Cardiac Cycle Overview

Cardiac Cycle

• Cardiac cycle encompasses cardiac events from one heartbeat's start to the next.
• It involves both sides of the heart.
• One cycle lasts 0.8 seconds, with a heart rate of 72 beats per minute.
• An electrocardiogram (ECG) tracks cardiac events.
• Valve openings/closings produce physiological heart sounds.

Phases of Cardiac Cycle

• Diastole: Heart muscle relaxes, chambers fill with blood.
  • Atrial Diastole: Atria relax, fill with blood from large veins.
  • Ventricular Diastole: Ventricles relax, fill with blood from atria.
• Systole: Heart muscle contracts, pumps blood from chambers into arteries.
  • Atrial Systole: Atria contract, push blood into ventricles.
  • Ventricular Systole: Ventricles contract, push blood into large arteries.

Isovolumetric Contraction

• Left ventricle contracts, mitral valve closes.
• No change in ventricle volume.
• Coincides with first heart sound (S1).

Rapid Ventricular Ejection

• Rapid blood flow from left ventricle into aorta.
• Aortic valve opens.
• Phase ends at the end of the ST segment on the ECG.

Reduced Ventricular Ejection

• Reduced blood ejection rate from ventricle to aorta.
• Coincides with beginning of T wave on ECG.

Isovolumetric Relaxation

• Relaxation of ventricles.
• Aortic valve closes.
• Coincides with second heart sound (S2).

Rapid Ventricular Filling

• Rapid blood filling from atrium to left ventricle.
• Mitral valve opens.
• Coincides with third heart sound (S3).

Reduced Ventricular Filling (Diastasis)

• Slower rate of ventricular filling.
• Longest phase of the cardiac cycle.

Heart Sounds

• Caused by blood flow through narrow passages, valve vibrations.
• Sound waves travel to skin, can be heard with a stethoscope.

First Heart Sound

• Produced during isovolumetric contraction phase.
• Resembles "lub".
• Corresponds to mitral and tricuspid valve closure.

Second Heart Sound

• Produced during isovolumetric relaxation phase.
• Resembles "dub".
• Corresponds to aortic and pulmonary valve closure.

Splitting of Second Heart Sound

• In younger patients, physiologically, S2 may be split (A2 and P2 separately audible).
• Splitting depends on inspiration/expiration. Inspiration delays the pulmonic valve closure.

Listening to Heart Sounds

• Part of cardiovascular examination.
• Essential components of CVS examination are general examination, inspection, palpation, and auscultation.
• Requires a stethoscope:
  • Bell to detect low-frequency sounds (S3&S4).
  • Diaphragm to detect high-frequency sounds (S1 & S2).
• Specific locations exist on the chest to listen for sounds from various heart valves.

General Principles for Listening to Heart Sounds

• Quiet environment is essential.
• Warm stethoscope is needed.
• Follow a sequence for consistency.
• Listen to each sound one at a time (rate, rhythm, S1, then S2, then abnormal sounds).
• Left-side heart sounds are often louder.