Cardiac Cycle Flashcards
(32 cards)
What is the cardiac cycle?
The sequence of events in one heartbeat including contraction and relaxation of atria and ventricles.
What is systole?
The contraction phase of the heart chambers.
What is diastole?
The relaxation phase of the heart chambers.
When do atria contract in the cardiac cycle?
During atrial systole, following the P wave.
What percentage of ventricular filling occurs before atrial systole?
About 70–80% of ventricular filling occurs passively, before atrial systole.
Here’s how it works:
1. Venous return brings blood into the atria (right atrium from the body, left atrium from the lungs).
2. As the atrioventricular (AV) valves (tricuspid and mitral) open, blood passively flows from the atria into the ventricles — this happens during ventricular diastole.
3. Atrial systole (the contraction of the atria) then tops off the ventricles with the remaining 20–30% of blood.
What is the ‘atrial kick’?
The additional 20–30% of ventricular filling caused by atrial contraction.
What is end-diastolic volume (EDV)?
The volume of blood in a ventricle at the end of diastole, ~130 mL.
What is isovolumetric contraction?
Initial phase of ventricular systole when ventricles contract but semilunar valves remain closed.
What is stroke volume (SV)?
The amount of blood ejected from each ventricle per beat, typically 70–80 mL.
What is end-systolic volume (ESV)?
The volume of blood remaining in a ventricle after contraction, ~50–60 mL.
What does the P wave on an ECG represent?
Atrial depolarization.
What does the QRS complex represent?
Ventricular depolarization (and atrial repolarization).
What does the T wave represent?
Ventricular repolarization.
What is the PR interval?
Time from beginning of atrial depolarization to start of ventricular depolarization.
What part of the ECG represents ventricular systole?
The QRS complex.
What part of the ECG represents ventricular diastole?
The T wave.
What causes the first heart sound (S1)?
Closure of the AV valves during ventricular contraction.
What causes the second heart sound (S2)?
Closure of the semilunar valves during ventricular diastole.
What is the third heart sound (S3)?
May be due to blood turbulence during ventricular filling.
What is the fourth heart sound (S4)?
Caused by atrial contraction pushing blood into a stiff ventricle.
How is cardiac output (CO) calculated?
CO = Stroke volume × Heart rate
What is preload?
The amount of stretch in ventricles at the end of diastole.
What is contractility?
The strength of ventricular contraction.
What is afterload?
The resistance ventricles must overcome to eject blood.
