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What is the Cardiac Cycle? – Video
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Video at a Glance
- Cardiac pressure is related to cardiac volume.
- During a cardiac cycle, ventricles start relaxing at the beginning of diastole and eject most of their contents.
- Next, the heart starts passively filling because blood is flowing through the atria into the ventricles based on minimal pressure from the pulmonary vein.
- The P wave makes the atria contract, causing atrial systole, which increases cardiac volume to approximately 130 ml.
- The QRS wave initiates ventricular depolarization, which marks the beginning of ventricular systole. During ventricular systole, the ventricles begin to contract as they depolarize, closing the mitral valve.
- Diastolic pressure above 60 mL opens the aortic valve, marking the beginning of diastole, while pressure below 60 mL closes the aortic valve.
- The heart sounds are S1, S2, and S3.
- S1 is caused by the blood pressure after the mitral valve closes, S2 occurs as the aortic valve opens, and S3 occurs in young, healthy patients due to rapid filling of the ventricles.
- The determinant of cardiac output is stroke volume multiplied by heart rate.
- Both tachycardia and bradycardia may lead to decreased cardiac output and cause organ hypoperfusion.
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