EKG I and II

Question 1

Limb leads

• Bipolar limb leads
• Augmented limb leads
• Precordial leads

Answer 1

• Bipolar limb leads
  
  • Lead I: right arm -, left arm + (0)
  • Lead II: right arm -, left leg + (+60)
  • Lead III: left arm -, left leg + (+120)
• Augmented limb leads
  
  • Lead aVR: right arm + (-150)
  • Lead aVL: left arm + (-30)
  • Lead aVF: left leg + (+90)
• Precordial leads
  
  • Leads V1 & V2: right side
  • Leads V3 & V4: middle
  • Leads V5 & V6: left side
• Positve (upward) deflection: signal moves toward positive electrode

Question 2

Waves

• P wave
• PR interval
• QRS complex
• T wave
• QT interval
• ST segment
• Increased signal size
• Decreased signal size

Answer 2

• P wave
  
  • Atrial contraction (systole)
  • Atrial tissue depolarization propagates inferiorly & leftward –> upward deflection
• PR interval
  
  • Time required for the wave to pass through atrium & AV node before ventricular activation
  • Normal = 120-200ms
• QRS complex
  
  • Ventricular depolarization
    
    • Q wave: downward component
    • R wave: upward component
    • S wave: downward component
  • Normal ≤ 100 ms
  • Incomplete bundle branch block = 100-200 ms
  • Bundle branch block > 100 ms
• T wave
  
  • Repolarization of the ventricle
• QT interval
  
  • Ventricular depolarization & repolarization
  • Normal < 440 ms
  • Correction: QTc = QT / √(preceding RR interval (s))
    
    • At HR = 60, QT = QTc
• ​​​ST segment
  
  • ​Diagnoses ischemia & myocardial injury
• Increased signal size
  
  • Muscular hypertrophy
• Decreased signal size
  
  • Loss of functioning muscle, heart attack

Question 3

Calibration

• Measure
• Normal

Answer 3

• Measure
  
  • Rectangular square wave
    
    • 5 mm wide
    • 10 mm high
  • Lead II = Lead I + Lead III
  • Lead I ≈ V6
• Normal
  
  • Paper speed = 25 mm/s
  • Gain setting = 10 mm/mV
  • Small box = 1mm = 40ms
  • Large box = 5mm = 200ms

Question 4

Heart rate

• Measure
• Normal
• Abnormal

Answer 4

• Measure
  
  • 60,000ms/min / (40ms * # small boxes)
  • Large boxes: 300 - 150 - 100 - 75 - 60
  • (# QRS in 6s strip) * 10
• Normal
  
  • HR = 60-100 bpm
• Abnormal
  
  • HR < 60 bpm: bradycardia
  • HR > 100 bpm: tachycardia

Question 5

Axis

• Measure
• Normal
• Abnormal

Answer 5

• Measure
  
  • Avg direction of electrical vector
  • Horizontal: Lead I (+ = right)
  • Vertical: Lead aVF (+ = down)
• Normal
  
  • Normal: -30 to +110
  • Positive Lead I & aVF
• Abnormal
  
  • -30 to -90: left axis deviation
  • +110 to +180: right axis deviation
  • +180 to =90: indeterminate axis

Question 6

Rhythm

• Normal
• Abnormal

Answer 6

• Normal
  
  • Sinus rhythm
  • HR = 60-100 bpm
  • • P wave in Lead II
• Abnormal
  
  • No clear P, irregularly irregular QRS: atrial fibrillation
  • Long QRS, normal HR: slow ventricular (accelerated idioventricular) rhythm
  • Long QRS, high HR: fast ventricular rhythm (ventricular tachycardia)

Question 7

P wave

• Normal
• Abnormal

Answer 7

• Normal
  
  • Always precede QRST
  • Always followed by QRST
• Abnormal
  
  • Prolongation of consecutively conducted P before dropped QRS: Mobitz Type I AV (Wenkebach) block
  • Dropped QRSs w/ no PR prolongation: Mobitz Type II AV block
  • Regular HR but no conducted P: 3^o AV block
  • Tall (>2.5) peaked P in II, >1.5 in V1 & V2: right atrial abnormality
  • Long (>4) P in II, negative P in V1: left atrial abnormality

Question 8

QRS complex

• Measure
• Normal
• Abnormal

Answer 8

• Measure
  
  • (Small boxes containing big & small peak) * 40
• Normal
  
  • QRS < 100ms
• Abnormal
  
  • QRS = 100-120ms: incomplete BBB or conduction delay
  • QRS > 120ms: bundle branch block
  • Rabbit ears in V1 & V2, wide S in I, V5, & V6: right (I)BBB
  • Broad/notched R & absent Q in I, V5, & V6: left (I)BBB / intraventricular conduction delay
  • LAD, aR in I & aVL, rS in II, III, & aVF: left anterior fascicular (hemi)block
  • RAD, rS in I & aVL, aR in II, III, & aVF: left posterior fascicular block
  • |R| in V1 > |S| in V1: right ventricular hypertrophy
  • Large |R| in V5 or V6: left ventricular hypertrophy
  • Long (>1) large (25% of total QRS height) Q: infarction

Question 9

PR interval

• Measure
• Normal
• Abnormal

Answer 9

• Measure
  
  • (Small boxes b/n P & R) * 40
• Normal
  
  • PR = 120-200ms
• Abnormal
  
  • PR < 120ms: accelerated AV conduction (Wolf-Parkinson-White Syndrome)
  • PR > 200ms: 1^o AV block

Question 10

QT interval

• Measure
• Normal
• Abnormal

Answer 10

• Measure
  
  • (Small boxes b/n Q & T) * 40
  • QTc = AT / √(RR interval)
• Normal
  
  • QTc < 440ms
• Abnormal
  
  • QTc << 440ms: hypercalcaemia
  • QTc > 440ms: hypocalcaemia

Question 11

ST segment & T wave

• Abnormal

Answer 11

• Abnormal
  
  • T inversion: ischemia
  • ST elevation: injury, acute infarction
    
    • With PR depression: pericarditis
    • With tall peaked T: early repolarization
    • With tall narrow peaked T: hyperkalemia
  • ST depression
    
    • ​With T inversion: Digoxin therapy
    • With short T, U waves: hypokalemia