Electrophysiology and Syncope Flashcards
What is the difference between
intrinsic and extrinsic causes
of sinus node dysfunction?
Intrinsic: (problem within the heart )ideopathic, ischemic, infiltrative, inflammatory, CT disease, post op, genetic
Extrinsic: (problem outside of the heart, part of another system): medications, drugs, electrolyte imbalance, hypothyroid, neural reflexes, neural syncope, intracranial HTN, hypothermia
What is the resting membrane potential in cardomyocytes compared to pacemaker cells?
Cardiomyocytes: -90 mV
Pacemakers: -60 mV
What feature allows pacemaker cells to continually fire at a consistent rate?
If channel slowly leaks Na+ so it gradually increases from -60 resting membrane potential to -40 threshold at which point slow Ca++ channels open and begin to depolarize.
It is the If channels that are the “clock” that never stops ticking and keeps the pacemaker in a consistent loop.
What are the inherent rates of the SA node, AV node, and His-Purkinje system? Why are they different from one another?
SA node: 60-100
AV node: 40-60
His-Purkinje system: 30-40
They are different so that the AV node can serve as a back-up or fail-safe for the SA node
and the His-Purkinje as a backup for the AV node
What are the key mechanisms of arrhythmia?
Problems with Automaticity:
- Abnormal impulse formation: more or less frequently than normal
- Abnormal impulse conduction: slowed or blocked such as in heart block
Problems with Triggered Activity
- Early AfterDepolarization (EAD): think Long QT or Torsades
- Delayed AfterDepolarization (DAD): think Digitalis or hypercalcemia
What are some causes of Bradycardia?
Failure of SA node
Conduction block (permanent or transient)
Uni or bidirectional
Drugs/medications
Ischemia
Fibrosis (eg: calcification in elderly)
Electrolyte imbalance (Na+, K+, Ca++)
Trauma
What mechanism causes Re-Entry Tachycardia?
- Two pathways, either due to an accessory pathway or damage to atrial cardiomyocytes
- Each pathway has different electrical properties pertaining to rate of depolarization and repolarization
- One side is momentarily blocked
This creates a continuous loop and is the MOST important mechanism of tachy arrhythmias!
In a nutshell how do you treat Bradycardia?
Reverse the cause, such as fixing electrolyte imbalances
If this does not work, then pacemaker.
In a nutshell, how do you treat tachycardia?
Reverse the cause
Try vagal maneuvers to control SVT
Cardioversion/defibrillation
Medications
Catheter ablation
Implanted defibrillator
Surgery
What are two kinds of Superventricular Tachycardia SVT and how do they affect treatment?
Automatic: treat the cause
Re-Entrant: need to fix with meds, catheter, cardioversion
What forms of tachycardia do not require heart medications or treatment?
Automatic problems:
- Sinus tachy: it is normal to be tachycardic in response to pain, infection, blood less, etc. If you fix the problems (with pain meds, antibiotics, etc), the tachy stops
- Atrial tachy and Multifocal Atrial Tachy (MAT): usually in response to hypoxia from lung disease. Treat the lungs and the tachy will stop.
- Junctional Tachy: usually due to ischemia, acid-base, electrolytes. Correct the problem and the tachy will stop.
What is the difference between stable and unstable tachycardia and how does that affect Tx?
Stable: no Sx, so you can take your time
Unstable: Serious Sx such as chest pain, altered mental status, hypotension, so do electrical cardioversion (defibrillation)
What is syncope?
A symtom, not a disease
Sudden temporary loss of consciousness, loss of postural tone, with variable onset (some with warning) and spontaneous, complete recovery.
Caused by abrupt reduction in cerebral blood flow.
1-6% of all hospital admissions
What affect does syncope have on a patient?
Anxiety
Decrease in activities of daily living
Driving restrictions
Loss or change of employment/profession
What are common causes of Syncope?
34%: unknown cause
24%: Neurally-Mediated (vasovagal, carotid sinus, situational)
11%: Orthostatic (drug induced, autonomic nervous system fail)
14%: Cardiac Arrhythmia (brady, tachy, long QT)
12%: Non-cardiovascular: psychogenic, metabolic, neurological
4%: Structural Cardiac: (aortic stenosis, hypertrophic cardiomyopathy, pulm HTN, PE, tamonade)
What are the more likely causes for younger patients as compared to older patients?
Younger: vasovagal, situational, psychiatric, genetic heart conditions such as Long QT, Brugada, WPW, hypertrophic cardiomyopathy
Older: mechanical or arrhythmic cardiac conditions, orthostatic hypotension, medications, neural, multifactorial
What is the most serious/deadly cause of syncope?
Cardiac
What are the key components of a workup for a patient with syncope?
Hx
PE
EKG
Echo
will be sufficient for 90% of patients
What is the relevant Hx for a patient with syncope?
Details of syncopal episode from pt and observers
Precipitating factors
Prodrome/warning signs
Duration and frequency of episodes
Recovery Sx
Cardiac Hx
FH of cardiac, syncope and sudden death
Medications (cause or clue to Dx)
What do you look for in terms of PE for a patient with syncope?
orthostatics
cardiac exam (re CHF, valves)
neuro exam
carotid sinus massage
How do you do carotid sinus massage test?
- Massage R carotid artery below the thyroid cartilage for 5-10 seconds
- Pause
- Massage the Left side
Postive test = 3 seconds of asystole or 50 mm Hg drop in BP
What might you look for on an EKG for a patient with syncope?
Brady or tachycardia
PR interval
Delta waves (WPW)
Long QT
Patterns re Brugada, Q waves, ST-T waves, Hypertrophic cardiomyopathy, ARVC, IVCD, Complete heart block
Why would you need an ambulatory EKG and what are some examples?
Unless you can get the patient to faint on command, you will need an ambulatory EKG to see what their heart is doing before/during syncope.
- Holter Monitor: 24-48 hours, good for frequent syncope
- Event Recorder: credit-card shaped item you press to your chest when you are feeling faint to capture the EKG.
- Implantable Loop Recorder (ILR): implantable under the skin, can last 3 years. Great for very infrequent syncope
- Zeopatch: like a bandaid on the chest to monitor for 14 days
What is a Head Up Tilt Test and how does it work?
When you go from laying down to standing, your sympathetic nerves fire initially, then your parasympathetic adjusts down. Some people’s parasympathetic system adjusts too much.
The Tilt Test moves the patient back and forth from nearly vertical to nearly horizontal, reproducing the pre-syncopal Sx so the patient can learn how to recognize them and control the syncope using vagal maneuvers.
How do you know when to admit a patient with syncope?
Unless they have at least one of the following, you do not need to admit them:
- Hx of CHF
- Hct < 30%
- EKG abnormal
- SOB
- Systolic BP <90
List three types of permanent pacemakers
Pacemakers are names based on (1) what chamber(s) are paced, (2) which are sensed, and (3) what action it takes. (R) means the rate changes based on activity.
DDD (R): Dual chambers paced, sensed, and acted upon
VVI (R) ventricle paced and sensed, and pacing Inhibited if it senses a rhythm
AAI (R): atrium paced and sensed, and pacing Inhibited if it senses a rhythm
What are the indications for pacing?
Symtomatic Bradycardia
- HR < 60
- Symptoms: syncope, presyncope, SOB, chest pain, confusion, palpitations, CHF, exercise intolerance
- Cause is not reversible
How do you decide whether the patient needs a single pacer or a dual pacer?
- Can the atrium be paced or sensed?
- Is there an AV block?
- Is there chronotropic incompetence? (natural pacemakers do not raise heart rate when needed such as exercise)
Examples:
If everything is working fine except the patient cannot increase heart rate when needed, then atrial pacer needed.
If the atrial rate is meeting needs, but there is AV block then a dual pacer is needed (to sense SA and pace ventricles)
What is vasovagal syncope and what causes it?
Emotions and/or stress cause a drop in preload which causes decreased flow to the brain.
If the patient does not lie down quickly, they will faint, and will experience 24 hours of fatigue afterwards.
How do you treat vasovagal syncope?
Acute: recognize the predromal signs, lie down, elevate feet and do isometric exercises such as clenching fists.
Chronic: stay hydrated, avoid triggers, get regular exercise (preload), wear support hose (preload), eat salty foods (if young without HTN).
Rx: Midodrine, a short-acting alpha agonist
No pacemaker needed.
How do you treat a patient
with orthostatic hypotensive syncope?
Tell them to never lie down!
Typically they have high BP when lying down, but low BP when sitting or standing. If you give them HTN meds, their BP will be too low most the time. So stop the BP meds and get the to use a hospital-type bed at 45 degrees or elevate the head of the bed.
