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ECG Curve Mechanism

Mechanism of ECG wave

Main Ventricular Vector

Mechanism of ecg electrical vectors
  • First, the thin ventricular septum is activated
    • A small septal vector (VS) is formed
    • Q wave
  • Then, the massive left ventricle is activated
    • A large main vector (VM) is formed
    • Simultaneously, the thin right ventricle is also activated
      • Small right ventricular vector
      • does not affect the direction of the main vector
    • R wave
  • Finally, the base of the left ventricle is activated
    • A small terminal vector (VT) is formed
    • S wave

  • You must imagine the vectors in 3D space
    • ECG leads record the vectors over time

ECG Leads

Wilson central terminal - electrical center of the heart and 12 ECG leads

Electrical Axis of the ECG Lead

Electrical axis of ECG lead with positive and negative pole
  • Each ECG lead has an electrical axis
  • Electrical vectors of the heart are projected onto the electrical axes of the ECG leads
    • and an ECG waveform is generated
    • Electrical vectors do not always originate from the central terminal

Positive and Negative ECG Deflection

Voltage vector projection on ECG with positive and negative deflection

Magnitude of the ECG Deflection

The magnitude of the deflection. Angle between vector and lead axis
  • The magnitude of the ECG deflection
    • depends on the angle between the vector and the axis of the ECG lead

  • The smaller the angle
    • the more directly the vector points towards the electrode (+)

Isoelectric ECG Deflection

Perpendicular voltage vector to the lead axis and no ECG deflection

Biphasic ECG Deflection

Continuously changing resultant voltage vector during heart cycle and ECG deflection
  • The myocardium depolarizes gradually
    • The electrical vector often rotates around a single point
    • e.g., ventricular depolarization
  • The ECG lead records vectors sequentially and generates the ECG curve
    • The 1st vector points away from the electrode (+)
    • The 2nd vector is perpendicular to the electrode (+)
    • The 3rd vector points towards the electrode (+)
    • Gradually, a biphasic ECG deflection is produced

Predominantly Positive ECG Deflection

Predominantly positive ECG deflection with vector rotation

Predominantly Negative ECG Deflection

Predominantly negative ECG deflection with vector rotation
  • The ECG curve captures 4 electrical vectors over time
  • The perpendicular vector is the boundary between the negative and positive deflections

ECG and Ventricular Vectors


Main electrical voltage vector during depolarization and ECG deflection in limb leads

Limb Leads


Main electrical voltage vector during depolarization and ECG deflection in chest leads

Chest Leads



ECG deflection during sinus rhythm

Sinus Rhythm

  • The ECG shows a sinus rhythm
  • Notice how the height of the QRS complexes changes in different leads



Sources

  • ECG from Basics to Essentials Step by Step
  • litfl.com
  • ecgwaves.com
  • metealpaslan.com
  • medmastery.com
  • uptodate.com
  • ecgpedia.org
  • wikipedia.org
  • Strong Medicine
  • Understanding Pacemakers





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Home /

ECG Curve Mechanism

Mechanism of ECG wave

Main Ventricular Vector

  • First, the thin ventricular septum is activated
    • A small septal vector (VS) is formed
    • Q wave
  • Then, the massive left ventricle is activated
    • A large main vector (VM) is formed
    • Simultaneously, the thin right ventricle is also activated
      • Small right ventricular vector
      • does not affect the direction of the main vector
    • R wave
  • Finally, the base of the left ventricle is activated
    • A small terminal vector (VT) is formed
    • S wave

  • You must imagine the vectors in 3D space
    • ECG leads record the vectors over time
Mechanism of ecg electrical vectors

ECG Leads

  • An ECG recording has 12 leads
    • Limb leads (I, II, III, aVF, aVL, aVR)
    • Chest leads (V1-V6)
    • Each lead "views" the vectors from a different angle
  • The leads "view" the electrical center of the heart
  • If the electrical vector is directed
    • Toward the surface lead - a positive deflection is formed
    • Away from the surface lead - a negative deflection is formed
Wilson central terminal - electrical center of the heart and 12 ECG leads

Electrical Axis of the ECG Lead

Electrical axis of ECG lead with positive and negative pole

  • Each ECG lead has an electrical axis
  • Electrical vectors of the heart are projected onto the electrical axes of the ECG leads
    • and an ECG waveform is generated
    • Electrical vectors do not always originate from the central terminal


Voltage vector projection on ECG with positive and negative deflection

Positive and Negative ECG Deflection

  • The heart's electrical vector
    • must always be projected onto the electrical axis of the ECG lead

  • A positive ECG deflection occurs
    • if the vector is directed towards the surface electrode (+)
  • A negative ECG deflection occurs
    • if the vector is directed away from the surface electrode (+)


The magnitude of the deflection. Angle between vector and lead axis

Magnitude of the ECG Deflection

  • The magnitude of the ECG deflection
    • depends on the angle between the vector and the axis of the ECG lead

  • The smaller the angle
    • the more directly the vector points towards the electrode (+)


Perpendicular voltage vector to the lead axis and no ECG deflection

Isoelectric ECG Deflection

  • If the vector is perpendicular to the lead axis
    • then no ECG deflection occurs

  • However, the electrical vector is "observed" by 12 ECG leads
    • Each ECG lead has a different direction of the electrical axis
    • the same vector is never isoelectric in all leads


Continuously changing resultant voltage vector during heart cycle and ECG deflection

Biphasic ECG Deflection

  • The myocardium depolarizes gradually
    • The electrical vector often rotates around a single point
    • e.g., ventricular depolarization
  • The ECG lead records vectors sequentially and generates the ECG curve
    • The 1st vector points away from the electrode (+)
    • The 2nd vector is perpendicular to the electrode (+)
    • The 3rd vector points towards the electrode (+)
    • Gradually, a biphasic ECG deflection is produced


Predominantly positive ECG deflection with vector rotation

Predominantly Positive ECG Deflection

  • The ECG curve records 4 electrical vectors over time
  • The perpendicular vector is the boundary between the negative and positive deflections


Predominantly negative ECG deflection with vector rotation

Predominantly Negative ECG Deflection

  • The ECG curve captures 4 electrical vectors over time
  • The perpendicular vector is the boundary between the negative and positive deflections

ECG and Ventricular Vectors

Main electrical voltage vector during depolarization and ECG deflection in limb leads Main electrical voltage vector during depolarization and ECG deflection in chest leads

Limb Leads

Chest Leads


ECG deflection during sinus rhythm

Sinus Rhythm

  • The ECG shows a sinus rhythm
  • Notice how the height of the QRS complexes changes in different leads



Sources

  • ECG from Basics to Essentials Step by Step
  • litfl.com
  • ecgwaves.com
  • metealpaslan.com
  • medmastery.com
  • uptodate.com
  • ecgpedia.org
  • wikipedia.org
  • Strong Medicine
  • Understanding Pacemakers