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Advanced Pacemaker OperationsModule 7

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Objectives

• Define: Blanking and refractory

• Complete VVI and DDD timing diagrams

– Correctly identifying PVARP, PVAB, PPAB, and TARP

– Identify events in refractory and blanking, and their effect on timing

– Correctly identify Marker Channel™ notations

• Identify upper rate behaviors

– Calculate 2:1 vs. Wenckebach rates

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Marker Channel™

• Very useful in helping you understand how the IPG is interpreting events

• Each manufacturer has its own code

• Medtronic’s code:

– AS Atrial Sense

– AP Atrial Pace

– AR Atrial Refractory

– VS Ventricular Sense

– VP Ventricular Pace

– VR Ventricular Refractory

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What Do You Think Would Happen Next If…

• The QRS was sensed by the atrial channel?

The next atrial pace would be inhibited because the pacemaker thinks the QRS is a P-wave.

Obviously, this is not how we want a DDD pacemaker to behave. This was a problem in early pacemakers.

Click for Answer

DDD 60

AS

AP

VP

Note: The Marker Channel tells you how the pacemaker is interpreting these events.

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What Do You Think Would Happen Next If…

• These T-waves were sensed by the ventricular channel?

VP

VS

VP

VSClick for Answer

Programmed: VVI 60

Actual Rate: 50 bpm or 1200 ms

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Blanking and Refractory Periods

• Blanking Period

– A period of time during which the sense amplifiers are off, and the pacemaker is “blind”

– Some blanking periods are programmable, some are non-programmable

• Refractory Period

– A period of time during which sensed events are ignored for timing purposes, but included in diagnostic counters

– Some refractory periods are programmable, some non-programmable

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Why Do We Use Refractory and Blanking Periods?

• Pacemaker sensing occurs when a signal is large enough to cross the sensing threshold

1.25 mV Sensitivity

Time

5.0 mV

2.5 mV

1.25 mV

Sensing does not tells us anything about the origin or morphology of the sensed event, only its “size.”

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SENSE!

Why Do We Use Refractory and Blanking Periods?

• By manipulating the sense amplifiers, we filter signals based on their relationship

The potential for digitizing these signals may someday allow pacemakers to discriminate signals based on morphology rather than just on their relationship.

Blanking Refractory

Time

5.0 mV

2.5 mV

1.25 mV

Sensing

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Let’s Look at the VVI Example Again…

• Now, is the T-wave sensed by the ventricular channel?

VP

VR

VP

VR

The T-wave falls in the ventricular refractory period (VR), and it is ignored for timing purposes.

Click for Answer

The VVI pacemaker is operating normally.

VVI 60

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• Note the addition of the Blanking and Refractory periods

VVI Timing

The pacemaker applies these periods to every timing cycle.

VP

VR

VP

VR

1000 ms 1000 ms

Blanking

Refractory

VRP 320 ms VRP 320 ms

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T-wave Sensing

• Is there another way to program the pacemaker to ignore the T-waves?

VP

VR

VP

VR

1000 ms 1000 ms

VRP 320 ms

BlankingRefractory

VRP 320 ms

We could program the pacemaker to be less sensitive (e.g., from 2.5mV to 5.0 mV). But then it might not sense every R-wave.

Click for Answer

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Dual Chamber Timing

Refractory and Blanking Periods

ARP PVARP

VRP

PVAB

Those affecting the atrial channel are indicated above the ECG baseline.

Those affecting the ventricular channel are indicated below the ECG baseline.

Red: Blanking

Orange: Refractory period

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ARP

Dual Chamber Timing

• Atrial Refractory and Blanking Periods

Atrial Blanking

Atrial Refractory

Period

Post Ventricular Atrial Blanking

Post Ventricular Atrial Refractory Period

PVARP

VRP

PVAB

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Dual Chamber Timing

• Ventricular Refractory and Blanking Periods

Post Atrial Ventricular Blanking Ventricular Refractory

Period

Ventricular Blanking

VRP

ARP PVARP

PVAB

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Dual Chamber Timing

• Atrial Pace (AP) - Ventricular Pace (VP) example

DDD 60

The pacemaker applies these periods every timing cycle.

A-A interval A-A interval

VRP

ARP PVARP

PVAB

VRP

ARP PVARP

PVAB

PAVV-A interval V-A interval

PAV

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Dual Chamber Timing

• Lower Rate (A-A) Interval

– A-A interval indicates the minimum rate the device will pace under normal circumstances (“escape interval,” “lower rate interval”)

– In dual chamber pacemakers we subdivide this into the A-V interval (PAV or SAV) and the V-A interval

• Normally, the device is designed to always use A-A timing – to maintain a steady atrial rate

VRP

ARP PVARP

PVAB

VRP

ARP PVARP

PVAB

A-A interval A-A interval

PAV PAV

V-A interval V-A interval

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Dual Chamber Timing

• Upper Tracking Rate (UTR)

– The maximum rate the ventricles will be paced 1:1 in response to atrial sensed events

UTR UTR

VRP

ARP PVARP

PVAB

VRP

ARP PVARP

PVAB

A-A interval A-A interval

SAV SAV

V-A interval V-A interval

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Dual Chamber Timing

• Tracking

– 1:1 tracking (atrial sense – ventricular pace) occurs at rates above the Lower Rate, but below the Upper Tracking Rate

1:1 tracking of any atrial sense

UTR

VRP

ARP PVARP

PVAB

A-A interval A-A interval

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In other words, the next atrial sense is getting closer to the previous ventricular event.

UTR

VRP

ARP PVARP

PVAB

SAV

A-A interval

V-A interval

VRP

ARP PVARP

PVAB

UTR

A-A interval

V-A intervalSAV

Dual Chamber Timing

• The pacemaker’s response to high atrial rates

– To a pacemaker, an increase in atrial rate means that V-A intervals are getting shorter

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Dual Chamber TimingUpper Rate Behavior

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Upper Rate Behavior

• Pacemaker Wenckebach

– Caused by the atrial rate exceeding the Upper Tracking Rate

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PVARP

A-A interval

Upper Rate Behavior

• Pacemaker Wenckebach– Prolongs the SAV until upper rate limit expires

– Produces gradual change in tracking rate ratio

UTR

ARP ARP PVARP

A-A interval

SAV SAV

UTR

ARP

PAV

PVARP

UTR

A-A interval

VP

VP

VP

AS

AP

AS

AR

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Wenckebach Example

• Pacemaker patient on an exercise test

– 4:3 Wenckebach operation

• Each AS (P-wave) is followed by an increasing SAV, and then the VP

• Eventually an atrial beat is not tracked, and a ventricular beat is dropped

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Wenckebach Example

This P-wave fell in the PVARP of the previous cycle.

It is refractory (AR), so it is ignored for timing.

It cannot start an SAV, so it is not followed by a ventricular pace.

This is normal upper rate pacemaker behavior.

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Upper Rate Behavior

• 2:1 Block

– Occurs when P-waves are faster than TARP

– TARP = SAV + PVARP

PVARPARP

SAVVP

AS

AR

PVARPARP

SAVVP

AS

AR

ARP

SAVVP

AS

TARP TARP TARP

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Upper Rate Behavior

• 2:1 Block

– Caused by the atrial rate exceeding the Total Atrial Refractory Period (TARP)

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Knowledge Check

• Given the following pacemaker parameters, what rhythm will result from an atrial rate of 130 bpm?

– UTR = 120 bpm

– SAV = 150 ms

– PVARP = 250 ms

– Pacemaker Wenckebach

• Given the same pacemaker parameters, what atrial rate would result in 2:1 block?

– An atrial rate above 150 bpm

Click for Answer

Click for Answer

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WenckebachNo

VentricularPacing

Upper Rate Behavior

UTR

Atrial Rate

Ven

tric

ular

Rat

e

LR1:1 AtrialTracking

2:1 Block

UTRLR TARP

= Ventricular Pacing

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WenckebachNo

VentricularPacing

Upper Rate Behavior

UTR

Atrial Rate

Ven

tric

ular

Rat

e

LR1:1 AtrialTracking

2:1 Block

UTRLR TARP

= Ventricular Pacing

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Increased Tracking

Increased Tracking

Achieving a Higher UTR without Block

• Decrease SAV • Decrease PVARP

PVARPARP

SAV

AS

AR

TARP

SAV

AS

SAV

AS

PVARPARP

TARP

PVARPARP

SAV

AS

AR

TARP

PVARPARP

SAV

AS

TARP

SAV

AS

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Achieving a Higher UTR without Block

• SAV and PVARP managed automatically

– Programming Rate-Adaptive AV to “On”

• This will automatically decrease the SAV/PAV as the atrial rate increases

– Programming PVARP to “Auto”

• This will automatically decrease the PVARP as the atrial rate increases

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If Long TARP is the Problem…

• Why not just program short AV Intervals or short PVARP?

– Short AV intervals may force ventricular pacing

– Short PVARP may allow retrograde conduction to be sensed

• Consider this ECG:

• The retrograde P-waves occur outside of PVARP.

• The pacemaker tracks the retrograde P-waves.

• This is called a Pacemaker Mediated Tachycardia (PMT).

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Status Check

AS

VR

AR

AP

VP

VS

An Atrial Sense (P-wave)

Ventricular Refractory

Atrial Refractory

Atrial Pace

Ventricular Pace

A Ventricular Sense (QRS or R-wave)

Click for Answer

Can you identify the following Marker Channel notations?

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Status Check

VRP VRP

VP

VP

V. Blanking V. Blanking

Lower Rate Interval Lower Rate Interval

Click for Answer

Can you complete this timing diagram?

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Status Check

• Show:

- Atrial Refractory during the AV Interval

- PVARP with PVAB

- VRP

Click for Answer

Atrial Refractory during the AV Interval

PVARP with PVAB

VRP

Complete this timing diagram

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Status Check

• You are called to evaluate this rhythm strip

– Obtained while the patient is having an exercise test

– Clinician thinks it is loss of capture

– Patient’s underlying rhythm is CHB

• What is going on?

Click for Answer2:1 block. P-waves

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Status Check

• What mode do you think this is?

• Calculate the Atrial and Ventricular rates

• Propose a programming solution to resolve this

Click for Answer DDD Mode. Atrial rate: 430 ms or 140 bpm, Ventricular rate: 860 ms or 70 bpm.

Increase the UTR and program RA-AV on, or Increase UTR and decrease PVARP.

430 ms 860 ms

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Status Check

• Given the following parameters, what will occur first as the patient’s atrial rate increases? Wenckebach or 2:1 block?

– Upper Tracking Rate: 120 bpm

– SAV = 200 ms

– PVARP = 350 ms

• 2:1 block will occur first

Click for Answer

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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.

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.