Cardiac Cycle Overview

• The cardiac cycle includes all events from the beginning of one heartbeat to the beginning of the next.
• The cycle includes a single "lub dub" sound, representing different phases of heart activity.
• A free guide is available for further study.

Phases of the Cardiac Cycle

1. Atrial Systole

   • Definition: Refers to the contraction of the atria.
   • Blood Flow:
     • Blood returns to the heart, filling the right side from the body and the left side from the lungs.
     • Contraction of the atria pushes blood into the ventricles.
   • Electrocardiogram (EKG):
     • P Wave: Represents atrial depolarization.
   • Pressure Changes:
     • Atrial contraction increases atrial pressure, pushing blood into the ventricles.
     • Results in a small pressure bump in both atria and ventricles.
   • End Diastolic Volume: Amount of blood in ventricles post atrial contraction.

2. Isovolumetric Contraction

   • Definition: Ventricles contract with no change in blood volume.
   • EKG:
     • QRS Complex: Shows ventricular depolarization.
   • Pressure Dynamics:
     • Atrioventricular valves close, sound is the "lub" in "lub dub."
     • Pressure in ventricles increases without volume change until it surpasses aortic pressure.
   • Atrial Pressure Bump: "c wave" caused by atrioventricular valves bulging into atria.

3. Ejection Phase

   • Definition: Blood is ejected into the arteries.
   • Pressure Dynamics:
     • Ventricular pressure surpasses arterial pressure, opening semilunar valves.
     • Systolic Pressure: Peak pressure reached in arteries.
   • Blood Flow:
     • Rapid followed by slow ejection due to resistance and pressure changes.
     • Stroke Volume: Blood ejected during ejection phase.
   • EKG:
     • T Wave: Indicates ventricular repolarization.

4. Isovolumetric Relaxation

   • Definition: Ventricles relax without volume change.
   • Pressure Dynamics:
     • Ventricular pressure falls, semilunar valves close producing the "dub" sound.
     • Dicrotic Notch: Brief aortic pressure increase as blood hits closed valve.

5. Ventricular Filling

   • Definition: Ventricles fill with blood.
   • Flow Process:
     • As ventricular pressure drops below atrial pressure, atrioventricular valves open.
     • Blood flows passively into ventricles.

Important Concepts

• Heart Sounds:
  • "Lub" is the sound of atrioventricular valves closing.
  • "Dub" is the sound of semilunar valves closing.
• Blood Pressure:
  • Systolic (120 mm Hg): High pressure during ejection.
  • Diastolic (80 mm Hg): Low pressure when relaxed.
• Cycle Repetition: The cardiac cycle repeats, sustaining life by continuously circulating blood.