ECGs

• Why is cardiac muscle described as myogenic?

  can initiate its own contraction and the muscles contract and relax even when not connected to the rest of the body
• What is fibrillation?

  unsynchronised contractions
• Why does the heart need a mechanism of coordinating contractions in all four chambers?

  atrial muscles contract more frequently than ventricular muslce -> causes fibrillation
• Which node controls the cardiac cycle and what does it do?

  the sinoatrial node (a small patch of myogenic muscle in the walls of the right atrium) and it acts as a pacemaker
• Why are delays important in impulse conduction during the cardiac cycle?

  to ensure the atria are completely empty and have stopped contracting before the ventricles contract
• What are the steps for the coordination of the heart cycle?

  1. SAN initiates a wave of excitation
  2. Wave of excitation spreads over atrial wall
  3. wave reaches AVN
  4. Atrial systole as both atria contract in a synchronised manner
  5. delays the wave of excitation at AVN due to non-conducting tissue
  6. excitation spreads down the bundle of His (septum) and splits into Purkinje fibres running up each ventricle wall
  7. ventricular systole from the apex of heart and spread upwards
• What do electrocardiograms do?

  + monitor electrical activity in heart (via skin)

  + can diagnose heart problems
• How do electrocardiograms work?

  sensors pick up excitation created by heart and convert them into trace
• ECG I

  The electrical wave that spreads from the SAN across the atria and which causes atrial systole

  A) P wave

  
• ECG II

  The interval time taken for the electrical wave to be conducted from the SAN to the ventricles, via the AVN.

  A) P wave

  B) PR interval

  
• ECG III

  ventricular systole - wave of excitation spreads across ventricles

  A) Q

  B) R

  C) S

  
• What is your heart rate?

  beats per minute
• ECG IV

  The interval time between the end of ventricular wave and the start of the wave to reset the ventricles

  A) T wave

  B) ST segment

  
• ECG V

  the wave resetting the ventricles during diastole

  A) T wave

  
• Describe a normal ECG trace.

  60-100bpm; evenly spaced; defined p, qrs, t waves

  
• What is bradycardia and how does it look on an ECG trace?

  + abnormally slow heart rate <60 bpm, but evenly spaced

  + increased fitness means heart pumps more blood with each contraction -> fewer beats required per minute

  + associated with athletic training, fainting attacks and hypothermia

  
• What is tachycardia and how does it look like on an ECG trace?

  + fast heart beat >100 bpm, evenly spaced

  + associated with exercise, fear, pain and haemorrhage

  
• What is atrial fibrillation? 


  + most common type of arrythmia (abnormal rhythm)

  + atria contract more frequently than ventricles (no clear p-wave and irregular baseline)

  + not all waves passed to ventricles so blood not effectively pumped

  + normal QRS shape (irregular beat of 75-190 bpm) -> normal conduction in AV node

  
• What is an ectopic heartbeat?


  + third beat is early ventricular beat which feels like a missing beat or extra beats e.g. palpitation

  + ectopic - unexpected event occurring out of sequence

  + P waves or QRS complexes occur out of sync with the rest of ECG

  
• What is ventricular fibrillation?

  + caused by problem in heat's electrical properties or disruption of normal blood supply to heart tissue

  + no discernible pattern (no QRS, P or T wave)

  + patients very likely to lose consciousness and needs urgent defibrillation