T3 L6: Introduction to ECG Flashcards
What is a syncytium?
one large ‘cell’ that has many nuclei that are not separated by a cell membrane (Eg. skeletal muscle cells)
What is a functional syncytium?
Many cells working as one (Eg. Cardiomyocytes)
What are the 3 types of cardiomyocyte?
Pacemaker, conducting and contractile
What is meant by speed of propagation?
The time it takes for the signal to get from one part of the heart to another
What is the speed of propagation of arterial and ventricular myocytes?
0.3-0.5 m/s
What is the speed of propagation of Purkinje fibres?
5 m/s
What is the speed of propagation of the AV node?
0.05 m/s
How are cardiomyocytes linked?
By low resistance pathways associated with gap junctions at the intercalated disc. Made of connexin
Where is the fibrous skeleton in the heart?
It separates the atria and ventricles
What structure conducts impulses from the SA node to the AV node?
The internodal bundles
What is the speed of propagation of the internodal bundles?
1.0 m/s. Without them, conducting via the atrial muscle would be 0.3-0.5 m/s
What is the delay that the AV node creates?
0.1-0.2 s
What is the purpose of the AV node delay?
To make sure the ventricles contract after the atria
Why do Purkinje fibres conduct faster?
They are large so have less resistance
What does the ECG truly measure?
The electrical activity of the heart measured on the skin
What is a Holter monitor?
A type of ECG that measures 24/7. Used for diagnosis
Where is lead II placed in a 12 lead ECG?
Negative on right arm, positive on left leg and ground can go anywhere but usually on the right leg
What is a lead?
A configuration of electrodes
What are bipolar leads?
Have a positive and negative end
What type of leads are the 12 standard leads made up of?
3 bipolar, 3 augmented, and 6 precordial
Which lead is used to create the rhythm strip in a 12 lead ECG?
lead II
What does the P wave show?
The depolarisation of atria in response to the SA node triggering
What does the PR segment show?
The delay of the AV node to allow filling of ventricles
What does the PRS complex show?
Depolarisation of ventricles triggering main pumping contractions
What does the ST segment show?
The beginning of ventricle repolarisation. It should be flat and at the same level as PQ
What does the T wave show?
ventricular repolarisation
