What happens to the ventricles during systole?

Ventricular Activity During Systole

During systole, the ventricles contract forcefully to eject blood into the pulmonary and systemic circulations, with the left ventricle generating higher pressures than the right ventricle while both chambers undergo complex mechanical changes including wall thickening, chamber volume reduction, and coordinated contraction of the interventricular septum.

Mechanical Events During Ventricular Systole

Left Ventricular Systole

• The left ventricle undergoes powerful contraction, generating systolic pressures necessary to overcome aortic resistance 1
• Systolic contraction reduces ventricular volume as blood is ejected through the aortic valve 1
• Peak left ventricular pressure typically occurs before the end of systolic ejection, creating a characteristic pressure-volume relationship 1
• The left ventricle ejects approximately 50-70% of its end-diastolic volume during normal systole (ejection fraction) 1
• In hyperdynamic states, the left ventricle ejects a greater than normal proportion of blood during systole 2

Right Ventricular Systole

• The right ventricle contracts with less force than the left ventricle, requiring only one-sixth the energy expenditure due to the lower resistance of the pulmonary circulation 1
• The right ventricular pressure-volume loop lacks the isovolumic phases seen in left ventricular contraction 1
• Right ventricular function is highly sensitive to changes in afterload, with minor increases in pulmonary pressure causing large decreases in stroke volume 1
• The crista supraventricularis (a unique muscle bridge in the right ventricle) contracts the tricuspid valve orifice while pulling the right ventricular free wall toward the interventricular septum during systole 1

Interventricular Septum

• The interventricular septum plays a crucial role as the "septal motor" of biventricular function 3
• During systole, the septum undergoes a twisting action that contributes to the forceful ejection of blood from both ventricles 3
• The septum maintains an oblique fiber orientation and midline configuration that is essential for optimal biventricular performance 3

Flow Dynamics During Systole

• In the left ventricle, systolic ejection creates high Reynolds numbers with potential for flow instability and turbulence 1
• The left ventricle generates flow with turbulent kinetic energy that can reach 0.15 m²/s² during systole 1
• In pathological conditions like aortic stenosis, turbulence increases significantly during systolic ejection due to the restricted orifice area 1

Pathological Considerations

• In hypertrophic cardiomyopathy, systolic contraction of the hypertrophied basal ventricular septum can encroach on the left ventricular outflow tract, contributing to obstruction 1
• Dynamic left ventricular outflow tract obstruction varies with loading conditions and contractility of the ventricle 1
• In mitral regurgitation, systolic pressure developed within the left ventricle causes retrograde ejection of blood into the left atrium through the incompetent mitral valve, creating two pathways for left ventricular ejection 1
• Right ventricular systolic function may be compromised by septal dysfunction, as disruption of normal septal anatomy affects biventricular performance 3

Clinical Assessment of Ventricular Systolic Function

• Left ventricular systolic function is commonly assessed through ejection fraction, with values categorized as normal, hyperdynamic, or varying degrees of reduction 1
• Right ventricular systolic function can be evaluated through fractional area change, ejection fraction, and other parameters 1
• The right-to-left ventricular ratio may be higher in systole than in diastole in certain pathological conditions like acute pulmonary embolism 4

Understanding the complex mechanics of ventricular systole is essential for proper assessment of cardiac function and diagnosis of various cardiovascular disorders that affect systolic performance.