14. Influence of individual cells on the
Unipolar Electrogram
The influence of any active cell upon the
unipolar recording is inversely
proportional to the distance between the
cell and the electrode
Because activation propagates from
cell-to-cell, active cells are organized
along a wave “front”
Consequently, the unipolar electrogram AP
is a summation of membrane currents
unipolar
14
17. Comparison of Unipolar versus
Bipolar Recording
E1 E2
Unipolar recordings measure an amplified
version of voltage at a single electrode (E1)
and retain both near and far field signal
components
Bipolar recordings measure the amplified
difference between two unipolar electrodes
(E1 - E2), which reduces common-mode
noise and far-field signal components
17
18. Unipolar versus Bipolar
E1 E2
Bipolar recordings approximate a
measure of the rate-of-change of the
wavefront
This measure is approximate because
cardiac wavefronts do not propagate
uniformly and the medium is not ideal
18
20. Propagating Activation
Wavefront
Depol. toward positive electrode Repol. toward positive electrode
Positive Signal Negative Signal
Depol. away from positive electrode Repol. Away from positive electrode
Negative Signal Positive Signal
20
21. Comparison of the Filtered and unfiltered Unipolar and Bipolar
Recordings
• Note the peak negative slope indicated by the arrow in the unfiltered
unipolar recording corresponds to the indicated negative peak in the
21 highpass-filtered unipole, confirming the approximation to rate-of-change.
22. Comparison of the Filtered and unfiltered Unipolar and Bipolar
Recordings
• Note the brief occurrence of the zero slope (arrow) in the unfiltered unipole
which corresponds with the zero-crossing and phase-reversal of the
highpass-filtered unipole. It also corresponds to the zero crossing of the
22 unfiltered bipole and the most positive peak of the filtered (32Hz) bipole.
23. Unipolar versus Bipolar Recording
Physical basis of electrograms - Summary
– The unipole records the perspective-view of the
wavefront
Wavefront = summation of the action potentials over space and time
Action potential = generated by membrane ion currents
– The bipole records the derivative (slope) of the unipole
– Bipolar recording (spatial) and the highpass filter
(temporal) are correlated, and have a lower sensitivity to
low frequencies (slow conduction) and higher sensitivity
to high frequencies (fast conduction)
23
27. Signal Filtering
Noise
Problems influencing the signal fidelity:
– Signal to noise ratio
– Distortion of the signal
To limit these a properly designed amplification system with
27 filters is required
28. Filtering
The leads record the raw electrical potential data
and send it to the amplifier.
The Amplifier increases the amplitude of the signals
Amplifier (often up to a factor of 10000).
The high-pass filter removes any base line drift or
High Pass Filter physiologic noise by cutting off anything below a set
value.
An isolation amplifier isolates the circuit from the
Isolation Amplifier patient (this can be done by transmitting the signals
optically).
The low-pass filter removes any environmental noise
Low Pass Filter by cutting off anything above a certain value.
The resultant signal is either the surface EKG or
intracardiac signals of interest.
28
29. Filtering
Surface ECG signals are concentrated in
the bandwidth between 1Hz - 80Hz.
Intracardiac ECG signals are
concentrated in the bandwidth between
15 - 60Hz
High Resolution ECG signals are
concentrated between a bandwidth of
0.05Hz - 300Hz
29
32. Filtering – Lowpass Filter
Lowpass Filter
V Corner Frequency
(Passes LF)
Pass-band Stop-band
f
cutoff frequency
(250 - 500 Hz)
A lowpass filter allows lower frequencies to pass through while reducing higher
frequencies, relative to an upper cutoff frequency. In conventional electrophysiology,
this cutoff (corner) frequency is typically in the range of 250 to 500 Hz.
32
33. Filtering
Highpass Filter
Highpass
Lowpass Filter
V Corner Frequency
repol (Passes LF) (Passes HF)
depol
Stop-band Pass-band
cutoff freq cutoff freq
f
cutoff frequency
(30 - 32 Hz) (250 - 500 Hz)
(30 - 32 Hz)
The highpass filter is the exact opposite of the lowpass filter in which higher
frequencies are now allowed to pass through while reducing lower
frequencies, relative to a lower cutoff (corner) frequency, which is typically
33 Hz.
30
34. Bandpass Filtering
Combined = Bandpass Filter (passes depolarization)
physiologic environmental
V
repol depol
Highpass Lowpass
cutoff freq cutoff freq f
(30 - 32 Hz) (250 - 500 Hz)
•The highpass reduces signal components related to physiologic noise, i.e., repolarization.
Thus the intent of these filter settings is to allow signal components related to depolarization to
pass.
•The lowpass section of the bandpass filter is intended to reduce environmental noise.
34
35. Filtering
Subtle point about highpass section:
V
32 Hz f
~16 Hz ~64 Hz
• The bandpass filters actually exhibit a gradual response to frequency, as shown in the figure, rather than
an idealized, straight-line response
• Frequencies below 16Hz (green), are reduced enough by the filter that they are essentially insignificant.
• At frequencies approximately twice the cutoff frequency (in this case 64 Hz) there is a range of frequencies
above this point in which the response of the filter is fairly flat and the signal components are passed
35
through essentially unchanged.
36. Filtering
Subtle point about highpass section:
approximates the derivative
V
Depolarization
f
~16 Hz ~64 Hz
• The red line shows a special filter response which computes the time-derivative of the signal.
• The gradual response of the highpass filter between 16 to 64 Hz is a reasonable approximation
of the rate-of-change for signal components that fall into that range of frequencies.
• The majority of the signal energy related to depolarization falls between 15-60 Hz. Thus unipolar
recordings made with a highpass filter set at 32 Hz are correlated with wavefront change. Note
both the highpass filtered unipole and the unfiltered bipole are both correlated with wavefront
36
change.
38. Expected Electrogram Progression
wavefront
A “QS”
receding Schematic Representation of RA
Stimulation of HRA portrays endocardial
breakthrough from the SA node network with
typical waveform morphologies:
50% – 50%
approaching & B • early “QS” “RS”
receding
• mid “RS”
• late “R”
wavefront
C approaching “R”
38
42. R Wave Amplitude is Dependent on the Amount
of Myocardium Involved
Large mass Small mass
myocardial myocardial
recruitment recruitment
Large mass or Large mass or
distance = Large distance = Large
amplitude amplitude
42
43. Amplitude of the ECG is effected by the size of
the Myocardium
43
44. Myocardial Characteristics and the Bipolar ECG
1. If the tissue is diseased
it will exhibit low-
frequency low amplitude
Healthy
electrograms, but if
healthy it will have high
frequency high-
amplitude electrograms
Disease
d 2. With a set distance
between the two
electrodes of the bipolar
Dead ECG, you can see the
activation time and thus
it tells you conduction
speed
44
45. R Wave Width is Dependent on the Conduction
Speed
Wide R Wave Narrow R Wave
Slow conduction Rapid conduction such as
across diseased or with myocardial recruitment
deep tissue results in post-exit results in a narrow
a wide duration duration
45
46. Unipolar Recording: Circus Movement
CL
1
1
CL Start
2
2 4
3
3
4
The red loop represents one cycle 1
length (CL) of the tachycardia
CL End
46
47. Unipolar Recording: Circus Movement
• The electrogram is a result of the
1 activation from “A” and “B”
• “A” = activation moving
toward the electrode
• “B” = activation moving away
from the electrode
B
A
CL
CL End
A
The red loop represents one cycle
length (CL) of the tachycardia
B
CL Start
1 1 1
47
48. Q wave (qs-RS) pattern
• QS Pattern at the arrhythmia
focus site
• A qs-RS pattern can occur when:
• There is a preferential pathway from the
arrhythmia focus
• Activation proceeds from a low to high
current generating region
• There is myocardium exhibiting
anisotropic conduction
Normally an arrhythmia focus has a negative deflection resulting in a QS
Pattern, but that is not always true
48
49. Unipolar Recording: Within Small Conducting
Channel
Preferential pathway
from the arrhythmia
focus
– Two components of Breakout site
activation occur:
Slow confined
conduction
* with large and
rapid activation
Rapid myocardial
breakout
conduction
49
51. Double Potentials
Barriers to
Turn around
conduction
point
3
2
1
*
Bipolar ECG Unipolar ECG
Turn around point = end of a fixed or functional barrier such as scar
51
tissue (fixed) or the crista terminalis (functional)
55. Double Potentials
Double potentials are indicative of a line of
block
Crista terminalis is an important anatomical
and functional barrier in atrial flutter
Lines of block are either fixed or functional
(anisotropy)
Atriotomy sites and the Eustachian ridge are
examples of fixed lines of block
Evidence exists that block in the region of the
crista terminalis during atrial flutter is a form of
functional conduction block
55
58. Utility of Unipolar Recording
Allows the recording of detailed
electrogram information from the distal
electrode of the ablation catheter
– Confirmation of the earliest activation site (QS
pattern)
– Analysis of the ST segment reveals the
degree of tissue contact
– Presence of ST elevation after ablation
confirms the tissue has been ablated
ST elevation: reflects myocardial tissue damage
58
59. Utility of Unipolar Recording
Confirmation of the earliest activation site (QS pattern)
QS Pattern
1
1-2
2
3
3-4
4
rS Pattern
59
61. Utility of Unipolar Recording
Analysis of the
ST segment
reveals the
degree of
Pre-ablation: strong tissue contact tissue contact
ST elevation:
reflects
myocardial
tissue
damage
61
61
ST elevation
62. Utility of Unipolar Recording
ST segment elevation post-ablation confirms the tissue has been damaged, thus the
tissue has been ablated
Pre-ablation Post-ablation
62
ST segment changes (elevation): Post-ablation
63. Unipolar Catheters
SVC
HEART
HRA
Ablation
catheter
Record unipolar recording between the distal
IVC
electrode of the ablation catheter (or the
electrodes on the CS catheter) and one of the
Reference electrodes reference electrodes in the IVC
63
64. Utility of Unipolar Electrogram Recording
Utility for determining the best
ablation site in WPW
PQS Pattern;
Recording multiple HIS
simultaneous unipolar
recordings
CS catheter with
electrodes all positive
(Uni 1-10)
64 Reference electrode is
64 negative
76. Special Uses of the CS: Catheter:
Bracketing Left-Sided Pathways
1 Wider
Narrow
Wider
The general location of a left sided AP can be located by bracketing the AP using the
CS electrograms.
• Intervals between the “A” and “V” waves, or vice versa, is wide-narrow-wide
• Determines the general location of the AP
76 • In the case above that is CS2-3
79. Electrogram Recordings - correlation with
surface ECG
Between dashed lines = A wave
Between solid lines = V wave
Between dashed & solid lines = H
potential if from the His catheter
79
82. Baseline Electrogram Recording Measurements
PR segment
NORMAL RANGE
P wave ST segment
PA (IACT) - 20-60 msec
AH - 50-130 msec
His - 10-25 msec
HV - 35-55 msec
P-A H-V
A-H
82
83. Display Sweep Speed
50mm/sec 200mm/sec
The EP doctor uses different paper speeds to analyze the data. The faster the
speed (100-200mm/sec), the more details he can see. The slower the speed
(25-50mm/sec), the easier to see the overall picture or induction of an
arrhythmia. The doctor will switch back and for between the various speeds.
The 12 lead uses 25 mm/second.
83
