PHARM 532 - Electrical Conductance Disorders (TEST 1)

Sinoatrial (SA) Node Location

Located within the wall of the right atrium

Arioventricular (AV) Node Location

Located in the right atrial wall near autonomic parasympathetic ganglia

Bundle of His (Atrioventricular Bundle) Location

Interventricular septum

Purkinje Fibers location

Extend to apex (bottom) of heart and out to outer ventricular walls

Heart Pacemakers

- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Bundle of His (Atrioventricular Bundle)
- Purkinje fibers

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

1) Sinoatrial (SA) node
2) Atrioventricular (AV) node
3) Bundle of His (Atrioventricular Bundle)
4) Purkinje fibers

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

Sympathetic activation --> increased conduction velocity in AV node via increasing rate of depolarization of action potentials

Parasympathetic (vagal) activation --> decreased conduction velocity in AV node via decreasing slope of phase 0 of the nodal action potentials

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?

Arrhythmias

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

- Phase 0: rapid depolarization
- Phase 1: initial repolarization
- Phase 2: plateau phase
- Phase 3: repolarization
- Phase 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?

- Phase 0: rapid depolarization involves Na+ and Ca2+
- Phase 1: initial repolarization involves K+ and Ca2+
- Phase 2: plateau phase involves Ca2+
- Phase 3: repolarization involves K+
- Phase 4: resting membrane potential near equilibrium potential for K+ involves K+, Na+, and Ca2+

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

Non-pacemaker has rapid depolarization ("fast response")

Pacemaker has spontaneous, slower depolarization ("slow response")

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

ECG Components

- P wave
- QRS complex
- T wave
- PR interval
- ST segment
- QT interval

P wave

Atrial depolarization

QRS Complex

Ventricular depolarization

T Wave

Ventricular repolarization

PR Interval

Atrial depolarization + AV nodal delay

ST Segment

Isoelectric period of depolarized ventricles

QT Interval

Duration of depolarization + repolarization - corresponds to action potential durations throughout ventricles

Sinus Rhythm

Rhythm of the heart

Sinus Bradycardia

HR < 60 bpm

Sinus Bradycardia Treatment

Pacemaker

Atrial Flutter

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

Atrial Flutter Treatment

- Ventricular rate control
- Electrical or pharmacological cardioversion
- Catheter-based radiofrequency ablation (RFA)
- Anti-coagulant medication
- Antiarrhythmic meds

Atrial Fibrillation

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

Atrial Fibrillation Treatment

- Cardioversion
- Anti-coagulant medication

Atrioventricular Block

Heart block

Atrioventricular Block Treatment

Pacemaker

Ectopic foci (premature ventricular complex)

- Can occur within the atria or ventricles
- Premature and bizarrely shaped QRS complexes

Ectopic Foci (Premature Ventricular Complex) Treatment

- Oxygen if hypoxic
- Antiarrhythmic meds
- Beta-blockers
- Electrolytes
- Ca2+ channel blockers

Ventricular Tachycardia

- HR 100-280 bpm
- Can be sustained or non-sustained (paroxysmal)

Ventricular Tachycardia Treatment

- Cardioversion
- Implantable cardioverter defibrillator (ICD)
- Catheter-based radiofrequency ablation (RFA)

Ventricular Fibrillation

Uncoordinated ventricular depolarizations

Ventricular Fibrillation Treatment

- Immediate defibrillation
- Catheter-based radiofrequency ablation (RFA)
- Implantable cardioverter defibrillator (ICD)

What are the most common arrhythmias in the US?

- Atrial flutter
- Atrial fibrillation

Less Serious General Symptoms of Arrythmia

•Palpitations
•Slow heartbeat
•Irregular heartbeat
•Feeling pauses between heartbeats

More Serious General Symptoms of Arrythmia

•Anxiety
•Dyspnea
•Syncope
•Dizziness
•Fatigue
•Sweating
•Chest pain

What techniques are typically used to diagnose arrhythmias?

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

What are some common risk factors for development of arrhythmia?

• Age
• Gender (F

What are some common causes of arrhythmia?

- Coronary artery disease
- Altered impulse formation
- Altered impulse conduction

Afterpolarization

Abnormal depolarizations that interrupt phase 2, phase 3, or phase 4 of the cardiac action potential

Afterpolarization Types

Early afterdepolarization (EAD) and Delayed afterdepolarization (DAD)

Early Afterdepolarization (EAD) Cause

Can be caused by anti-arrhythmia drugs such as quinidine, dofetilide, ibutilide

Delayed Afterdepolarization (DAD)

Caused by abnormal Ca2+ release from the sarcoplasmic reticulum and digoxin