Week 3 - Cardiac Rhythm Management Devices Flashcards
What are the intrinsic rates of the:
- SA node
- Atrial cells
- AV node
- HIS Bundle/Bundle Branch
- Purkinje Cells
- Myocardial cells
- SA node: 60-100
- Atrial cells: 55-60
- AV node: 45-50
- HIS Bundle/Bundle Branch: 40-45
- Purkinje Cells: 35-40
- Myocardial cells: 30-35
How do pacemakers function?
Sense intrinsic cardiac electric potentials then electrical impulses are mechanically transmitted to the heart stimulating (triggering) myocardial contraction
What are the two types of pacemaker leads?
Unipolar (been phased out over last 15 years) – pulse generator functions as the Anode
Bipolar – both cathode and anode are present in the lead itself
*advantage - less susceptible to EMI
What are implantable cardioverter-defibrillator (ICD) used to treat?
Used to directly treat a cardiac tachydysrhythmia such as V-tach or SVT
-if ICD senses a ventricular rate that exceeds the programmed cut-off rate, a cardioversion/defibrillation is initiated
What is overdrive pacing?
Device paces rapidly for a number of pulses to attempt pace-termination of tachycardia
- delivers a burst of pacing stimuli which gain control of the heart, stopping the V-Tach
- pacemaker then continues controlling the heart at a normal rate
What does each pacemaker letter mean?
I: Pacing – O (none), A (atrium), V (ventricle), D (dual)
II: Sensing – O (none), A (atrium), V (ventricle), D (dual)
III: Response – O (none), I (inhibited), T (triggered), D (dual)
IV: Programmability – O (none), P (programmable), M (multiprogrammable), C (communicating), R (rate modulation)
V: Anti-tachycardia Function – O (none), P (pacing), S (shock), D (dual)
What are the most common pacemaker modes?
AAI
VVI
DDD
Describe the AAI pacemaker mode
Atrial only anti-bradycardia pacing – Atrium is sensed as well as paced
Failure of the atrium to produce an intrinsic beat within an appropriate time window (determined by lower rate limit), results in atrial pacing pulse emission
*no reaction if the atrium fires normally
*relies on normal AV conduction
Describe the VVI pacemaker mode
Ventricular only pacing – no atrial sensing or pacing (no atrioventricular synchrony
Any failure of the ventricle to produce an intrinsic beat within a certain rate limit, results in a ventricular pacing pulse
May be used in those with slow rate A-frb to ensure adequate ventricle response
Describe the VAT pacemaker mode
A sensed atrial beat triggers ventricular pacing
Patients with complete AV block but normal sinus node function need a pacemaker to ensure a ventricular depolarization follows each spontaneous atrial depolarization
Allows physiologic pacing because the paced ventricular rate will “track” the spontaneous atrial rate – allows for overall increased HR in response to increased metabolic demand
Describe the DDD pacemaker mode
Dual chamber pacing and sensing – most common in permanent pacemakers
Every atrial and ventricular event is sensed “Smart Mode”
- If ventricular response is not seen within a programmed limit, a ventricular pace is initiated
- If atrial activity is absent within a certain rate, it will be paced and then followed by a ventricular pace if there is no intrinsic response
What are pacemaker asynchronous modes?
Pacing device emits a pacing pulse regardless of intrinsic cardiac rhythm
No sensing – AOO, VOO, DOO
May be used in heart transplant, emergencies
Can cause R on T – paced activity occurs when the membrane attempts to repolarize before depolarization is complete
*sends heart in to v-fib
What are rate responsive pacemakers?
Pacemakers that contain sensors that automatically adjust the pacing rate to meet the patients cardiac output needs
Used in patients with sinus node dysfunctions
What are the different rate response technologies for the following sensors:
- Activity Sensor
- Minute Ventilation Sensor
- QT interval based sensor
- Contractility sensors
Activity Sensor: measures mechanical stress to piezoelectric crystals as a result of motion or acceleration
Minute Ventilation Sensor: measures transthoracic impedance change between pacemaker lead and pulse generator
QT-Interval-Based Sensor: measures evoked QT interval changes as estimate of adrenergic tone
Contractility Sensor: measures peak endocardial acceleration as estimate of contractility and global LV function
When is biventricular pacing used?
Developed for treatment of heart failure
Pt’s usually have EF of less than 30%
“Synchronization of heart beat”
Where are the pacemaker leads placed in the heart for biventricular pacing?
Standard pacemaker lead is positioned in right atrium (tracking of sinus node) – used to optimize AV delay in order to improve ventricular filling
Standard pacemaker lead is placed in right ventricle (capture/pacing of RV)
Specialized pacemaker lead is threaded through the coronary sinus into a lateral cardiac vein so the tip resides within the vein lying over top the LV (capture/pacing of LV)
What are the preop considerations for a patient with a pacemaker?
Determine the type of device
- ID card
- AICD?
- Interrogation? (mode, dependency, lower rate limit, response to magnet, battery life)
Rhythm strip ECG
What is the recommended minimum Cardiac Rhythm Device data collection for periop assessment of a pacemaker?
- Device type, manufacturer, model
- Is the device or lead under recall or advisory (??)
- Date and hospital of implant and date of most recent follow-up
- Follow-up clinic and physician
- Minimum anticipated battery longevity
- Pacing dependency, pacing mode, and rate-modulation sensor
- Recent activity: atrial and ventricular pacing activity, VT, and VF detection
- Response to magnet (eg, asynchronous pacing, suspended tachycardia detection)
- Expected response to magnet removal (eg, resume original settings, other)
How do you determine if a patient is dependent on their pacemaker?
Verbal History:
- does pt have history of syncope? is this what caused the implantation of the pacer?
- does pt have history of AV ablation?
- does pt recall being told that he has 3rd degree heart block?
Interrogation
What does failure to capture in a pacemaker mean?
The pacemaker generates a pacemaker spike but does not produce a depolarization
What does failure to sense in a pacemaker mean?
The pacemaker does not recognize normal beats and generates an unnecessary pacemaker spike
What does failure to output in a pacemaker mean?
The pacemaker does not generate a pacemaker spike when it is needed
What preop preparation needs to happen for a pacemaker?
If pacemaker function is questioned, it must be interrogated
If the pt has an AICD, this function needs to be disabled
-events have occurred where AICD misinterprets electromagnetic interference as a tachydysrhythmia and a shock is delivered – induces VF
What happens when a magnet is placed over an AICD?
- A magnet correctly applied to an AICD often results in suspension of tachyarrythmia therapy
- For most AICDs there is no way to detect appropriate magnet placement
- Some AICDs may have no magnet response
- Some can be permanently disabled by magnet application
*call EP – make sure you ask what specific response to magnet is
*pacemaker function of AICDs is not affected by magnet
Should rate-responsive pacemakers be disabled for surgery?
Consideration should be given to disabling the rate responsive mode of the pacemaker
- increase in RR and TV and the use of electrocautery have been reported to increase the paced rate
- pt movement and the use of vibrating saws has induced tachycardia
Does the pacemaker mode need to be altered preoperatively?
- Depends on device dependency and how much suspected electromagnetic interference (EMI) will be of concern.
- The closer the cautery probe is to the pulse generator the greater the risk of adverse interactions – Head, neck, shoulder and thoracic procedures
- Some devices have a “sleep-mode” – this may need to be deactivated if surgery is late at night
What are the concerns of electromagnetic interference with pacemakers?
Monopolar “bovie” electro cautery is of most concern
- ventricular oversensing which causes pacemaker inhibition
- sometimes pacemaker response is to pace asynchronously at the programmed lower rate (noise reversion usually at a rate of 58 or so)
- physical damage to device can result in pacemaker failure
When is electromagnetic interference of a pacemaker more likely to occur?
- If surgery is <15 cm (6in) from the device or leads (ex: intrathoracic, shoulder, etc) or above the umbilicus
- If monopolar cautery rather than bipolar cautery is to be used
- If long (5 seconds) or frequent (5 seconds between) bursts of cautery to be used
- If the device has unipolar leads or bipoler leads programmed in unipolar mode or with very high sensitivity
When should you consider asynchronous mode to avoid EMI of a pacemaker?
Patients who are completely pacer dependent – 3rd degree heart block, AV ablation
Head, neck, shoulder, and thoracic surgery
How can you avoid EMI of a pacemaker?
- If cautery is far from pacemaker – usually not a problem
- Place cautery pad far from pacemaker
- Ask if surgeon can use bipolar
- Ask surgeon to use short bursts and let surgeon know if there is pacemaker inhibition
- Place magnet over pacemaker when there is interference??
What do you need to do to the ECG monitoring for a pacemaker?
Must include the ability to detect pacer spikes
Must switch to “diagnostic” or “pacemaker” mode
*sometimes spikes will still not appear because the signals are weak – try changing lead placement or lead monitoring
What are intra-op monitoring considerations for a pacemaker?
- Must include the ability to ensure the paced activity actually produces mechanical systole – pulse ox, art line waveform
- If pt has biventricular pacer, consider continuous CO monitoring – pt may need increased HR during periop period to meet increased oxygen demand
- Minimize effects of EMI
- Must have back up pacing plan (external pads, transvenous pacing, defibrillator, emergency drugs)
- Know EP pager number
What electrolyte and metabolic disturbances may increase the pacing threshold resulting in failure to pace?
Acidosis
Alkalosis
Hyperkalemia
Hypoxemia
Myocardial Ischemia
Severe Hyperglycemia
What are the special operative considerations for a pacemaker during Lithotripsy?
Cardiac generator must be excluded from the lithotripter field
If the lithotripter triggers their output on the R wave, atrial pacing should be disabled to prevent the lithotripter from inappropriately firing on the atrial pacing artifact
What are the considerations for ECT for a pt with a pacemaker?
AICDs should be deactivated
Possible requirement of asynchronous mode to avoid oversensing
ASA suggest that a temporary pacing system be available if mode is not asynchronous
How should external defibrillation pads be placed on a patient with a pacemaker?
Placed so that the route of current is perpendicular to the axis of pacing system
What are the post-op considerations for a patient with a pacemaker?
- Consult EP to reactivate AICD or to reprogram pacemaker if the mode had been altered
- If there were any problems intra-op, EP should interrogate pacer
- Confirmation of device functionality should be preformed at completion of surgery
What is the following pacemaker mode?
AAI
What is the following pacemaker mode?
Atrial Failure to Capture
What is the following pacemaker mode?
DDD
What is the following pacemaker mode?
DDD
What is the following pacemaker mode?
DOO with R on T
What is the following pacemaker rhythm?
Failure to Capture
What is the following pacemaker rhythm?
Failure to Capture
What is the following pacemaker rhythm?
Failure to Output
What is the following pacemaker rhythm?
Failure to Sense
What is the following pacemaker rhythm?
Failure to Sense
What is the following pacemaker mode?
VVI
What is the following pacemaker mode?
VVI
What is the following pacemaker mode?
VVI rate 60 A-Fib
What is the following pacemaker mode?
VVI
