GRAPHIC CARDIAC CYCLE

Cardiac Cycle Overview

  • Understanding the phases of the cardiac cycle is essential for analyzing heart function.

  • Graphical representations are useful in clinically interpreting the cardiac cycle.

Types of Graphs

  • Pressure-Volume Loop

    • X-axis: Left ventricular volume.

    • Y-axis: Left ventricular pressure.

  • Wiggers Diagram

    • Illustrates pressure and volume changes during the cardiac cycle with multiple factors.

Pressure-Volume Loop Phases

## 1. Ventricular Filling
- Begins at a volume of approximately 60 mL.
- Volume Change: Increases significantly.
- Pressure Change: Increases slightly due to ventricular muscle relaxation to accommodate blood volume.

## 2. Isovolumetric Ventricular Contraction
- Characterized by a constant volume, which means:
- Pressure: Rapid increase as the ventricle contracts against closed valves (no blood is ejected).
- Volume does not shift along the X-axis.
- Pressure rises steeply in this phase.

## 3. Ventricular Ejection
- As ventricular pressure rises, blood is ejecting from the ventricle:
- Pressure Change: Continues to increase until equal to or greater than the aortic pressure.
- Volume Change: Decreases as blood leaves the ventricle, thus moving left along the X-axis.
- Momentum assists in ejection, resulting in a gradual decrease in pressure post-ejection.

## 4. Isovolumetric Ventricular Relaxation
- Occurs when ventricular pressure falls below aortic pressure, causing the valves to close:
- Volume Change: Remains constant during this brief rest phase.
- Pressure Change: Sharp decline as the ventricle relaxes.

Wiggers Diagram Overview

  • The Wiggers diagram adds complexity by including additional relevant pressure and volume variables.

  • Graph Structure:

    • Upper portion represents Pressure.

    • Lower portion represents Volume.

    • Individual lines represent:

      • Maroon line for Arterial Pressure (Aorta).

      • Bright red line for Ventricular Pressure.

      • The shaded areas signify different cardiac cycle portions.

Phases in Wiggers Diagram

  • Yellow Shaded Area: Represents isovolumetric ventricular contraction, with pressure increasing dramatically.

  • Orange Shaded Area: Corresponds to the phase of ventricular ejection, where volume drops as blood is forced out.

  • Dark Purple Shaded Area: Represents isovolumetric ventricular relaxation, showing a fall in pressure while volume remains steady.

  • Ventricular Filling: Noted in the diagram with rapid filling and slower filling phases, including the atrial kick:

    • Pressure in the ventricle remains low during this filling process.

Cardiac Cycle Summary

  • Systole: The phase when the ventricle is contracting (encompasses isovolumetric contraction and ventricular ejection).

  • Diastole: The phase when the ventricle is relaxing (encompasses isovolumetric relaxation and ventricular filling).

  • Notable observation: The heart spends more time in diastole than in systole, allowing for adequate filling and preparation for the next contraction.

Additional Information

  • Ability to correlate graphs with:

    • Valve dynamics (opening and closing).

    • Heart sounds (S1, S2).

    • Electrical activity (P wave, QRS wave initiation).