CRM 1, 2, 3 - Introduction, Fundamental Basics, Devices and Leads Flashcards
What does ICD stand for?
-Implantable Cardioverter Defibrillator
Functions of device (pacemaker)
-Surgically implanted device which emits electrical signals to treat bradycardia
-Monitors intrinsic and paced beats
-Controls timing and system operations
Functions of device (ICD)
-Has capacitance to hold a high energy charge and is able to deliver a defibrillation shock
-ICD may form part of the shock vector (active can)
Functions of leads
-Acts as a conductor
-Deliver electrical stimuli from the impulse generator to the myocardium
-Carries intrinsic signals from the heart to the impulse generator
-Form part of shock vector (in ICD)
What are the different types of leads?
-Transvenous intracardiac
-Epicardial
-Coronary sinus
-Leadless
What type of rhythms would we think about pacing?
-Bradycardias
What rhythms would we think about shocking?
-VF
What are CRT (cardiac resynchronisation therapy) devices used for?
-Heart failure
Brief description of pacemaker
-Implanted electronic device
-That emits impulses to treat bradycardias
Brief description of ICD
-Implanted device
-Delivers anti-tachy pacing and shock therapy for ventricular arrhythmias
-Also treats bradycardias
Brief description of CRT
-Implanted device
-Treats heart failure by correcting electrical discordance by pacing both right and left ventricles
What happens at the anode?
-Electrons leave and move away
What happens at the cathode?
-Electrons enter or come towards
When does current flow?
-Only flows in a closed circuit
Describe electron and current flow
-Electrons flow from the negative pole to the positive pole
-Current flows from the positive pole to the negative pole
How does battery in pacemaker produce electricity to stimulate the heart?
-The battery has a positive and negative pole
-A chemical reaction between electrolytes produces an electron flow (energy)
What happens as battery ages?
-The oxidative and reductive processes between the electrolyte and the electrodes causes the internal resistance to increase
What type of battery do pacemakers use?
-Lithium-Iodine battery
What is the load in a pacemaker battery?
-The endocardium of the ventricle
Anode and cathode in load/battery
Load:
Anode = positive
Cathode = negative
Battery:
Anode = negative
Cathode = positive
How are electrons formed in a pacemaker battery?
Battery:
-Oxidation occurs at the anode
-Each atom of Li loses one electron
2Li -> 2Li+ + 2e-
-Reduction occurs at the cathode
-Each molecule of I combines with 2 electrons
I2 + 2e- -> 2I-
How does a pacemaker battery work?
-At the anode of the battery, electrons are released from lithium atoms - to form Li+ ions
-The electrons repel each other and are pushed outside of the battery and become the electrical flow (circuit)
-The electrons enter the cathode where they combine with iodine to form 2I- ions
-The positive lithium and negative iodine ions combine to form lithium iodide
-Lithium iodide is a poor conductor - the build-up of LiI increases the internal resistance of the battery over time
What can act as the anode in a pacemaker battery?
-The can (which contains the battery)
-The proximal pole on the pacing lead
What direction do electrons flow between anode and cathode?
-Electrons leave the anode (AWAY)
-Electrons enter the cathode (COME)
Where do leads for dual chamber ICD go?
-Right atrium
-Right ventricle
Unipolar vs Bipolar
Unipolar:
-Big circuit
-Anode is in can, Cathode in wire
Bipolar:
-Small circuit
-Anode and Cathode in wire
Voltage formula
V = IR
What is loss of capture?
-Pacing spike followed by no depolarisation
What is capture?
-Pacing spike followed by something
Explain pacing pulse width and height
Pulse duration = width
Voltage = height
Pulse duration x height = total amount of energy
What is the pacing threshold?
-The minimum amount of energy contained within the pulse width and voltage that is needed to pace the heart
What does pacing right ventricle look like on ECG?
-LBBB
What does pacing left ventricle look like on ECG?
-RBBB
LBBB on ECG
-Negative in V1
-Positive in V6
RBBB on ECG
-Positive in V1
-Negative in V6
Why does Right ventricle pacing look like LBBB?
-In LBBB, left side is blocked so right side is depolarised first
-Right side is depolarised first in RV pacing
What should you look out for during RV pacing
-Whether catheter has gone into LV
-Will look like RBBB
What is the threshold test?
-Lowest voltage that produces capture
-Must state units (mV and mS)
What are rheobase and chronaxie?
Rheobase
-Lowest stimulation voltage at any pulse width
Chronaxie
-Pulse duration at twice the rheobase
(Anything above the curve will be captured)
What do we program the pacing device to?
2 x pulse amplitude (volts) (most common)
3 x pulse width (ms)
Why shouldn’t pacemaker sense T waves
-It might think T waves are QRS complexes and reset timer for pacing
What do we want to/not want to sense?
+ atrial depolarisation
+Ventricular depolarisation
-Noise
-T waves
-Myopotential
What would happen if RV lead fell into the RA
-It would sense P waves as QRS complexes
-As a result, it would not pace
Benefits of sensing
-No inappropriate pacing
-Saves battery
-Reduces risk of arrhythmias
-Allows intrinsic arrhythmias/ectopics to be identified/measured
Which is the most/least sensitive?
-Most sensitive = right (little number)
-Least sensitive = left
Components of a pacemaker
-Can - casing
-Header - connector
-Battery - power source
-Diodes/resistors/microchips/oscillators
Components of CRT/ICD
Describe the can and header in a pacemaker
-Hermetically sealed
-Titanium - biocompatible, light, strong
-Houses all the components
-Protects the components and the lead connectors from bodily fluids
-Can act as a conductor (e.g. in unipolar pacing configurations, as part of the shocking vector in ICDs
-Leads are attached via the header
Function of diodes and resistors
-Manage current flow and direction
-Restricts/limits the flow of current
Function of crystal oscillator
-time clock for timing cycles
Function of microchip
-A mini computer for sensing, pacing, memory, demographics, programmable algorithms
-Can have uploads via a programmer
Function of sensors
-Used in rate response
E.g.
-Piezoelectric crystal
-Accelerometer
Metabolic sensors:
-minute ventilation
-QT
-temperature
Function of battery
-Provides energy
Function of capacitor
-ICD component
-Charges up
-Holds charge for shock therapy of VF
What type of battery is used in ICD?
-Vanadium iodide
What type of battery is used in pacemaker
-Lithium iodide
Why do pacemaker batteries use lithium iodide?
-High electrochemical potential
-High energy density - powerful
-Low cost
-Lightweight
-Predictable discharge and predictable impedance rise as it ages
What happens to lithium battery as it ages?
-It gets coated as it ages
-The more coating, the higher the impedance
What does ERI stand for?
Elective Replacement indicator (low battery)
What does EOL stand for?
End Of Life (no battery)
What impacts battery life?
-Type
-Discharge
-Consumption
-Tissue resistance (Higher resistance, battery lasts longer)
-Use
Battery life expectancy equation
-Battery capacity / Current drain expressed in ampere hours
Example of battery life equation
-Convert to same units
-Convert hours to years
What type of battery in ICD?
Lithium Silver Vanadium
-Large charge stored in a small volume
-Distinctive discharge curve - ERI has a distinct ‘point’
Features of ICD leads
Insulation:
-Prevents electrical current escaping to the tissue, protects conductor from corrosion
-Separates conductors in bipolar and ICD leads
Conductor:
-Carries electrical impulse to the heart and carries intracardiac signals to the device.
-In ICDs - delivers shock therapy
Connector:
-Attaches the pacing lead to the impulse generator and assures safe transmission of current without electrical leakage
Lead electrodes:
-Deliver the impulse and record intracardiac signals. Are part of the shock vector in ICD
Distal tip electrode - Cathode
Proximal ring electrode - Anode
What are the black dots?
Electrodes
-Gives options to pace across different areas
Features of pacing/shocking leads
-Flexible
-Strong - subjected to loading forces
-Reliable - Perform continuously in a hostile environment
-Biocompatible - must not be rejected or cause clots
-Insulated - electrical conductive wires must be insulated
-Thin - to pass down a vein
Features of the conductor
-Thin
-Nickel or silver alloy
-Low resistance to electrical current
-Corrosion resistant
-Flexible and durable
Features of connector
-Attaches pacing lead to the impulse generator/device
-Assures safe transmission of current and intracardiac signals without current leakage
-Different connectors for different systems
Different types of connector
IS-1 International Standard 1
DF-1 Defibrillation lead 1-3 connectors
DF-4 Defibrillation - 1 connector
Features of IS-1 connector
-3.2mm short pin, sealing rings
-Can be bipolar or unipolar - bipolar will have a terminal ring (anode) and a second lead sealing ring
-Can be bipolar or unipolar - the ‘modern’ lead for pacemaker systems
Advantages/disadvantages of polyurethane and silicone as leads
What are the different methods of implantation for a pacemaker
-Transvenous - introduced to the RV or RA via a vein (cephalic, subclavian)
-Epicardial - placed directly on the heart on the epicardium (Thoracotomy surgery)
Polarity in unipolar and bipolar circuits
Unipolar:
-Tip of lead is negative pole
-Can is positive pole
Bipolar:
-2 poles on lead itself
-Proximal pole ring (positive)
-Distal pole tip (negative)
Advantages/disadvantages of unipolar/bipolar circuits
What are the different types of lead electrode fixation?
Passive - placed in the endocardium without penetrating the muscle - tined
Active - fixated into the muscle - helix, corkscrew
Advantages/disadvantages of active/passive fixation
Length of atrial leads vs ventricular leads
-Atrial leads are shorter than ventricular leads
-Atrial leads = 52-53cm
-Ventricular leads = 58-59cm
What is special about coronary sinus/left ventricle leads?
-They can have multiple poles for pacing
-This is to ensure LV capture
Why are leads steroid eluting?
-Stops acute threshold rise
-Slow release, suppresses inflammation
