Impulse Conduction and Arrhythmias Quiz

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Questions and Answers

What type of atrioventricular block is characterized by complete conduction failure?

Fourth Degree AV Block

First Degree AV Block

Second Degree AV Block

Third Degree AV Block (correct)

What is the origin site for rhythmic activity that initiates heart contractions?

Bundle of His

AV Node

Purkinje Fibers

Sino-Atrial Node (correct)

Which term describes an early heartbeat originating from the atria?

Atrial Premature Beat (correct)

Atrial Flutter

Ventricular Tachycardia

Atrial Fibrillation

What does the T wave represent in an electrocardiogram (EKG)?

Ventricular Repolarization Signup and view all the answers

What is a characteristic of the electrical activity in the AV node?

Regions of slow electrical activity Signup and view all the answers

During reentry in WPW syndrome, what happens to the impulse at the blocked site?

It can later propagate from a different direction. Signup and view all the answers

What does the QRS complex signify in an electrocardiogram (EKG)?

Ventricular Depolarization Signup and view all the answers

What type of arrhythmia is classified as having an origin in the atrium and manifests as an abnormal increase in heart rate?

Atrial Tachycardia Signup and view all the answers

What can excessive action potential duration lead to?

Early After Depolarizations (EADs) Signup and view all the answers

Which type of arrhythmia results from disturbances in impulse conduction?

First degree AV block Signup and view all the answers

Which of the following is NOT a type of triggered activity arrhythmia?

Myocardial infarct Signup and view all the answers

Which condition is most likely to prolong the QT interval?

Drug induced long QT syndrome Signup and view all the answers

Which ion channel malfunction is primarily associated with LQT1?

IKs - K channel Signup and view all the answers

What is a common consequence of decreased repolarizing currents throughout the heart?

Ventricular arrhythmias Signup and view all the answers

Which condition is characterized by complete conduction failure?

Third degree AV block Signup and view all the answers

Which arrhythmia is NOT associated with an inherited long QT syndrome?

Cardiomyopathy Signup and view all the answers

Study Notes

Impulse Conduction

First degree AV block: Prolonged conduction time between the atria and ventricles.
Second Degree AV Block: Episodic conduction failure, some impulses fail to reach the ventricles.
Third Degree AV Block: Complete conduction failure, no impulses from the atria reach the ventricles.
AV block can occur in the AV node and/or His-Purkinje system.

Impulse Conduction Failure

Premature beat can be blocked in part of the re-entry pathway, allowing later impulse propagation from a different direction in WPW syndrome.
Healing myocardial infarct with scar tissue can contribute to conduction failure.

Types of Arrhythmias

Arrhythmias are classified by their origin (sinus node, atrium, AV node, ventricle) and nature (premature beat, tachycardia, fibrillation).
Examples include atrial premature beat, atrial tachycardia, atrial fibrillation, ventricular premature beat, ventricular tachycardia, and ventricular fibrillation.

Rhythm

Rhythmic activity originates at the SA node.
Regions of slow electrical activity include the SA node and AV node.
Slow propagation is usually accompanied by slow (Calcium Mediated) action potential upstrokes.
Fast propagation requires a large current source.
Current flows longitudinally from a region of depolarization, changing the potential of surrounding tissue.
Electrical gradients tend to dissipate.

Electrocardiogram (EKG, ECG)

Current flow can be detected at the body surface if the source is large enough.
The EKG measures electrical activity of the heart.
The P-Wave corresponds to atrial excitation.
The QRS complex corresponds to ventricular depolarization.
The T wave corresponds to ventricular repolarization.

Initiating Events for Triggered Arrhythmias

Triggered arrhythmias arise from two types of afterdepolarizations:
- Early After Depolarizations (EADs)
- Delayed Afterdepolarizations (DADs)

Excessive Action Potential Duration

Prolonged action potential duration can lead to EADs.

Disturbances of Impulse Initiation

Normal Sinus Rhythm: Heart rate between 60-100 beats per minute (bpm).
Sinus Tachycardia: Heart rate above 100 bpm.
Sinus Bradycardia: Heart rate below 60 bpm.

Disturbances of Rhythm - Arrhythmias

Arrhythmias can result from regional disease, triggered activity, or abnormal electrical properties throughout the heart.
Regional disease can lead to differences in electrical properties in the heart, such as in myocardial infarct or WPW syndrome.
Abnormal electrical properties throughout the heart can cause arrhythmias.

Arrhythmias Associated with Long QT Interval

Prolonged QT interval can result from decreased repolarizing currents in heart cells.
Long QT syndrome can lead to ventricular arrhythmias and sudden cardiac death.
Causes include drug induced and familial (inherited) long QT syndrome due to malfunction of K or Na channels.

Basis of Individual Ionic Currents

INa: Sodium channel (LQT3).
Ito: Potassium channel.
IKr: Potassium channel (ERG) (LQT2).
IKs: Potassium channel (KvLQT) (LQT1).
ERG channel is a frequent target for drugs that can block the channel, leading to a prolonged QT interval and arrhythmias.
Drugs can also block other K channels.
Drugs that can prolong QT interval are listed in Tables 2 & 3 at http://heart.bmjjournals.com/cgi/content/full/89/11/1363.

Familial (Inherited) Long QT Syndrome (LQTS)

Mutations in proteins involved in LQTS can cause abnormal protein function and lead to decreased K current.
This results in a long QT interval, arrhythmias, and sudden cardiac death.
Proteins involved in familial long QT syndrome include:
- INa: Sodium channel (LQT3) (5-10%).
- IKr: Potassium channel (ERG) (LQT2) (~30-40%).
- IKs: Potassium channel (KvLQT) (LQT1) (~50%).

Excessive AP Prolongation

Excitatory currents can re-activate and interact with other currents, leading to further prolongation of the action potential.

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Description

Test your knowledge on impulse conduction, various types of AV blocks, and the classification of arrhythmias. This quiz covers essential concepts related to cardiac conduction failures and rhythm disturbances. Enhance your understanding of these critical cardiac functions and their implications in clinical settings.