Overview
This lecture covers the basics of heart failure, focusing on preload, afterload, and inotropy, and explains the pressure-volume loop and its clinical implications for heart failure management.
Preload, Afterload, and Inotropy Concepts
- Preload is the initial stretching of cardiac muscle fibers, represented by the blood volume returning to the heart.
- Afterload is the resistance the heart must overcome to eject blood, similar to pulling a cart uphill (blood pressure).
- Inotropes increase the force of heart contraction but do not address excess preload or afterload.
- Decreasing preload (diuresis) and afterload (antihypertensives) can make the heart's work easier.
Pressure-Volume Loop Basics
- The pressure-volume loop graphs left ventricular pressure against volume during a cardiac cycle.
- Isovolumetric contraction: Pressure rises without volume change, with all heart valves closed.
- Ejection phase: Aortic valve opens, and blood is pumped out; pressure and volume decrease.
- Isovolumetric relaxation: Pressure falls without volume change after aortic valve closes.
- Filling phase: Mitral valve opens, and the ventricle fills with blood.
End-Systolic Pressure-Volume Relation (ESPVR)
- ESPVR is a line showing the relationship between end-systolic pressure and volume; it indicates heart contractility.
- In heart failure, ESPVR becomes flatter and shifts towards the volume axis, indicating lower contractility.
Clinical Implications in Heart Failure
- Lowering afterload in heart failure significantly increases stroke volume compared to normal hearts.
- In severe heart failure, further lowering blood pressure is not possible, and stroke volume remains low.
- Inotropes may be used if patients are severely compromised and cannot improve with preload or afterload reduction.
- Key management principle: prioritize afterload reduction to improve cardiac output in heart failure.
Key Terms & Definitions
- Preload — The volume of blood in the ventricles at the end of diastole.
- Afterload — The resistance the left ventricle must overcome to circulate blood.
- Inotrope — A medication that increases the force of heart muscle contraction.
- Pressure-volume loop — A graphical representation of the cardiac cycle showing changes in pressure and volume.
- ESPVR (End-Systolic Pressure-Volume Relation) — A marker of ventricular contractility derived from the pressure-volume loop.
- Stroke volume — The amount of blood ejected by the ventricle with each heartbeat.
Action Items / Next Steps
- Review pressure-volume loop diagrams and practice drawing ESPVR for normal and heart failure scenarios.
- Focus study on medications that reduce preload and afterload in heart failure management.