Cardiac Rhythm Management

Rate control medication

slow down the fast rates of abnormal rhythms

Rhythm control medication

suppress abnormal rhythms from occurring

Rate Control Medications:

beta blockers: metoprolol, atenolol they slow impulses passing through AV node

calcium channel blockers: verapamil, diltiazem

Rhythm Control Medications:

antiarrhythmic medications

potassium channel blockers: aminodarone, sotalol, tikosyn, dofetilide

sodium channel blockers: flecainide, rythmol, aka propafenone

Permanent Pacemaker (PPM)

pacemaker therapy is required when there is a problem with the heart’s conduction system that results in slow heartbeats

sick sinus syndrome

heart block

pacemakers work on demand

monitors intrinsic rhythm, paces when rate falls below programmed pacing rate

ICD Therapy

an ICD, or implantable cardioverter defibrillator is for people who are at risk of having a life threatening heart rhythm such as VT or VF

rapid irregular beats originate in the lower chamber of the heart and can lead to sudden cardiac arrest

indicated for patients who have a weak heart, ejection fraction <40% from a heart attack or muscle injury, at risk for having VT and VF

if the heart beats too slow, it will act as a pacemaker and pace the heart

if the device detects a ventricular arrhythmia, it will deliver pacing and shock therapy to convert the heart to a normal rhythm

CRT Therapy

cardiac resynchronization therapy or CRT delivers pacing stimuli to resynchronize the pumping function of the heart

left bundle branch block slows electrical conduction to left ventricle resulting in an out of sync heartbeat

pacing lead placed through coronary sinus into venous anatomy

CRT-D and CRT-P Devices

CRT-D provides CRT pacing and defibrillation

CRT-P provides CRT pacing only

Class I

benefits outweigh risk. procedure or treatment should be performed

Class IIa

benefits still outweigh risk, considered reasonable to perform procedure

Class IIb

benefits equal to risk. May consider performing procedure or treatment. Additional studies needed

Class III

risk is greater than or equal to the benefit. Procedure should not be performed and could be harmful to the patient

Voltage

is the force or the push that causes an electron to move through a circuit

is measured in volts, represented with the letter V

called pacing amplitude in the context of external stimuli delivered to the heart

Current

is the flow of electrons through a completed circuit

is measured in milliamps (mA) represented with the letter I

Impedance

is the opposition or the resistance to current

is measured in ohms, represented with the letter R

often referred to as resistance

Ohm’s Lam

represents the relationship between voltage, current, and impedance

V = IR formula states the voltage is equal to current in amps multiplied by resistance in ohms

if we know any two of these variables, we can solve for the third

Cathode

a negatively charged electrode that is the source of electrons entering an electrical device

tip electrode of pacing lead (-)

an electrode that is in contact with cardiac tissue

delivers electrical impulses in attempt to depolarize cardiac tissue

negatively charged when electrical current is flowing

Anode

a positively charged electrode by which electrons leave an electrical device

ring electrode of pacing lead (+)

an electrode that receives electrical impulses after depolarization of cardiac tissue

positively charged when electrical current is flowing

Conduction Pathway

electrons flow out the lead tip, through the blood and the tissue of the heart, and then return to the anode

Pacing Spike

a pacing spike is the graphical representation on the ECG of a delivered pacing impulse

delivered energy should cause myocardial stimulation or capture heart muscle

Myocardial Capture

Capture is a function of:

Amplitude:

the amplitude of the impulse must be large enough to cause depolarization (capture)

the amplitude of the impulse must be sufficient to provide an appropriate pacing safety margin (2:1) based on pacing threshold

Pulse width:

the pulse width must be long enough for depolarization to disperse to the surrounding tissue

Amplitude

the strength of the impulse expressed in volts

Pacing Threshold

the minimum amount of energy needed to consistently capture cardiac tissue

voltage over time for calculation

Pulse Width

the duration of the current flow expressed in milliseconds

Supernormal period

when a cell will respond to a weaker than normal stimulus

on the ECG, this correlates to the end of the downslope on the T wave up until the return to resting state

Effective refractory period

correlates to the absolute refractory period but also includes a small segment of phase three

stimulus may cause the cell to depolarize minimally, but not result in a propagated action potential

may see movement at the cellular level from an external stimulus, such as pacing impulse, but that impulse will not cause widespread depolarization of cardiac tissue

Capture

enough energy

tissue is not refractory

Loss of Capture

not enough energy

tissue is not refractory

Functional Non Capture

enough energy

tissue is refractory

Sensing

is the identifying of cardiac depolarization from an intracardiac electrogram

each signal represents cardiac depolarization occurring at a particular point in the heart

sensing can also be described as the difference in electrical potential between two points: the cathode and anode

Nearfield

are close range signals and have a sharp looking morphology

Farfield

are farther range signals and typically have a rounded morphology

Slew rate

is a measurement of an intrinsic signal’s slope or change over time

measured in volts per second

Frequency

is the amount an event occurs over time

measured in hertz

Sensitivity

is the ability for a device to sense an intrinsic electrical signal

is also a value that can be programmed based on a sensing measurement

measured in mV

more sensitive the device programming, the more it can see and the lower that programmed value will be

Unipolar Pacing System

cathode: tip electrode on lead

anode: pulse generator (can)

large antenna

Bipolar Pacing System

cathode: tip electrode on lead

anode: ring electrode on lead

small antenna

Electricity in Cardiac Pacing - Battery

a device that produces electricity; may have several primary or secondary cells arranged in parallel or series

Electricity in Cardiac Pacing - Capacitor

an electrical device characterized by its ability to store an electrical charge

Lead Breakage - Insulation Breach

decreases the resistance in the lead, which causes an increase in flow

Lead Breakage - Conductor or Coil Damage

increase in resistance in the lead, which cause a decrease in flow

Programmer

interfaces with the device, collects patient and device information, used for testing and programming

Lead

implanted through a patient’s venous anatomy and placed in either or both the right atrium and right ventricle; LV lead placed through CS into coronary venous anatomy for CRT devices

Pulse generator

metal device encased in titanium

the header is where the leads connect to the pulse generator

Circuit board

capacitors, resistors, accelerometers, reed switch, crystal oscillators, telemetry coil

Pacemaker Header

is part of device where the electrical connection is made between the lead and the generator

International Standard - 1 (IS-1)

lead enters the connecter block and is then held in place by a set screw

Passive fixation

leads utilize tines which embeds into the trabeculae

Active fixation

leads utilize a helix or a screw

extendable / retractable active fixation most common lead; fixation tool rotated clockwise to extend

Endocardial Leads

also known as transvenous leads

are placed in the heart through venous access

Epicardial Leads

also known as myocardial leads

are placed on the epicardium surgically

may be placed during open heart surgery or valve surgery, pediatric cases, and for patients with comprised venous access

Steroid Eluting Leads

today all pacing leads are steroid eluting

steroid collar built into lead

leads to decrease inflammation, which in turn decreases thresholds, and increases the device longevity

Lead Insulation - Silicone

reliable, flexible, and pliable

stickier and more difficult to navigate, prone to abrasions

Lead Insulation - Polyurethane

resistance to low friction in the blood, high abrasion resistance

stiffer, less pliable, history of failure

55D most current

Lead Insulation - Optim

combination of both insulation types thought to create a strong, lubricious, and abrasion resistant lead that is also flexible

Porous Tip Electrode

tip electrode is porous

porous design increases the overall surface area of the electrode, which increases contact with tissue and facilitates better sensing

keeps electrode small for pacing stimulation

Coaxial design

one insulated coil is surrounded by a second insulated coil

damage to the other coil would still provide an opportunity to reprogram the lead to unipolar

Coradial design

the coils are wrapped around each other and separately insulated

tend to be thinner

lead failure are more likely to involve a fracture of the cathode wire

Terminal pin

portion of the lead that connects to the header on the pulse generator

IS-1

5/6 mm unipolar

3.2 mm low profile

Selective Capture

if capturing only the specific part of the conduction system

also known as PURE capture

Non selective Capture

if capturing the conduction system and some of the surrounding tissue

also known as Fusion

SSI

single chamber pacing

single chamber sensing

inhibition in response to sensing

program to AAI or VVI

AAI

atrial pacing

atrial sensing

inhibition in response to sensing

no ventricular support

not commonly implanted in the US

AOO

atrial pacing

no sensing

asynchronous mode

magnet application to AAI pacemaker

VVI

ventricular pacing

ventricular sensing

inhibition in response to sensing

longstanding persistent or permanent AF with SVR

VOO

ventricular pacing

no sensing

asynchronous mode

magent application to VVI pacemaker

Single chamber Modes

AAI (R)

AOO

VVI (R)

VOO

DDD

sensing and pacing in both chambers, inhibition and triggering in response to sensing

intrinsic p wave: atrial inhibition

intrinsic r wave: ventricular inhibition

intrinsic p wave with no intrinsic r wave: ventricular triggering

DDI

sensing and pacing in both chambers, inhibition in response to sensing

no atrial tacking

DOO

dual chamber pacing, no sensing

asynchronous mode

magnet application to DDD pacemaker

VDD

pacing in the ventricle, sensing in both chambers, inhibition and tracking in response to sensing

single VDD lead

atrial electrode floating blood

VDI

pacing in the ventricle, sensing in both chambers, inhibition in response to sensing

no atrial tracking

Dual Chamber Modes

DDD (R)

DDI (R)

DOO

VDD (R)

VDI (R)

Refractory Periods

programmable

begins after every sensed or paced beat

device will not respond to intrinsic signals

typically 250 ms

Alert Period

not directly programmable

begins when refractory period expires

device will inhibit if it senses an intrinsic signal

Automatic intervals

pacing intervals initiated by paced beat

measured from pacing spike to pacing spike

Escape intervals

pacing interval initiated by sensed beat

measured from intrinsic beat to pacing spike

Rate Hysteresis

separately programmed escape interval

program hysteresis rate slower than programmed rate

Search Hysteresis

device periodically extends the pacing interval to search for intrinsic beats

no intrinsic beat: switches back to normal pacing interval

intrinsic beat: switches to hysteresis interval

Oversensing

device senses non-cardiac signals that it should ignore

sensitivity should set low enough to detect cardiac signals, but not low enough to detect extra cardiac signals

oversensing leads to underpacing - inappropriate inhibition from oversensing leads to underpacing

gaps in the paced rhythm: measure backwards to find where device over sensed

Undersensing

device ignores cardiac signals that should sense

set high enough to ignore extra cardiac signals, but not high enough to ignore cardiac signals

inappropriate inhibition from oversensing leads to overpacing

Loss of Capture and Causes

pacing impulses does not lead to cardiac depolarization

every pacing spike should lead to immediate depolarization

patient’s intrinsic rhythm will take over at slower rate

lead failure

lead dislodgment

perforation

most common: device output set too low

Loss of Output

no pacing impulses at all

most common cause: connector pin out of header

patient may be very symptomatic

requires invasive intervention

Fusion

pacemaker’s output pulse combines with intrinsic beat to create hybrid depolarization

ventricular lead in apex

intrinsic depolarization starting in His bundle

intrinsic signal starts just before pacing interval expires

device paces and signals meet halfway

mix between paced and intrinsic beat

Pseudofusion

pacemaker paces but has no effect on depolarization

ventricular lead in apex

intrinsic depolarization starting His bundle

intrinsic signal starts just before pacing interval expires

device paces after surrounding tissue has already depolarized

intrinsic morphology with pacing spike