How do we monitor anaesthesia? -- ECG

Question 1

1. What does ECG stand for?
2. Indications for the use of ECG?

Answer 1

1. Electrocardiography.
2. • Arrhythmia detected on auscultation.
     - Investigation of syncope.
     - Investigation of suspected CV disease.
     - Monitoring for arrhythmias in sick animals e.g. in ICU.
     - Monitoring during anaesthesia.

Question 2

1. What lead do we run anaesthesia ECG on?
2. What info will be gained from ECG?
3. What can we identify from ECG?
4. What cannot be identified from ECG?
5. How can ECH trace still be seen several minutes after an animal has died?

Answer 2

1. Lead II only.
2. HR and ECG trace.
3. • Cardiac function.
     – HR.
     – Electrolyte imbalances.
     – Myocardial hypoxia.
     – Arrhythmias.
4. Info on CO / myocardial performance or BP.
5. Pulseless electrical activity / Electromechanical Dissociation (EMD).

Question 3

How to attach the ECG limb electrodes to the animal.

Answer 3

• Clips that attach to adhesive pads are placed on the paws.
• Crocodile clips used w/ surgical spirit or ultrasound gel to improve contact. These are painful in the conscious animal.

Question 4

1. Where are the red, yellow, green/black probes placed in small animals?
2. Where are the red, yellow, green/black probes placed in large animals / equines?

Answer 4

1. Red on right fore.
   Yellow on left fore.
   Green/black on left hind.
2. Red on the neck.
   Yellow on sternum.
   Green/black over lateral thorax.

Question 5

1. On ECG, what does the P wave represent?
2. Why is P wave small?
3. On ECG, what does QRS complex represent?
4. Why is the QRS complex so large?

Answer 5

1. Atrial depolarisation, prior to contraction.
2. Atria small in terms of muscle mass.
3. Ventricular depolarisation
4. The ventricles are larger in terms of their muscle mass.

Question 6

1. What does the T wave represent?
2. What if the P wave is tall?
3. What if the P wave is wide?
4. What if the QRS complex is tall?
5. What if the QRS complex us wide?

Answer 6

1. Ventricular repolarisation.
2. Right atrial enlargement.
3. Left atrial enlargement.
4. Hypertrophy.
5. Left bundle branch block may be indicated.

Question 7

1. What if the S wave is deeper?
2. What if the S wave is wider?
3. What us represented by changes in T wave?

Answer 7

1. Right ventricular hypertrophy.
2. Right bundle branch block.
3. Myocardial ischaemia or electrolyte disorders.

Question 8

What are common ECG traces seen with GA?

Answer 8

• Tachycardias.
• Bradycardias.
• Heart block.
• Premature ventricular contractions (VPC / PVC).
• Fibrillation.

Question 9

1. What heart cells give ability to contract?
2. What heart cells give the ability to generate an impulse? – term for this ability?

Answer 9

1. Working myocardial cells.
2. Self-excitatory cells. – automaticity

Question 10

1. What is the dominant pacemaker in the heart and where is it located? – why is it referred to as dominant pacemaker?
2. Where else in the heart could start a beat if needed?

Answer 10

1. Sinoatrial node at the top of the right atrium. — Fastest rate of firing and acts as the conductor for the rest of the heart cells.
2. Atrioventricular node, bundle of His, right and left bundle branches and the Purkinje fibres.

Question 11

What rate of beats can each part of the heart that can start of beat generate?

Answer 11

SA node = 60-160bpm.
AV node = 40-60bpm.
Bundle of His = 40-60bpm.
Bundle branches/Purkinje fibres = 20-40bpm.

Question 12

What is an arrhythmia.

Answer 12

A change in rhythm, rate or origin that differs from the normal cardiac cycle.

Question 13

1st degree AV block.

Answer 13

Electrical struggling to get through and is being held up at the first step of the cycle but still manages to get through so have some delay between P wave and QRS complex (this gap normally closer than gap between QRS complex and T wave.

Question 14

2nd degree AV block.
(2 types)

Answer 14

Wenckebach – progressive lengthening of PR interval until eventually lose beats and the electrical impulse is blocked. The steadiness is a useful warning.
Mobitz – Still have intermittent passage through the AV node but have no pre-warning, meaning PR interval constant until beat just goes and is gone.

Question 15

3rd degree AV block.

Answer 15

Complete heart block so signal will not pass AV node. Fatal as zero CO and therefore no supply to major organs. But other areas of the heart will generate electrical impulse if needed as a safety mechanism, but the signals are weaker and the HR will be slower. The trace will be very irregular due various parts of the heart stepping in.

Question 16

Ventricular tachycardia.

Answer 16

A very rapid HR (complexes close together) caused by very abnormal complexes that have been generated by the ventricles (large and wide trace complexes). Odd normal complex seen some of the time. Can occur prior to arrest.

Question 17

Ventricular premature complex.

Answer 17

Can be caused by high sympathetic tone e.g. caused by pain, excitement, stress, hypoxia, hypercapnia, electrolyte and acid-base disturbances and some drugs.
The odd VPC not clinically significant. But if frequent, multifocal, or in series, can affect BP so treatment may be warranted.

Question 18

1. How does a normal equine ECG trace differ from a small animal patient?
2. Why is it different in this way?
3. Consideration for horses?

Answer 18

1. The QRS complex upside down.
2. A base apex lead system is used as opposed to the traditional limb lead system used in SA spp.
   The leads are in a sagittal plane rather than a frontal plane.
3. Horses have an extensive Purkinje network system, so cannot see changes in the QRS morphology to make interferences about structural changes within the heart. i.e. won’t be able to detect right or left ventricular enlargement.

Question 19

Technical problems with ECG use.

Answer 19

Poor electrical contact.
Leads may fall off.
Electrical interference i.e. diathermy / phones / microwaves.
Movement interference.

Question 20

What should you do if you observe a weird trace on ECG?

Answer 20

Check you have your leads on the correct limbs.
Check the placement of the leads.
Try to print screen shot / video.