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Single and Dual Chamber Pacemaker Timing
Module 6
1
Objectives
• Identify VVI, AAI, DDI, and DDD pacing on an ECG strip
• Identify basic dual chamber timing concepts
– Rate intervals
– Inhibition
– Triggering
• Complete a simple VVI and DDD timing diagram
– Demonstrating rate calculation
– Demonstrating inhibition
– Demonstrating magnet application
2
Pacemaker Mode
• Defines the chambers that are paced/sensed
• Defines how the pacemaker will respond to intrinsic events
• Defines if rate modulation is available (i.e., DDDR)
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NBG Code
I
II
III
IV
V
Chamber(s)
Paced
Chamber(s)
Sensed
Response to
Sensing
Rate
Modulation
Multisite
Pacing
O = None
O = None
O = None
O = None
O = None
A = Atrium
A = Atrium
T = Triggered
R = Rate
A = Atrium
V = Ventricle
V = Ventricle
I = Inhibited
D = Dual (A + V)
D = Dual (A + V)
D = Dual (T + I)
S = Single (A or V) S = Single (A or V)
modulation
V = Ventricle
D = Dual (A + V)
NBG Code – The Usual Pacing Modes
I
II
III
IV
V
Chamber(s)
Paced
Chamber(s)
Sensed
Response to
Sensing
Rate
Multisite
Modulation Pacing
O = None
O = None
O = None
O = None
O = None
A = Atrium
A = Atrium
T = Triggered
R = Rate
A = Atrium
V = Ventricle
V = Ventricle
I = Inhibited
D = Dual (A + V)
D = Dual (A + V)
D = Dual (T + I)
S = Single (A or
S = Single (A or V)
V)
• Examples
– DDD
– VVI
– DDDR
– VVIR
– DDIR
– AAI
modulation
V = Ventricle
D = Dual (A + V)
Rate and Interval Review
• Calculated on the horizontal axis
– At 25 mm/s speed
• Each small box = 40 ms
• Each bold box = 200 ms
How do you convert intervals to rate?
Click for Answer
60,000 / (Interval in ms) = Rate in bpm
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VVI Mode
• Chamber paced: Ventricle
• Chamber sensed: Ventricle
• Response to sensing: Inhibited
– A ventricular sense:
• Inhibits the next scheduled ventricular pace
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VVI Example
• Chamber paced: Ventricle
• Chamber sensed: Ventricle
• Response to sensing: Inhibition
– VVI 60 = Lower Rate timer of 1000 ms
• Pacing every 1 second if not inhibited
Lower Rate Timer 1000 ms
V
P
V
P
Lower Rate Timer 1000 ms
Lower Rate Timer ….
V
P
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VVI Example
VVI 60
• Chamber paced: Ventricle
– VVI 60 = Lower Rate timer of 1000 ms
• Pacing every 1 second if not inhibited
A ventricular sense interrupts
the pacing interval, resets the
lower rate timer, and inhibits
the next scheduled paced (x)
• Chamber sensed: Ventricle
• Response to sensing: Inhibition
Lower rate timer 1000 ms
Lower rate timer 1000 ms
x
V
P
V
P
V
S
V
P
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VOO Mode
VOO 60
The intrinsic ventricular event
cannot be sensed, and thus, does
not interrupt the pacing interval.
1000 ms
V
P
1000 ms
V
P
Chamber paced: Ventricle
Chamber sensed: None
Response to sensing: None
1000 ms
V
P
V
P
VOO results in fixed-rate pacing in
the ventricle. Placing a magnet
over the pacemaker usually results
in this behavior at known rates, for
example, 85 ppm.
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DDD Mode
• Chamber paced: Atrium & ventricle
• Chamber sensed: Atrium & ventricle
• Response to sensing: Triggered & inhibited
– An atrial sense:
• Inhibits the next scheduled atrial pace
• Re-starts the lower rate timer
• Triggers an AV interval (called a Sensed AV Interval or SAV)
– An atrial pace:
• Re-starts the lower rate timer
• Triggers an AV delay timer (the Paced AV or PAV)
– A ventricular sense:
• Inhibits the next scheduled ventricular pace
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DDD Examples
The Four Faces of DDD
• Atrial and ventricular pacing
A
P
V
P
A
P
V
P
– Atrial pace re-starts the lower rate timer and triggers an AV delay
timer (PAV)
• The PAV expires without being inhibited by a ventricular sense, resulting
in a ventricular pace
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DDD Examples
The Four Faces of DDD
• Atrial pacing and ventricular sensing
A V
P S
A
P
V
S
– Atrial pace restarts the lower rate timer and triggers an AV delay
timer (PAV)
• Before the PAV can expire, it is inhibited by an intrinsic ventricular event
(R-wave)
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DDD Examples
The Four Faces of DDD
• Atrial sensing, ventricular pacing
A
S
V
P
A
S
V
P
– The intrinsic atrial event (P-wave) inhibits the lower rate timer and
triggers an AV delay timer (SAV)
• The SAV expires without being inhibited by an intrinsic ventricular event,
resulting in a ventricular pace
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DDD Examples
The Four Faces of DDD
• Atrial and ventricular sensing
A V
S S
A V
S S
– The intrinsic atrial event (P-wave) inhibits the lower rate timer and
triggers an AV delay timer (SAV)
• Before the SAV can expire, it is inhibited by an intrinsic ventricular event
(R-wave)
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Dual Response to Sensing
DDD
• The pacemaker can:
– Inhibit and trigger
– A P-wave inhibits atrial pacing and triggers an SAV interval
– An atrial pace triggers a PAV interval
– An R-wave inhibits ventricular pacing
• We’ll see later how a PVC can affect atrial timing
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Nuggets
• Note that in both the single and dual chamber examples:
– When the device paces – for the purposes of timing – capture is
assumed
• Some newer devices have algorithms to check for capture
– Sensing is critical to timing
• If the device fails to sense, undersensing, it will usually pace
• If it “oversenses,” e.g., senses myopotentials, it will inhibit pacing
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Remember This Strip?
• Intermittent loss of capture (LOC)
– Note how the underlying timing is unaffected by the failure to
capture
– For timing purposes, pace = capture
DDD
Review question:
Name some possible
causes for this
condition.
Click for Answer
Incomplete fracture, insulation failure, lead dislodgement, poor
connection in header, programming error, change in pacing
thresholds…
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Diagnose This Strip
• Undersensing, the device fails to reliably “see” P-waves
How do we know
this is
undersensing?
DDD
Click for Answer
Because:
• The atrial lower rate timer is not inhibited – there are atrial pacing spikes
• The intrinsic P-waves do not start an SAV
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DDI Mode
• Chamber paced: Atrium & ventricle
• Chamber sensed: Atrium & ventricle
• Response to sensing: Inhibited
– An atrial sense:
• Inhibits the next scheduled atrial pace
• Re-starts the lower rate timer
– An atrial pace:
• Re-starts the lower rate timer
• Starts an AV delay timer (the Paced AV or PAV)
– A ventricular sense:
• Inhibits the next scheduled ventricular pace
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DDI Example
• Why would we want a dual chamber pacing mode that
does not trigger an SAV?
P
P
P
P
P
P
P
P
P
P
P
P
What rhythm
is this?
Click for Hint
The underlying rhythm is an atrial tachycardia.
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DDI Example
• Why would we want to use DDI?
– To control pacemaker timing during atrial tachycardias
• Avoids a fast paced ventricular response to AT/AF
• May limit patient symptoms during AT/AF
Click to change
DDD – tracking the AF
DDI – Not tracking the AF
540ms = 110bpm
This function has come to be called “Mode Switching”
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Status Check
• Calculate the atrial rate
• Measure the P-R interval
• Measure the QRS duration
Click for Answer
Atrial Rate: 70 bpm (860 ms)
P-R: 120 ms
QRS: About 100 ms
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Status Check
Which pacemaker modes could be operating on this strip?
•
Assume normal pacemaker operation
Click for Answer
A. DDD – Yes, the intrinsic rate could be faster than the lower rate, and
A. DDD
B. VVI
C. AAI
the PAV/SAV is longer than the P-R interval.
B. VVI – Yes, the ventricular rate is faster than the lower rate, thus
inhibiting the IPG.
C. AAI – Yes, the atrial rate is faster than the lower rate, thus inhibiting
the IPG.
D. DOO
D. DOO – No, DOO results in fixed rate pacing.
No sensing is possible,
no inhibition is possible.
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Status Check
Which pacemaker modes could be operating on this strip?
•
Assume normal pacemaker operation
Click for Answer
A. DDD – Yes, this is very likely the DDD mode.
A. DDD
B. VVI
C. AAI
D. DOO
B. VVI – Yes, it could be, but the consistent A-V relationship should
make us suspicious.
C. AAI – No, not possible. Cannot have ventricular pacing in the
AAI mode.
D. DOO – No, DOO results in fixed rate pacing. No sensing is
possible, no inhibition is possible. We would see atrial and
ventricular pacing if this was DOO.
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Status Check
Which pacemaker modes could be operating on this strip?
•
Assume normal pacemaker operation
Click for Answer
A. DDD – Yes, this is very likely the DDD mode.
This is sometimes called
“tracking,” as the ventricle is tracking the atrium.
A. DDD
B. DDI – Not possible.
B. DDI
C. VOO – Not likely because of the consistent AV intervals.
C. VOO
D. DOO
The consistent AV intervals suggest the P-wave is
triggering an SAV. DDI inhibits only, triggering not possible.
Unable to
diagnose until we see the IPG response to an intrinsic ventricular event
(evidence of sensing).
D. DOO – No, DOO results in fixed rate pacing.
No sensing is possible,
no inhibition is possible. We would see atrial and ventricular pacing if this
was DOO.
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Brief Statements
Indications
•
Implantable Pulse Generators (IPGs) are indicated for rate adaptive pacing in patients who ay benefit from increased
pacing rates concurrent with increases in activity and increases in activity and/or minute ventilation. Pacemakers are
also indicated for dual chamber and atrial tracking modes in patients who may benefit from maintenance of AV
synchrony. Dual chamber modes are specifically indicated for treatment of conduction disorders that require restoration
of both rate and AV synchrony, which include various degrees of AV block to maintain the atrial contribution to cardiac
output and VVI intolerance (e.g. pacemaker syndrome) in the presence of persistent sinus rhythm.
•
Implantable cardioverter defibrillators (ICDs) are indicated for ventricular antitachycardia pacing and ventricular
defibrillation for automated treatment of life-threatening ventricular arrhythmias.
•
Cardiac Resynchronization Therapy (CRT) ICDs are indicated for ventricular antitachycardia pacing and ventricular
defibrillation for automated treatment of life-threatening ventricular arrhythmias and for the reduction of the symptoms of
moderate to severe heart failure (NYHA Functional Class III or IV) in those patients who remain symptomatic despite
stable, optimal medical therapy and have a left ventricular ejection fraction less than or equal to 35% and a QRS
duration of ≥130 ms.
•
CRT IPGs are indicated for the reduction of the symptoms of moderate to severe heart failure (NYHA Functional Class
III or IV) in those patients who remain symptomatic despite stable, optimal medical therapy, and have a left ventricular
ejection fraction less than or equal to 35% and a QRS duration of ≥130 ms.
Contraindications
•
IPGs and CRT IPGs are contraindicated for dual chamber atrial pacing in patients with chronic refractory atrial
tachyarrhythmias; asynchronous pacing in the presence (or likelihood) of competitive paced and intrinsic rhythms;
unipolar pacing for patients with an implanted cardioverter defibrillator because it may cause unwanted delivery or
inhibition of ICD therapy; and certain IPGs are contraindicated for use with epicardial leads and with abdominal
implantation.
•
ICDs and CRT ICDs are contraindicated in patients whose ventricular tachyarrhythmias may have transient or
reversible causes, patients with incessant VT or VF, and for patients who have a unipolar pacemaker. ICDs are also
contraindicated for patients whose primary disorder is bradyarrhythmia.
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Brief Statements (continued)
Warnings/Precautions
• Changes in a patient’s disease and/or medications may alter the efficacy of the device’s programmed
parameters. Patients should avoid sources of magnetic and electromagnetic radiation to avoid
possible underdetection, inappropriate sensing and/or therapy delivery, tissue damage, induction of an
arrhythmia, device electrical reset or device damage. Do not place transthoracic defibrillation paddles
directly over the device. Additionally, for CRT ICDs and CRT IPGs, certain programming and device
operations may not provide cardiac resynchronization. Also for CRT IPGs, Elective Replacement
Indicator (ERI) results in the device switching to VVI pacing at 65 ppm. In this mode, patients may
experience loss of cardiac resynchronization therapy and / or loss of AV synchrony. For this reason,
the device should be replaced prior to ERI being set.
Potential complications
• Potential complications include, but are not limited to, rejection phenomena, erosion through the skin,
muscle or nerve stimulation, oversensing, failure to detect and/or terminate arrhythmia episodes, and
surgical complications such as hematoma, infection, inflammation, and thrombosis. An additional
complication for ICDs and CRT ICDs is the acceleration of ventricular tachycardia.
• See the device manual for detailed information regarding the implant procedure, indications,
contraindications, warnings, precautions, and potential complications/adverse events. For further
information, please call Medtronic at 1-800-328-2518 and/or consult Medtronic’s website at
www.medtronic.com.
Caution: Federal law (USA) restricts these devices to sale by or on the order of a physician.
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Brief Statement: Medtronic Leads
Indications
• Medtronic leads are used as part of a cardiac rhythm disease management system. Leads are
intended for pacing and sensing and/or defibrillation. Defibrillation leads have application for patients
for whom implantable cardioverter defibrillation is indicated
Contraindications
• Medtronic leads are contraindicated for the following:
• ventricular use in patients with tricuspid valvular disease or a tricuspid mechanical heart valve.
• patients for whom a single dose of 1.0 mg of dexamethasone sodium phosphate or dexamethasone
acetate may be contraindicated. (includes all leads which contain these steroids)
• Epicardial leads should not be used on patients with a heavily infracted or fibrotic myocardium.
• The SelectSecure Model 3830 Lead is also contraindicated for the following:
• patients for whom a single dose of 40.µg of beclomethasone dipropionate may be contraindicated.
• patients with obstructed or inadequate vasculature for intravenous catheterization.
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Brief Statement: Medtronic Leads (continued)
Warnings/Precautions
• People with metal implants such as pacemakers, implantable cardioverter defibrillators (ICDs), and
accompanying leads should not receive diathermy treatment. The interaction between the implant and
diathermy can cause tissue damage, fibrillation, or damage to the device components, which could
result in serious injury, loss of therapy, or the need to reprogram or replace the device.
• For the SelectSecure Model 3830 lead, total patient exposure to beclomethasone 17,21-dipropionate
should be considered when implanting multiple leads. No drug interactions with inhaled
beclomethasone 17,21-dipropionate have been described. Drug interactions of beclomethasone
17,21-dipropionate with the Model 3830 lead have not been studied.
Potential Complications
• Potential complications include, but are not limited to, valve damage, fibrillation and other arrhythmias,
thrombosis, thrombotic and air embolism, cardiac perforation, heart wall rupture, cardiac tamponade,
muscle or nerve stimulation, pericardial rub, infection, myocardial irritability, and pneumothorax.
Other potential complications related to the lead may include lead dislodgement, lead conductor
fracture, insulation failure, threshold elevation or exit block.
• See specific device manual for detailed information regarding the implant procedure, indications,
contraindications, warnings, precautions, and potential complications/adverse events. For further
information, please call Medtronic at 1-800-328-2518 and/or consult Medtronic’s website at
www.medtronic.com.
Caution: Federal law (USA) restricts this device to sale by or on the order of a physician.
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Disclosure
NOTE:
This presentation is provided for general educational purposes
only and should not be considered the exclusive source for this
type of information. At all times, it is the professional
responsibility of the practitioner to exercise independent
clinical judgment in a particular situation.
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