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Questions and Answers
What characterizes a third-degree AV block?
What characterizes a third-degree AV block?
- Impulse transmitted from atria to ventricle
- Regular P waves followed by QRS complexes
- Complete AV dissociation (correct)
- Increased heart rate
In a third-degree AV block, the P waves and QRS complexes are related to each other.
In a third-degree AV block, the P waves and QRS complexes are related to each other.
False (B)
What type of rhythm can occur in the ventricles due to a third-degree AV block?
What type of rhythm can occur in the ventricles due to a third-degree AV block?
Junctional rhythm
In a third-degree AV block, impulses are _____ transmitted from the atria to the ventricles.
In a third-degree AV block, impulses are _____ transmitted from the atria to the ventricles.
Match the following features of a third-degree AV block with their descriptions:
Match the following features of a third-degree AV block with their descriptions:
What is the heart rate (HR) threshold for tachyarrhythmias?
What is the heart rate (HR) threshold for tachyarrhythmias?
Triggered activity is one of the causes of tachyarrhythmias.
Triggered activity is one of the causes of tachyarrhythmias.
Name one origin of impulses in tachyarrhythmias.
Name one origin of impulses in tachyarrhythmias.
In tachyarrhythmias, a heart rate greater than 100 bpm indicates __________.
In tachyarrhythmias, a heart rate greater than 100 bpm indicates __________.
Match the causes of tachyarrhythmias to their descriptions:
Match the causes of tachyarrhythmias to their descriptions:
Which of the following is characterized by re-entry circuits?
Which of the following is characterized by re-entry circuits?
Triggered activity includes both early and late after depolarizations.
Triggered activity includes both early and late after depolarizations.
Name one cause of wide QRS complex in tachyarrhythmias.
Name one cause of wide QRS complex in tachyarrhythmias.
A common mechanism for atrial tachycardia is __________.
A common mechanism for atrial tachycardia is __________.
Match each tachyarrhythmia with its associated feature:
Match each tachyarrhythmia with its associated feature:
What is the primary purpose of the sinoatrial (SA) node?
What is the primary purpose of the sinoatrial (SA) node?
Injunctional rhythm, the electrical impulse originates from the sinoatrial node.
Injunctional rhythm, the electrical impulse originates from the sinoatrial node.
What are the three degrees of atrioventricular (AV) block?
What are the three degrees of atrioventricular (AV) block?
A type of block that involves blockage in all three bundle branches is called a ______ block.
A type of block that involves blockage in all three bundle branches is called a ______ block.
Match the following types of block with their descriptions:
Match the following types of block with their descriptions:
Which channel is primarily involved in depolarization of cardiomyocytes?
Which channel is primarily involved in depolarization of cardiomyocytes?
All fascicular blocks are classified together into one category.
All fascicular blocks are classified together into one category.
What indicates possible sinus node dysfunction on an electrocardiogram (ECG)?
What indicates possible sinus node dysfunction on an electrocardiogram (ECG)?
Which of the following is a characteristic feature of AVNRT?
Which of the following is a characteristic feature of AVNRT?
In AVNRT, the impulse originates from the sinoatrial node.
In AVNRT, the impulse originates from the sinoatrial node.
What is the heart rate typically observed in narrow QRS tachycardia?
What is the heart rate typically observed in narrow QRS tachycardia?
In AVNRT, the P waves are inverted in leads ______, ______, and ______.
In AVNRT, the P waves are inverted in leads ______, ______, and ______.
Match the following components of ECG interpretation with their descriptions:
Match the following components of ECG interpretation with their descriptions:
What is a common clinical finding in first degree AV block?
What is a common clinical finding in first degree AV block?
In second degree AV block Type I, there is at least one missed beat among the conducted beats.
In second degree AV block Type I, there is at least one missed beat among the conducted beats.
What may lead to the development of first degree AV block?
What may lead to the development of first degree AV block?
In first degree AV block, the PR interval is prolonged and measured at greater than _____ ms.
In first degree AV block, the PR interval is prolonged and measured at greater than _____ ms.
Match the following types of second degree AV block with their characteristics:
Match the following types of second degree AV block with their characteristics:
Which of the following is NOT an extrinsic cause of SA nodal dysfunction?
Which of the following is NOT an extrinsic cause of SA nodal dysfunction?
Tachy-brady syndrome is characterized by alternating periods of tachycardia and bradycardia.
Tachy-brady syndrome is characterized by alternating periods of tachycardia and bradycardia.
What is a common heart rate for idioventricular rhythm (IVR)?
What is a common heart rate for idioventricular rhythm (IVR)?
A ________ block is characterized by absent QRS complexes on an ECG.
A ________ block is characterized by absent QRS complexes on an ECG.
Match the following ECG manifestations of SA node dysfunction with their descriptions:
Match the following ECG manifestations of SA node dysfunction with their descriptions:
What characterizes a first-degree AV block?
What characterizes a first-degree AV block?
Type I second-degree AV block is also known as Mobitz type I.
Type I second-degree AV block is also known as Mobitz type I.
Name one cause of complete AV block.
Name one cause of complete AV block.
In advanced 2:1 AV block, there are __________ P waves for every QRS complex.
In advanced 2:1 AV block, there are __________ P waves for every QRS complex.
Match the type of AV block with its description:
Match the type of AV block with its description:
What is the normal value for ejection fraction in Heart Failure with Preserved Ejection Fraction (HFPEF)?
What is the normal value for ejection fraction in Heart Failure with Preserved Ejection Fraction (HFPEF)?
The SA node is responsible for the heart's maximum pacemaker potential.
The SA node is responsible for the heart's maximum pacemaker potential.
What term describes the heart's ability to beat in the absence of stimuli?
What term describes the heart's ability to beat in the absence of stimuli?
In heart failure with reduced ejection fraction (HFrEF), the ejection fraction is _____ than 50%.
In heart failure with reduced ejection fraction (HFrEF), the ejection fraction is _____ than 50%.
Match the cardiac functions with their respective terms:
Match the cardiac functions with their respective terms:
Which type of AV block is characterized by a progressively prolonging PR interval leading to a missed QRS complex?
Which type of AV block is characterized by a progressively prolonging PR interval leading to a missed QRS complex?
Type II AV block is considered a benign condition.
Type II AV block is considered a benign condition.
What is a common symptom of Type II AV block?
What is a common symptom of Type II AV block?
In Mobitz Type I AV block, the PR interval __________ until a beat is dropped.
In Mobitz Type I AV block, the PR interval __________ until a beat is dropped.
Match the following AV block types with their characteristics:
Match the following AV block types with their characteristics:
Study Notes
Third Degree AV Block
- No electrical impulses travel from the atria to the ventricles.
- Complete AV dissociation is present
- Regular P waves and regular QRS complexes are present
- P waves and QRS complexes are unrelated to each other
Heart Blocks & Bradyarrhythmias
- SA Node: Sinoatrial Node
- Sinoatrial Block: Blockage in the sinoatrial node, can lead to reduced or absent electrical impulses originating from the node.
- AV Block (1°, 2°, 3°): Atrioventricular block, delay or interruption of electrical impulse from atria to ventricles, classified in 3 degrees of severity.
- Fascicular Block: Blockage within the bundle of His.
Types of Block
- Unifascicular: Blockage in one bundle branch.
- Bifascicular: Blockage in two bundle branches.
- Trifascicular: Blockage in all three bundle branches.
Specific Block Types
- LAFB: Left Anterior Fascicular Block
- LPFB: Left Posterior Fascicular Block
- RBBB: Right Bundle Branch Block
Sinus Node Dysfunction
- Causes: Intrinsic or extrinsic factors
- Intrinsic: Sick sinus syndrome
- Extrinsic: hyperkalemia, drugs (digoxin, beta-blockers, calcium channel blockers), ↑ PaCO2, hypothermia, hypothyroidism, ↑ intracranial tension
- ECG: Absent or abnormal P waves
- Compensation Mechanisms:
- Junctional rhythm: heart rate 40-60 bpm. No P waves
- Abnormal P wave: Possible sinus node issue
Tachyarrhythmias
- Tachyarrhythmias: Heart rate (HR) > 100 bpm. Narrow QRS complex or Wide QRS complex
- Causes: Enhanced automaticity, triggered activity, re-entry.
- Origin of Impulses:
- Ventricular:
- Above bifurcation of Bundle of His: Purkinje fibers, leads to synchronous activation of ventricles.
- Normal/Narrow QRS complex.
- Ventricular:
Abnormal Rhythms
- Atrial Tachycardia: Focal or multifocal, all three mechanisms of tachycardia.
- Junctional Tachycardia:
- Ventricular Tachycardia:
- Ischemic VT
Triggered Activity
- Early after depolarization: Long QT syndrome, Torsades de pointes.
- Late after depolarization: Increased sympathetic activity and intracellular Ca2+
- RVOT VT (Right ventricular outflow tract VT).
- LVOT VT (Left ventricular outflow tract VT)
- Sympathetic VT
Re-Entry
- Precipitated by PAC (Premature atrial complex) or PVC (Premature ventricular complex)
- Highly responsive to DC cardioversion
- Micro Re-entry Circuits:
- AVNRT (Atrioventricular nodal re-entry tachycardia)
- Brugada syndrome
- Atrial fibrillation
- Macro Re-entry Circuits: - AVRT (Atrioventricular re-entry tachycardia) - Atrial flutter - Scar VT
Causes Based on QRS
- Wide QRS: VT (Scar VT or Long QT syndrome)
- Slightly wide QRS: Supraventricular arrhythmia with BBB (Bundle branch block).
- Narrow QRS:
- Automaticity: Sinus/junctional/atrial tachycardia.
- Re-entry: AVNRT/AF/atrial flutter/AVRT.
Note
- Paroxysmal atrial tachycardia with AV block: Possible association with digoxin toxicity, may be precipitated by hypokalemia, tachycardia may result from enhanced automaticity
Narrow QRS Tachycardia
- ECG Interpretation:
- HR: 150 bpm (calculated as 1500/10)
- QRS complex: Narrow
- P-wave morphology: Normal, indicating impulse originates from the SA (sinoatrial) node
AVNRT (Atrioventricular Nodal Reentrant Tachycardia) Features
- Can occur in structurally normal hearts.
- More common in females.
- Generally has a good prognosis.
Mechanism of AVNRT
- Normal Heartbeat: Sinoatrial node (SAN) initiates impulse, travels through fast and then slow pathways, fast pathway activates the ventricles, impulse travels through the slow pathway and dissolves into the slow pathway before getting through the fast pathway to the ventricles.
- AVNRT: Premature impulse from the ventricle. Slow pathway starts to recover while fast pathway is still refractory, impulse enters then continues to the fast pathway, impulse goes retroactively to the atria.
AVNRT Diagram Explanation
- Normal: Impulse originates from the SAN and travels through the fast and slow pathways that activate the ventricles simultaneously.
- AVNRT: Premature impulse starts from the ventricle, goes through the fast pathway and moves retroactively towards the AV node. Slow pathway recovers, fast pathway is refractory and the impulse continues towards the ventricles.
P waves
- Inverted in leads II, III, and aVF.
- QRS complexes: Narrow
First Degree AV Block
- Causes: Beta-blockers, calcium channel blockers
- C/F (Clinical Findings): Asymptomatic, soft S1, Cannon waves on JVP
- ECG: Delay in impulses from atria to ventricle, prolonged PR interval (>100ms), regular sinus rhythm, normal P wave and QRS complex, every P wave is followed by a QRS complex, synchronous contraction of atria and ventricles.
- Management: No Rx needed, very good prognosis.
Second Degree AV Block
- Classification: Mobitz Type I (Wenckebach), Mobitz Type II, Advanced 2° AV block
- Mobitz Type I: at a time - Only 1 beat missed, ≥ 2 beats conducted
- Mobitz Type II - Does not meet the criteria of type I.
- Advanced 2° AV block - Criteria for Mobitz is not met.
- ECG: Prolonged PR Interval.
SA Nodal Dysfunction Causes
- Extrinsic:
- Hyperkalemia
- Drugs: digoxin, beta-blockers, calcium channel blockers (CCB)
- ↑ PaCO2 (Hypercapnia)
- Hypothermia
- Hypothyroidism (myxedema coma)
- ↑ Intracranial Tension (ICT)
- Intrinsic: Sick sinus syndrome
Other ECG Manifestations of SA Node Dysfunction
- Sinus Pause/Arrest: Distance A > B (Image shows a graphic of sinus pause/arrest)
- Sino-atrial Exit Block: Distance A = B (Image has a graphic demonstrating the concept)
- Tachy-Brady Syndrome: (Image depicts a graphic of this condition)
- Idioventricular Rhythm (IVR):
- Wide QRS complex
- HR up to 40 bpm: IVR
- HR 40-100 bpm: Accelerated IVR (AIVR)
- HR > 100 bpm: Ventricular tachycardia
- AV Block: Absent QRS complexes
AV Blocks
- Complete AV block with complete AV dissociation
- Accelerated idioventricular rhythm with complete AV dissociation
- Junctional tachycardia with complete AV dissociation
Summary
- ECG tracings illustrating different degrees of AV block (1° AV block, Type I 2° AV block, Type II 2° AV block, Advanced 2:1 AV block, Advanced 3:1 AV block, Complete AV block (AV nodal), Complete AV block (infranodal)
SA NODAL DYSFUNCTION
- Cardiac Terminology & Pacemaker Potential: (The document includes a table summarizing cardiac terminologies with meaning and regulator)
- Chronotropy: Heart rate
- Inotropy: Myocardial contractility
- Dromotropy: Cardiac conduction velocity
- Bathmotropy: Cardiac excitability
- Lusitropy: Cardiac relaxation
- Heart failure (HF)
- HF with ↓ ejection fraction (HFrEF): EF < 50%
- HF with preserved ejection fraction (HFPEF): EF > 50%
- Older classification: (The table shows classification of heart failure based on systolic and diastolic dysfunction)
- Impaired contractility (Systolic dysfunction)
- Impaired relaxation (Diastolic dysfunction)
Pacemaker Potential
- Automaticity: Ability of the heart to beat in the absence of stimuli.
- Seen In: SA node (pacemaker, maximum potential), AV node (distal part), atrial cells, His-Purkinje system, ventricular myocardium.
- Phases:
- PM potential: K⁺ channel (TOK: Transient Outward K⁺, IRK: Inward Rectifying K⁺), HCN (Hyperpolarization activated Cyclic Nucleotide Channel) - Funny currents.
AV Blocks
-
Mobitz Type I
- Pathology: AV Nodal
- QRS Complex: Narrow
- Etiology: Benign
- PR Interval: Progressively prolongations (Wenckebach phenomena), progressively shortens
- RR Interval:
- Presentation: Asymptomatic
- Associated MI: Associated with infranodal block, rare, due to structural heart disease, may be asymptomatic or may have a permanent pacemaker
- Causes:
- Site of Block: AV node
-
**Mobitz **Type II
- Pathology: Infranodal
- QRS Complex: Wide
- Etiology: Malignant
- PR Interval: Constant
- RR Interval: Constant.
- Presentation: Symptomatic, hemodynamic compromise, Stokes-Adams syndrome
- Associated MI: Associated with inferior wall MI (IWMI), SX/SLE/↑K+/Amyloid.
-
Additional information:
- Advanced 2° AV block: Diagram showing the pattern
- Active space: (A segment of text separating the blocks)
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Description
Test your understanding of heart blocks and their classifications, including third-degree AV block and various types of fascicular blocks. This quiz will cover key concepts necessary for mastering cardiac physiology and related disorders.
