Download CRT: FU - ECG Analysis

CRT Electrograms
Mazen Tawfik, MD
Ain Shams University
Introduction
– All device therapy relies on the ECG for
quick & reliable assessment of system
function.
– For any device, an ECG should be done in
the acute phase, to verify proper capture
and sensing, and further ECG evaluations
should occur during regular follow up.
– The CRT device presents some challenges in
ECG interpretation, even for those
experienced in analyzing ECGs from
conventional PMs and ICDs.
CRT EGMs
• Basics of EGMs
– Electrical energy from the heart causes
deflections on the tracing.
– The deflections are based on the path the
electrical energy uses to travel through the
heart.
– Understanding the electrical flow through
the heart is the first step in making sense of
CRT EGMs.
CRT EGMs
• ECG analysis of a CRT device focuses on:
– Is the device capturing both ventricles?
– Is the LV lead in its proper place?
– Is there is any remarkable device or
rhythm behavior that may need to be
addressed?
CRT EGMs
• The primary GOAL is :
o To differentiate between :
 LV pacing
 RV pacing
 Biventricular pacing
o Based on changes in the electrical
axis.
Direction of Depolarization
ECG Axis
ECG Principle
ECG Lead
Depolarization Front
(positive pole)
(axis)
+
+
Deflection
of QRS
ECG Principle
One Cardiac Event, Different Deflections
Standard ECG Leads
-
I
-
+
-
III
II
+
+
Einthoven
Standard ECG Leads
-
-
+
+
+
III
II
Einthoven
I
Standard ECG Leads
Superior
aVR, aVL
aVR
aVL
Right
I Left
V6
III, aVR,
V1
V1
V2
aVF
III
Inferior
V3
V4
V5
II
II, III, aVF
I, aVL,
V5 , V6
Normal Sinus Rhythm (Unpaced Heart)
Direction of Depolarization Vector
RV
LV
BiV
Conduction Pathways
RV Apical Pacing
aVR
I
aVL
V1
I
V2
III
V3
II
II
III
aVF
aVR
V4
V5
aVL
aVF
Schüller, Faraeus 1981
V6
pos.: I, aVL
neg.: II, III, aVF
+/-: aVR
LV Pacing
aVR
I
aVL
V1
I
III
V2
V3
aVR
V4
aVL
V5
aVF
Schüller, Faraeus 1981
V6
II
II
III
aVF
pos.: aVR, V1
neg.: I, II
+/-: III
Mean Pacing Axes Observed in VIGOR CHF Clinical Trial
Experience with the
VIGOR CHF
demonstrates the
relationship between BV,
RV, and LV axes and
their distribution.
Although the patient
population axes are
variable, for a given
individual, the BV axis is
always superior and in
between the RV and LV
pacing axes.
Results
Leads I and III Best Show Changes
Electrical waveforms & ECG morphology
Lead I for Right sided cardiac activity
Lead III for Left sided cardiac activity
Observed ECG Morphologies: BV to RV Pacing
BiV  RV
BiV  RV
BiV  RV
Experience with the VIGOR CHF study confirms that the axis
shift from BV to RV pacing is reflected in increasing positivity
of the QRS in Lead I. Although the axes may start and end in
different places, the shift is always towards the patient’s left.
Loss of Capture
Think Positive
BiV  RV
BiV  LV
Think Positive
• Perform threshold test while simultaneously
monitoring Leads I and III.
• Both lead I and III are classically negative.
• If the amplitude of Lead I shows increasing
positivity, then the patient has gone from BV
pacing to RV pacing.
• If the amplitude of Lead III shows increasing
positivity, then the patient has gone from BV
pacing to LV pacing.
Output Decrease
I
II
III
aVR
aVL
aVF
Polarity change in I, III
Asirvatham et al. 2004
Loss of LV capture
Output Increase
I
II
III
aVR
aVL
aVF
Polarity change in I, III
Asirvatham et al. 2004
LV capture
Loss of Capture
Summary
Leads
BV to RV
BV to LV
Lead I
Increase in
Positivity
Little or no
change
Lead III
Little or no
change
Increase in
Positivity
Clinical Application; Capture Testing
• Capture testing:
 Old tied output devices.
 Modern independent output devices.
Tied-Output Devices
• Older CRT systems had a single ventricular
output for LV and RV stimulation.
• “Tied” outputs delivered simultaneous pacing
pulses to LV and RV and required both outputs
to be programmed to the same output settings,
etc.
• RV and LV channels are electrically tied
together.
• RV and LV output and sensing functions cannot
be programmed independently.
• Although no longer implanted, it is possible to
still see such devices in PM clinics.
Tied-Output System
Loss of Capture in a Tied-Output System
• In a tied-output system, the loss of
ventricular capture (either RV or LV) will
result in a changed ventricular
morphology on the tracing.
• When a CRT device loses RV capture, it
starts to pace LV only; likewise the loss
of LV capture means the device is RV
pacing only.
Capture Tests in Tied-Output Devices
• Capture tests use the standard step-down
protocol:
– Outputs are decreased in small incremental
steps until capture is lost
• Most patients will have different RV and LV
thresholds.
• This means a capture test will cause the loss of
pacing in one ventricle before the other.
• The device will transition from:
– CRT to LV only to no pacing
– CRT to RV only to no pacing
• These transitions are observable on the tracing as
changes in the QRS morphology.
Capture Tests in Tied-Output Devices
• A change in QRS morphology indicates a
transition in pacing (from BV to singleventricle pacing).
• If the QRS on Lead I gets more positive,
then LV capture was lost and the device is
pacing the RV only.
• If the QRS on Lead I gets more negative,
then RV capture was lost and the device is
pacing the LV only.
• Keep stepping down until all pacing is lost
to find both thresholds.
Loss of LV Pacing in Tied-Output Device
Loss of LV Pacing in Tied-Output Device
Loss of RV Pacing in Tied-Output Device
Loss of RV Pacing in Tied-Output Device
Fusions and Pseudofusions
Anodal Stimulation
• All electricity travels in a circuit (from pole to pole).
• With a bipolar lead, both poles are on the lead itself.
• With a unipolar lead:
– The electrode on the lead is the cathode (negative
pole).
– The pulse generator itself is the anode (positive
pole).
• When using a unipolar LV lead, it gets more
complicated:
– The electrode on the LV lead is the cathode
(negative pole).
– An electrode on the RV lead is the anode (positive
pole).
• This phenomenon (which requires a unipolar LV lead)
is called Anodal stimulation.
Anodal Stimulation
• Requires unipolar LV
pacing.
• The stimulating output
pulse from the LV forms
a circuit with the RV
lead.
• This means that RV and
LV will be stimulated
simultaneously
• This causes.
simultaneous RV and LV
capture.
Capture Test with Anodal Stimulation
Anodal stimulation
LV Only Pacing
Loss of LV Capture
Independent Outputs
• All CRT devices manufactured
today offer independent
ventricular outputs:
– Different output settings
available for LV and RV.
– Can be timed differently
(e.g. RV before LV).
• In some devices, there is only
sensing in the RV lead (no LV
sensing)
• The tip electrodes on both RV
and LV leads are the
cathodes (negative poles)
• Capture testing can be
performed by programming
the device to RV only or LV
only pacing.
CRT Set to LV Pacing Only
CRT Set to RV Pacing Only
Capture Test in Independent Output Device
Capture Test in Independent Output Device
Annotations
• Annotations show you what the CRT-D
device was “thinking” as events occurred.
• VP is the conventional annotation for
ventricular paced event.
• A “hook” to the right indicates RV pacing,
while a “hook” to the left shows LV pacing.
Remember!!
• The normal ‘ECG stuff’ can also occur in
CRT tracings:
Summary
• Looking at a CRT tracing can be a challenge, but
it always comes back down to the basics.
• CRT EGMs require the clinician to be able to
visualize the flow of energy through the heart.
• CRT rhythm strips usually involve multiple
leads, however, Leads I,II, and III provide the
clinician with the needed information along
with the EGMs.
• Lead I will be positive and Lead III negative
during RV pacing.
• Lead I will be negative and Lead III positive
during LV pacing.
Summary
• In older tied-output systems, watch for
the transitions in QRS morphology
during capture testing.
• Anodal stimulation can occur with
unipolar LV pacing.
• In independent-output systems,
program RV or LV pacing for capture
testing.
Summary
• It is important to look at the morphologies of
the QRS complexes and recognize that changes
(polarity and/or width) generally indicate that
something has changed in the CRT function.
• The goal of CRT is as close to 100% pacing as
possible, but it is still not uncommon to see
intrinsic events, including fusions,
pseudofusions and occasional PVCs, on a CRT
tracing.
Summary
• It is therefore a good practice to keep examples
of rhythm strips from previous follow-up visits
in the patient records.
• A change in QRS morphology can be indicative
of a lead problem, device problem, or other
device setting that may require clinical
attention.
• Furthermore, there is considerable variation in
QRS morphology among patients and it is good
idea to have templates of a particular patient’s
ventricular morphologies in hand.