ECGs

Question 1

Indications to carry out an ECG?

Answer 1

• Bradycardia.
• Tachycardia.
• Irregular heart rhythm.
• Pulse defects.
• (Syncope, weakness).
• ECGs do not determine cause, only tell you what the arrhythmia is.

Question 2

1. Normal HR range in dogs.
2. Normal HR range in cats.

Answer 2

1. 60-120bpm.
2. 120-240bpm.

Question 3

1. Electrodes attached to the patient for ECG.
2. What do the leads provide?
3. What do waves of depolarisation and re-polarisation provide?
4. Angle on re- or depolarisation wave and size of vector/deflection.

Answer 3

1. Red on right forelimb.
   Yellow on left forelimb.
   Green on left hindlimb.
   Black on right hindlimb.
2. Different views of the same electrical activity in the heart.
3. Vector (from de- and repolarisation waves moving in opposite directions).
4. If parallel to wave direction, larger.
   If at angle e.g. 90 degrees, smaller or tiny.

Question 4

ECG from human med perspective…
1. Lead I.
2. Lead II.
3. Lead III.

Answer 4

1. RA to LA.
2. RA to LL.
3. LA to LL.
   *number of Ls.

Question 5

1. Where does normal depolarisation in heart start?
2. Then where does most of the depolarisation travel to?
3. So which lead is parallel to this path?

Answer 5

1. Right atrium (SA node).
2. Left ventricle (site of most myocardial tissue).
3. Lead II.

Question 6

ECG fills in gaps between actual leads.

Answer 6

Augmented limb leads:
- aVR towards right arm.
- aVL towards left arm.
- aVF towards the feet.
So now have 6 leads at 60 degrees to each other instead of 3 leads at 120 degrees to each other.

Question 7

1. Which leads are “below the horizon”?
2. Which leads are “on the horizon”?
3. Which leads are “above the horizon”?

Answer 7

1. III, aVF, II.
2. I.
3. aVR, aVL.

Question 8

1. SA node location.
2. AV node location.
3. Bundle of His location.
4. Purkinje fibres location.

Answer 8

1. Roof of right atrium.
2. AV valve.
3. Septum - has a left branch bundle and a right branch bundle.
4. Apex of the heart.

Question 9

1. P wave.
2. PQ.
3. QRS.
4. T.

Answer 9

1. Atrial depolarisation.
2. Time in AV node (purposely slower).
3. Ventricular depolarisation.
4. Ventricular repolarisation.

Question 10

ECG analysis.

Answer 10

• HR.
• Overall rhythm:
  – regular, regularly irregular, irregular.
• P for every QRS, QRS for every P:
  – consistently and reasonably related.
• Complex morphology:
  – most important –> do QRS look normal (narrow and positive in lead II) or wide and bizarre?
• Final ECG Dx:
  – e.g. 3rd degree AV block.

Question 11

HR on ECG…
1. Average HR best for?
2. Calculating average HR?
3. Instantaneous HR best for?
4. Calculating instantaneous HR?

Answer 11

Average HR.
1. - best for irregular rhythms (e.g. sinus arrhythmia, atrial fibrillation).
2. - count number of R waves over a set period of time.
- Bic biro (w/ cap on) is 15cm long.
– 50mm/s = 3 secs (multiply no. complexes by 20).
– 25mm/s = 6 secs (multiply no. complexes by 10).
Instantaneous HR.
3. - best for regular rhythms (e.g. sinus rhythm, 3rd degree AV block), deciding whether a complex is premature.
4. - Measure distance between consecutive R waves in mm (small boxes on ECG paper).
– 50mm/s = 3000/ no. small boxes.
– 25mm/s = 1500/ no. small boxes.

Question 12

Considerations once HR calculated?

Answer 12

• Is it normal?
• Is it bradycardic?
• Is it tachycardic?
• Is the trace appropriate for the situation?

Question 13

1. Regular and slow cardiac rhythm.
2. Normal rate and regular cardiac rhythm.
3. Regular and fast cardiac rhythm.
4. Regularly irregular cardiac rhythm.
5. Irregularly irregular cardiac rhythm.

Answer 13

1. Sinus bradycardia.
   3rd degree AV block.
2. Sinus rhythm.
3. Supraventricular tachycardia.
   Ventricular tachycardia.
4. Sinus arrhythmia (more normal in dogs than cats).
5. Atrial fibrillation.

Question 14

1. Slow and irregular cardiac rhythms.
2. Normal rate and irregular cardiac rhythm.
3. Fast and irregular cardiac rhythms.

Answer 14

1. • Sinus arrhythmia.
     - 2nd degree AV block.
2. • Sinus arrhythmia.
3. • Atrial fibrillation.
     - Frequent supraventricular/ventricular premature complexes.

Question 15

What if P waves and QRS complexes are not consistently or reasonably related?

Answer 15

Atrioventricular (AV) blocks preventing normal travel of impulses through from the atria to the ventricles.
*remember PQ = interval of time where AV nodal conduction is happening.

Question 16

1. 1st degree AV block.
2. 2nd degree AV block.
3. 3rd degree AV block.

Answer 16

1. • All P waves conducted – QRS for every P.
     - Increased PQ interval.
2. • Some, but not all, P waves conducted.
     - Type I – progressive increase in PQ interval followed by a dropped QRS (associated w/ high vagal tone).
     - Type II – fixed PQ interval (associated w/ pathology w/in AV node).
3. No P waves conducted.

Question 17

Back up pacemakers (ventricular escapes).

Answer 17

Fire at decreasing rates as go down the conduction system.
Move further down the conduction system the more severe the disease.
The lower the heart rate, the more severe/progressed the disease.

Question 18

Supraventricular vs ventricular complexes.

Answer 18

Supraventricular (either from SA node or atrial myocardium) = narrow.
- Anything starting in the atrium, come through the AV node and using the specialised conduction system which is v fast, meaning the ventricle depolarises v close together.
- e.g. sinus tachycardia, SV premature complexes, SV tachycardia (atrial fibrillation).
Ventricular (either from back up pacemakers or ventricular myocardium) = much wider.
- Anything from the ventricular myocardium conducts cell-to-cell instead using conduction system so is much slower and therefore wider on trace.
- e.g. ventricular premature complexes, ventricular tachycardia, accelerated idioventricular rhythm (<180bpm).

Question 19

1. Atrial fibrillation….
2. In comparison to other supraventricular tachycardias.

Answer 19

1. • Irregular supraventricular rhythm.
     - No P waves.
2. Others are regular and have P waves present (but these are often hidden in the QRS complex).

Question 20

Ventricular tachycardia.

Answer 20

• > 3 ventricular premature complexes in a row.
• Have singles, couplets, triplets, or runs of ventricular tachycardia.
• Complexes go straight from R wave into T wave, back into T wave, back into R wave……

Question 21

Accelerated idioventricular rhythm.

Answer 21

• > 3 ventricular escape complexes in a row.
• Usually associated w/ systemic disease.
  – Splenic mass / torsion, GDV, sepsis etc.
  – Treat the underlying cause.

Question 22

When to treat arrhythmias.

Answer 22

Check for underlying disease (cardiac or systemic).
Always stabilise heart failure!
Clinical signs: weakness, collapse, poor output signs (pulses, perfusion).
HR, frequency of arrhythmia, malignancy.
Antiarrhythmic drugs can be pro-arrhythmic – do not use unless needed.

Question 23

Treatment of bradyarrhythmia.
E.g. 3rd degree AV block, high grade 2nd degree AV block.

Answer 23

Medical:
- Vagolytics:
– Atropine, glycopyrrolate.
- Sympathomimetics:
– Terbutaline, theophylline.
Surgical:
- Permanent pacemaker implantation.

Question 24

Tachyarrhythmia drugs covered in antiarrhythmic drug lecture!!!