pacing and sensing with inhibition but w/o tracking
• AV sequential pacing (D) with dual chamber sensing (D) and inhibition
without P synchronous pacing
• Indication  presence of paroxysmal AF/Afl
• Commonly programmed as a mode switch to avoid tracking

18. Timing cycles

19. Timing Circuits
• Lower rate/ Lower rate interval- lowest rate the pacemaker will pace
• A paced or sensed event resets or restarts the timer

20. Single & dual chamber timing cycles
Works like clock

21. 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
• 60,000 / Pacing rate in ppm = ms
• 60,000 / 60 ppm = 1000 ms
• 60,000 / Interval in ms = ppm
• 60,000 / 1000 ms = 60 ppm
ms ppm
60,000

22. Base rate or lrL

23. Hysteresis
• Allows the rate to drop below programmed pacing LRL
• Advantages
• Rate & Search Hysteresis

24. Not pacing
Still not pacing
Falls below Hysteresis
Then
Paces at Base Rate

25. VVI MODE
• Automatic interval starts from a paced complex (to the next paced complex)
• Escape interval starts from a sensed complex (to the next paced complex)
If the intervals are equal:
•No hysteresis
If the escape interval > automatic interval:
•Hysteresis
Automatic Interval Escape Interval

26. VVI MODE (with hysteresis)
1000 ms
850 ms
Escape interval = 1000 ms (60 ppm)
Automatic interval = 850 ms (70 ppm)

27. Rate Hysteresis
• Allows the intrinsic rate to drop below the Hysteresis rate before
pacing will occur
• Looks like you have a separate rate for pacing and sensing
• The purpose of Hysteresis is to promote intrinsic conduction

28. AV Interval
• Sensed AV Interval – 30msec less than Paced
• Paced AV interval

29. Differential atrioventricular interval
• The differential AVI to provide an intra‐atrial conduction time of
equal duration whether atrial contraction is paced or sensed.
• Sensed AV delay (SAV), commences only when the atrial
depolarization is detected by the pacemaker
• Commonly occurs 20–60 ms after the onset of the P wave on a
surface ECG
• Conversely, the AVI initiated with atrial pacing, referred to as
paced AV delay (PAV), commences immediately with the pacing
artifact

30. VA interval
• ATRIAL ESCAPE INTERVAL
• Interval between a paced/sensed ventricular event to the next atrial
event
• Only present in dual‐chamber pacing modes, regardless of
tracking feature (DDD, DDI, DVI).
• Not programmable (LRI – AV interval)
• Starts with Vs or Vp
• Ends with Ap or As
• PVC resets

31. Upper tracking rate / URI
• PREVENTS RAPID VENTRICULAR RATE in response to rapid atrial rate
eg AF/AT
• “Maximum rate at which the VENTRICLE can be paced in response to
SENSED ATRIAL EVENT”

32. Programming UTI
• Typically programmed to 120 bpm
• Young active patients – 150 to 180 bpm
• Patients with angina- 100 to 110 bpm

33. Refractory and Blanking periods
• Refractory period- Sensing present but no action
• Blanking period- No sensing, no action

34. Blanking period

35. Refractory period
Prevents T wave
OVERSENSING

38. Various BPs and RPs
Blanking period Time Importance
Atrial blanking period 30-50ms Non programmable,
Avoids atrial sensing of
its own beat
Post ventricular atrial
blanking period
220 ms Avoids sensing of
ventricular beat ()
Long PVAB decreases
detection of AF, Afl
Ventricular blanking
period
50-100 ms Non programmable,
avoids ventricular
sensing of its paced
beat
Post atrial ventricular
blanking period
<60 ms If the PAVB period is too
long, R on T ventricular
arrhythmia

39. Various BPs and RPs
Refractory period Importance
Ventricular refractory
period
Prevents sensing of T
wave
Atrial refractory period AVI (120-200 ms)
Post ventricular atrial
refractory period
Avoids sensing of
retrograde P wave (PMT),
far field R waves

40. Timing cycles based on
pacing modes

41. Asynchronous modes
• Single chamber pacing modes (AOO, VOO)
• pace the assigned chamber at LRL (only timing cycle), which is not reset by
any intrinsic cardiac event due to lack of sensing
• In dual‐chamber or AV sequential asynchronous (DOO) pacing
• interval from atrial to ventricular pacing (AVI) and the interval from
ventricular pacing to the subsequent atrial pacing – the ventriculoatrial
interval (VAI) also referred to as the atrial escape interval (AEI) – are fixed

42. • Atrial inhibited pacing
(AAI)
• atrial blanking period
(ABP)
• atrial refractory period
(ARP)
• LRL (A–A interval)
Atrial inhibited pacing (AAI)

43. • Ventricular inhibited (VVI)
pacing
• Ventricular blanking period (VBP)
• Ventricular refractory period
(VRP)
• LRL (V–V interval)
Ventricular inhibited pacing (VVI)

44. • DDD pacing mode
• LRL = VAI + AVI
• post‐atrial ventricular blanking period (PAVB)
• post‐ventricular atrial blanking period (PVAB)
• post‐ventricular atrial refractory period
(PVARP)-
sensed or paced ventricular event initiates
a refractory period on the atrial channel
• difference between PVAB and PVARP is that
while the first one occurs only after VP event,
PVARP occurs after either VS or VP event.
• PVARP is designed to prevent ventricular
tracking of a retrograde P wave
DDD pacing mode

45. PVARP and TARP
• The PVARP is a programmable interval in dual‐ chamber pacing
modes with atrial sensing (DDD, DDI, VDD), initiated after a
sensed or paced ventricular event
• To avoid inappropriate tracking of sensed signals due to
retrograde P waves.
• If an atrial event occurs during PVARP, timing cycles (VAI, LRL)
are not reset.
• Nevertheless, sensing of atrial signals during PVARP allows
proper mode switch (non‐ tracking pacing mode) when atrial
fibrillation, flutter, or tachycardia occurs

46. PVARP and TARP
PVARP
TARP
AV
AV VA / AEI
The combination of the PVARP and the AVI establishes the total
atrial refractory period (TARP)
TARP is the limiting factor for the upper rate limit (URL) or so‐
called MTR in P‐synchronous dual‐chamber pacing modes

47. Rate modulated pacing

48. Sensor function
• Refers to the modulation of the paced rate in response to an
input signal other than the presence or absence of native
depolarization.
• Based on
• (i) motion (either acceleration or vibration)
• (ii) changes in impedance as a measure of minute ventilation and/or
contractility (Closed Loop Stimulation, Biotronik, Germany)
• (iii) duration of the QT interval

49. Sensor function
• Temporarily adjusts the rate of the
pacemaker.
• If the patient is active and rate
modulation is enabled, the heart rate
is determined by either the native rate
or the SIR, whichever is faster.
• The SIR behaves in a manner
identical to the programmed base
rate.
• In essence, the sensor‐driven pacing
rate acts as if the LRL has been
increased.
• Rate modulation requires a
programmed URL, referred to as the
maximum sensor rate.

50. MSR vs MTR
• Although the MSR and MTR are closely related, they are not
identical.
• The tracking rate refers to the rate at which the pacemaker is
sensing and tracking intrinsic atrial activity.
• The MTR is the maximum ventricular‐paced rate that is allowed
in response to sensed atrial rhythms.
• The MTR may result in fixed block, Wenckebach, fallback, or
rate‐smoothing responses, depending on the design of the
system

51. base rate behaviour

52. BASE RATE BEHAVIOR
• Ventricular based timing
• Atrial based timing
VA / AEI
A A

53. Upper rate behaviour

54. Upper Rate Behaviour
• The pacemaker’s response to sensed rapid atrial rates.
• A rapid atrial rate is a rate > Upper Rate Limit (URL) or Ventricular Tracking
Limit (VTL)
• VTL= a rate beyond which 1:1 tracking will NOT occur
= “the absolute speed limit in the ventricle”

55. Page 61
Upper Rate Pacing Characteristics
• Upper rate behavior refers to how a dual-chamber pacemaker will behave when the
atrial rate exceeds the programmed max tracking rate
• There are three types of upper rate behavior
• 1:1 Tracking
• Pacemaker Wenckebach
• 2:1 Block
• The key to upper rate behavior is in the atrium
• Observed only when the device is tracking intrinsic P waves (A sense/V pace)

56. Page 62
Upper Rate Pacing Characteristics
Pacemaker Wenckebach
W
As Vp As Vp
MAXIMUM TRACKING RATE
TARP
PVARP
AV
TARP
PVARP
AV

57. Page 64
Upper Rate Pacing Characteristics
2:1 Block
AV
PVARP
TARP
MAXIMUM TRACKING RATE
AV
PVARP
TARP
Vp (As) Vp
2:1 Rate = 60,000 / TARP
As As

59. Page 66
Upper Rate Pacing Characteristics
1:1
Wenckebach
2:1 Block
TARP
MTR
LRL
Sinus
Rate
Upper Rate Behavior is determined by TARP and MTR

60. Page 67
Upper Rate Pacing Characteristics
1:1
Wenckebach
2:1 Block
TARP
MTR
LRL
Sinus
Rate
MTR = 140 ppm AV = 100 ms PVARP = 300 ms TARP = 400 ms
Upper Rate Operation – 2:1 Block > MTR
2:1 Block Point = 60,000/TARP = 60,000/400 = 150 bpm

61. Page 68
Upper Rate Pacing Characteristics
Upper Rate Operation – 2:1 Block < MTR
1:1
2:1 Block
MTR
TARP
LRL
Sinus
Rate
MTR = 140 ppm AV = 200 ms PVARP = 300 ms TARP = 500 ms
2:1 Block Point = 60,000/TARP = 60,000/500 = 120 bpm

62. Special algorithms

63. Managed Ventricular Pacing(MVP) Mode
• To minimise the amount of ventricular pacing
• A mode inside a DDD Pacemaker
• Is in AAI mode as long as there is good AV conduction
• Atrial pacing (thus minimising Ventricular pacing)

64. DDD <----> AAI
• Pacemaker automatically detects AV conduction (Conduction tests)
and switches the modes
• Thereby minimising the VENTRICULAR pacing

65. Ventricular safety pacing
• Oversensing of atrial pacing artifact
• Ventricular pacing inhibition
• To prevent atrial cross talk, PAVB
• Sometimes trailing edge of pacing artifact
• Occasionally sensed by ventricular channel
• Inhibition of ventricular pacing output
• DDD pacing mode has safety mechanism
called ventricular triggering period or
cross talk sensing window

66. Blanking Period
Cross talk sensing window
AV
Alert Period

67. Blanking Period
Cross talk sensing window
Ventricular
Safety Pacing
AV

68. Ventricular safety pacing
• If activity is sensed on the ventricular sensing amplifier during
the initial part of AVI (possible cross‐talk present), a ventricular
output is triggered (safety pacing).
• This early ventricular pacing typically occurs with a short (100–
120 ms) or programmed AVI.
• Occurrence of cross‐talk and safety pacing should be
suspected if AV pacing is noted at a shorter than programmed
AVI on ECG.

69. Ventricular safety pacing

70. Alert Period
• Definition:
• The portion of the timing cycle where the device senses electrical activity
(e.g. cardiac) and responds in a preset or programmed manner
PVARP
TARP
A
V
AV VA / AEI
AP

71. Alert Period
• Definition:
• The portion of the timing cycle where the device senses electrical activity
(e.g. cardiac) and responds in a preset or programmed manner
PVARP
TARP
A
V
AV VA / AEI
AP
VV
VRP AP
Pacing Interval
ASW

72. Page 79
Dual-chamber Timing
VA = V-V – AV
V-V = VA + AV
Lower Rate = 60 ppm
V-V = 1000 ms
AV Delay = 200 ms
VA = 1000 ms – 200 ms = 800 ms
Timing Intervals – Example:

73. Blanking Period
Cross talk sensing window
AV
Alert Period

74. Crosstalk
• Sensing of the atrial output pulse by the ventricular sense
amplifier

75. Crosstalk Inhibition
• Inappropriate inhibition of the ventricular spike due to
sensing of the atrial output pulse by the ventricular
sense amplifier.

76. Crosstalk Sensing Window
• A short period of time that starts at the end of the ventricular
blanking period
• If during this time interval the ventricular lead senses an
event (may be crosstalk, may also be a PVC), a ventricular
output pulse is delivered after 110 ms = SAFETY PACING
• This 110 ms time period = Non Physiologic AV delay

77. Safety Pacing
• Designed to prevent inhibition due to “crosstalk”
• Delivers a ventricular pace 110 ms after an atrial paced event

78. Blanking Period
Cross talk sensing window
AV
Alert Period

79. Blanking Period
Cross talk sensing window
Ventricular
Safety Pacing
AV

80. Algorithm for Atrial Arrythmia

81. Rate smoothing

82. Automatic Mode Switch Base Rate
• Automatic mode switching is a programmable option in all current-generation pacemakers for
patients with paroxysmal atrial tachyarrhythmias.
• When the atrial rate exceeds the programmed mode switch rate, the device automatically
changes its mode to either the VVI or DDI, in which ventricular tracking of atrial-sensed events do
not occur.

83. Atrial Flutter Response

84. • Sinus Preference
• timing cycle attempts to maintain sinus rhythm, i.e., sinus preference
• If sinus rhythm is detected within that programmable rate, the sinus rhythm is then allowed to
predominate.
• Atrial Fibrillation Prevention Algorithms
• shorter atrial pacing cycle after a premature atrial contraction to prevent the “short-long” cycle that
typically occurs,
• incremental atrial pacing rate to overdrive sinus rhythm and/or atrial premature contractions, and
• faster pacing following a mode switch episode.

85. Mode switch/fall back

89. Rate drop response

90. Noise reversion response
• All manufacturers have a noise reversion algorithm to prevent
asystole or inappropriate bradycardia
• Exposed to an external source that can generate inappropriate
sensing, such as electromagnetic interference (EMI).
• Most algorithms will label these signals as electrical “noise” if
they exceed physiological rates (400–600 bpm)
• Once the counter of the noise reversion algorithm is met, the
device will adopt an asynchronous pacing mode

91. Noise reversion response

92. Magnet response
• Used in special circumstances, such as
• (i) temporary asynchronous pacing (such as in a
pacemaker‐dependent individual who will undergo a procedure
where pacing inhibition is likely due to EMI) and
• (ii) assessment of pacing and battery status (latter determined
by base pacing rate).

93. Magnet response
• Single‐ and dual‐chamber pacemakers will almost always result
in asynchronous pacing (AOO, VOO, DOO)
• Battery status
• In contrast to pacemakers, defibrillators will not display
asynchronous pacing mode, but will inhibit detection of
ventricular arrhythmia (disabling therapies)

94. Pacemaker mediated tachycardia
• Endless loop tachycardia or pacemaker circus movement
tachycardia
• Repetitive retrograde VA conduction.
• PMT can only occur in DDD or VDD pacing modes
(P‐synchronous ventricular pacing)

95. PMT
• A retrograde P wave initiating PMT can be triggered by
• (i) PVC
• (ii) at the end of ventricular threshold testing in VVI mode,
where the device switches immediately to DDD pacing mode
sensing retrograde P wave

96. Pmt
Not captured
Atrial threshold testing
Atrial threshold testing

98. Prevention and termination of pmt
• Programming the PVARP longer than VA conduction during ventricular
pacing
• PVARP extension after PVC, since they are the most common triggers

99. For questions 3 and 4:
A 75 year old male with complete heart block and an old
anterior myocardial infarct has a DDD pacemaker with the following settings:
Low rate - 60 ppm MTR - 120 ppm
AV delay - 150 msec PVARP - 250 msec
V refractory period - 300 msec PVAB - 100 msec
3. The pacemaker Wenckebach window would be how long:
1. 50 msec
2. 100 msec
3. 150 msec
4. 200 msec

100. For questions 3 and 4:
A 75 year old male with complete heart block and an old
anterior myocardial infarct has a DDD pacemaker with the following settings:
Low rate - 60 ppm MTR- 120 ppm
AV delay - 150 msec PVARP - 250 msec
V refractory period - 300 msec PVAB - 100 msec
3. The pacemaker Wenckebach window would be how long:
1. 50 msec
2. 100 msec
3. 150 msec
4. 200 msec

101. For questions 3 and 4:
A 75 year old male with complete heart block and an old
anterior myocardial infarct has a DDD pacemaker with the following settings:
Low rate - 60 ppm MTR - 120 ppm
AV delay - 150 msec PVARP - 250 msec
V refractory period - 300 msec PVAB - 100 msec
4. The pacemaker for the above 75 year old patient will reach
its 2: 1 block point at what rate?
1. 120 ppm
2. 150 ppm
3. 160 ppm
4. Would not reach a 2: 1 block point

102. For questions 3 and 4:
A 75 year old male with complete heart block and an old
anterior myocardial infarct has a DDD pacemaker with the following settings:
Low rate - 60 ppm MTR- 120 ppm
AV delay - 150 msec PVARP - 250 msec
V refractory period - 300 msec PVAB - 100 msec
4. The pacemaker for the above 75 year old patient will reach
its 2: 1 block point at what rate?
1. 120 ppm
2. 150 ppm
3. 160 ppm
4. Would not reach a 2: 1 block point

103. Thank you