Single and Dual Chamber Pacemaker Timing
Module 6
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• 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
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• 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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I
Chamber(s)
Paced
O = None
A = Atrium
V = Ventricle
D = Dual (A + V)
S = Single (A or V)
II
Chamber(s)
Sensed
O = None
A = Atrium
V = Ventricle
D = Dual (A + V)
S = Single (A or V)
III
Response to
Sensing
O = None
T = Triggered
I = Inhibited
D = Dual (T + I)
IV
Rate
Modulation
O = None
R = Rate modulation
V
Multisite
Pacing
O = None
A = Atrium
V = Ventricle
D = Dual (A + V)

I
Chamber(s)
Paced
O = None
A = Atrium
V = Ventricle
D = Dual (A + V)
S = Single (A or
V)
• Examples
– DDD
– DDDR
– DDIR
II
Chamber(s)
Sensed
O = None
A = Atrium
V = Ventricle
D = Dual (A + V)
S = Single (A or V)
III
Response to
Sensing
O = None
T = Triggered
I = Inhibited
D = Dual (T + I)
IV
Rate
Modulation
O = None
R = Rate modulation
V
Multisite
Pacing
O = None
A = Atrium
V = Ventricle
D = Dual (A + V)
– VVI
– VVIR
– AAI

• 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?
60,000 / (Interval in ms) = Rate in bpm
Click for Answer
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• Chamber paced: Ventricle
• Chamber sensed: Ventricle
• Response to sensing: Inhibited
– A ventricular sense:
• Inhibits the next scheduled ventricular pace
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• 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 Lower Rate Timer 1000 ms
Lower Rate Timer ….
V
P
V
P
V
P
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VVI 60
• Chamber paced: Ventricle
– VVI 60 = Lower Rate timer of 1000 ms
• Pacing every 1 second if not inhibited
• Chamber sensed: Ventricle
• Response to sensing: Inhibition
A ventricular sense interrupts the pacing interval, resets the lower rate timer, and inhibits the next scheduled paced (x)
Lower rate timer 1000 ms Lower rate timer 1000 ms x
V
P
V
P
V
S
V
P
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VOO 60
1000 ms
The intrinsic ventricular event cannot be sensed, and thus, does not interrupt the pacing interval .
1000 ms 1000 ms
V
P
V
P
Chamber paced: Ventricle
Chamber sensed: None
Response to sensing: None
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.
V
P
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• 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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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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The Four Faces of DDD
• Atrial pacing and ventricular sensing
A
P
V
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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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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The Four Faces of DDD
• Atrial and ventricular sensing
A
S
V
S
A
S
V
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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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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Which pacemaker modes could be operating on this strip?
• Assume normal pacemaker operation Click for Answer
A. DDD
B. VVI
C. AAI
D. DOO
A. DDD –
Yes, the intrinsic rate could be faster than the lower rate, and 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 –
No, DOO results in fixed rate pacing. No sensing is possible, no inhibition is possible.
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Which pacemaker modes could be operating on this strip?
• Assume normal pacemaker operation Click for Answer
A. DDD
B. VVI
C. AAI
D. DOO
A. DDD –
Yes, this is very likely the DDD mode.
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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Which pacemaker modes could be operating on this strip?
• Assume normal pacemaker operation Click for Answer
A. DDD
B. DDI
C. VOO
D. DOO
A. DDD –
Yes, this is very likely the DDD mode. This is sometimes called
“tracking,” as the ventricle is tracking the atrium.
B. DDI –
Not possible. The consistent AV intervals suggest the P-wave is triggering an SAV. DDI inhibits only, triggering not possible.
C. VOO –
Not likely because of the consistent AV intervals. 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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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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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 1-800-3282518 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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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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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 1-800-3282518 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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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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