Electrocardiogram (ECG)

• An electrocardiogram (ECG) is a recording of the changes in the electrical potential difference of the heart, which occur during depolarization and repolarization of the myocardial cells and are plotted against time.
• The body itself is a conduction system therefore this activity can be monitored from electrodes placed on the surface.

Uses

• Documentation and analysis of cardiac arrhythmias.
• Monitoring, eg heart rate and rhythm during general anesthesia or drug therapy (rarely).

Advantages

• Non-invasive.
• Relatively easy to perform.
• Can permanently document dysrhythmias that may also be difficult to definitively diagnose on auscultation alone.
• Can be used for long-term heart rate and rhythm recording to diagnose intermittent dysrhythmia in the investigation of collapse (rarely performed in cattle).
• Can be used throughout anaesthesia to monitor cardiac function.

Disadvantages

• Many potential sources of artefacts, e.g:
  • Electrical interference, e.g. poor electrode contact, improper grounding, other electrical equipment, fluorescent lighting, patient in contact with damp or metal surface.
  • Patient movement, e.g. muscle tremor, shivering, breathing, moving.
  • Interference from holder.
• There is no useful information on cardiac chamber size from measurement of the height and duration of the components of large animal ECG in contrast to companion animal species.

Technical problems

• Operator must be able to identify artifacts and adjust equipment accordingly.

Alternative techniques

• Auscultation: is first line technique to identify Dysrhythmias Dysrhythmias, to measure heart rate and identify heart murmurs.

Time required

Preparation

• A few minutes to attach electrodes and assess quality of trace, may need to clip very hairy animals.

Procedure

• Length of time depends on investigation required.
  • An animal being monitored through general anaesthesia will need a longer monitoring period.
  • Experience will make little difference to this once a consistent quality trace is obtained.
• Even for short duration monitoring a representative trace, free from artefacts that reflects an appropriate resting heart rate should be obtained.