CRM12: ICD Flashcards
What arrhythmias do defibrillators treat?
-VT
-VF
What conditions cause high risk of SCD?
-Brugada
-ARVC
-Long QT
-HCM
-Valve disease
-Non-ischaemic CM
-HCM
Indications for ICD
-Survived a cardiac arrest caused by either VT or VF
-Sustained VT causing syncope or significant haemodynamic compromise
-Sustained VT with LVEF of 35% or less
-Familial cardiac condition with high risk of sudden cardiac death (long QT, HCM, Brugada, ARVC)
-Undergone surgical repair of congenital heart disease
Primary prevention vs Secondary Prevention
Primary
-At risk of SCD but no documented arrhytmia
-Preventative
Secondary
-Survived threatening arrhythmia
-Probability of another event is high
What class indication is given to ICDs in primary prevention?
-Class I indication
-LVEF<35% due to prior MI
-Who are at least 40 days post MI
-NYHA Class II/III
Contraindications for ICDs (Class 3 indications)
-Syncope of undetermined cause
-Incessant VT or VF
-Terminal illness with projected life expectancy of <12 months
-Drug refractory HF, NYHA class IV who are not candidates for transplantation
Class I, II and III for ICD
Features of ICD battery
-Made from Lithium Silver Vanadium Oxide
-Large charge needs to be stored in a small volume
-Long shelf life is essential
-Battery current produced by process of oxidation and reduction
-Distinctive discharge curve (2 regions of nearly constant voltage before ERI)
Features of ICD capacitor
-Capacitor acts as reservoir. It can store electricity
-Ability of capacitor to store an electrical charge is called capacitance
-Capacitor consists of 2 conducting surfaces, separated by insulating material
-Capacitor charged by removing charge from one plate to another
-Automatic capacitor maintenance
-Increased charging time due to lower battery voltage
Features of ICD electrodes
-Multilumen lead construction
-Active lead fixation
-Coiled conductors have low electrical resistance to deliver charge effectively
-Single or dual coil leads
Different types of ICD electrodes
DF-1:
2 x high voltage
1 x pacing
-Can remove HV component
DF-4:
-4 pole defibrillator and pacemaker connector system
How do you identify pacemaker or defibrillator?
-Lead with coil (thicker) is defibrillator lead
When would you use dual coil leads instead of single?
-Very dilated heart which requires more energy (heart failure)
-If ICD is on right side, you can capture more of the myocardium with 2 coils
Types of sensing vectors in ICD and downsides
Dedicated/True bipolar - traditional sensing
-Sensing/pacing between tip and ring
-Can get T wave oversensing
Integrated bipolar - larger sensing vector, can often get larger R waves
-Sensing/pacing between tip and coil
-Depending on position of lead can lead to Atrial oversensing
Mechanisms that cause VT and VF
-Abnormal automaticity
-Re-entry
-Triggered activity - early afterdepolarisations and delayed afterdepolarisations
How do shocking vectors work?
-Shocking occurs between a combination of the device and coil
-If the device is part of the shocking system it is called active can
-Device can be removed from system in dual coil lead system
How are shocking vectors reversed in the event of an ineffective shock?
What is the waveform of shock therapy?
-Biphasic waveforms shown to improve defibrillation
1st phase: designed to depolarise/extend refractory period of all ventricular cells
2nd phase: designed to remove residual charge from cells that were not captured
What is ATP (AntiTachycardia Pacing)?
-Pain free way of terminating VT
-A precisely timed extrastimulus delivered during the excitable gap can terminate the tachycardia
-Most effective in VT caused by re-entry mechanism (e.g. monomorphic slower VT)
What are the 2 main types of ATP?
-Burst
-Ramp
Burst vs Ramp ATP
Burst
-Programmable number of stimuli are delivered at fixed cycle length
-Faster than the rate of VT
Ramp
-Programmble number of stimuli are delivered at increasingly shorter intervals within the ramp
Complication of ATP
-ATP can be pro-arrhythmic
-ATP can cause acceleration of VT
-Ramp has been shown to cause acceleration more than Burst
What 3 measurements are done at implant?
-Impedance
-Sensing
-Capture
Equipment in ICD implant
-Device
-ICD lead - single coil vs dual coil
-Pacing lead for atrium of dual chamber device
-Peelaway sheaths - size appropriate
-Testing cables
-Programmer
-External defibrillator
-ECG
