Card 4203 pacemaker midterm M1

CRMD

life saving devices that are for patients with various cardaic conduction disturabnces and tachyarrythmias

What do CMRD devices do

regulate brady through artifical pacing, resynch ventricles in heart failure, antitachy pacing and defib therapy, monitor arrhythmias

what are some CMR devices

pacemakers, CRT devices, ICD's, ILR

2 components of a pacemaker system

pulse generator and the leads

what does the pulse generator do

deliever electrical impulses to the heart, located in the pectoral region either in the L or R side of the chest ( mainly L)

header of a pulse generator

sits on top of the pulse generator, contains 1 or more open channels to allow of the connection of leads

intergrated circut

contains the components that make the pacemaker function

telemetry

refers to the capability of non-invasive communication between a programmer and the implanted pulse generator

reed switch

activated by applying a magnet to the device, which elicits a specific magnet response

capacitor

acts as a voltage multiplier to deliver a pacing pulse at a voltage higher than the stored capacity of the battery of 2.8 V

Ex) pacing the vents at 3.5v @0.4msec

accelerometer

a small spring board that moves in relationship to the patients activities, it creates a signal that correlates to increases in pacing rate

battery

powers the components in the pulse generator

pacemaker leads

provides a connective pathway from the pulse generator to the heart. the energy is delivered to the heart via the leads and when the pacemaker senses a interistic depol signal, the energy is carried back to the pacemaker via the lead

4 components of the pacemaker lead

1. the connector pin

2. the lead body

3. the electrode( distal end)

4. fixation mechanism

the connector pin

the connector pin and header must match for the pulse generator to function. the standard leads and headers are the IS-1. adaptors may be necessary

lead body

1 or 2 conductor wires run the length from the connector pin to the electrodes. will be either coaxial or coradial

coaxial lead design

there is a inner conductor wire that is surrounded by a layer of insulation and a second wire that extends to the proximal anode electrode surrounding the insulated inner wire

coradial lead design

each wire is indy coated with insulation and the 2 coated wires are laid side-by-side to form a spring like apperance

electrodes

transmit electrical energy from the conductor wire to the surface of the heart. a small surface area electrode stimulation increases efficiency but larger surface area electrodes enhance sensing.

- we use a electrodes with a small radius and a complex surface structure

fixation mechanism

prevents the leads from dislodging after implanting

types of fixation devices

passive- fins/tines- in the trabeculations of the endocardial surface

active- extendable/retractable or a fixed screw on the tip, screwed into the myocardium

steriod eluting leads

leads that store a small amount of steriods ( dexamethasone) behind the distal electrode, the steriods help with inflamation that can cause an acute rise in capture threshold after lead implantation

unipolar leads

1 wire and 1 electrode. current travels from the pulse generator through the wire to the cathode tip and then back through to the anode tip, less complex than bipolar but more EMI problems

uncoated window

important to place this window away from the pectoral muscle due to the possiblity of stimulation when the electrical impulse is travelling back to the generator

oversensing

A lot of spikes for no reason, more likely to occur in unipolar leads because of the larger window for sensing

Bipolar leads

2 wire and 2 electrodes within the heart. current flows through one of the wires to the distal tip (cathode) and then back to the proximal electrode (anode) and then back up to complete the circuit

sensing configurations

unipolar-visualise pacemaker spikes

bipolar-minimize the posibiliy of oversensing

ohms law

V=I x R

voltage (V)

the electrical force that makes current move through a conductor

impedance (R)=omhs

the resistance to the flow of current by an electrical circut or device

current (I)= amps

the transfer of electrical charge through a cross-section of a conductor

we use milliamps as a unit

Convert volts to millivolts by 1000 or move the decimal three places to the right.

Convert amps to milliamps by 1000 or move the decimal three places to the right.

What will the current be if

Voltage = 5 V

impedance = 250 ohms (Ω)?

I = V/R:

5 V x 1000 = 5000 mV / 250 Ω = 20 mA

high lead impedance?

less current= pacemaker longevity will be extended

low lead impedance?

more current= short life span for the pacemaker

what does ohms law do

determines how much current is available for pacing output stimulus and how the lead issue may affect pacemaker longevity

how can leads become compromised

fracture, break, exessive flexing or overstressing, improper connection to the pulse generator

what resistance amount would be considered a fracture in the lead

a rise of > 200 ohms

what happens if fluid/insulation break gets into the pacemaker generator

it will lower the lead impedance. a drop of >200omhs would be seen

CRMD batteries

-They need to be safe as they will be implanted inside the body

-Have high-energy density to save on size and weight

-Have a predictable performance and are highly reliable

-Have a long service life to limit the number of surgical procedures that need to be performed

main power source for the pulse generator

lithium iodine- stable, long lasting, and has a predictable battery depletion curve. generates around 2.8 V and drops to 2.65 V when 90% battery life has been reached

what is the anode made of

lithium

what is the cathode made of

iodine

The ionic movement from the anode to the cathode happens through?

lithium iodine electrolyte

beginning of life ohms

0-1k ohms

needs replacement ohms

10-12k ohms

end of life ohms

>15k ohms

when does a battery need to replaced

2.65V

what if we need a voltage higher than 2.8V?

we would use a voltage doubler or tripler

the battery capacity is one of the major determinants of pulse generator longevity

based of the spesific chemistry and the size of the cell

what is the capacity in which a current can be drawn from the cell

0.5-2.0 AH

what other kind of battery can we use

carbon monfluride

when is lithium for a batter not good

when it is paired with an iodine cathode- internal resistance builds up and it can impact the batterys performance

what kind of battery does an ICD use

lithium/silver vanadium oxide or lithium/manganese dioxide

what is artifical pacing

delivery of electrical impulses of sufficient strength to cause depol

pacing capture

stimulus delivered outside of the myocardiaum refractory period causing a wave of depol

factors that affect the ability of the pacing stimulus to capture

1. Programmed voltage and pulse width of the pacing pulse

2. Integrity of the pacemaker system

component issue within pulse generator, loose set screw or lead fracture may result in loss of capture

3. Proximity of the distal pacing electrode to myocardium

dislodged lead post-implant maybe floating in the chamber

4. Viability of the myocardium

distal lead electrode placed in scar tissue from previous myocardial infarction

5. Stimulation of myocardial cells maybe be affected by the following:

drugs that can increase stimulation threshold - propaferone, flecainide, quinidine and procainamide

decreased sympathetic tone or enhanced vagal tone during periods of rest or sleep

severe metabolic disorders such as acidosis/alkalosis, hypoxemia, hyperkalemia, hyperglycemia

cardiac arrest, cardioversion, defibrillation

stimulation threshold

minimum amount of electrical stimulus needed to consistantly capture the myocardium outside of the hearts refractory period

Amplitude

measured in voltage, can be programmed up to 7.5 V

Pulse width

measured in milliseconds, length of time a stimulus is applied for, can be 2.0 ms

what is the most common programmed setting

2.5V @ 0.4msec

what is the safety margin

either double the voltage or triple the pulse width

When pulse widths are ≥ 0.3ms at a given voltage

tripling pulse width is not typically selected. It is less efficient (expend more energy), while not providing further safety. In this case, the voltage should be doubled to provide an adequate safety margin.

stimulation threshold test

involves decrementing the voltage or pulse width until loss of capture is seen on the ECG tracing. The stimulation threshold is the last pacing output to capture the heart.

example of stimulation threshold testing

In this example, the pulse width is held constant at 0.4ms while the voltage is decremented until loss of capture is seen. Loss of capture occurs at 0.9V so the ventricular stimulation threshold is 1.0V @ 0.4ms

strength duration curve

plots the combination of values (pulse amplitude/pulse width or voltage/milliseconds) at which capture occurs.

what does a strength duration curve demonstrate

It demonstrates graphically that at very high pulse amplitudes, only short pulse widths are needed to capture; as the pulse amplitude decreases, the pulse width must be increased to assure capture.

what the key leandmarks of the strength duration curve

the rheobase and the chronaxie

rheobase

The lowest point on this curve at infinitely long pulse duration. An increase in pulse width beyond this value does not provide more effective stimulation.

chronaxie

The pulse amplitude at twice the rheobase is called the chronaxie; the pulse width setting is desirable to minimize energy consumption while still maintaining an adequate safety margin.

the rheobase - The lowest point on this curve at infinitely long pulse duration

the chronaxie (chronaxie = 2 x rheobase).- The pulse amplitude at twice the rheobase

All points above the curve indicate sufficient stimulus to capture.

All points below the curve indicated sub-threshold stimulus.

sensing

the ability of the pacing system to detect and respond to intrinsic cardiac signals.

The amplitude of the signal that is detected will depend upon-

-the mass of the muscle under the electrode

-the contact of the electrode(s) with the myocardium

-the orientation of the electrodes relative to -the advancing wave of depolarization.

what do the filters in the pulse generator do

-sense only signals which have the same frequency components as P waves and R waves

-reject both low-frequency and high-frequency signals.

frequency range of P and R waves

10-50 Hz

frequency

rate of change of the signal over time

slew rate

represents the maximal rate of change of the electrical potential between the sensing electrodes and it is the first derivative of the electrogram (dV/dt).

slew rate measurements

at implant should exceed 0.5 V/sec for P waves;

0.75 V/sec for R wave measurements.

the higher the slew rate,

the higher the frequency content and the more likely the signal will be sensed.

-T wave, are much less likely to be sensed because of a low slew rate and lower frequency density.

pacemaker sensitivity

The greater the number, the less sensitive the device is to intracardiac signals.

The smaller the number, the more sensitive the device is to seeing intracardiac signals AND other signals we may not want it to see.

oversensing

pauses, when a signal gets past the filter and causes the pacemaker to misinterpret those signals as intrinsic P or R waves. When this occurs, the pacemaker inhibits sending a pacing stimulus to the atrium or ventricle

Need to make the pacemaker "less" sensitive

examples of oversensing

Skeletal myopotentials. T

Far-field events.

T waves.

Lead integrity issue.

loose set screw

EMI

undersensing

occurs when the pacemaker fails to see intrinsic atrial or ventricular activity and paces asynchronously. need to make it "more" sensitive

common reasons for undersensing

-improperly programmed sensitivity setting

-low myocardial voltage signal (post MI)

-lead integrity issue

-electrolyte abnormality.

magnet response

application to a CRMD is a simple way to acquire basic information about the device, temporarily disables tachycardia therapies,

reed switch

puts the pacemaker into a asynchronous pacing mode- which makes the pacemaker no longer sense but continuously paces

reasons to apply a magnet to a crmd

-Determine the battery status of the device.

-Let the clinician know what type of pacemaker is implanted.

-Troubleshoot potential issues with the device.

-Pace asynchronously when oversensing is present.

-Suspend ICD tachy therapies when issues present.

potential complications with magnet application

-Magnet application and asynchronous pacing have been known to initiate atrial or ventricular tachyarrhythmias in vulnerable patients with ischemic or recently infarcted hearts, with a history of VT/VF or with history of SVTs/Afib/Aflutter.

-there is a possibility of initiating an endless loop tachycardia when AV synchrony is lost during magnet application.

-Magnet application can possibly trigger the EOL indicator and change the pacing mode from dual chamber to single chamber.

class recommendations

Class I

Benefit >> Risk

Evidence and/or general agreement that a given treatment or procedure is beneficial, useful, effective

Class IIa

Benefit > Risk

Weight of evidence/opinion is in favour of usefulness/efficacy

Class IIb

Benefit = Risk

Usefulness/efficacy is less well established by evidence/opinion

Class III

Risk > Benefit

Evidence or general agreement that the given treatment or procedure is not useful/effective, and in some case may be harmful

diagnostic assesment

In order for a patient to be indicated for a CRMD, their cardiac condition should be documented by one or more diagnostic assessments.

sympotoms due to brady, tach or HF

Presyncope or syncope

General fatigue, poor or decreased exercise tolerance

Decreased mental acuity

Palpitations, skipped or irregular beating, or rapid heart rates

Signs and symptoms of heart failure: shortness of breath, jugular venous distension, enlarged liver on palpation, weight gain, ankle edema.

12 lead

A 12 lead ECG or rhythm strip during the symptomatic episode provides a definitive diagnosis. An ECG may also provide information about structural heart disease such as LBBB, Q waves, prolonged QT interval, etc.

ambulatory ecg monitor

Bradycardia or conduction disease secondary to structural heart disease is often intermittent in nature which makes it difficult to capture at the time of a 12 lead ECG. Prescribing a holter monitor or event recorder maybe effective in confirming symptoms with the rhythm disturbance

ETT

Exercise tolerance testing is performed to assess chronotropic response to exercise and to assess for presence of exercise induced arrhythmias and myocardial ischemia.

Carotid Sinus Massage

Carotid sinus massage (CSM) is performed to confirm if carotid sinus hypersensitivity and cardioinhibitory to carotid sinus pressure is the cause of presyncope or syncope. CSM is performed under continuous ECG monitoring.

tilt table test

Tilt table testing is performed to evaluate whether syncope is related to a cardioinhibitory response or vasodepressor response.

ILR

an implantable loop recorder (ILR) may be prescribed for the patient with persistent symptoms. The ILR is a leadless, subcutaneous cardiac monitor that can be implanted for up to 3 years. An ILR is the approximate size of a USB memory stick and can be effective for identifying abnormal rhythms.

EP studies

An EP study is effective in determining the need for a pacemaker but it is rarely chosen to solely assess for pacemaker insertion. An EP study may be used as an additional tool in the evaluation of patients with syncope in whom bradycardia is suspected but has not been documented with other non-invasive diagnostic assessments. EP studies may also be conducted to confirm if supraventricular or ventricular tachycardias are the cause of presyncope or syncope

ICD indication

people with a high risk of ventricular tachyarrhythmias

primary prevention

a patient that has cardiac disease but no significant vent tachy arrythmia