Sinus Rhythm

• Describe the P wave

  Small, rounded, 2.5 mm, 0.08 - 0.12 sec in duration, positive waveform in lead II and biphasic in V1, atria thin-walled structures approximately 1mm in thickness, representing atrial depolarisation.
• Represents ventricular depolarisation, 0.12 sec in duration (3 small squares), rS complex in V1, R wave progression, qR complex in V6, demonstrates the increasing wall thickness of the ventricular myocardium from right to left, heart depolarises from endocardium to epicardium
• Describe T wave

  Ventricular repolarisation, asymmetrical, slow ascending limb, steep descending limb, heart repolarises outside to inside i.e. epicardium to endocardium
• What are things to consider when looking at the morphology of ECG?

  • Position of Electrode
  • Orientation of patient's heart within the thorax e.g pregnant lady, elderly
  • Thickness of myocardium - more myocardium equals more electroactivity
  • The speed at which the heart changes polarity from positive to negative
  • Rate of depolarisation and repolarisation
• Describe the SA node

  The SA node is the heart's intrinsic pacemaker. They are up the right atrium, to the entrance of the SVC. 15ml long and 3ml wide. Has the ability to spontaneously depolarise. More innervated with sympathetic nervous system than parasympathetic
• Describe the AV node. 


  The AV node sits low in the right atrium, down by the septum's intake. It slows down conduction because the atria have just been stimulated. We need the atria to contract before the ventricles contract. The AV node will slow down; conduction will have a lower velocity than the atria. It will then come down the bundle of HIS. Then, it will bifurcate to the left and right bundle branches and travel down the Purkinje fibres.
• What's the only electrical connection with the upper and lower chambers?

  Bundle of HIS
• Can electro activity be seen at the Sa node?

  No, as it is too small to be detected from the skin surface (about -90 millivolts).
• What are the limb leads and their potential difference?

  Lead 1 - Right arm to left arm: Right arm positive, left arm negative

  Lead 2 - Right arm to left leg (foot): Right arm negative, left foot positive

  Lead 3 - Left arm to left foot: Left arm negative. left foot positive

  aVR - Right arm

  aVL - Left arm

  aVF - Foot
• What does equiphasic/biphasic mean?

  As much positive as negative
• What does P wave being notched mean?

  Atrial dilation
• What does tall peaked P wave represent?

  People with hypertension or large right atrium
• What does it mean when right atrium component is bigger than the left one?


  Right atrium enlargement. If the left atria was bigger than the right atria, it would suggest left atria enlargement.
• What is PR interval?


  The time from atrial depolarisation to ventricular depolarization can also be defined as the beginning of the P wave to the first positive or negative deflection. When the atria have made its way from the AV node down a bundle of HIS and have bifurcated, then arrived at the Purkinje fibre.
• What should PR interval be?


  0.12 - 0.2 (three small squares to five small squares/1 big square).
• Q wave duration?


  Less than 0.04. It can't be more than 0.04
• Explain progression (R wavw).


  When the chest electrodes moves from right to left, and they do, the amplitude of the R wave gets bigger. Peak in 4 dip in 5 and 6 or peak in 5 and dip in 6. R wave amplitude dips in V4, which will cause the amplitude of V5 to dip a little bit.