Cardiac Pacing for the Surgeons

8/2/2019 Cardiac Pacing for the Surgeons

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Cardiac Pacing for the Surgeons

Dr. Rezwanul HoqueMBBS, MS, FCPS, FRCSG, FRCSEd

Associate ProfessorDepartment of Cardiac surgery

BSMMU, Dhaka, Bangladesh


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A pacemaker or artificial pacemaker is a medical device designed to regulate

the beating of the Heart.

The purpose of an artificial pacemaker is to stimulate the heart when either the

heart's native pacemaker is not fast enough or if there are blocks in the heart's

electrical conduction system preventing the propagation of electrical impulses

from the native pacemaker to the lower chambers of the heart, known as theventricles.

Pacemaker
http://en.wikipedia.org/wiki/Image:Pacemaker_GuidantMeridianSR.jpg


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An ICD(Implantable cardioverter & defibrillator) is a specialized device designed to

directly treat a cardiac tachydysrhythmia.

If a patient has a ventricular ICD and the device senses a ventricular rate that exceeds

the programmed cut-off rate of the ICD, the device performs

cardioversion/defibrillation.

Alternatively, the device, if so programmed, may attempt to pace rapidly for a number

of pulses to attempt pace-termination of the ventricular tachycardia.

The newer devices are a combination of ICD and pacemaker in one unit. These

combination ICD/pacemakers are implanted in patients who require both devices.

ICD


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Transvenous

Transcutaneous

EpicardialTransesophageal


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Acute myocardial infarction with:

CHB, Mobitz type 2 AV block, medically refractory symptomatic bradycardia,

alternating BBB, new bifascicular block, new BBB with anterior MI

In absence of acute MI : SSS, CHB, Mobitz type 2 AV block

Treatment of tachyarrhythmias : VT


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Transcutaneous pacing

Transcutaneous pacing (TCP), also called external pacing, is recommended for theinitial stabilization of hemodynamically significant bradycardia of all types.

The procedure is performed by placing two pacing pads on the patient's chest, either

in the anterior/lateral position or the anterior/posterior position.

The rescuer selects the pacing rate, and gradually increases the pacing current

(measured in ma) until electrical capture (characterized by a wide QRS complex with a

tall, broad T wave on the ECG) is achieved, with a corresponding pulse.

Pacing artifact on the ECG and severe muscle twitching may make this determination

difficult.

External pacing should not be relied upon for an extended period of time. It is an

emergency procedure that acts as a bridge until transvenous pacing or other therapies

can be applied.


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Transvenous pacing

Transvenous pacing, or temporary internal pacing, is an alternative to transcutaneous

pacing.

A wire is placed under sterile conditions via a central venous catheter. The distal tip of

the wire is placed into either the right atrium or right ventricle. The proximal tip of thewire is attached to the pacemaker generator, outside of the body.

Transvenous pacing is often used as a bridge to permanent pacemaker placement.

Under certain conditions, a person may require temporary pacing but would not

require permanent pacing. In this case, a temporary pacing wire may be the optimal

treatment option.


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Epicardial pacing

Epicardial pacing wires are routine leads used for temporary cardiac pacing after open

heart surgery.

During surgery the heart is subjected to stress which can lead to myocardial ischemia

and cardiac depression.

Temporary pacing may be necessary to re-establish electrical conduction.

Atrial wires (a wires) are positioned on the right atrial surface and exit the chest wall to

the right of the sternum. Atrial wires are attached via a connecting cable to A marked

terminals on the pacemaker box.

Ventricular wires (v wires) are positioned on the right ventricular surface and exit thechest wall to the left of the sternum. Ventricular wires are attached via connecting cable

to V marked terminals on the pacemaker box.

If a skin wire is used it is attached to positive pole and the ventricular wire is attached to

negative pole of the generator.

Epicardial pacing after open heart surgery allows for the treatment of dysrhythmias, the

improvement of hemodynamic functioning, and to maintain backup rate with maze

procedure.

The patient should remain on a cardiac monitor 2-hours after the removal of epicardial

wires. The patient cannot have an MRI while pacing wires are in place.


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FAILURE TO CAPTURE/PACE:

MEASURES:

Secure connections

Replace battery/pacemaker as needed

Increase ma

Reduce sensitivity (turn mv dial counter clockwise or to a higher numericalsetting).

Reverse polarity

Check stimulation threshold

Monitor electrolytes and ABG

Obtain EKG to check for ischemia (ST depression)


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Eliminate any electrical interference.Note: check to ensure that all electrical equipment attached to the patient isgrounded

Replace battery/pacemaker as needed

If undersensing [not recognizing patients' own rhythm]increase sensitivity(turn mv dial clockwise to lower mv numerical value)

Note: this will make the pacemaker more sensitive to patients own rate

If oversensing [when A-V pacing, the pacemaker may sense the atrial pacingspike as the qrs complex and not fire (cross talk) or the patient is havingbreakthrough rate and pacemaker does not fire] decrease sensitivity (turn mvdial counter clockwise to raise the numerical mv value)

Note: this will make the pacemaker less sensitive to the patient's rate.

If patient has an adequate underlying rhythm, turn off the pacemaker


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When to consider PPM

Patients with symptoms directly attributable tobradycardia (even SB)

Disease within AV node as manifest by extreme PRprolongation, normal QRS

Disease belowAV node as manifest by normal or mildlyprolonged PR and wide QRS

Disease in His purkinje system (less stable thanabove)


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Degree Pacemaker necessary Pacemakerprobablynecessary

Pacemaker notnecessary

Third Symptomatic congenitalcomplete heart block

Aquired symptomatic completeheart block

Atrial fibrillation with completeheart block

Acquired asymptomaticcomplete heart block

Second Symptomatic type ISymptomatic type II Asymptomatictype IIAsymptomatictype I at intra-Hisor infra-His levels

Asymptomatic typeI at supra-His (AVnodal) block

First Asymptomatic orsymptomatic


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Pacemaker Pacemaker probably

necessary

Pacemaker not

necessary

Symptomatic bradycardia Symptomatic patients withsinus node dysfunction

with documented rates of


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Pacing for HemodynamicImprovement

Hypertrophic Obstructive

Cardiomyopathy

Cardiac ResynchronizationTherapy

Evolving Indications for Pacing

Long QT syndromes

Sleep apneaNeurally mediated syncope


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Patient

Lead

Pacemaker

Programmer

Lead

Pacemaker


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Basic pacemaker function

Modern pacemakers usually have multiple functions.

The most basic form listens to the heart's native electrical rhythm, and if the device

doesn't sense any electrical activity within a certain time period, the device will stimulatethe vetricles of heart with a set amount of energy, measured in joules.

The more complex forms include the ability to sense and/or stimulate both the atrial

and ventricular chambers.


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Permanent pacing

Permanent pacing with an implantable pacemaker involves placement of one or more

pacing wires within the chambers of the heart. One end of each wire is attached to the

muscle of the heart. The other end is screwed into the pacemaker generator.

The pacemaker generator is a hermetically sealed device containing a power sourceand the computer logic for the pacemaker.

Most commonly, the generator is placed below the subcutaneous fat of the chest wall,

above the muscles and bones of the chest.

The outer casing of pacemakers is so designed that it will rarely be rejected by the

body's immune system. It is usually made of titanium, which is very inert in the body.


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Codes are combined to describe:

Mode of pacing

Mode of sensing

How the pacemaker will respond to the

presence or absence of intrinsic beats


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Responseto Sensing

III IV

NASPE / BPEG Generic (NBG) Code

Bernstein, A.D., et al. PACE 2002; 25:260-264

Letters Used:

O

R

None

Atrium

Ventricle

Dual A+V

O O None O None None O None

A A Atrium T TriggeredRate

Modulation

A Atrium

V V Ventricle I Inhibited V Ventricle

D D Dual A+V D Dual T+I D Dual A+V

Chamber(s)Paced

Chamber(s)Sensed

RateModulation

MultisitePacing

Category:

I II VPosition:

SingleA or V

S S SingleA or V

Manufacturers Designation Only:


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Pacemaker energy output is dependent upon the signal amplitude and pulsewidth. Signal amplitude is measured in electrical units of volts ormilliamperes. Pulse width is a measure of output duration and is measured inmilliseconds. For proper permanent pacer operation, signal amplitude andwidth are set high enough to reliably achieve capture of the myocardium, yetlow enough to prolong battery life.

Pulse generators can be set to a fixed-rate (asynchronous) or demand(synchronous) mode. In the fixed-rate mode, an impulse is produced at a setrate and has no relationship to the patient's intrinsic cardiac activity. Thismode carries a small but inherent danger of producing lethal dysrhythmiasshould the impulse coincide with the vulnerable period of the T wave. In thedemand mode, the sensing circuit searches for an intrinsic depolarization

potential. If this is absent, a pacing response is generated. This mode canclosely mimic the intrinsic electric activity pattern of the heart.


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Ventricular pacing

No sensing

Ventricular asynchronous pacing at lower programmedpacing rate

VOO

Ventricular lead


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VVI

Ventricular Lead (I)

Ventricular pacing

Ventricular sensing

Sensed intrinsic QRS inhibits ventricular pacing


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AOO

Atrial pacing

No sensing

Atrial asynchronous pacing at lower programmed pacingrate

Atrial Lead


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AAI

Atrial pacing

Atrial sensing

Intrinsic P-wave inhibits atrial pacing

Atrial Lead (I)


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Pacing in atrium and ventricle

Sensing in atrium and ventricle

Intrinsic P-wave and intrinsic QRS can inhibit pacing

Intrinsic P-wave can trigger a paced QRS

VentricularLead (I)

Atrial Lead(T/I)

DDD Pacing


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Dual-chamber pacing capable of pacing and sensing in both the atrial and ventricularchambers of the heart

Four distinct patterns can be observed with DDD pacing

Sensing in the atrium and sensing in the ventricle (AsVs)

Sensing in the atrium and pacing in the ventricle(P wave tracking) (AsVp)

Pacing in the atrium and sensing in the ventricle (ApVs)

Pacing in the atrium and pacing in the ventricle (ApVp) Adapts to changes post-implant

May resemble AAI, VAT, VDD, DVI modes

Will strive to maintain AV synchrony with variable atrial rates and AV conduction

DDD Pacing


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In rate-responsive pacing (modes ending with R), sensor(s) inthe pacemaker are used to detect changes in physiologic needsand increase the pacing rate accordingly

Sensors

Detect changes in metabolic demand

Sense motion or physiologic indicator

accelerometer or minute ventilationDefinition: Chronotropic Incompetence

inability to increase and maintain heart rateappropriately with exercise*

*Ellenbogen, Kenneth A. Cardiac Pacing and ICDs. Malden, Mass.: Blackwell Pub.,2005.


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Example of dual-chamber, rate-responsive pacing


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Mode Selection Considerations

Status of Atrial Rhythm- Intrinsic vs. Paced- Presence of Atrial Tachyarrhythmias:

Acute/Chronic

Status of AV ConductionNormal -Slowed-Blocked

Presence of ChronotropicIncompetence


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Mode Representative Indications

VVI Rare Need for Pacing Simple; System Desirable (Old, Debilitated Patient; Very Young)

VVIR Chronic AF With Symptomatic Pauses; Inadequate Ventricular Response

After AV Nodal Ablation for Rate Control in AF

AAI Symptomatic Sinus Pauses With Otherwise Normal Sinus Node Function and Intact AV

Conduction

AAIR Sinus Node Dysfunction With Intact AV Conduction and No Atrial Arrhythmias

VDD AV Block With Normal Sinus Node Function; Uses Single Lead; No Atrial Pacing,

Therefore Not Appropriate for Patients With Sinus Bradycardia

DDD AV Block With Normal Sinus Node Function

DDDR AV Block With Sinus Node Dysfunction; Mode Switching Feature if AnyParoxysmal Atrial Arrhythmias

DDIR An Alternate to DDDR for Patients Who Require Dual-Chamber Pacing but Have

Paroxysmal Atrial Arrhythmias Does Not Permit Atrial Tracking in Sinus Rhythm


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Biventricular Pacing (BVP)

A biventricular pacemaker, also known as CRT (cardiac resynchronisation therapy) is a

type of pacemaker that can pace both ventricles (right and left) of the heart.

By pacing both sides of the heart, the pacemaker can resynchronize a heart that doesnot beat in synchrony, which is common in heart failure patients.

CRT devices have three leads, one in the atrium, one in the right ventricle, and a final

one is inserted through the coronary sinus to pace the left ventricle.

CRT devices are shown to reduce mortality and improve quality of life in groups ofheart failure patients.


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Coronary sinus lead

Right atrial lead

Right ventricular lead

N Engl J Med 2003


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LV lead

RV coil

SVC coil

RA lead


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Venous accessPneumothorax, hemothoraxAir embolismPerforation of central veinInadvertent arterial entry

Lead placementBrady tachyarrhythmiaPerforation of heart, veinDamage to heart valve

GeneratorPocket hematomaImproper or inadequate connection of lead


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Lead-relatedThrombosis/embolizationSVC obstructionLead dislodgementInfectionLead failure

Perforation, pericarditis

Generator-relatedPainErosion, infectionMigration

Damage from radiation, electric shock

Patient-relatedTwiddler syndrome


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Fatigue, dizziness, hypotension

Caused by pacing the ventricle asynchronously, resulting in AV dissociation orVA conduction

Mechanism: atrial contraction against a closed AV valve and release of atrialnatriuretic peptide

Worsened by increasing the ventricular pacing rate, relieved by lowering the

pacing rate or upgrading to dual chamber system

Therapy with fludrocortisone/volume expansion NOT helpful


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Failure to output

Failure to output occurs when no pacing spike is present despite an indication to

pace. This may be due to battery failure, lead fracture, a break in lead insulation,

oversensing (inhibiting pacer output), poor lead connection at the takeoff from the

pacer, and "cross-talk" (i.e., a phenomenon seen when atrial output is sensed by a

ventricular lead in a dual-chamber pacer).

Management of pacer output complications includes medications to increase the

intrinsic heart rate and placement of a temporary pacer. A chest radiograph is

warranted to check pacer leads, with close scrutiny to evaluate for possible lead

fracture, which occurs most commonly at the clavicle/first rib location. The

patient's pacer identification card should be obtained and his/her

electrophysiologist/cardiologist consulted.


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Failure to capture

Failure to capture occurs when a pacing spike is not followed by either an

atrial or a ventricular complex.

This may be due to lead fracture, lead dislodgement, a break in lead

insulation, an elevated pacing threshold, myocardial infarction at the lead

tip, certain drugs (eg, flecainide), metabolic abnormalities (eg, hyperkalemia,acidosis, alkalosis), cardiac perforation, poor lead connection at the takeoff

from the generator, and improper amplitude or pulse width settings.

Management of pacer capture complications is the same as for output

complications, with extra consideration given to treating metabolic

abnormalities and potential myocardial infarction.


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Oversensing

Oversensing occurs when a pacer incorrectly senses noncardiac electrical activity and

is inhibited from correctly pacing.

This may be due to muscular activity, particularly oversensing of the diaphragm or

pectoralis muscles, electromagnetic interference such as MRIs, or lead insulation

breakage. More recently, cellular phones held within 10 cm of the pulse generator

may elicit this response.

Undersensing

Undersensing occurs when a pacer incorrectly misses intrinsic depolarization and

paces despite intrinsic activity.

This may be due to poor lead positioning, lead dislodgment, magnet application, lowbattery states, or myocardial infarction. Management is similar to that for other types

of failures.


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Operative failures

A final category of pacer failures is termed operative. This includes malfunction

due to mechanical factors, such as pneumothorax, pericarditis, infection, skin

erosion, hematoma, lead dislodgment, and venous thrombosis.

Treatment depends on the etiology.

Pneumothoraces, being dependent on size, may require chest thoracostomy.

Erosion of the pacer through the skin, while rare, requires pacer replacement

and systemic antibiotics. Hematomas may require drainage. Lead dislodgmentusually occurs within 2 days following implantation of a permanent pacer and

may be seen on chest radiography. If the lead is floating freely in the ventricle,

malignant arrhythmias may develop. Thrombosis is rare and usually presents as

unilateral arm edema. Treatment includes arm elevation and anticoagulation.

Advanced life support protocols, including defibrillation, may safely be executed

in patients with pacemakers in place. Sternal paddles are placed at a safe

distance (10 cm) from the pulse generator. Temporary transcutaneous pacing

may become necessary in cases of myocardial infarction.


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MedicalMRI

Lithotripsy

Electrocautery/cryosurgery

External defibrillators

Therapeutic radiation

NonmedicalArc welding equipment

Automobile engines

Radar Transmitters


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Devices with pacemaker function

Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter-

defibrillator) are implanted.

These devices are often used in the treatment of patients at risk from sudden cardiac

death.

An ICD has the ability to treat many types of heart rhythm disturbances by means of

pacing, cardioversion, or defibrillation.


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Secondary prevention of SCD:VF arrest, sustained VT not secondary to reversible

cause

Primary prevention of SCD:

LVEF < 36%, class II-III symptoms of CHF

CAD, h/o MI, LVEF 40%, inducible sustained VT

Familial or inherited conditions with high risk for SCD:HCM, long QT syndrome, Brugada syndrome


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Pacemaker programming can be performed noninvasively by an electrophysiologist or

cardiologist. Because of the myriad of pacemaker types, patients should carry a card

with them providing information about their particular model.

This information is crucial when communicating with the cardiologist about a pacer

problem.

Most pacemaker generators, however, have an x-ray code that can be seen on a

standard chest x-ray. The markings, along with the shape of the generator, may assist

with deciphering the manufacturer of the generator and pacemaker battery.

This may be helpful in the event a patient neither recalls the company nor has thepermanent pacemaker card.


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Placing a magnet over a permanent pacemaker causes sensing to be inhibited by

closing an internal reed switch. This only temporarily "reprograms" the pacer into the

asynchronous mode, where pacing is initiated at a set rate. It does not turn the

pacemaker off.

Each pacemaker type has a unique asynchronous rate for beginning-of-life (BOL),

elective replacement indicator (ERI), and end-of-life (EOL).

Therefore, application of a magnet can determine if the pacer's battery needs to be

replaced.

Further interrogation, or manipulating of the device, should be performed by an

individual skilled in the technique.Patients should carry a card that contains information about their particular

pacemaker, since these rates are dependent on the manufacturer and the model.


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Cardiac Pacing for the Surgeons

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