The cardiac cycle and the ECG
How the heart beats: the conduction system, systole and diastole with their sounds, cardiac output, and reading the waves of the electrocardiogram up to the most common abnormalities.
- 48 cards
- 4 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- The steps
- Scenarios
- Understand
A few cards from the deck
Systole: what is it?
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The phase in which the ventricles contract and eject blood into the aorta and the pulmonary trunk.
It begins when the atrioventricular valves close, the first heart sound.
Conduction of the cardiac impulse: which step comes after "Sinoatrial node"?
- Atrial muscle
- Atrioventricular node
- Bundle of His
- Right and left bundle branches
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Atrial muscle
The impulse starts in the sinoatrial node, crosses the atria, waits in the atrioventricular node, then rushes down to the ventricles.
Diastole: what is it?
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The phase in which the ventricles relax and fill.
It begins when the semilunar valves close, the second heart sound.
On the ECG, the PR interval is long but every P wave is followed by a QRS. Where is the slowing?
- In the atrioventricular node
- In the sinoatrial node
- In the Purkinje fibres
- In the valves
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In the atrioventricular node
That is a first-degree atrioventricular block: passage from atria to ventricles is delayed.
Sinoatrial node: what is it?
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A cluster of cells in the right atrium that depolarise on their own and set the heart's rhythm.
It is the natural pacemaker, 60 to 100 beats a minute at rest.
Why does the sinoatrial node set the rhythm rather than another cell?
- Its automaticity is the fastest: it depolarises the others before they fire on their own
- It is the only tissue in the heart able to depolarise on its own
- It takes its orders directly from the brain through the vagus nerve
- It is the only tissue that carries the impulse to the ventricles
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Its automaticity is the fastest: it depolarises the others before they fire on their own
If the sinoatrial node falls silent, the atrioventricular node takes over, more slowly.