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ECG Interpretation. Arrhythmias of Formation Chapters 4-5. Types of Arryhthmias:. Sinus Problems: Formed in the sinus node, but irregular Ectopic Problems: Formed outside of the sinus node Conduction Problems: Formed in the sinus node, but conduction in error

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ECG Interpretation

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ECG Interpretation

Arrhythmias of Formation

Chapters 4-5

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Types of Arryhthmias:

  • Sinus Problems: Formed in the sinus node, but irregular

  • Ectopic Problems: Formedoutside of the sinus node

  • Conduction Problems: Formed in the sinus node, but conduction in error

  • Pre-Excitation Problems: “Short circuits” in normal conduction

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Causes of Arrhytmias:

  • Hypoxia: Lung disease

  • Ischemia: CAD, angina (local hypoxia)

  • Sympathetic Stimulation: Nervous, exercise, CHF, hyperthyroidism

  • Drugs: Caffeine, cocaine, stimulants…many antiarryhtmic drugs…

  • Electrolyte Disturbances: K+, Ca++, Mg++

  • Bradycardia: “Escape” rhythms…

  • Stretch: CHF, hypertrophy, valve disease

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Rhythm ID: Algorithm

  • P-Wave: rate and rhythm

  • QRS: rate and rhythm - shape

  • P-R Interval: Is AV conduction normal? P:QRS regular?

  • T Wave and QT Interval

  • Any unusual complexes?


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Clinical Manifestations:

  • Asymptomatic – generally benign

  • Palpitations – Awareness may cause anxiety

  • Compromised CO – Syncope

  • Myocardial Ischemia – tachy

  • CHF – Chronic insufficiency

  • Sudden Death – Cardiac arrest

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Define “Normal”

  • Regular Atrial and Ventricular Rhythms: 1P : 1 QRS

  • Rates: 60-100

  • P Morphology: small, round, regular and positive in Lead II

  • QRS Morph: Similar size and shape

  • Positive T waves in Lead II

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  • 1.SA Node “fires”

  • 2. Right and Left Atria Depolarize

  • 3. AV Node “pauses”

  • Questions:

    • P waves present?

    • Regular rhythm?

    • 1/QRS?



SA Node



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Sinus Rhythms

  • Normal Sinus Rhythm: 1P/QRS: 60-100 bpm

  • Sinus brady: 1P/QRS: <60 bpm

  • Sinus tachy: 1P/QRS: >100 bpm

  • Sinus Arrhythmia: 1P/QRSNormalIrregularities caused by inspiration/expiration – more noticeable in children / elderly

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ABSENT PQRS Complex: Sinus Arrest:

  • Causes:

    • Heart disease, acute infection, VAGAL stimulation (Bush’s Pretzel Problem?)

    • Sick Sinus Syndrome: Usually in elderly – more irregular


    • Rare and asymptomatic

    • Frequent and symptomatic

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Atrial Arrhythmias:

  • PAC: Premature Atrial Contraction

  • Atrial Tachycardias: SVT – with or without blocks, PAT

  • Atrial Flutter:

  • Atrial Fibrillation

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Premature Atrial Contractions:

  • Ectopic

  • Triggered by: Alcohol, nicotine, anxiety, fatigue, fever, and infections

  • Usually benign

  • Clinical Manifestations: Palpitations or “skipped beats”

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  • Irregular P-R rhythms

  • Premature, irregular P waves (sometimes “lost” in the T wave)

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Atrial Tachycardias:

  • Also: Supra Ventricular Tachycardia (PSVT)

  • Rates: 100-250 bpm

  • Regular Rhythms

  • “Hidden” P waves (could be inverted – indicating a Junctional focus PSVT)

  • PAT = Common in warm-up/cool down and doesn’t respond to Carotid Massage (don’t try this!)

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Afib – Aflut…

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Atrial Fibrillation: Atrial Fib and/or


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Atrial Flutter: 2:1 Ventricular “capture”

Ventricles can only respond to every other

Atrial conduction

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Multi-focal origins -chaotic

Rate: >400 bpm


Atrial Cardiac Output is lost :

One focus - organized

Rate: 200-400 bpm

Atrial Cardiac Output is compromised

Fibrillation vs. Flutter?

Atria contribute ~20% of the total

Cardiac output: A-Fib is non-lethal

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Summarize: Sinus and Atrial Rhythms

  • Sinus: Normal, Tachy, Brady

  • Absent P: Sinus Arrest, A-fib, Junctional (PSVT), PAT

  • Weird P: A-Flut, PAC

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Formation Arrhythmias

Junctional and Ventricular

Chapters 6-7

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  • Form in the AV (Junction) Node

  • May be an “Escape” rescue if SA node fails to fire or conduct

    • Escape Rate ~40-60 bpm

  • May be an “Ectopic” Irritable Focus

    • Ectopic Rate ~ 60-100 bpm

  • Responds to vagal stimulus

  • P Waves inverted, missing or after the QRS

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Ventricles: QRS Rhythms

  • Regular rhythms?

    • R-R intervals equivalent

  • Regular “irregular” rhythms?

    • R-R intervals equivalent with occasional irregularities

  • Irregular rhythms?

    • R-R intervals irregular

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Regular “Irregular”

  • Premature Beats: PVC

    • Widened QRS, not associated with preceding P wave

    • Usually does not disrupt P-wave regularity

    • T wave is “inverted” after PVC

    • Often Followed by compensatory ventricular pause

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Notice a Pattern in the PVC’s?

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PVC Patterns:

  • PVC: 1 Isolated beat

  • Couplet: 2 consecutive PVC’s

  • Bigeminy: PVC every other beat

  • Non-Sustained VT: >3 beats for less than 1 minute

  • Sustained VT: > 1 minute of ventricular tachycardia

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Irregular Ventricular Rhythms: CHAOTIC

  • Ventricular Fibrillation:

    • Multi-focal origins

    • Irregular wave morphologies

    • Cardiac Output = 0

    • Coarse vs. Fine V-Fib

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Clinical Manifestations – PVC’s

  • Often benign BUT

  • Compromised CO

  • Possibly precipitate a lethal arrhythmia: Vtach, VFib

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More on PVC’s

  • Cardiac Output: Pulse deficit = reduced CO (~20%)

  • One PVC usually asymptomatic

  • Symptoms: LOC or dizziness demand treatment

  • Risk of Lethal Arrhythmias: V-Tach more dangerous in CAD

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Rules of Malignancy:

  • Frequency: > 6 / minute

  • Runs: 3+ consecutive

  • Multiform

  • “R on T”

  • PVC’s during MI

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What is the threat of sustained Ventricular Tachycardia?1. What happens to diastole? 2. What happens to Cardiac Output? 3. What happens to myocardial perfusion?4. What happens to myocardial VO2?

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Winslow Homer: “The Stile”

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