1. Pacemaker ECGs Dr. K Chan Ruttonjee and Tang Shiu Kin Hospitals
HK-IN-PACE Heart Rhythm Refresher Course Module 3: ECG Interpretation
Pacemaker ECGs
Dr. K Chan
Ruttonjee and Tang Shiu Kin Hospitals

2. Outline
PPM ECG – Morphology
PPM ECG - Troubleshooting

3. PPM ECG - Morphology
CM Yu et al. Cardiac Resynchronisation Therapy

5. RV Apical vs Septal Pacing
RV Septum
RV Apical
CM Yu et al. Cardiac Resynchronisation Therapy

7. Biventricular pacing
CM Yu et al. Cardiac Resynchronisation Therapy

8. ECG morphology in BiV pacing
Loss of LV capture  Lead I : Loss of negativity
Loss of RV(A) capture  Lead III: Loss of negativity

9. CM Yu et al. Cardiac Resynchronisation Therapy

10. RV Apical Pacing ECG – Any problem?

11. RV Lead inside LV

12. BiV Pacing ECG

13. BiV Pacing ECG – Any problem?

14. PPM ECG Troubleshooting

15. Common PPM ECG Problems:
CorePace Module 4: Troubleshooting
Common PPM ECG Problems:
Oversensing
Undersensing
Noncapture
No output
Pseudomalfunction
The causes of undersensing, oversensing, noncapture, lack of output, and pseudomalfunctions vary. However, each of these anomalies compromises the pacemaker’s ability to supplement intrinsic conduction.

16. Is there any pacing spike? No pacing spike – No output
True malfunction
Over-sensing ( of T, P, R waves; myopotential, EMI, crosstalk…)
New implant: Open circuit (conductor #, loose set-screw, pin/header mismatch, air in pocket)
Old implant: Insulation or component failure, battery depletion
Pseudo-malfunction (Functional over-sensing)
Sleep rate
Rate hysteresis
Mode switching
PMT intervention
MVP (Managed ventricular pacing – Medtronic)

17. Oversensing The sensing of an inappropriate signal
CorePace Module 4: Troubleshooting
Oversensing
...Though no activity is present
Marker channel shows intrinsic activity...
Ventricular Oversensing
If a pacemaker is oversensing, you will see signals on the marker channel that do not correspond to the ECG pattern. In this example, the pacemaker recorded a ventricular pulse on the marker channel. However, no activity was demonstrated on the ECG strip. Pauses or intervals longer than the programmed lower rate will occur in single chamber systems. Dual chamber systems may show tracking at the upper rate with atrial oversensing.
This ECG exhibits oversensing that may be attributed to:
Lead insulation failure (a decrease in lead impedance will be seen)
Make-and-break fracture
A lead connection problem
(Note: The information below transitions into the next slide.)
Insulation failure—a common cause of oversensing—occurs when myopotentials are detected at the site of the insulation break. Lead fracture is another common cause of oversensing. As the frayed ends of conductor wires “make and break” contact, the pacemaker senses these “make and break” signals, which results in oversensing.
Oversensing may also occur if the lead is loose in the connector block.
The sensing of an inappropriate signal
Can be physiologic or nonphysiologic

18. Absent pacing spike – Ventricular Oversensing
1mV
Oversensing of noise  Inhibition of pacing
Decreasing sensitivity  No more noise oversensing
 Normal pacemaker output
2mV
4mV

19. Ventricular Over-sensing

20. Cross-talk : Ventricular inhibition due to far-field sensing of atrial output

21. Over-sensing – What to do?
Ask history:
Use of electronic equipments – oversensing of EMI
Arm movements – oversensing of myopotentials
Check CXR:
Lead dislodgement (e.g. Dislodged A lead sensing V)
Lead fracture/ insulation break
Loose set screws
Check PPM
Lead impedance
High  Lead #
Low  Lead insulation break
Battery depletion/Circuit failure
Real time EGM – any oversensing of T waves/ Cross talk
Programming – Rate hysteresis/ sleep rate/ PMT/
Blanking/Refractory period – long enough to prevent cross-talk / oversensing

22. Is there any pacing spike? Too many pacing spikes
True malfunction
Undersensing:
Patient factor: MI/ CMP/ Electrolytes/ Drugs / Arrhythmias AF, VF, VT
Lead factor: Lead dislodgement; loose set screw (New implant) ; Lead maturation / insulation break or fracture (Old implant); Suboptimal lead position  Small EGM
Pacemaker factor: Low sensitivity; battery depletion; circuit failure; stuck reed switch  magnet mode operation
Pseudo-malfunction: Functional undersensing
Mode related: Magnet mode, Noise mode, PMT intervention, mode switching, DVI Mode
Timing cycle related: pacemaker Wenckebach
Refractory/blanking period related: Long blanking/refractory period; pseudofusion & safety pacing; post PVC PVARP extension

23. Undersensing – What to do?
Ask history:
Symptoms of MI/ CHF
Antiarrhythmics/ diuretics
Check CXR:
Lead dislodgement (e.g. Dislodged A lead sensing V)
Lead fracture/ insulation break
Loose set screws
Check PPM
Battery status/ sensitivity/ mode/ blanking/refractory periods

24. CorePace Module 4: Troubleshooting
Undersensing
An intrinsic depolarization that is present, yet not seen or sensed by the pacemaker
P-wave not sensed
An intrinsic depolarization occurs in the atrium, but this depolarization is not sensed by the pacemaker. Therefore, the pacemaker sends an inappropriate pacing pulse to that chamber. Undersensing can be thought of as “overpacing.”
In this example, an AAI pacemaker is programmed to inhibit the atrial pacing pulse when a P-wave is sensed. Because the P-wave was not sensed, the pacemaker delivered an atrial pulse. If a pacemaker is undersensing, you will not see appropriate atrial sense markers on the marker channel.
Atrial Undersensing

25. Is there any caputre? Loss of capture
True Noncapture:
Lead factor:
New implant: Lead dislodgement, inflammation, loose set screw
Old implant: lead maturation/ fibrosis ; Lead insulation failure/ fracture
Pacemaker factor:
Battery depletion, recording system artefact
Patient factor:
MI/ CMP/ Metabolic/ Electrolytes abnormalities/ Drugs
Functional noncapture (pseudomalfunction)
Mode related: Atrial asynchronous mode: DDI / DVI Mode ; Magnet mode/ Noise reversion mode/ Mode switch
Blanking / referactory period related: Long refractory /blanking period; PVARP extension post PVC
True undersensing  pacing at absolute refractory period
Others: Saftey pacing; ectopic activation (PVC,BBB)

26. Loss of capture

27. Loss of capture: No evidence of depolarization after pacing artifact
CorePace Module 4: Troubleshooting
Loss of capture:
No evidence of depolarization after pacing artifact
This ECG strip shows loss of atrial capture, followed by a scheduled ventricular pace. Following the ventricular pulse, the marker channel recorded an intrinsic P-wave.
Loss of capture

28. Pseudomalfunctions Pseudomalfunctions are defined as:
CorePace Module 4: Troubleshooting
Pseudomalfunctions
Pseudomalfunctions are defined as:
Unusual
Unexpected
Eccentric
ECG findings that appear to result from pacemaker malfunction but that represent normal pacemaker function
Pseudomalfunctions should be ruled out as the cause(s) of an anomalous ECG strip before corrective measures are taken.

29. Pseudomalfunctions: Rate related
CorePace Module 4: Troubleshooting
Pseudomalfunctions:
Rate related
AV interval/refractory periods related
PPM Mode related

30. Rate Changes related to normal PPM operation:
CorePace Module 4: Troubleshooting
Rate Changes related to normal PPM operation:
Magnet operation
Timing variations
A-A versus V-V timing
Upper rate behavior
Pseudo-Wenckebach; 2:1 block
Electrical reset
Battery depletion
PMT intervention
Rate response
Each of these device features has an impact on pacing rates. These rate changes will appear on an ECG strip.

31. CorePace Module 4: Troubleshooting
Magnet Operation
Magnet application causes asynchronous pacing at a designated “magnet” rate
Magnet operation varies within different product lines and from manufacturer to manufacturer, but will usually involve a rate change when the magnet is applied. The Threshold Margin Test (TMT) is part magnet operation for most of Medtronic’s devices. The following operation describes magnet operation and TMT for most Medtronic devices:
Three beats at 100 bpm, followed by a magnet rate of 85
The third beat has an automatic pulse width decrement of 25% (loss of capture would indicate that the stimulation safety margin is inadequate)
Dual chamber devices will shorten the AV delay to 100 ms
Elective replacement indicators will change the rate from 85 to 65 and the mode from dual to single chamber pacing
It is important to remember that magnet modes vary from manufacturer to manufacturer, and from device to device. While recent Medtronic devices use the above rule of thumb, many older devices used the programmed lower rate as the magnet rate, or would decrease the rate by a certain percentage as a battery depletion indicator.
Kappa devices have a feature called Extended TMT. Extended TMT is a programmable feature and will operate as follows: TMT is performed at 100 ppm with the pulse width reduced by 25% on the third pulse, 50% on the fifth pulse, and 75% on the seventh pulse. This type of operation is extremely useful in assessing adequate safety margins, by simply using a magnet.

32. A to A vs. V to V Timing A-A Timing
CorePace Module 4: Troubleshooting
A to A vs. V to V Timing
A to A = 1000 ms
A-A
Timing
V-A = 800
AV = 200
AV = 150
V-A = 850
Atrial rate is held constant at 60 ppm
A to A = 1000 ms
A to A = 950 ms
AV = 200
AV = 150
V-V
Timing
V-A = 800
V-A = 800
Whether a device employs A–A versus V–V timing is important to know when troubleshooting ECG strips. If a device algorithm uses an A–A timing scheme, it will maintain a stable atrial rate regardless of intrinsic conduction that occurs from the atrium to the ventricle. Ventricular- based timing maintains a stable V–A interval that will allow for paced rates greater than the lower rate limit, if intrinsic conduction occurs between the atrium and ventricle.
Atrial rate varies with intrinsic ventricular conduction

33. CorePace Module 4: Troubleshooting
Upper Rate Behavior
Pseudo-Wenckebach operation will cause a fluctuation in rate
Pseudo-Wenckebach has the characteristic Wenckebach pattern of the PR interval gradually extending beat-to-beat until a ventricular beat is dropped. Pseudo-Wenckebach occurs when the intrinsic atrial rate begins to exceed the upper rate limit. The ventricular response to the intrinsic atrial event cannot exceed the upper rate limit, so the AV interval is lengthened until the upper rate expires and a ventricular pace can be delivered. An atrial sensed event eventually falls into the refractory period and is not seen, and therefore not followed, by a ventricular pace.
In this example, the atrial rate has exceeded the upper rate interval, and Wenckebach operation is in effect. Every third P-wave falls into a refractory period and thus is not tracked by the pacemaker.

34. CorePace Module 4: Troubleshooting
Upper Rate Behavior
2:1 block operation will cause a drastic drop in rate
2:1 block is characterized by atrial rates that occur at intervals less than the total atrial refractory period (TARP). Every other P-wave falls into the refractory period and is therefore not proceeded by a paced ventricular event. Patients who experience 2:1 block, particularly those who are active at the time the event occurs, will feel the precipitous drop in rate, which is cut in half.

35. Electrical Reset and Battery Depletion
CorePace Module 4: Troubleshooting
Electrical Reset and Battery Depletion
Reset may occur due to exposure to electromagnetic interference (EMI) – e.g., electrocautery, defibrillation, causing reversion to a “back-up” mode
Rate and mode changes will occur
Device can usually be reprogrammed to former parameters
Elective replacement indicators (ERI) can resemble back-up mode
Interrogating device will indicate ERI (“Replace Pacer”)
Electrical reset, or “back-up,” modes are usually exhibited by a rate change and often by a mode change.
Electrocautery uses radiofrequency current to cut or coagulate tissues. For example, a pacemaker may interpret the radiofrequency signal as an intrinsic event, which would result in inappropriate inhibition of a pacing pulse and could cause the pacemaker to revert to a back-up mode.
Defibrillation may damage both the pulse generator and cardiac tissue because it delivers a large amount of electrical energy in the vicinity of the pacemaker. If the pacemaker’s protective mechanisms are overwhelmed by defibrillation, the back-up mode will be activated.
Elective replacement indicators are often similar to back-up modes.

36. CorePace Module 4: Troubleshooting
PMT Intervention
Designed to interrupt a Pacemaker-Mediated Tachycardia
PMT is tachycardia that is induced by pacemaker operation. If PMT occurs, it will affect rate changes as seen on the ECG strip.
PMT intervention will extend the PVARP to 400 ms following 8 consecutive events.

37. Rate Responsive Pacing
CorePace Module 4: Troubleshooting
Rate Responsive Pacing
An accelerating or decelerating rate may be perceived as anomalous pacemaker behavior
If a patient is active it is easy to equate rate increases with rate responsive pacing. Some patients may experience “false positive” increases in rate from their sensors. In the case of a piezoelectric crystal, the pacemaker may begin pacing at a faster rate if, for example, the patient is either lying on the side that the pacemaker is implanted on or experiencing a bumpy car ride.
Minute ventilation sensors measure the change in respiration rate and tidal volume. If a patient experiences rapid respiration resulting from a cause other than exercise (e.g., hyperventilation), the pacemaker may begin pacing at a faster rate.
VVIR / 60 / 120

38. Rate Changes May Occur Due to Therapy-Specific Device Operation
CorePace Module 4: Troubleshooting
Rate Changes May Occur Due to Therapy-Specific Device Operation
Hysteresis
Rate drop response
Mode switching
Sleep function
Hysteresis, rate drop response, mode switching, and sleep function have varying degrees of impact on the rate.

39. CorePace Module 4: Troubleshooting
Hysteresis
Allows a lower rate between sensed events to occur; paced rate is higher
Hysteresis Rate 50 ppm
Lower Rate 70 ppm
Hysteresis provides the capability to maintain the patient’s intrinsic heart rhythm as long as possible, while providing back-up pacing if the intrinsic rhythm falls below the hysteresis rate. Because hysteresis exhibits longer intervals between sensed events, it may be perceived as oversensing.

40. CorePace Module 4: Troubleshooting
Rate Drop Response
Delivers pacing at high rate when episodic drop in rate occurs
Pacing therapy indicated for patients with neurocardiogenic syncope
Rate drop response therapy will exhibit pacing at high rates if detection criteria are met. Rate drop response therapy prevents a precipitous decrease in the rate, which is essential for patients experiencing neurocardiogenic syncope.

41. CorePace Module 4: Troubleshooting
Mode Switching
Device switches from tracking (DDDR) to nontracking (DDIR) mode
Mode switching is used to prevent the tracking of paroxysmal atrial tachycardias in the DDD/R and VDD modes. In this strip, an atrial arrhythmia is detected and mode switch occurs.
After the “MS” designation (for mode switch) in the middle of the strip, a gradual rate decrease occurs as a result of the mode change and the rate smoothing operation.

42. Sleep Function 30 30 mins. mins. CorePace Module 4: Troubleshooting
Lower
Rate
Sleep 30
mins. 30
mins.
A gradual rate decrease to the sleep rate (below the lower rate) will be seen as a programmed bedtime approaches.
Bed Time
Wake Time
Time

43. AV Intervals/Refractory Periods May Appear Anomalous Due to:
CorePace Module 4: Troubleshooting
AV Intervals/Refractory Periods May Appear Anomalous Due to:
Safety pacing
Blanking
Rate-adaptive AV delay
Sensor-varied PVARP
PVC response
Noncompetitive atrial pace (NCAP)
This section describes the impact of safety pacing, blanking, rate-adaptive AV delay, sensor-varied PVARP, PVC response, and NCAP on AV intervals and refractory periods.

44. Ventricular Safety Pace
CorePace Module 4: Troubleshooting
Safety Pacing
Designed to prevent inhibition due to “crosstalk”
Delivers a ventricular pace 110 ms after an atrial paced event
Ventricular Safety Pace
If atrial undersensing is occurring, ventricular safety pacing may be implemented. For example, if a P-wave is unsensed, the scheduled atrial pace is delivered shortly after the unsensed P-wave. The scheduled atrial pace initiates a PAV of which the first 110 msec is the ventricular safety pacing window.

45. CorePace Module 4: Troubleshooting
Blanking
Blanking is the first portion of the refractory period during which the pacemaker is “blind” to any activity. Blanking is designed to prevent multiple detection of a single paced or sensed event by the sense amplifier. However, if the blanking period is too long, it may not sense an event and cause inappropriate pacing.
Programmed parameters for the above strip are as follows: DDDR mode, lower rate 60, upper rate 125 ppm, AV delay 200ms, PVARP 225 ms, PAVB period 44 ms.
In the strip above, the first complex shows a paced atrial event followed by a conducted R wave. The V-A interval times out to produce an atrial paced event in the second complex, which falls very close to the intrinsic R wave. As the V-A interval times out again, the A pace falls coincident with the intrinsic R- wave. The R-wave is not sensed because it fell into the ventricular blanking period following the atrial paced event. The V-pace was delivered on the T-wave at 200 ms just as programmed. This lack of sensing is often termed “Functional Undersensing.”
A change in the lower rate (up or down) or changing the A-V interval (in this example) will allow the R-waves to fall outside the blanking period.
DDDR / 60 / 125 / 200 / 225

46. Rate-Adaptive AV Delay
CorePace Module 4: Troubleshooting
Rate-Adaptive AV Delay
AV interval shortens as rate increases
Rate-adaptive AV delay is designed to mimic the intrinsic response to increasing heart rate. In a normal heart, PR intervals decrease as the heart rate increases. Conversely, as the heart rate decreases, PR intervals increase. The rate-adaptive AV delay can be programmed to mimic the normal physiologic response of the PR interval to increasing heart rates.
PAV delay with no activity: 150 ms
PAV with activity: 120 ms

47. Long PVARP with little activity Shorter PVARP with increased activity
CorePace Module 4: Troubleshooting
Sensor-Varied PVARP
PVARP will shorten as rate increases
The duration of the PVARP will shorten during higher activity when sensor-varied PVARP is enabled.
Long PVARP with little activity
Shorter PVARP with increased activity

48. PVC Response PVARP will extend to 400 ms DDD / 60 / 120 PVARP 310 ms
CorePace Module 4: Troubleshooting
PVC Response
PVARP will extend to 400 ms
A pacemaker cannot distinguish a PVC from any other ventricular event. PVC response designates a PVC as a ventricular sensed event following a ventricular event with no intervening atrial event. When a PVC is detected, and PVC response is programmed on, the PVARP is extended in order to avoid sensing the retrograde P-wave that could occur as a result of the PVC.
A pacemaker defined PVC will initiate a V-A interval. This extended PVARP (if PVC response is on) and subsequent resetting of the timing interval may appear anomalous on an ECG.
DDD / 60 / 120 PVARP 310 ms

49. Noncompetitive Atrial Pace (NCAP)
CorePace Module 4: Troubleshooting
Noncompetitive Atrial Pace (NCAP)
Prevents atrial pacing from occurring too close to relative refractory period, which may trigger atrial arrhythmias
If NCAP is implemented, the scheduled atrial pace will be delayed until at least 300 msec have elapsed since the refractory-sensed P-wave occurred. To keep the ventricular rate from experiencing the same delay, the ensuing PAV can be shortened.

50. A Change in Pacing Modes May Be Caused By:
CorePace Module 4: Troubleshooting
A Change in Pacing Modes May Be Caused By:
Battery depletion indicators (ERI/EOL)
Electrical reset
Mode switching
Noise reversion
The Elective replacement indicator (ERI) is designed to alert the clinician at least three months before the battery voltage drops to a level at which noncapture or inconsistent pacing would result. The end of life (EOL) indication is designed to give the patient and physician adequate time to replace the device.
Battery depletion may necessitate a mode switch prior to battery failure. For example, the mode may be switched from DDD to VVI or from DOO to VOO.

51. CorePace Module 4: Troubleshooting
Noise Reversion
Sensing occurring during atrial or ventricular refractory periods will restart the refractory period. Continuous refractory sensing is called noise reversion and will:
Cause pacing to occur at the sensor-indicated rate for rate-responsive modes
Cause pacing to occur at the lower rate for non- rate-responsive modes
The portion of the refractory period after the blanking period ends is commonly called the “noise sampling period.” A sensed event in the noise sampling period will initiate a new refractory period and blanking period.

52. Noise Reversion CorePace Module 4: Troubleshooting
This example involves a VVI device in a patient with VT. The SR events are occurring due to the rapid ventricular rate. Subsequently, pacing is occurring at the lower rate due to noise reversion.

53. Pacemaker-Mediated Tachycardia (PMT)
CorePace Module 4: Troubleshooting
Pacemaker-Mediated Tachycardia (PMT)
A rapid paced rhythm that can occur with atrial tracking pacemakers

54. PMT is the Result of: Retrograde conduction
CorePace Module 4: Troubleshooting
PMT is the Result of:
Retrograde conduction
Tracking fast atrial rates (physiologic or non-physiologic)
There are two situations that can induce a pacemaker-mediated tachycardia (PMT):
Retrograde conduction
High rate atrial tracking, caused by atrial flutter or fibrillation or by atrial oversensing

55. Retrograde Conduction
CorePace Module 4: Troubleshooting
Retrograde Conduction
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.
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, the upper tracking rate has not yet expired so the SAV interval is extended. A ventricular pace is initiated at the end of the upper tracking rate. Because the SAV interval was extended, the AV conduction pathways have recovered and the ventricular pace causes another retrograde P-wave.
The sequence continues, which results in a sustained PMT.

56. Retrograde Conduction May Be Caused By:
CorePace Module 4: Troubleshooting
Retrograde Conduction May Be Caused By:
Loss of A-V synchrony due to:
Loss of sensing/capture
Myopotential sensing
Premature ventricular contraction (PVC)
Magnet application

57. High Rate Atrial Tracking is Caused By:
CorePace Module 4: Troubleshooting
High Rate Atrial Tracking is Caused By:
Supra-ventricular tachyarrhythmias
Atrial over-sensing
Atrial fibrillation, atrial flutter, etc. can quickly drive the paced ventricular rate to the upper rate limit. Similarly, oversensing caused by myopotentials or extraneous noise will be tracked, as seen on the ECG above.

60. PPM ECG Workshop