Definitions
What does ECG stand for, and what does it measure?
Electrocardiogram
Traces the electrical conduction of the heart that causes contractions
What is the very first wave noted in a normal heart beat?
P wave
Usually positive (tracks up)
What is a sinus arrythmia?
Normal P-QRS-T complex, but rate speeds up and then slows down cyclically (usually in conjunction with respiration)
When do we treat arrythmias?
Symptomatic
- Hypotensive (Systolic <100)
- Sustained tachycardia (>180 in dogs, >250 in cats)
Risk of sudden death
- Boxers, Dobermans
- Otherwise unstable
What is this arrythmia? #1
Sinus arrythmia
What is bradycardia, and what are it's cut offs?
Abnormally slow heart rate
- <100 bpm in cats/small dogs
- <60 bpm in medium dogs
- <50 bpm in large dogs
What is the second wave in a normal heart beat?
QRS complex
First negative, then positive
What is ventricular tachycardia?
Extremely fast heart beat that originates in the ventricles, instead of the atria
What arrythmia does lidocaine IV treat?
Ventricular tachycardia - slows conduction and allows repolarization
What is this arrythmia? #2
Ventricular Premature Contractions (VPCs)
What is tachycardia, and what are its cut offs?
Abnormally fast heart rate
- 50% increase above individual P baseline
- >220 bpm in cats
- >160 bpm on dogs
What is the last wave in a normal heart beat?
T wave
Usually positive
What are VPCs? What do we get when there are multiple in a row?
Ventricular premature contractions are when the ventricles depolarize and contract on their own, instead of waiting for the atria to depolarize first.
Multiple VPCs in a row create V-tach.
What drug do we give to treat brady-arrythmias?
Atropine
What is this arrythmia? #3
Ventricular tachycardia
What is an arrythmia? Name 3 examples.
Abnormal rhythm to the heart rate
- Sinus arrythmia
- Brady-arrythmia (most common under GA)
- Ventricular tachycardia
- Atria fibrillation
- AV block (1st, 2nd, and 3rd degree)
- Ventricular premature contractions (VPCs)??
- Ventricular bigeminy/trigeminy
What does the P wave indicate?
Depolarization of the L and R atrium
Generated by the SA node, and is the pacemaker
What is AV block?
The electrical impulse from the atria is delayed in reaching the ventricles (or never make it at all).
What are some surigical causes for brady-arrhythmias?
Anything that stimulates the vagus nerve:
- GI disease
- Brachycephalics
- Ocular traction
Some mu opioids (methadone, fentanyl)
What is this arrythmia? #4
3rd degree AV block
P waves without associated QRS complexes, and VPCs
Why can abnormalities in the ECG be so concerning?
- Poor cardiac output
- Heart chambers not beating in correct order
- Sudden death
What does the QRS complex indicate?
Ventricular depolarization as it travels through the heart
What is atrial fibrillation?
Extremely fast depolarization of atria without sufficient repolarization or conduction to ventricles
Irregularly irregular rhythm - "tennis shoes in the dryer"
What are other causes (not surgical or cardiac related) causes of arrythmias?
- Too deep under anesthesia
- Hypothermia
- Profound hypoxemia
- Hyperkalemia
What is this arrythmia? #5
Atrial fibrillation
Irregularly irregular
Don't confuse with motion/shivering artefact!