2 Electrical conductance disorders

Where are the pacemaker cells located within the heart?

SA node: wall of the right atrium

AV node: right atrial wall near autonomic parasympathetic ganglia

Bundle of his: interventricular septum

Purkunje fibers: extend to apex (bottom) of heart and out to outer ventricular walls

What is the normal path of an electrical signal through the heart?

SA node, atria, AV node, Bundles of His, Purkinje fibers

What effect do sympathetic and parasympathetic activation have on the rate of depolarization and action potentials?

Sympathetic (fight or flight) --> increased conduction velocity in AV node via increasing rate of depolarization of AP --> reduces normal delay of conduction through AV nodes --> reduces time between atrial and ventricular contraction (INCREASES)

Parasympathetic (rest and digest) --> decreased conduction velocity in AV node via decreasing slope of phase 0 of the nodal AP --> slows depolarization of adjacent cells --> reduced velocity of conduction (DECREASES)

What potential effect could an interrupted or abnormal signal at any point in the electrical pathway have on contraction of the atria and/or ventricles?

Arrhythmia

Which part of the cardiac action potential in non-pacemaker cells is denoted by which phase?

0: Rapid depolarization
1: Initial repolarization
2: Plateau phase
3: Repolarization
4: resting membrane potential near equilibrium potential for K+

Which ions and channels are responsible for each of the five (5) phases of the cardiac action potential in non-pacemaker cells?

0: Rapid depolarization --> increase conductance of voltage-gated Na+, Na+ moves into cell --> Long-last Ca2+ channels open when membrane depolarizes, Ca2+ moves into cell

1: Initial repolarization --> Caused by opening of K+ channels and rapid inactivation of fast Na+ channels

2: Plateau phase --> repolarization delayed due to open Ca2+ channels

3: Repolarization --> Ca2+ channels close --> K+ flows out of cell

4: resting membrane potential near equilibrium potential for K+

- Na+/K+ ATPase pump 3 Na+ out of cell 2 K+ in cell

- Na+/Ca2+ exchange 3 Na+ into cell and 1 Ca2+ out of cell

- Ca2+ ATPase pump moves Ca2+ out of cell

- Membrane permeable to K+ which allows K+ to leak out of cell and restore equilibrium

What are the differences in shape of the action potentials in pacemaker vs non-pacemaker cells?

Pacemaker cells do not have a phase 1 or 2 and have no true resting potential
- Slower depolarization
- Ca2+ is main cause of depolarization

What are the differences in duration and shape of the atrial and ventricular action potentials compared to action potentials seen in skeletal muscle cells and neurons?

Nerve cell: ~1ms
Skeletal muscle cell: ~2-5 ms
Cardiac muscle cell: 200-400ms

What stage of electrical propagation do each of the waves of a normal ECG signify?

P-wave: atrial depolarization
QRS complex: ventricular depolarization
T wave: ventricular repolarization
PR interval: atrial depolarization plus AV nodal delay
ST segment: isoelectric period of depolarized ventricles
QT interval: duration of depolarization plus repolarization corresponds to AP durations throughout ventricles

How do each of the waves of a normal ECG correspond to cardiac function?

Waves show cardiac conduction

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Sinus rhythm

Normal sinus rhythm- Very regular- Minimal cyclical fluctuation- Atrial contraction always followed by ventricular contraction

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Sinus bradycardia

Heart beats too slow, longer wider waves

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Atrial flutter

Depolarization currents arise from SA but atrial rate too high for all impulses to be conducted through the AV node

FAST

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Atrial fibrillation

Depolarization currents arise from non-SA node sites throughout the atria

No discernable P wave and irregular ventricular rate

FAST, RANDOM

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Atrioventricular block (in general, not necessary to identify the three types)

Conduction delay in area of AV conduction system

Prolonged PR Interval, each type is progressively longer

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Ectopic foci (premature ventricular complex)

No P wave
Large and inverted T wave
Premature and bizarrely shaped QRS complex

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Ventricular tachycardia

Characterized by widened QRS

Describe and/or identify the typical ECG tracings for each of the following rhythms and arrhythmias (these are the ONLY ECG strips I expect you to know): Ventricular fibrillation

Uncoordinated ventricular depolarizations

What are the most common arrhythmias in the US?

Atrial flutter
Atrial Fibrilation

What are the general symptoms of arrhythmias?

Less serious
- palpitations
- slow heart beat
- irregular heart beat
- feeling pauses between heart beats

More serious
- anxiety
- dyspnea
- syncope
- dizziness
- fatigue
- sweating
- chest pain

What techniques are typically used to diagnose arrhythmias?

- Electrocardiogram to evaluate the electrical activity of the heart
- Holter monitoring (24h portable ECG)
- Echocardiogram
- Exercise stress test
- Tilt table test

What are some common risk factors for development of arrhythmia?

- Age
- Gender M>F
- Stress
- Renal failure
- HTN
- Previous MI
- Congenital heart disease
- Thyroid disorders
- OTC cough and cold medications
- Anti-arrythmia medications
- Anabolic steroids
- Diabetes
- Obstructive sleep apnea
- Electrolyte imbalance
- Alcohol
- Caffeine
- Nicotine
- Chronic lung disease
- Pulmonary embolism
- Emphysema
- Asthma

What are some common causes of arrhythmia?

1. Coronary artery disease (CAD): Myocardial ischemia or infarction starves cardiomyocytes of oxygen, causing them to become depolarized causing altered impulse formation or conduction

2. Altered impulse formation

- Changes in rhythm

- Caused by changes in the automaticity (spontaneous activity) of pacemaker cells or

abnormal generation of action potentials at sites other than the SA node (termed ectopic

foci).

3. Altered impulse conduction

- Complete or partial block of electrical conduction

- Can lead to tachyarrhythmias

4. Changes in cardiac structure that accompany heart failure

- E.g., dilated or hypertrophied cardiac chambers

5. Electrolyte disturbances

- Primarily K+ and Ca2+

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Sinus bradycardia

Symptoms:

- Decreased cardiac output --> decreased arterial pressure

- Syncope and other symptoms related to hypotension

Treatment: Pacemaker

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Atrial flutter

Symptoms:

- Palpitations

- Fluttering

- Dyspnea

- Anxiety

Treatment:

- Ventricular rate control

- Electrical or pharmacological cardioversion

- Catheter based radio frequency (RFA)

- Anti-coagulant medication

- Anti-arrhythmic meds

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Atrial fibrillation

Symptoms: during activity, shortness of breath and impaired perfusion of active muscles

Treatment: Cardioversion, anti-coagulant medication

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Atrioventricular block (in general, not necessary to identify the three types)

Symptoms: Asymptomatic

- Except 3rd degree: fatigue, dizziness, light-headed, presyncope, syncope

Treatment: pacemaker

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Ectopic foci (premature ventricular complex)

Symptoms:

- Asymptomatic

- Palpitations and neck and/or chest discomfort

- Feeling of heart “stopping”

- Syncope

- Hypotension

Treatment:

- Oxygen if hypoxic

- Antiarrhythmic meds

- Beta-blockers

- Electrolytes

- Ca2+ channel blockers

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Ventricular tachycardia

Symptoms:

- Palpitation

- Light-headedness and syncope

- Chest pain

- Anxiety

- Sensation of neck fullness

- dyspnea

Treatment:

- cardioversion

- implantable carioverter defibrillator

- catheter base radiofrequency ablation (RFA)

Describe the basic symptoms, effect on cardiac output (if any) and treatment approaches (if any) for each of the following arrhythmias (these are the ONLY arrhythmias I expect you to know): Ventricular fibrillation

Symptoms:

- complaints of chest pain, fatigue, palpitations, and other nonspecific complaints up to 4 weeks prior to VF

Treatment:

- Immediate defibrillation

- Catheter-based radiofrequency ablation (RFA)

- Implantable cardioverter defibrillator (ICD)

What are afterdepolarizations and what causes them?

Early afterdepolarizations
- Occur during late phase 2 or phase 3
- Likely to occur when AP durations are prolonged
- EAD characterized by long QT interval
- Can be cause by anti-arrhythmia drugs
- Blocked by magnesium

Delayed afterdepolarization
- Occurs at end of phase 3 or early in phase 4
- Results in tachyarrhythmias
- Caused by abnormal Ca2+ release from the sarcoplasmic reticulum
- Can also be caused by digoxin
- Blocked by verapamil or quinidine

Cardiac action potentials have a much longer action potential than both nerve and skeletal muscle action potentials. True or False

True

The normal path of an electrical signal through the heart would be best described as:

a. SA node, atria, AV node, Bundles of His, Purkinje fibers
b. SA node, ventricles, AV node, Bundles of His, Purkinje fibers
c. AV node, ventricles, SA node, Bundles of His, Purkinje fibers
d. AV node, atria, SA node, Bundles of His, Purkinje fibers

a. SA node, atria, AV node, Bundles of His, Purkinje fibers

Phase 0 of the cardiomyocyte action potential represents

a. Rapid depolarization
b. There is no Phase 0
c. The plateau phase
d. Rapid repolarization

a. Rapid depolarization

The most effective initial treatment for ventricular fibrillation is:

a. Valsalva maneuver
b. Immediate defibrillation
c. Nothing as this is not a pathological condition
d. Anti-coagulation medication

b. Immediate defibrillation

The blood vessels with the thickest layer of smooth muscle are:
A: Arteries
B: Arterioles
C: Capillaries
D: Veins

A: Arteries

Phase 0 of the action potential in cardiac contraction cells involves:

A: Potassium channels
B: Sodium channels
C: Calcium channels
D: Hydrogen channels

B: Sodium channels

The QRS complex in the ECG represents:
A: Atrial depolarization
B: Ventricular depolarization
C: Ventricular repolarization
D: Nothing

B: Ventricular depolarization

General symptoms of arrhythmia include all of the following EXCEPT:
A: Palpitations
B: Anxiety
C: Dizziness
D: Death

D: Death

Treatment options for arrhythmia include all of the following EXCEPT:
A: anti-arrhythmic medication
B: Exercise stress test
C: Cardioversion
D: Pacemaker

B: Exercise stress test

The P wave in the ECG indicates the beginning of:
A: Atrial contraction
B: Atrial conduction
C: Ventricular contraction
D: Ventricular conduction

A: Atrial contraction