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Questions and Answers
What type of atrioventricular block is characterized by complete conduction failure?
What is the origin site for rhythmic activity that initiates heart contractions?
Which term describes an early heartbeat originating from the atria?
What does the T wave represent in an electrocardiogram (EKG)?
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What is a characteristic of the electrical activity in the AV node?
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During reentry in WPW syndrome, what happens to the impulse at the blocked site?
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What does the QRS complex signify in an electrocardiogram (EKG)?
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What type of arrhythmia is classified as having an origin in the atrium and manifests as an abnormal increase in heart rate?
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What can excessive action potential duration lead to?
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Which type of arrhythmia results from disturbances in impulse conduction?
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Which of the following is NOT a type of triggered activity arrhythmia?
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Which condition is most likely to prolong the QT interval?
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Which ion channel malfunction is primarily associated with LQT1?
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What is a common consequence of decreased repolarizing currents throughout the heart?
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Which condition is characterized by complete conduction failure?
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Which arrhythmia is NOT associated with an inherited long QT syndrome?
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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.
