Systolic function assessment

Ejection Fraction - The Heart's Squeeze

• Definition: The percentage of blood pumped out of a ventricle with each contraction. It is the primary index of ventricular systolic function.
• Formula: $EF (%) = (SV / EDV) \times 100$
  • SV (Stroke Volume) = EDV − ESV
  • EDV: End-Diastolic Volume
  • ESV: End-Systolic Volume
• Normal Range: 55-70%
• Heart Failure Classification:
  • HFrEF (reduced EF): ≤ 40%
  • HFmrEF (mid-range EF): 41-49%
  • HFpEF (preserved EF): ≥ 50%

⭐ In severe, acute aortic regurgitation, EF can be normal or even high due to the large total stroke volume (forward + regurgitant flow), masking significant LV dysfunction.

SV & CO - The Pumping Metrics

• Stroke Volume (SV): Volume of blood pumped from the left ventricle per beat.
  • $SV = EDV - ESV$
• Cardiac Output (CO): Volume of blood pumped per minute.
  • $CO = SV \times HR$
  • Normal range: 4-8 L/min.
• Ejection Fraction (EF): Percentage of blood leaving the ventricle each contraction; a key index of systolic function.
  • $EF = (SV / EDV) \times 100%$
  • Normal EF is >55%.
• Determinants of SV:
  • 📌 SV CAP: Contractility, Afterload, Preload.

⭐ The Fick principle allows for the calculation of cardiac output based on oxygen consumption: $CO = \text{O}_2 \text{ consumption} / (\text{arterial O}_2 - \text{venous O}_2)$.

Advanced Echo - Beyond the Basics

• Speckle Tracking Echocardiography (STE):

  • Measures myocardial deformation (strain).
  • Global Longitudinal Strain (GLS) is the key metric; normal is -18% to -25%.
  • Less angle-dependent and more reproducible than older Doppler methods.
  • Detects subclinical dysfunction before LVEF drops.

• 3D Echocardiography:

  • Provides more accurate and reproducible measurements of LV volumes, mass, and ejection fraction.
  • Eliminates geometric assumptions inherent in 2D echo (e.g., Simpson's biplane).

⭐ High-Yield Pearl: Global Longitudinal Strain (GLS) is a strong independent predictor of mortality in patients with heart failure, even with a preserved ejection fraction (HFpEF).

PV Loops - The Systolic Story

A pressure-volume (PV) loop graphically represents the work done by the left ventricle in one cardiac cycle. The width of the loop is the stroke volume, and its area approximates stroke work.

• Isovolumetric Contraction (A → B): Ventricle contracts, pressure ↑, volume is constant. Begins with mitral valve closure, ends with aortic valve opening.
• Systolic Ejection (B → C): Aortic valve opens; ventricular volume ↓ as blood is ejected.
• Contractility (Inotropy): Represented by the End-Systolic Pressure-Volume Relationship (ESPVR). A steeper ESPVR slope indicates ↑ contractility.

⭐ Increased afterload (e.g., hypertension) narrows the PV loop by increasing end-systolic pressure and volume, thus decreasing stroke volume.

High‑Yield Points - ⚡ Biggest Takeaways

• Ejection Fraction (EF) is the cornerstone of systolic function assessment; normal is >55%.
• EF is calculated as (EDV − ESV) / EDV and is highly dependent on preload and afterload.
• Stroke Volume (SV) and Cardiac Output (CO) are fundamental measures of pump function but are also load-dependent.
• dP/dt max, the rate of ventricular pressure rise, is a sensitive index of myocardial contractility.
• Transthoracic echocardiography is the primary non-invasive tool to quantify systolic function.
• Systolic heart failure is classically defined by a reduced EF (<40%).