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What is an ECG?
The ECG is a record of the average electrical potential generated in the heart muscle and graphed in terms of voltage against time during the different phases of the cardiac cycle
Where are contractions in the heart initiated?
The sinoatrial node
What node joins the atria to the ventricles electrically?
The atrioventricular node
Describe how electrical impulses travel through the heart
SA node --> right atrial muscle --> left atrial muscle --> AV node --> Bundle of his --> bundle branches --> endocardium --> purkinjie fibres --> epicardium
What is a dipole?
A negative and positive charge separated by a distance
If the positive end of the dipole is nearer the + electrode then what deflection in the voltage trace occurs?
Upward
During depolarisation ... ions enter the cardiomyocyte? What happens to the polarity of the cell?
positive ions eg Na+The inside of the cell becomes positive (normally negative) and the outside becomes negative (normally positive)
During repolarisation what happens to the polarity of the cardiomyocyte?
The inside of the cell becomes negative and the outside of the cell becomes positive
The ... wave is linked to atrial depolarisation?
P wave
The ... wave is linked to early ventricular depolarisation?
Q wave
The ... wave is associated with ventricular depolarisation?
R wave
The ... wave is associated with late ventricular depolarisation?
S wave
The ... wave is associated with ventricular repolarisation?
T wave
What is the PR interval?
The time between atrial depolarisation and ventricular depolarisation
What is the QT interval?
The length of time the ventricles remain depolarised
What is the QRS complex?
The time taken for ventricular depolarisation to occur once the wave of depolarisation has passed through the AV node from the atria
What is the PP interval?
The time between atrial depolarisation
What is the RR interval?
The time between ventricular depolarisation
What part of the heart is Lead 1 good at looking at?
The atria
What is Lead 2 good at looking at?
The heart as a whole
What are the colours of the ECG leads and the limbs they are attached to?
Right forelimb = red
Left forelimb = yellow
Right hindlimb (earth) = black
Left hindlimb = green
The RR interval can be used to calculate ...?
the heart rate
What is the term for an abnormal heart rhythm?
Arrhythmia
3d information gained from the lead system can provide information about what in a dog heart?
Chamber enlargement
True or false: the ECG can provide some information regarding electrolyte imbalance?
True, as electrical activity of the heart is dependent upon changes in ion concentration
If there is increased potassium what change will be seen on an ECG?
An increased T wave ("more T more pots")
What speed can ECGs be run at?
25mm/sec or 50mm/sec
What is an irregularly irregular heart rhythm called?
Sinus arrhythmia
Is sinus arrhythmia a physiological or pathological arrhythmia?
Physiological - due to a combination of inspiring and changes in intrathoracic pressure
Define ventricular systole / ventricular diastole
Systole - the period of ventricular contraction
Diastole - the period of ventricular relaxation
What are the four heart sounds? What are they associated with?
S1 = 'lub'. This is associated with the mitral and tricuspid valves closing.
S2 = 'dub'. This is associated with the aortic and pulmonary semilunar valves shutting.
S3 = 'whoosh'. Associated with rapid ventricle relaxation.
S4 = 'dub'. This is associated with turbulence during atria contraction.
What sound can be heard when a valve does not work properly?