Electrophysiology and Syncope

Question 1

What is the difference between

intrinsic and extrinsic causes

of sinus node dysfunction?

Answer 1

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

Question 2

What is the resting membrane potential in cardomyocytes compared to pacemaker cells?

Answer 2

Cardiomyocytes: -90 mV

Pacemakers: -60 mV

Question 3

What feature allows pacemaker cells to continually fire at a consistent rate?

Answer 3

I_f 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 I_f channels that are the “clock” that never stops ticking and keeps the pacemaker in a consistent loop.

Question 4

What are the inherent rates of the SA node, AV node, and His-Purkinje system? Why are they different from one another?

Answer 4

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

Question 5

What are the key mechanisms of arrhythmia?

Answer 5

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

Question 6

What are some causes of Bradycardia?

Answer 6

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

Question 7

What mechanism causes Re-Entry Tachycardia?

Answer 7

1. Two pathways, either due to an accessory pathway or damage to atrial cardiomyocytes
2. Each pathway has different electrical properties pertaining to rate of depolarization and repolarization
3. One side is momentarily blocked

This creates a continuous loop and is the MOST important mechanism of tachy arrhythmias!

Question 8

In a nutshell how do you treat Bradycardia?

Answer 8

Reverse the cause, such as fixing electrolyte imbalances

If this does not work, then pacemaker.

Question 9

In a nutshell, how do you treat tachycardia?

Answer 9

Reverse the cause

Try vagal maneuvers to control SVT

Cardioversion/defibrillation

Medications

Catheter ablation

Implanted defibrillator

Surgery

Question 10

What are two kinds of Superventricular Tachycardia SVT and how do they affect treatment?

Answer 10

Automatic: treat the cause

Re-Entrant: need to fix with meds, catheter, cardioversion

Question 11

What forms of tachycardia do not require heart medications or treatment?

Answer 11

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.

Question 12

What is the difference between stable and unstable tachycardia and how does that affect Tx?

Answer 12

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)

Question 13

What is syncope?

Answer 13

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

Question 14

What affect does syncope have on a patient?

Answer 14

Anxiety

Decrease in activities of daily living

Driving restrictions

Loss or change of employment/profession

Question 15

What are common causes of Syncope?

Answer 15

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)

Question 16

What are the more likely causes for younger patients as compared to older patients?

Answer 16

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

Question 17

What is the most serious/deadly cause of syncope?

Answer 17

Cardiac

Question 18

What are the key components of a workup for a patient with syncope?

Answer 18

Hx

PE

EKG

Echo

will be sufficient for 90% of patients

Question 19

What is the relevant Hx for a patient with syncope?

Answer 19

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)

Question 20

What do you look for in terms of PE for a patient with syncope?

Answer 20

orthostatics

cardiac exam (re CHF, valves)

neuro exam

carotid sinus massage

Question 21

How do you do carotid sinus massage test?

Answer 21

• 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

Question 22

What might you look for on an EKG for a patient with syncope?

Answer 22

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

Question 23

Why would you need an ambulatory EKG and what are some examples?

Answer 23

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

Question 24

What is a Head Up Tilt Test and how does it work?

Answer 24

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.

Question 25

How do you know when to admit a patient with syncope?

Answer 25

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

Question 26

List three types of permanent pacemakers

Answer 26

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

Question 27

What are the indications for pacing?

Answer 27

Symtomatic Bradycardia

1. HR < 60
2. Symptoms: syncope, presyncope, SOB, chest pain, confusion, palpitations, CHF, exercise intolerance
3. Cause is not reversible

Question 28

How do you decide whether the patient needs a single pacer or a dual pacer?

Answer 28

1. Can the atrium be paced or sensed?
2. Is there an AV block?
3. 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)

Question 29

What is vasovagal syncope and what causes it?

Answer 29

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.

Question 30

How do you treat vasovagal syncope?

Answer 30

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.

Question 31

How do you treat a patient

with orthostatic hypotensive syncope?

Answer 31

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.