Volume overload



Volume overload refers to the state of one of the chambers of the heart in which too large a volume of blood exists within it for it to function efficiently. Ventricular volume overload is approximately equivalent to an excessively high preload. It is a cause of cardiac failure.

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 Right 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
 * Valvular heart disease
 * Tricuspid regurgitation
 * Pulmonary regurgitation
 * Congenital heart defects
 * Atrial septal defect, also causing right atrial volume overload