Cardiac shunts is when the blood flow follows a pattern in the heart that deviates from the normal circuit of the circulatory system

Circulatory system

The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

. It may be described as right-left

Right-to-left shunt

A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles...

, left-to-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic

Pulmonary-to-systemic shunt

A pulmonary-to-systemic shunt is a cardiac shunt which allows, or is designed to cause, blood to flow from the pulmonary circulation to the systemic circulation...

. The direction may be controlled by left

Left heart

Left heart is a term used to refer collectively to the left atrium and left ventricle of the heart; occasionally, this term is intended to reference the left atrium, left ventricle, and the aorta collectively....

 and/or right heart

Right heart

Right heart is a term used to refer collectively to the right atrium and right ventricle of the heart; occasionally, this term is intended to reference the right atrium, right ventricle, and the pulmonary trunk collectively....

 pressure

Blood pressure

Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

, a biological or artificial heart valve

Artificial heart valve

An artificial heart valve is a device implanted in the heart of a patient with heart valvular disease. When one of the four heart valves malfunctions, the medical choice may be to replace the natural valve with an artificial valve. This requires open-heart surgery.Valves are integral to the normal...

 or both. The presence of a shunt may also affect left and/or right heart pressure either beneficially or detrimentally.

Terminology

The left and right sides of the heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 are named from a dorsal view, i.e., looking at the heart from the back or from the perspective of the person whose heart it is. There are four chambers in a heart: an atrium (upper) and a ventricle (lower) on both the left and right sides. In mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s and bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, blood from the body goes to the right side of the heart first . Blood enters the upper right atrium

Right atrium

The right atrium is one of four chambers in the hearts of mammals and archosaurs...

, is pumped down to the right ventricle

Right ventricle

The right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....

 and from there to the lungs via the pulmonary artery. Blood going to the lungs is called the pulmonary circulation

Pulmonary circulation

Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...

. When the blood returns to the heart from the lungs via the pulmonary vein, it goes to the left side of the heart, entering the upper left atrium

Left atrium

The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...

. Blood is then pumped to the lower left ventricle

Left ventricle

The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...

 and from there out of the heart to the body via the aorta. This is called the systemic circulation

Systemic circulation

Systemic circulation is the part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. This physiologic theory of circulation was first described by William Harvey...

. A cardiac shunt is when blood follows a pattern that deviates from the systemic circulation, i.e., from the body to the right atrium, down to the right ventricle, to the lungs, from the lungs to the left atrium, down to the left ventricle and then out of the heart back to the systemic circulation.

A left-to-right shunt is when blood from the left side of the heart goes to the right side of the heart. This can occur either through a hole in the ventricular or atrial septum that divides the left and the right heart or through a hole in the walls of the arteries leaving the heart, called great vessels

Great vessels

Great vessels is a term used to refer collectively to the four large vessels that bring blood to and from the heart. These are:*Superior vena cava*Inferior vena cava*Pulmonary artery*AortaAll four pulmonary veins are considered apart of the great vessels...

. Left-to-right shunts occur when the systolic blood pressure in the left heart is higher than the right heart, which is the normal condition in birds and mammals.

Congenital shunts in humans

The most common congenital heart defect

Congenital heart defect

A congenital heart defect is a defect in the structure of the heart and great vessels which is present at birth. Many types of heart defects exist, most of which either obstruct blood flow in the heart or vessels near it, or cause blood to flow through the heart in an abnormal pattern. Other...

s (CHDs) which cause shunting are the atrial septal defect

Atrial septal defect

Atrial septal defect is a form of congenital heart defect that enables blood flow between the left and right atria via the interatrial septum. The interatrial septum is the tissue that divides the right and left atria...

 (ASD) (aka. patent foramen ovale), ventricular septal defect

Ventricular septal defect

A ventricular septal defect is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart.The ventricular septum consists of an inferior muscular and superior membranous portion and is extensively innervated with conducting cardiomyocytes.The membranous...

 (VSD), patent ductus arteriosus

Patent ductus arteriosus

Patent ductus arteriosus is a congenital disorder in the heart wherein a neonate's ductus arteriosus fails to close after birth. Early symptoms are uncommon, but in the first year of life include increased work of breathing and poor weight gain...

 (PDA). In isolation, these defects may be asymptomatic

Asymptomatic

In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...

, or they may produce symptom

Symptom

A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...

s which can range from mild to severe, and which can either be acute

Acute (medicine)

In medicine, an acute disease is a disease with either or both of:# a rapid onset, as in acute infection# a short course ....

 or have delayed onset. However, these shunts are often present in combination with other defects; in these cases, they may still be asymptomatic, mild or severe, acute or delayed, but they may also work to counteract the negative symptoms caused by another defect (as with d-Transposition of the great arteries).

Biological

Some acquired shunts are modifications of congenital ones: a balloon septostomy

Balloon septostomy

Balloon septostomy is the widening of a foramen ovale, patent foramen ovale , or atrial septal defect via cardiac catheterization using a balloon catheter...

 can enlarge a foramen ovale

Foramen ovale (heart)

In the fetal heart, the foramen ovale , also ostium secundum of Born or falx septi, allows blood to enter the left atrium from the right atrium. It is one of two fetal cardiac shunts, the other being the ductus arteriosus...

 (if performed on a newborn), PFO or ASD; or prostaglandin

Prostaglandin

A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....

 can be administered to a newborn to prevent the ductus arteriosus

Ductus arteriosus

In the developing fetus, the ductus arteriosus , also called the ductus Botalli, is a shunt connecting the pulmonary artery to the aortic arch. It allows most of the blood from the right ventricle to bypass the fetus's fluid-filled lungs. Upon closure at birth, it becomes the ligamentum arteriosum...

 from closing. Biological tissue

Biological tissue

Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

s may also be used to construct artificial passages.

Mechanical

Mechanical shunts are used in some cases of CHD to control blood flow

Circulatory system

The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

 or blood pressure. One example is the modern version of the Blalock-Taussig shunt

Blalock-Taussig shunt

The Blalock–Taussig shunt is a surgical procedure to give palliation to cyanotic heart defects which are common causes of blue baby syndrome...

.