Electrocardiography

• The cardiac cycle describes the series of events that take place in the heart over the duration of a single heartbeat
• The cardiac cycle consists of a period of contraction (systole) and relaxation (diastole)
• The cardiac cycle can be mapped by recording the electrical activity of the heart with each contraction using an electrocardiograph to generate an electrocardiogram
• Each normal heart beat should follow the same sequence of electrical events:

  • The P wave represents depolarisation of the atria in response to signalling from the sinoatrial node (atrial contraction)
  • The QRS complex represents depolarisation of the ventricles (ventricular contraction), triggered by signals from the AV node
  • The T wave represents repolarisation of the ventricles (ventricular relaxation) and the completion of a standard heart beat
• Intervals allowing for blood flow in the cardiac cycle include the PR interval and ST segment
• Data generated via electrocardiography can be used to identify various heart conditions, including:

  • Tachycardia (elevated resting heart rate = >120 bpm)
  • Bradycardia (depressed resting heart rate = <40 bpm)
  • Arrhythmias (irregular heartbeats)
  • Fibrillations (unsynchronised contractions of either atria or ventricles leading to dangerously spasmodic heart activity)