Medicine Marrow Pg No 387-396 (ECG)
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Questions and Answers

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.

    False

    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.

    <p>not</p> Signup and view all the answers

    Match the following features of a third-degree AV block with their descriptions:

    <p>P waves = Regular and independent from QRS complexes QRS complex = Regular but unrelated to P waves AV dissociation = Complete lack of communication between atria and ventricles ECG pattern = Characteristic pattern showing P waves not followed by QRS complexes</p> Signup and view all the answers

    What is the heart rate (HR) threshold for tachyarrhythmias?

    <p>100 bpm</p> Signup and view all the answers

    Triggered activity is one of the causes of tachyarrhythmias.

    <p>True</p> Signup and view all the answers

    Name one origin of impulses in tachyarrhythmias.

    <p>Ventricular</p> Signup and view all the answers

    In tachyarrhythmias, a heart rate greater than 100 bpm indicates __________.

    <p>tachycardia</p> Signup and view all the answers

    Match the causes of tachyarrhythmias to their descriptions:

    <p>Enhanced automaticity = Increased rate of impulse generation by pacemaker cells Re-entry = Impulse re-circulating around a circuit Triggered activity = Abnormal impulses generated after depolarization Ventricular impulses = Originating below the bifurcation of the Bundle of His</p> Signup and view all the answers

    Which of the following is characterized by re-entry circuits?

    <p>Atrial Flutter</p> Signup and view all the answers

    Triggered activity includes both early and late after depolarizations.

    <p>True</p> Signup and view all the answers

    Name one cause of wide QRS complex in tachyarrhythmias.

    <p>Ventricular Tachycardia</p> Signup and view all the answers

    A common mechanism for atrial tachycardia is __________.

    <p>automaticity</p> Signup and view all the answers

    Match each tachyarrhythmia with its associated feature:

    <p>AVNRT = Micro re-entry circuit Scar VT = Wide QRS Tachycardia Atrial Flutter = Macro re-entry circuit Torsades de pointes = Early after depolarization</p> Signup and view all the answers

    What is the primary purpose of the sinoatrial (SA) node?

    <p>To initiate electrical impulses for heartbeats</p> Signup and view all the answers

    Injunctional rhythm, the electrical impulse originates from the sinoatrial node.

    <p>False</p> Signup and view all the answers

    What are the three degrees of atrioventricular (AV) block?

    <p>1°, 2°, 3°</p> Signup and view all the answers

    A type of block that involves blockage in all three bundle branches is called a ______ block.

    <p>trifascicular</p> Signup and view all the answers

    Match the following types of block with their descriptions:

    <p>LAFB = Left Anterior Fascicular Block LPFB = Left Posterior Fascicular Block RBBB = Right Bundle Branch Block Unifascicular = Blockage in one bundle branch</p> Signup and view all the answers

    Which channel is primarily involved in depolarization of cardiomyocytes?

    <p>L-type calcium channels</p> Signup and view all the answers

    All fascicular blocks are classified together into one category.

    <p>False</p> Signup and view all the answers

    What indicates possible sinus node dysfunction on an electrocardiogram (ECG)?

    <p>Absent P Waves</p> Signup and view all the answers

    Which of the following is a characteristic feature of AVNRT?

    <p>More common in females</p> Signup and view all the answers

    In AVNRT, the impulse originates from the sinoatrial node.

    <p>False</p> Signup and view all the answers

    What is the heart rate typically observed in narrow QRS tachycardia?

    <p>150 bpm</p> Signup and view all the answers

    In AVNRT, the P waves are inverted in leads ______, ______, and ______.

    <p>II, III, aVF</p> Signup and view all the answers

    Match the following components of ECG interpretation with their descriptions:

    <p>Heart Rate of 150 bpm = Calculated using 1500/10 Normal P-wave morphology = Indicates impulse from sinoatrial node Narrow QRS complex = Suggests rapid ventricular activation AVNRT = Atrioventricular Nodal Reentrant Tachycardia</p> Signup and view all the answers

    What is a common clinical finding in first degree AV block?

    <p>Cannon waves on JVP</p> Signup and view all the answers

    In second degree AV block Type I, there is at least one missed beat among the conducted beats.

    <p>True</p> Signup and view all the answers

    What may lead to the development of first degree AV block?

    <p>Beta-blocker or calcium channel blockers</p> Signup and view all the answers

    In first degree AV block, the PR interval is prolonged and measured at greater than _____ ms.

    <p>100</p> Signup and view all the answers

    Match the following types of second degree AV block with their characteristics:

    <p>Mobitz Type I = Progressively longer PR interval until a beat is dropped Mobitz Type II = Dropped beats without preceding PR interval changes Advanced 2° AV Block = Does not meet criteria for Mobitz classification</p> Signup and view all the answers

    Which of the following is NOT an extrinsic cause of SA nodal dysfunction?

    <p>Sick sinus syndrome</p> Signup and view all the answers

    Tachy-brady syndrome is characterized by alternating periods of tachycardia and bradycardia.

    <p>True</p> Signup and view all the answers

    What is a common heart rate for idioventricular rhythm (IVR)?

    <p>up to 40 bpm</p> Signup and view all the answers

    A ________ block is characterized by absent QRS complexes on an ECG.

    <p>AV</p> Signup and view all the answers

    Match the following ECG manifestations of SA node dysfunction with their descriptions:

    <p>Sinus Pause/Arrest = Distance A &gt; B Sino-atrial Exit Block = Distance A = B Tachy-Brady Syndrome = Alternating periods of slow and fast heart rates Idioventricular Rhythm (IVR) = Wide QRS complex</p> Signup and view all the answers

    What characterizes a first-degree AV block?

    <p>Prolonged PR interval</p> Signup and view all the answers

    Type I second-degree AV block is also known as Mobitz type I.

    <p>True</p> Signup and view all the answers

    Name one cause of complete AV block.

    <p>Accelerated idioventricular rhythm</p> Signup and view all the answers

    In advanced 2:1 AV block, there are __________ P waves for every QRS complex.

    <p>two</p> Signup and view all the answers

    Match the type of AV block with its description:

    <p>1° AV block = Prolonged PR interval Type I 2° AV block = Progressive PR interval until dropped beat Type II 2° AV block = Dropped beats without PR prolongation Complete AV block = Total dissociation between atrial and ventricular activity</p> Signup and view all the answers

    What is the normal value for ejection fraction in Heart Failure with Preserved Ejection Fraction (HFPEF)?

    <p>EF &gt; 50%</p> Signup and view all the answers

    The SA node is responsible for the heart's maximum pacemaker potential.

    <p>True</p> Signup and view all the answers

    What term describes the heart's ability to beat in the absence of stimuli?

    <p>Automaticity</p> Signup and view all the answers

    In heart failure with reduced ejection fraction (HFrEF), the ejection fraction is _____ than 50%.

    <p>less</p> Signup and view all the answers

    Match the cardiac functions with their respective terms:

    <p>Chronotropy = Heart rate Inotropy = Myocardial contractility Dromotropy = Cardiac conduction velocity Lusitropy = Cardiac relaxation</p> Signup and view all the answers

    Which type of AV block is characterized by a progressively prolonging PR interval leading to a missed QRS complex?

    <p>Type I (Mobitz Type I)</p> Signup and view all the answers

    Type II AV block is considered a benign condition.

    <p>False</p> Signup and view all the answers

    What is a common symptom of Type II AV block?

    <p>Hemodynamic compromise</p> Signup and view all the answers

    In Mobitz Type I AV block, the PR interval __________ until a beat is dropped.

    <p>progressively lengthens</p> Signup and view all the answers

    Match the following AV block types with their characteristics:

    <p>Mobitz Type I = Asymptomatic, PR interval progressively prolongs Mobitz Type II = Symptomatic, constant PR interval, often malignant Advanced 2° AV block = Differentiated from Type I and II by unique RR pattern</p> Signup and view all the answers

    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.

    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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    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.

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