What does an electrocardiograph do?
- Monitors heart rate, cardiac rhythym and axis deviation.
- Records electrical activity of the heart.
What does a normal heart contraction require?
Normal electrical conduction of activating electrical impulses through cardiac muscle tissue.
What are ECGs taken for?
- Diagnosing cardiac diseases and abnormal cardiac rhythym (arrythmia)
- Aids in detection of enlaged heart
- Aids in detection of electrolyte, systemic or metabolic disorders
- Anaesthetic monitoring
- Useful in cardiac arrest cases and CPR
- Useful in diagnosing ventricular fibrillation
Where in the heart does deoxygenated blood enter and where does it go?
Right side of heart.
Pumped to lungs.
Where in the heart does oxygenated blood enter and where does it go?
Comes from the lungs and enters left side of heart.
Pumped to the body.
What is a trace?
The recorded electroactivity on heat sensitive paper
What does an ECG represent?
Amplitude and duration of electical activity
What happens in each heart contraction?
Each contraction of the heartis preceded by an electrical wave font that stimulates the heart to contract and relax in preperation for next heart beat.
What is Depolarization?
Contraction of the myocardium
What is Repolarization?
Relaxation of cells after depolarization
What is systole?
Contraction of the ventricals
What is diastole?
The filling of ventricles (relax)
What are the parts to an ECG?
- P Wave
- QRS Interval
- ST/T wave
- PR interval
- QRS Duration
- QT Interval
- RR Interval
- PP interval
Attempt to draw a typical ECG printout.
What does each ECG lead have?
Each lead has a positive and negative pole which is attached to the skin of the animal and can be used to measure the spread of the eclectrical activity within the heart.
Different leads allow you to look at the heart from different angles. Each angle is called a lead.
Describe Alligator Clips
- Good for once off ECGs
- Clips should be placed on loose folds of skin at the elbows and knees.
- Requires a conducting medium (eg spirit) just sufficient enough to wet clip and hair through skin.
Describe ECG pads
- Good for lengthy ECGs eg during surgery
- Can be taped to patient's feet to provide a ore reliable contact with the skin.
- Gel is required - some pads come with gel
How do you read an ECG Strip?
- ECG paper is a grid where time is measured along the horizontal axis
- Each sml sq is 1mm in length and represents 0.04 secs
- Each lrg sq is 5mm in length and represents 0.2 secs
- Voltage is measured along the vertical axis
- 10mm is equal to 1mV in voltage
How do you measure the heart rate on ECG paper?
- ECG paper moves at a standardized 25mm/sec.
- Vertical lines can be used to measure time.
- There is a 0.20 sec between 2 of the large lines.
- ECG paper usually has special markings every 3 seconds
What should you check before doing an ECG?
- Machine contains enough paper
- Pen is in centre of paper
- Lead clips are clean
- Aqaquete amount of elctrode gel available
- Machine is earthed
What are the 3 basic controls on an ECG machine?
Paper speed: faster the paper speed the more spread out the heart beat is across page
Calibration settings: sets the height of the complexes typically Icm/mV
Filter: can help reduce the impact of artefacts on the recorded trace, but always have it turned off initially.
How would you position a dog and a cat for an ECG reading?
Dog: right lateral recumbancy
Cat: sternal recumbancy
Why do you not want to sedate an animal for an ECG reading?
Sedation, esp with alpha 2 agonists, may alter cardiac rythym
What 4 questions should you ask when trying todetermine if a rhythm is normal or abnormal ?
- Is there a P for every QRS?
- Is there a QRS for every P?
- Are the Ps and QRSs consistently and reasonably related?
- Are the Ps and QRSs all the same?
What does it mean if you do not have a P wave before a QRS complex?
Ventricals have depolarized without preceeding depolarization of the atria
What can cause the absence of a P wave before a QRS complex?
- Ventricular depolarization
- Junctional depolarization
- Atrial standstill
- Sinus arrest with escape complexes
What is A-fib?
When the atria have random and irregular depolarization usually caused by enlarged atria.
Won't see P waves, oscillating baseline but normal ventricular depolarization.
What will atrial standstill look like and what would youthink if you saw it
Will be no P waves at all because the atria are completley inactive.
Always think high K.
What does it mean if there is a P wave but no QRS to follow?
What is it called when there is not a consistent relationship between P waves and QRS complexes?
What is it called if there is variation in P wave aplitude?
Wandering pacemaker. Can be normal in dogs.
Most common irregularly irregular heart rhythm?
Normal heart rate for cat and dog and rabbit?
Dog: 70-180bpm depends on breed
What does the P wave of an ECG represent?
Depolarisation of R & L atria
What does the QRS interval of an ECG trace represent?
R & L ventricular depolarisation.
Durig this phase, valves of heart are closed
What does the ST/T wave of an ECG trace represent?
What does the PR interval of an ECG trace represent?
time interval from onset of atrial depolarisation (P wave) to onset of ventricular depolarisation (QRS complex)
What does the QRS duration of an ECG trace represent?
duration of ventricular muscle depolarisation
What does the QT interval of an ECG trace represent?
duration of ventricular depolarisation and repolarisation
What does the RR interval of an ECG trace represent?
duration of ventricular cardiac cycle (indicator of ventricular rate)
What does the PP interval of an ECG trace represent?
duration of atrial cycle (indicator of atrial rate)