Atrial Fibrillation, Pacemakers and Implantable cardioverters Flashcards
What is AF
AF is the result of continuous and rapid activation of the atria by multiple asynchronous electrical impulses. It may be an idiopathic condition or may be associated with structural cardiac defects or medical conditions.
What is lone atrial fibrillation.
When AF occurs in the absence of a structural cardiac lesion or when it is not precipitated by a medical condition.
List the common precipitants of paroxysmal AF
ETOH Caffeine Nicotine Emotional stress Thyrotoxicosis
Describe the electrical activity that occurs during AF
Atria fibrillate due to multiple co-existent re-entry circuits.
Re-entry circuits may originate from:
- Disparities in repolarisation rates
- Differing conduction rates between normal and ischaemic myocardium
- Differences in the refractory period between endocardial and epicardial lesions
What are the two principles of chemical cardioversion? give the class of the antiarrythmic and an example of each
Block the re-entrant circuits in the atria by:
Suppressing depolarization (Na channel - phase 0 of AP) - e.g. flecainide (Class I)
Prolonging repolarization (K channel - phase 3 of AP) - ibutilide (Class III)
Classify and give examples of the anti-arrhythmic agents
Class (Receptor)
Drug
IA (Na channels and K channels)
Quinidine
Procainamide
Disopyramide
IB (Na channels)
Lidocaine
Phenytoin
IC (Na Channels)
Flecainide
II (Beta adrenoreceptors) Propranalol Atenolol Sotalol Esmolol Amiodarone
III (K channels) Bretrlium Ibutilide Sotalol Dofetilide
IV (Calcium channels)
Verapamil
Diltiazem
Amiodarone
Describe the pharmacological strategies for rate control in AF
Beta antagonist or Calcium Channel Blocker. Sole agent or, if needed, it may be combined as below
Digoxin + Beta antagonist. Useful if good LV function
Digoxin + Calcium Channel Blocker. Useful for rate control with poor LV function
Amiodarone. Indicated if the above therapies fail to control rate
What scoring system is used to determine need for anticoagulation and risk for bleeding in AF
CHA2DS2-Vasc (≥ 3 points –> indication for anticoagulation)
- CHF
- HPT
- Age < 65 ; 65 - 75 ; > 75
- DM
- Sex: Female
- Stroke (2)
- Vascular disease history (MI/PVD)
HAS-BLED (> 2 points suggests high risk of bleeding)
- HPT
- Abnormal LFT
- Abnormal Renal fxn
- Stroke
- Bleeding Hx or predisposition
- Labile INR
- Elderly > 65
- Drugs (Aspirin/Clopidogrel/NSAID)
- Alcohol
What is the R on T phenomenon
It is the reason why electrical cardioversion is synchronized with the patient’s R wave. There is a brief period just before the peak of the T-wave during which the ventricles have repolarized but the rest of the hear has not repolarized. A shock at this point depolarizes only the repolarized portion of the ventricle which results in homogenous myocardial tissue that is prone to develop VF (i.e. there is no polarization).
What is the time period after the onset of AF for safe cardioversion without anticoagulation
24 hours
When can elective cardioversion take place if AF started > 24 hours ago
4 weeks of anticoagulation required first –> if this is not possible atrial thrombus should be excluded by transoesophageal echo under sedation.
Describe a practical anaesthetic approach to synchronized cardioversion
Propofol ± LMA (opioids not required unless ETT necessary)
What are the priorities in the pre-operative assessment for a patient with AF
Establish duration of AF, aetiology, Rx and Rx duration Whilst arranging for any required investigations depending on symptoms/history
K normal
Exclude digoxin toxicity (nausea, headache, visual disturbance and ventricular ectopics.) if dose > 375 mcg digoxin/day
ECG - rate controlled 60 -90 bpm
ECHO - Assess MV, LV and Left atrial size
What medication should be used in the setting of critical illness and paroxysmal AF where digoxin and BB cannot be used
Amiodarone
- 300 mg IV over 1 hour
- 900 mg IV over 23 hours
Amiodarone does not restore sinus rhythm but maintains it once it is restored
How should warfarin administration change leading up to surgery
Low risk patients (non-valvular AF)
- STOP warfarin 4 days before (unless very minor surgery)
- Bridging anticoagulation with LMWH may be required for high risk patients
How should aspirin administration be altered leading up to surgery
Minor surgery - continue aspirin
Major surgery or when risk of minor bleeding significant (intracranial surgery) –> STOP aspirin 7 days before surgery
How should patients on warfarin be treated when emergency surgery is required
Vit K, FFP, PCC
Discuss options for pharmacological management of intra-operative AF
AV NODAL BLOCKERS
Esmolol
- Onset 6 - 10 mins
- Offset 20 mins after stopping infusion
- B1 selective (tolerated by patients with pulm disease)
- Disadvantage: -ive inotropy
Diltiazem/verapamil
- Less titratable than esmolol
- Advantage: less negative inotropy (preferable in heart failure)
VAGOTONIC AGENTS
Digoxin
- Inhibition of Na-K ATPase –> reduced IC [K+] slows AV conduction and slows pacemaker cells
- Also has indirect effects through increased vagal activity
- Peak effect: 2 hours (must be temporarily supplemented with other agents if rapid control of ventricular rate is required)
What are the two most common implantable cardiac devices and when are these used
Permanent pacemakers (PPMs) and implantable cardioverter defibrillators (ICDs) are used in patients with fixed or intermittent bradycardias associated with inadequate cardiac output
What are the most common indications for pacemakers?
Sick Sinus Syndrome
3rd degree heart block
2nd degree heart block (symptomatic)
Chronic AF or flutter with symptomatic bradycardia
What are the indications for Implanted cardioverter defibrillators
Patient’s at high risk of VF or VT due to underlying cardiac disease
E.g.
- Previous cardiac arrests
- Electro-physiological studies indicating a high risk of future event
What information is recorded at implantable device follow up visits?
‘Sensing threshold”
‘Pacing threshold’
Remaining battery life
Why is the PAcing box containing the microprocessor positioned subcutaneously
So that the box can be interrogated and reprogrammed remotely using an external control device when necessary
How long to batteries last
5 - 8 years
How can microprocessor be programmed
To respond to electrophysiological stimuli
- To pave when there is failure of AV conduction
- To inhibit pacing during sinus rhythm
To respond to physiological demand
- Piezo electric crystal senses increased exertion
- SvO2 sensor
What system is used to standardise the description of permanent pacing and defibrillation systems
Five letter international classification system
What does pacemaker described by VVI00 mean. Explain each position in the system.
V - paces the ventricle V - Senses in the ventricle I - Inhibited by sensed activity 0 - not programmable 0 - Doesn't have anti-tachycardia functions
Positions:
- Chamber paced (A, V, D, 0)
- Chamber sensed (A, V, D, 0)
- Response to sensing (0, Triggered T, I inhibited, D Dual)
- Programmability (0, P = simple, M = multi-programmable, C = communicating, R = rate responsiveness)
- Anti-tachycardia functions (0, D - Dal, P = Pace, S = Shock)
What are the two most common pacemakers in use according to the five letter international classification system
VVI and DDD
VVI
V - Ventricular paced
V - Ventricular sensed
I - Inhibitory response to sensing
- —> Used in patients in whom there is a disorder of AV conduction and when AV synchronization is not vital, as the atrial kick will be lost
- —-> Do not maintain sequential relationship between atria and ventricles
- —> being superseded by DDD devices
DDD
- Dual sensed
- Dual paced
- Dual response: Triggered and inhibited
Maintain sequential relationship between atria and ventricles
What is this device: 000MS
No pacer No sensor No response Multi-programmable Anti-tachycardia = Shock
This is a cardioverter defibrillator
What is this device: VAT
Paced ventricules
Sensed in atria
Response triggered
This device triggers pacing of the ventricles in response to the atrial rate
What information would you want from a patient with a pacemaker?
Reason for implantation Date of implantation Previous and current symptoms Palpitations Syncope/near syncope The continued presence of symptoms may suggest that the pacemaker is not functioning correctly Follow-up and latest check
What is a common cause of pacemaker dysfunction
Lead fracture
- weight lifting/trauma
What are common sites for lead fracture
Exiting box
Entering subclavian vein from SVC
Crossing of first rib
Which patients should be discussed with cardiology prior to surgery
- Symptoms/Ix suggestive of malfunction
- Pts lost to PM follow up
- Pts with rate responsive Pms and cardioverter defibrillators - may require disabling prior to surgery: CARDIOVERTER DEFIBRILLATORS MAY OTHERWISE INTERPRET DIATHERMY AS A RHYTHM THAT REQUIRES A DC SHOCK. CAN USUALLY BE REACTIVATED IN RECOVERY
Which implantable cardiac devices require cardiology consult prior to surgery
Rate responsive pacemakers
Cardioverter defibrillators
Diathermy may be interpreted as a rhythm requiring a DC shock
Which devices interfere with implantable cardiac devices
Monopolar diathermy (interpreted as intrinsic cardiac electrical activity by the device –> inhibition of pacing or switching to backup mode)
MRI - high risk of interference with pacing and heating of leads.
Describe use of Transcutaneous Electrical Nerve Stimulators/Lithotripsy/external defibrillators/nerve stimulators in patients with implantable cardiac devices
These devices may be used safely, but should be kept as far from the pacing box as possible and used for minimum possible duration.
How might a PPM cause an intra-operative tachycardia
Rate responsive devices might cause tachycardia as a result of the following
- Fasciculations with SUX
- Shivering
- Increased Ventilator rate
- Alteration: Temp/SvO2/pH
What is pacing threshold
The pacing threshold is the lowest pacemaker output voltage at which electrical capture occurs in the myocardium and paced beats are seen on the ECG at the selected pacing rate. When calibrating, an initial device output voltage around 4 V may be used and then adjusted to threshold. Once determined, an output voltage equal to three times the threshold should be set to allow a large margin of safety. If the pacing threshold is set too low, the myocardium fails to capture the pacing stimulus.
How can the following conditions interfere with pacemaker function: Hypoxia Hypercapnoea Acidosis Electrolyte abnormalities Cardio-active drugs
By altering the pacing threshold (usually set 3 times higher than the voltage required during calibration to account for changes in intra/extracellular ion concentrations and pacing threshold)
If the electro-physiological milieu is changed significantly this might effect the devices function
List the types of interference that can occur with a pacemaker during anaesthesia
- Diathermy
- Rate responsiveness (shivering/fasciculation/Ve/T/SvO2)
- Alteration of pacing threshold (electrophysiological milieu)
- Lead displacement
When might a magnet be used in the perioperative management of patients with pacemakers and why
In an emergency where other measures have failed and there is total loss of pacemaker activity
Magnets usually activate V00 mode by movement of a ferromagnetic switch within the device.
- Possibility of R on T phenomenon
- May trigger unpredictable programming
Describe extra checks required for patients with pacemakers
Watch ECG, Pads on if defib deactivated.
Classify the critical incidents related to implanted cardiac devices
- Inappropriate pacing
- Reverse unwanted rate responsiveness ( T/Minimize movement/ph/SvO2)
Unwanted pacing poses risk of R on T phenomenon and surgery should be terminated and expert advice sought if resolution not possible
- Failure to pace
- Box failure
- Lead displacement
Catastrophic in patients with inadequate underlying cardiac activity = bradycardia or asystole
FiO2 100% Inform surgeon CPR Percussion pacing (rhythmic praecordial thumps and check ECG) Isoprenaline infusion Transthoracic pacing (capture ±80 mA)
Why is a valsalva maneuvre useful in a patient with a VVI pacemaker undergoing preoperative assessment
If the pacemaker is working in demand mode, a bradycardia below its set rate will trigger pacing to commence.
Which of the following are recommended and which are not recommended for a patient with a pacemaker undergoing surgery?
Use of bipolar diathermy Obtain post-op check Disabling rate responsiveness Non-depolarising muscle relaxant Use of suxamethonium Use of monopolar diathermy CVP monitoring for all patients Reprogramming using a magnet
Recommended
Use of bipolar diathermy
Obtain post-op check
Disabling rate responsiveness
Non-depolarising muscle relaxant
Not recommended
Use of suxamethonium
Use of monopolar diathermy
CVP monitoring for all patients
Reprogramming using a magnet
