Cardiovascular (5)

• Pacemaker


  • Also called sinoatrial node and atrioventricular node
  • Found in upper part of right atrium
  • Sinoatrial node (SA) near entry of vena cava
  • Atrioventricular node (AV) at lower end of atrial septum
  • Paces the atrial and ventricular networks
• Sympathetic nerve stimulation


  Increases rate of rise of pacemaker potential and heart rate
• Parasympathetic nerve (vagus) stimulation


  Decreases rate of rise of pacemaker potential and heart rate
• Circulating catecholamines


  Increase rate of rise of pacemaker potential and heart rate, e.g. noradrenaline increases muscle contractility, increasing stroke volume
• Reading an ECG (Part 1)


  P point caused by depolarization of atrial contractile fibers, atrial systole causes wave to level off
• Reading an ECG (Part 2)


  QRS complex caused by depolarization of ventricular contractile fibers, ventricular systole causes leveled off S-T segment
• Reading an ECG (Part 3)


  T wave caused by repolarization of ventricular contractile fibers, ventricular diastole causes T wave to level off