Week 6

• What does an electrocardiogram (ECG) record?

  Electrical changes at the skin surface resulting from depolarisation and repolarisation of the heart muscle

  
• Who developed the ECG and when?

  Einthoven developed the ECG at the start of the 20th century
• How did Waller demonstrate the use of the ECG?

  By immersing his pet bulldog's paws in saline and connecting electrodes to a galvanometer
• What is the purpose of ECG electrodes?

  To record action potentials generated by the conduction system of the heart
• What does the ECG machine print out?

  Electrical waveforms, often called an ECG trace
• Do ECGs have limitations?

  Yes, ECGs have many limitations
• How can limitations of ECGs be potentially overcome?

  By changing the paper speed
• What should be done if ECG machines do not provide requisite information?

  Rely on more advanced equipment, such as echocardiography
• Is it possible for a person to have a heart attack and still have a normal ECG?

  Yes, it is possible
• What is the current management option for a patient presenting with symptoms of a heart attack?

  They are sent straight for echocardiography
• Can ECGs be used in isolation for a definitive diagnosis?

  No, confirmation is required by more advanced procedures
• Why are artefacts likely to occur on an ECG?

  Because ECG electrodes record action potentials from other muscle tissues if a person moves
• What does ECG paper consist of?

  • Horizontal and vertical lines measuring duration and amplitude
  • Large squares with thick red lines and small squares with thin red lines
  • Each large square comprises 25 small squares

  
• What is the area of each small square on ECG paper?

  The area is $1 \text{ mm}^2$
• What happens if the ECG machine is set at a higher speed?

  The trace will display waves not visible at a lower speed
• What is the normal paper speed for an ECG machine?

  25 mm/sec
• Where must ECG electrodes be placed for accurate recordings?

  In the correct position on the body
• What are the limb electrodes placed on?

  The right arm, left arm, left leg, and the right leg as an earth electrode
• What does the P wave represent in an ECG?

  Atrial depolarisation
• What does the PR interval indicate?

  The time between atrial depolarisation and ventricular depolarisation
• What does the Q wave represent?

  Normal left-to-right depolarisation of the interventricular septum
• What does the R wave indicate?

  Ventricular depolarisation
• What does the T wave represent?

  Ventricular repolarisation
• What is the U wave thought to represent?

  Purkinje repolarisation
• What does the J wave indicate?

  The end of depolarisation and the beginning of repolarisation
• What does the ST segment represent?

  The interval between ventricular depolarisation and repolarisation
• What is the J point?

  The approximate end of depolarisation and the beginning of repolarisation
• What does the QRS complex represent?

  Ventricular contraction
• How does heart rate vary?

  It changes with day-to-day activities and varies between genders
• What is the normal heart rate range?

  60 – 100 bpm
• What is tachycardia?

  A heart rate greater than 100 bpm
• What is bradycardia?

  A heart rate less than 60 bpm
• How is rhythm analyzed in an ECG?

  By looking at a rhythm strip, usually from Lead II
• What is the purpose of the rhythm strip in a 12-lead ECG?

  It is usually a 10-second recording from Lead II
• What are the steps to analyze rhythm in an ECG?

  1. Determine if the rate is normal, tachycardia, or bradycardia
  2. Examine the pattern of QRS complexes for regularity
  3. Assess QRS morphology as narrow or wide
  4. Check for presence or absence of P waves
  5. Evaluate response to vagal manoeuvres

  
• What does a narrow QRS complex indicate?

  Sinus, atrial, or junctional origin
• What does a wide QRS complex indicate?

  Ventricular origin or supraventricular conduction
• What do absent P waves suggest?

  Sinus arrest or atrial fibrillation
• What do present P waves indicate?

  Morphology and PR interval may suggest sinus, atrial, junctional, or retrograde from the ventricles
• How does sinus tachycardia respond to vagal manoeuvres?

  It gradually slows during the manoeuvre but resumes on cessation