PNC III EXAM 4

• Cardiac Conduction System


  • Electrical stimulation = Depolarization
  • Mechanical contraction = Systole
  • Electrical relaxation = Repolarization
  • Mechanical relaxation = Diastole
• Electrical Cardiac Conduction System In Order

  • Sinoatrial node
  • Atrioventricular node
  • Bundle of His
  • Right & Left Bundle Branches
  • Purkinje Fibers
• ECG graph paper

  Large box = 0.20 seconds

  Small box = 0.04 seconds
• Waveforms


  • P waves – atrial depolarization
  • QRS – ventricular depolarization
  • T waves – ventricular repolarization
  • U waves – Purkinje Fiber recovery
  • PR – delay of AV node to allow filling of ventricles
• P wave


  • Atrial depolarization
  • 0.11 seconds or less
• QRS Complex


  • Ventricular depolarization
  • Composed of 3 different waves: Q wave (negative deflection), R wave (positive deflection), S wave (negative deflection)
  • Not all QRS will have all 3
  • 0.12 seconds or less
• T wave represents ventricular repolarization
• The atria repolarize too but their repolarization wave is hidden within the QRS
• PR Interval


  • Measure: Start of P wave to start of next waveform
  • Indicates time for impulse to travel from the atria to ventricles
  • 0.12 to 0.20 seconds
• ST Segment


  • Straight line after QRS complex
  • Depression or elevation of this line indicates myocardial injury or ischemia
• QT Interval


  • Measure: Start of QRS to end of T
  • Represents ventricular depolarization and repolarization
  • 0.32 – 0.40 seconds (varies)
  • Prolonged QT may precipitate a lethal ventricular arrhythmia (torsades)
• PP Interval


  • Measure: Start of 1 P wave to the start of the next
  • Used to analyze atrial rate & rhythm
• RR Interval


  • Measure: From R wave to R wave
  • Used to analyze ventricular rate & rhythm
• Method of Analysis


  1. Determine atrial and ventricular rate

  2. Determine atrial and ventricular regularity

  3. Examine the P wave

  4. Examine PR interval

  5. Examine QRS complex
• Step 1: Determine Rate (Method 1 - Quick, less accurate)

  1. 6 Second Strip: Atrial Rate = Count number of PP intervals x 10

  2. Ventricular Rate = Count number of RR intervals x 10

  3. Can be used on regular and irregular strips
• Step 1: Determine Rate (Method 2 - Accurate)

  1. Atrial Rate = 1500 ÷ PP interval small boxes

  2. Ventricular Rate = 1500 ÷ RR interval small boxes

  3. Can be used only on regular strips, not irregular
• Normal Sinus Rhythm (NSR)

  • Impulse origin: SA Node
  • Rate: A&V rate 60 – 100 bpm
  • Regularity: A&V Regular
  • P waves: Identical, precede QRS
  • PR Interval: 0.12 – 0.20, consistent
  • QRS: 0.04 – 0.12, consistent. Each follows a P wave
  • P : QRS Ratio: 1:1
• Sinus Bradycardia (SB)


  • Impulse origin: SA Node
  • Rate: A&V rate <60 bpm
  • Regularity: A&V Regular
  • P waves: Identical, precede QRS
  • PR Interval: 0.12 – 0.20, consistent
  • QRS: 0.04 – 0.12, consistent. Each follows a P wave
  • P : QRS Ratio: 1:1
• Sinus Bradycardia Presentation


  • Asymptomatic
  • Symptomatic: Hypotension, SOB, Mental status changes, Angina
• Sinus Bradycardia Treatment


  • Asymptomatic = no treatment
  • Address the cause
  • Hold CCB/BB
  • Prevent vagal stimulation
  • IVP Atropine
  • If this fails emergency transcutaneous pacing, dopamine, or epinephrine
• Sinus Tachycardia (ST)


  • Impulse origin: SA Node
  • Rate: A&V rate >100 bpm
  • Regularity: A&V Regular
  • P waves: Identical, precede QRS (can get buried in preceding t wave)
  • PR Interval: 0.12 – 0.20, consistent
  • QRS: 0.04 – 0.12, consistent. Each follows a P wave
  • P : QRS Ratio: 1:1
• Sinus Tachycardia Causes


  • Stress, Pain, Fever, Anxiety, Exercise, ↓ or ↑ volume, Shock, Substances: Epinephrine, norepinephrine, dopamine, Caffeine, nicotine, Illicit drugs
• Sinus Tachycardia Presentation


  • Asymptomatic
  • Symptomatic: ↓ CO, Hypotension, Syncope, Pulmonary edema
• Sinus Tachycardia Treatment


  • Treat the cause
  • Vagal maneuvers
  • IV BB or CCB
  • Adenosine
  • Synchronized cardioversion
• Sinus Arrhythmia


  • Impulse origin: SA Node
  • Rate: A&V rate 60 – 100 bpm
  • Regularity: Irregular
  • P waves: Identical, precede QRS
  • PR Interval: 0.12 – 0.20, consistent
  • QRS: 0.04 – 0.12, usually normal
  • P : QRS Ratio: 1:1
• Premature Atrial Complex (PAC)

  • Impulse origin: Irritable area in atria
  • Rate: Depends on underlying rhythm
  • Regularity: Irregular (though underlying rhythm may be regular)
  • P waves: Early; may have a different shape. Other P waves consistent
  • PR Interval: 0.12 – 0.20, not consistent
  • QRS: 0.04 – 0.12, consistent. Each follows a P wave
  • P : QRS Ratio: Usually 1:1
• Premature Atrial Complex (PAC) Causes


  • Substances: Caffeine, Alcohol, Nicotine
  • Electrolytes: Hypokalemia
  • Atrial injury: Ischemia, Infarction
• Premature Atrial Complex (PAC) Presentation


  • Asymptomatic
  • "My heart skipped a beat"
• Premature Atrial Complex (PAC) Treatment


  • Often no treatment
  • If >6 per minute, treat the cause to prevent more serious arrhythmias
• Atrial Fibrillation (A fib)

  • Impulse origin: Multiple areas in atria/ pulmonary veins
  • Rate: A: 300-600 bpm, V: Varies. Can be controlled or uncontrolled.
  • Regularity: Irregular
  • P waves: No discernable p waves; irregular waves of varying amplitude
  • PR Interval: Unmeasurable
  • QRS: 0.04 – 0.12, consistent
  • P : QRS Ratio: Many : 1
• Atrial Fibrillation (A fib) Risk Factors

  • Increasing age, Hypertension, Diabetes, Obesity, Heart failure, Valvular heart disease, Myocardial infarction, Thyroid, renal, and hepatic disease, Smoking, Exercise, Family history, And more ++
• Atrial Fibrillation (A fib) Presentation

  • Some asymptomatic
  • Loss of atrial kick, SOB, Hypotension, Dyspnea on exertion, Fatigue, Chest pain, Palpitations, Pulse deficit
• Atrial Fibrillation (A fib) Treatment

  • Prevent embolism: Warfarin
  • Control V rate: BB, CCB
  • Converting to NSR: Amiodarone, Electrical cardioversion
  • Cardiac rhythm therapies: Ablation, Maze / Mini-Maze
• Atrial Flutter


  • Impulse origin: Single area in atria
  • Rate: A: 250-400 bpm, V: 75-150 bpm
  • Regularity: A: Regular, V: Can be regular or irregular
  • P waves: Saw-toothed shape
  • PR Interval: Unmeasurable
  • QRS: 0.04 – 0.12, consistent
  • P : QRS Ratio: 2:1, 3:1, or 4:1
• Atrial Flutter Presentation


  • Some asymptomatic
  • Loss of atrial kick, SOB, Hypotension, Chest pain
• Atrial Flutter Treatment


  • Prevent embolism: Warfarin
  • Control V rate: BB, CCB, Vagal maneuvers, Adenosine
  • Converting to NSR: Amiodarone, Electrical cardioversion
  • Cardiac rhythm therapies: Ablation
• Premature Ventricular Complex (PVCs)

  • Impulse origin: Ventricle
  • Rate: A&V: Depends on underlying rhythm
  • Regularity: A: Can be regular, V: Irregular (early QRS)
  • P waves: Some can be hidden by early QRS
  • PR Interval: <0.12 seconds
  • QRS: 0.12 and longer; bizarre/abnormal shape (1 shape = unifocal, >1 shape = multifocal)
  • P : QRS Ratio: 0:1 or 1:1
• Premature Ventricular Complex (PVCs) Causes

  • Substances: Caffeine
• Trigeminy (Q 3 beats) is a type of PVC
• Atrial Flutter Risk Factors

  • Increasing age
  • Hypertension
  • Diabetes
  • Obesity
  • Heart failure
  • Valvular heart disease
  • Myocardial infarction
  • Thyroid, renal, and hepatic disease
  • Smoking
  • Exercise
  • Family history
  • And more ++