ECG
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Questions and Answers

What is the primary function of the ECG machine?

  • To record a graphical record of electric potentials generated by the heart muscle
  • To amplify the potentials detected on the surface of the body (correct)
  • To characterize arrhythmias and conduction disturbances
  • To display the ECG on a special graph paper in voltage and time

    • What is the main difference between a Computer/Portable ECG and an Ambulatory ECG (Holter monitor)?

  • Computer/Portable ECG can characterize arrhythmias, while Ambulatory ECG cannot
  • Computer/Portable ECG records a short period, while Ambulatory ECG records continuously for 24-72 hours (correct)
  • Computer/Portable ECG is used in hospitals, while Ambulatory ECG is used in veterinary clinics
  • Computer/Portable ECG uses electrodes attached to the limbs, while Ambulatory ECG uses multiple leads

    • What is the purpose of an Event monitor?

  • To record only 1 or 2 leads when the patient triggers it during clinical signs (correct)
  • To display the ECG on a special graph paper in voltage and time
  • To record a graphical record of electric potentials generated by the heart muscle
  • To characterize arrhythmias and conduction disturbances

    • What term is used to describe the movement of the waveform away from the baseline in either a positive or negative direction?

    <p>Waveform</p> Signup and view all the answers

    What term is used to describe the line between waveforms?

    <p>Segment</p> Signup and view all the answers

    What term is used to describe the normal cardiac rhythm where depolarization begins at the SA node?

    <p>Sinus rhythm</p> Signup and view all the answers

    What is the term used to describe an abnormal heart rhythm?

    <p>Arrhythmia</p> Signup and view all the answers

    What is the term used to describe an increase in heart rate?

    <p>Tachycardia</p> Signup and view all the answers

    What is the term used to describe a decrease in heart rate?

    <p>Bradycardia</p> Signup and view all the answers

    What does the vertical axis in an ECG represent?

    <p>Amplitude in millivolts</p> Signup and view all the answers

    What does a wider complex on the ECG indicate?

    <p>Fibrosis</p> Signup and view all the answers

    What does the P wave represent in an ECG tracing?

    <p>Discharge of the SA node</p> Signup and view all the answers

    How is left atrial and ventricular enlargement denoted on an ECG?

    <p>Wide and notched P wave</p> Signup and view all the answers

    In small animals, at what paper speed is ECG conventionally recorded?

    <p>50 mm/sec</p> Signup and view all the answers

    What determines if the paper speed for ECG can be 25 mm/sec in small animals?

    <p>Heart rate below 120 beats/min</p> Signup and view all the answers

    What is the sum of all the electrical currents generated by the heart called?

    <p>Cardiac vector</p> Signup and view all the answers

    What is the direction of the cardiac vector perpendicular to?

    <p>The border between depolarized and repolarized areas</p> Signup and view all the answers

    What is the purpose of the Einthoven's triangle?

    <p>To view the heart from different angles</p> Signup and view all the answers

    What does depolarization refer to in the context of cardiac electrophysiology?

    <p>The shift in the electrical charge from negative to positive</p> Signup and view all the answers

    What follows depolarization during an action potential in excitable cells?

    <p>Repolarization</p> Signup and view all the answers

    What determines when the next action potential can occur in cells?

    <p>Refractory period duration</p> Signup and view all the answers

    How are changes in the amplitude, frequency, or shape of signals described in electrophysiology?

    <p>'Deflections'</p> Signup and view all the answers

    Study Notes

    ECG Terminology

    • Heart Rate: number of heartbeats per minute
    • Waveform: movement away from the baseline in either a positive or negative direction
    • Segment: a line between waveforms
    • Interval: a waveform and a segment
    • Complex: several waveforms
    • Tachycardia: increase in heart rate
    • Bradycardia: decrease in heart rate
    • Sinus Rhythm: normal cardiac rhythm where depolarization begins at the SA node
    • Arrhythmia: abnormal heart rhythm

    How ECG Works

    • When cardiac impulses pass through the heart, the electrical current spreads into adjacent tissues
    • Electrodes can record the APs (action potentials)
    • A dipole (positive and negative charge separated by a small distance) can generate local current flow and a small electrical field
    • Standard calibration paper speed is 25 mm/sec in humans, 50 mm/sec in small animals
    • The horizontal axis represents time in milliseconds
    • The vertical axis represents amplitude in millivolts

    ECG Components

    • Each component of an ECG tracing reflects an electrical event occurring in a specific part of the heart
    • The sequence of electrical events follows specific anatomic pathways within the heart
    • In health, these events are precise and consistent
    • ECG evaluation includes determination of heart rate, heart rhythm, and waveform morphology (amplitude and duration)

    ECG Waves and Intervals

    • P Wave: represents depolarization of atrial muscle
    • QRS Complex: represents ventricular depolarization
    • T Wave: represents ventricular repolarization
    • PR Interval: represents the time between P wave and QRS complex
    • QT Interval: represents the time between QRS complex and T wave

    ECG Leads

    • Einthoven's Triangle: electrodes are placed in the 2 arms (RA, LA) and 1 leg (LL)
    • Lead I: records voltage between LA and RA
    • Lead II: records voltage between LL and RA
    • Lead III: records voltage between LL and LA
    • Standard bipolar leads (I, II, and III) provide information on the frontal plane of the heart

    ECG Types

    • In-hospital ECG: computer, portable, Alivecor Vet monitor, KardiaMobile
    • Ambulatory ECG (Holter monitor): records continuously for 24, 48, or 72 hours on multiple leads simultaneously
    • Event monitors: external event monitor and implantable event monitor (implanted subcutaneously)
    • Veterinarian Dr. Vieira's lecture goals:
      • Know the major indications for an ECG
      • Understand ECG terminology
      • List the ECG waves and describe their significance
      • List the most important segments/intervals and their significance

    ECG History

    • Willem Einthoven introduced the term "electrocardiogram" in 1893
    • Einthoven proposed the placement of electrodes for ECG recording, which is now known as Einthoven's Triangle

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