Approach to the ECG Flashcards
What is the definition of ECG?
The ECG is a recording of changes in electrical potential difference occurring during the depolarisation and repolarisation of the myocardium plotted against time.
i.e. It is is a Voltage - Time Graph
Where do you connect each colour lead to (Red, Yellow, Green, Black)?
Red - Right forelimb
Yellow - Left forelimb
Green - Left hindlimb
Black - Right hindlimb (Earth)
What is lead I?
Lead I = Right fore to Left fore
What is lead II?
Lead II = Right fore to left hind
What is lead III?
Lead III = left fore to left hind
Which lead normally has the largest QRS?
Lead II
What is a Sinus Arrhythmia?
Regular irregular pattern
-occurs at normal HR
What does sinus arrhythmia indicate?
High vagal tone - which is normal in healthy dogs
What is a wandering pacemaker?
Variable P wave morphology
Is sinus arrhythmias normal in cats?
No!
Look for causes of enhanced vagal tone
-feline asthma
- Compromised respiration
What is Sinus arrest?
- Sinus arrest definition: pause of >2 preceding R-R intervals
- May be seen as part of accentuated sinus arrhythmia (e.g.
brachycephalic breed). - Periods of sinus arrest (up to 5 seconds) are normal in sleeping dogs (shown by Holter monitoring)
What is a ventricular premature complex?
*Wide QRS with oppositely directed T wave
*looks like zig-zag lines
*contraction initiated by purkinje fibers not SA node
How would you treat ventricular tachycardia?
*Lidocaine IV
-prevent ventricular fibrillation + death
What are the systemic causes of ventricular premature complex?
*Gastric dilation volvulus
*Splenic lesions / splenectomy
*Sepsis
*Pancreatitis
*Pyometra
*Thoracic trauma
*CNS lesions
What is a first degree AV block?
*P : QRS ratio = 1:1
*P-R interval = prolonged
What is a morbitz type I second degree AV blocks?
– Also called the “Wenckebach phenomenon”
– Shows high vagal tone
– Normal in resting horse
– Variable P-R interval before “dropped” P wave
– Not normal in dog, associated with high vagal tone
What is a morbitz type II second degree AV block?
*Constant P-R interval
*But some times the P waves aren’t conducted so no QRS.
What is a third degree AV block?
No association between P waves and QRS complexes
What can happen if a supraventricular tachycardia is sustained?
- v fast HR - 300bpm
*Can lead to congestive heart failure - use drugs to slow conduction through AV node
With atrial fibrillation what needs to be controlled?
What drugs would you use?
*Control ventricular response to atrial fibrillation
*use drugs to slow conduction across AVN - diltiazem / digoxin
Whilst looking at lead II if an R wave height is over 3.0mV what does this tell us?
Left ventricle enlargement
If QRS complex is longer than 0.06seconds what does this tell us?
Ventricular hypertrophy
If P wave is more than 0.04seconds what does this tell us?
Left atrium enlargement
What does a tall P wave tell us?
Right atrial enlargement
