Volume overload

Pathophysiology

In accordance with the Frank–Starling law of the heart, the myocardium contracts more powerfully as the end-diastolic volume increases. Stretching of the myofibrils in cardiac muscle causes them to contract more powerfully due to a greater number of cross-bridges being formed between the myofibrils within cardiac myocytes. This is true up to a point, however beyond this there is a loss of contractile ability due to loss of connection between myofibrils; see figure.

Various pathologies, listed below, can lead to volume overload. Different mechanisms are involved depending on the cause, however the common theme is that of a high cardiac output with a low or normal afterload. The output may be high due to the inefficiency in valve disease, or it may be high due to shunting of blood in left-to-right shunts and arteriovenous malformations.

Left ventricular volume overload may produce inverted u waves on the electrocardiogram.

Causes

Causes may be considered according to which chamber is affected.

Left ventricular volume overload

• Valvular heart disease
  • Aortic regurgitation
  • Mitral regurgitation, also causing left atrial volume overload
• Congenital heart defects
  • Patent ductus arteriosus
  • Ventricular septal defect, also causing left atrial volume overload
• Arteriovenous malformation and fistula
  • Giant hepatic haemangioma
  • High-output haemodialysis fistula Right ventricular volume overload
• Valvular heart disease
  • Tricuspid regurgitation
  • Pulmonary regurgitation
• Congenital heart defects
  • Atrial septal defect, also causing right atrial volume overload

References

References

1. Costanzo, Linda S.. (2007). "Physiology". Lippincott Williams & Wilkins.
2. Klabunde, Richard E. "Cardiovascular Physiology Concepts". Lippincott Williams & Wilkins, 2011, p. 74.
3. (2005). "The patient U wave". Cardiovasc Res.
4. [http://www.echoincontext.com/int2/skillI2_04.asp Left Ventricular Volume Overload] {{Webarchive. link. (2013-03-05 , Discussion of echocardiography findings.)
5. (1982). "Left atrial volume overload in mitral regurgitation: a two dimensional echocardiographic study". Am J Cardiol.
6. Gardiner M, Eisen S, Murphy C. Training in paediatrics: the essential curriculum. Oxford University Press, Oxford 2009.