Cardiac Cycle / ECGs Flashcards
What is meant by atrial systole?
The contraction of the atria - atrial pressure and ventricle volume increases.
What is meant by ventricular systole?
The contraction of the ventricles - increase in aortic pressure, rapid pressure increase and volume decrease in ventricles.
What is meant by diastole?
The heart relaxes and fills with blood.
When and why does the semilunar valve open and close?
Initially, ventricle pressure > aortic pressure. Therefore the semilunar valve opes to allow blood to move from the ventricle to the aorta.
As the volume of blood in the right ventricle decreases, pressure decreases to below aortic pressure - semilunar valve snaps shut to prevent backflow into the ventricle.
When and why do the atrioventricular valves open and close?
Initially, pressure in the atria > pressure in the ventricles - atrioventricular valve is open and blood flows from atrium to the ventricle.
The ventricle contracts and pressure rises to above the atrial pressure - atrioventricular valve snaps shut to prevent blood moving from ventricle back to atrium.
What makes the audible heartbeat?
- atrioventricular valves closing (lub sound)
- semilunar valve closing (dub sound)
What is the function of the sino-atrial node (SAN)?
The SAN is located in the right atrium and produces a wave of electrical excitation / depolarisation.
This causes the atria to contract (atrial systole) and initiates the heartbeat.
What is the role of non-conducting tissue?
The layer of non-conductive tissue prevents the transmission of the excitation directly into the ventricles.
What is the function of the atrioventricular node (AVN)?
The wave of electrical excitation reaches and stimulates the AVN, which imposes a slight delay and stimulates the bundle of His.
What is the bundle of His?
A bundle of conducting tissue made of Purkyne fibres which penetrate through the septum before reaching the apex (bottom) of the heart.
What happens to the bundle of His at the heart’s apex?
It splits into two branches and the Purkyne fibres spread out through the ventricle walls - the impulse is carried from the apex up, causing ventricular systole.
Starting at the apex is more efficient in emptying the ventricles.
What is meant by myogenic?
The cardiac muscle is myogenic - meaning it has it’s own intrinsic rhythm (around 70 bpm).
What is an ectopic heartbeat?
Extra heartbeats that are out of rhythm - fairly common but can be linked to serious conditions if frequent.
The extra beats are followed by a longer than normal pause.
What is atrial fibrillation?
Atrial fibrillation is an example of arrhythmia (abnormal rhythm of the heart).
It involves rapid electrical impulses being generated in the atria which will contract up to 400 times a minute. Only some impulses pass on to ventricles - heart does not pump blood effectively.
What is meant by tachycardia?
Tachycardia refers to very rapid heartbeats of over 100 bpm.
This is normal during exercise / fevers / high level of emotion. Abnormalities may be caused by problems in the heart’s electrical control - medicine / surgery may be necessary.
What is meant by bradycardia?
Bradycardia is where the heart rate slows down to below 60 bpm.
Training makes the heart beat more slowly and efficiently. Severe bradycardia may require an artificial pacemaker.
