Updated: 7/4/2019

Electrocardiogram (ECG)

0%
Topic
Review Topic
0
0
N/A
N/A
Questions
4 4
0
0
0%
0%
Videos
1 1
https://upload.medbullets.com/topic/108017/images/080817vldcardiacheartexcitation.jpg
https://upload.medbullets.com/topic/108017/images/04042018mdstep1ecgecganatomy.jpg
https://upload.medbullets.com/topic/108017/images/04032018mdstep1cardslimbleadsupdated.jpg
https://upload.medbullets.com/topic/108017/images/04042018mdstep1ecgdeflectionleadi.jpg
https://upload.medbullets.com/topic/108017/images/04042018mdstep1ecgprecordialleadsupdated.jpg
Introduction
  • The electrocardiogram (ECG) records the flow of electrical impulses throughout the heart
  • Electrical currents flow from negatively charged areas to positively charged areas
    • depolarization currents flowing towards a positive electrode will lead to an upward deflection seen in the ECG reading 
    • repolarization currents flowing away from the positive electrode will lead to a downward deflection seen in the ECG reading 
    • the ECG records the sum of the electrical forces that flow through the heart
      • the ECG deflections depend on how these electrical forces align to a specific ECG lead 
        • e.g., lead aVR, a right-arm electrode, will demonstrate a positive deflection when electrical activity points towards the right arm 
C1: Snapshot: Y
C2: Content/grammar: Y
C3: Images/Videos: N
C4: Questions: Y
C5: References: N
ECG Lead Reference
  • There are 6 limb leads and 6 chest lead, which comprise the 12-lead ECG 
    • limb leads 
      • aVR, aVL, and aVF
      • I, II, III
      • the limb leads read electrical forces in the frontal view
    • chest (precordial) leads 
      • V1-V6
      • the precordial leads read electrical forces in the perpendicular plane
Conduction Pathway
  • Depolarization normally begins at the sinoatrial (SA) node 
    • the SA node is located at the junction of the superior vena cava and right atrium
  • Depolarization from the SA node spreads to the right and left atria
  • After the right and left atria, the wave of depolarization reaches the atrioventricular (AV) node
    • there is an expected delay in the transmission of depolarization to the ventricles at the AV node
  • The impulse then goes to the bundle of His and then the right and left Purkinje fibers
  • Pacemaker rates
    • SA > AV > bundle of His/Purkinje/ventricles
  • Speed of transmission
    • bundle of His = Purkinje fibers > atria > ventricles > AV node
ECG And Conduction Pathway 
 
ECG Basics
ECG Finding
Information
P wave
  • Represents atrial depolarization
PR interval
  • Represents the time from the start of atrial depolarization to the start of ventricular depolarization
  • Normally < 200 msec
QRS complex 
  • Represents ventricular depolarization
  • Normally < 120 msec
ST segment
  • Represents an isoelectric point in ventricular depolarization
  • Correlates with phase 2 (plateau) of ventricular action potential 
T wave 
  • Represents ventricular repolarization
  • Becomes peaked in hyperkalemia and flattened in hypokalemia 
U wave
  • Believed to represent ventricular repolarization but during the late phase
  • Becomes prominent in hypokalemia
J point
  • The point between the end of the QRS complex and the beginning of the ST segment
 
 

Please rate topic.

Average 5.0 of 10 Ratings

Questions (4)
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Evidence (1)
VIDEOS (1)
Topic COMMENTS (13)
Private Note