Right-to-left shunt

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A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. [1] This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles.

Contents

Clinical Significance

A right-to-left shunt occurs when:

  1. there is an opening or passage between the atria, ventricles, and/or great vessels; and,
  2. right heart pressure is higher than left heart pressure and/or the shunt has a one-way valvular opening.

Small physiological, or "normal", shunts are seen due to the return of bronchial artery blood and coronary blood through the Thebesian veins, which are deoxygenated, to the left side of the heart.

Causes

Congenital defects can lead to right-to-left shunting immediately after birth: [2]

A mnemonic to remember the conditions associated with right-to-left shunting involves the numbers 1-5, as follows:

A mainstem intubation with an endotracheal tube can lead to right-to-left shunting.[ citation needed ] This occurs when the tip of the endotracheal tube is placed beyond the carina. In this way only one lung is oxygenated and oxygen-poor blood from the non-ventilated lung dilutes the oxygen level of blood returning from the lungs in the left ventricle.

Eisenmenger syndrome

An uncorrected left-to-right shunt can progress to a right-to-left shunt; this process is termed Eisenmenger syndrome. [3] This is seen in Ventricular septal defect, Atrial septal defect, and patent ductus arteriosus, and can manifest as late as adult life. This switch in blood flow direction is precipitated by pulmonary hypertension due to increased pulmonary blood flow in a left-to-right shunt. The right ventricle hypertrophies to compensate for this pulmonary hypertension, so the right ventricular pressure becomes higher than the pressure in the left ventricle. Because of this switch in the pressure gradient, blood starts flowing right to left, forming a right-to-left shunt. As with any right-to-left shunt, there is decreased blood flow to the lungs, resulting in decreased oxygenation of blood and cyanosis.

Tetralogy of Fallot

The most common cause of right-to-left shunt is the Tetralogy of Fallot, a congenital cardiac anomaly characterized by four co-existing heart defects.

  1. Pulmonary stenosis (narrowing of the pulmonary valve and outflow tract, obstructing blood flow from the right ventricle to the pulmonary artery)
  2. Overriding aorta (aortic valve is enlarged and appears to arise from both the left and right ventricles instead of the left ventricle, as occurs in normal hearts)
  3. Right ventricular hypertrophy (thickening of the muscular walls of the right ventricle, this is a result of the increased amount of work the heart has to do)
  4. Ventricular septal defect (a hole exists in the septum that divides the left and right ventricles)


Outside of heart-related conditions, right-to-left shunts of the heart can be seen with Pulmonary Arteriovenous Malformations (PAVMs).

Symptoms

Early cyanosis is a symptom of a right-to-left shunt. [2] A right-to-left shunt results in decreased blood flow through the pulmonary system, leading to decreased blood oxygen levels (hypoxemia). Hypoxemia manifests as cyanosis, causing "blue babies."

Diagnosis

Differentiation between a right-to-left shunt and pulmonary disease is often aided clinically by the results of a hyperoxia test.[ citation needed ] Using high levels of inspired oxygen should have little effect on the dissolved O2 in the blood because highly oxygenated blood is diluted by shunted (low oxygenation) blood.

Shunt equation

Reptiles

Because most reptiles have a single ventricle and all reptiles have both a right aortic arch and a left aortic arch, all reptiles have the capacity for right-to-left shunt. [ citation needed ]

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<span class="mw-page-title-main">Tetralogy of Fallot</span> Type of congenital heart defect

Tetralogy of Fallot (TOF), formerly known as Steno-Fallot tetralogy, is a congenital heart defect characterized by four specific cardiac defects. Classically, the four defects are:

<span class="mw-page-title-main">Cyanosis</span> Decreased oxygen in the blood

Cyanosis is the change of body tissue color to a bluish-purple hue, as a result of decrease in the amount of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Cyanosis is apparent usually in the body tissues covered with thin skin, including the mucous membranes, lips, nail beds, and ear lobes. Some medications may cause discoloration such as medications containing amiodarone or silver. Furthermore, mongolian spots, large birthmarks, and the consumption of food products with blue or purple dyes can also result in the bluish skin tissue discoloration and may be mistaken for cyanosis. Appropriate physical examination and history taking is a crucial part to diagnose cyanosis. Management of cyanosis involves treating the main cause, as cyanosis isn’t a disease, it is a symptom.

dextro-Transposition of the great arteries Medical condition

dextro-Transposition of the great arteries is a potentially life-threatening birth defect in the large arteries of the heart. The primary arteries are transposed.

<span class="mw-page-title-main">Blue baby syndrome</span> Two situations that lead to cyanosis in infants

Blue baby syndrome can refer to conditions that cause cyanosis, or blueness of the skin, in babies as a result of low oxygen levels in the blood. This term has traditionally been applied to cyanosis as a result of:.

  1. Cyanotic heart disease, which is a category of congenital heart defect that results in low levels of oxygen in the blood. This can be caused by either reduced blood flow to the lungs or mixing of oxygenated and deoxygenated blood.
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<span class="mw-page-title-main">Congenital heart defect</span> Defect in the structure of the heart that is present at birth

A congenital heart defect (CHD), also known as a congenital heart anomaly, congenital cardiovascular malformation, and congenital heart disease, is a defect in the structure of the heart or great vessels that is present at birth. A congenital heart defect is classed as a cardiovascular disease. Signs and symptoms depend on the specific type of defect. Symptoms can vary from none to life-threatening. When present, symptoms are variable and may include rapid breathing, bluish skin (cyanosis), poor weight gain, and feeling tired. CHD does not cause chest pain. Most congenital heart defects are not associated with other diseases. A complication of CHD is heart failure.

A cyanotic heart defect is any congenital heart defect (CHD) that occurs due to deoxygenated blood bypassing the lungs and entering the systemic circulation, or a mixture of oxygenated and unoxygenated blood entering the systemic circulation. It is caused by structural defects of the heart such as right-to-left or bidirectional shunting, malposition of the great arteries, or any condition which increases pulmonary vascular resistance. The result may be the development of collateral circulation.

<span class="mw-page-title-main">Ventricular septal defect</span> Medical condition

A ventricular septal defect (VSD) is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart. The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one common ventricle. The ventricular septum consists of an inferior muscular and superior membranous portion and is extensively innervated with conducting cardiomyocytes.

<span class="mw-page-title-main">Eisenmenger syndrome</span> Medical condition

Eisenmenger syndrome or Eisenmenger's syndrome is defined as the process in which a long-standing left-to-right cardiac shunt caused by a congenital heart defect causes pulmonary hypertension and eventual reversal of the shunt into a cyanotic right-to-left shunt. Because of the advent of fetal screening with echocardiography early in life, the incidence of heart defects progressing to Eisenmenger syndrome has decreased.

<span class="mw-page-title-main">Hypoplastic left heart syndrome</span> Type of congenital heart defect

Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect in which the left side of the heart is severely underdeveloped and incapable of supporting the systemic circulation. It is estimated to account for 2-3% of all congenital heart disease. Early signs and symptoms include poor feeding, cyanosis, and diminished pulse in the extremities. The etiology is believed to be multifactorial resulting from a combination of genetic mutations and defects resulting in altered blood flow in the heart. Several structures can be affected including the left ventricle, aorta, aortic valve, or mitral valve all resulting in decreased systemic blood flow.

<span class="mw-page-title-main">Transposition of the great vessels</span> Group of congenital heart defects

Transposition of the great vessels (TGV) is a group of congenital heart defects involving an abnormal spatial arrangement of any of the great vessels: superior and/or inferior venae cavae, pulmonary artery, pulmonary veins, and aorta. Congenital heart diseases involving only the primary arteries belong to a sub-group called transposition of the great arteries (TGA), which is considered the most common congenital heart lesion that presents in neonates.

<span class="mw-page-title-main">Pulmonary atresia</span> Medical condition

Pulmonary atresia is a congenital malformation of the pulmonary valve in which the valve orifice fails to develop. The valve is completely closed thereby obstructing the outflow of blood from the heart to the lungs. The pulmonary valve is located on the right side of the heart between the right ventricle and pulmonary artery. In a normal functioning heart, the opening to the pulmonary valve has three flaps that open and close.

<span class="mw-page-title-main">Persistent truncus arteriosus</span> Medical condition

Persistent truncus arteriosus (PTA), often referred to simply as truncus arteriosus, is a rare form of congenital heart disease that presents at birth. In this condition, the embryological structure known as the truncus arteriosus fails to properly divide into the pulmonary trunk and aorta. This results in one arterial trunk arising from the heart and providing mixed blood to the coronary arteries, pulmonary arteries, and systemic circulation. For the International Classification of Diseases (ICD-11), the International Paediatric and Congenital Cardiac Code (IPCCC) was developed to standardize the nomenclature of congenital heart disease. Under this system, English is now the official language, and persistent truncus arteriosus should properly be termed common arterial trunk.

<span class="mw-page-title-main">Tricuspid atresia</span> Medical condition

Tricuspid atresia is a form of congenital heart disease whereby there is a complete absence of the tricuspid valve. Therefore, there is an absence of right atrioventricular connection. This leads to a hypoplastic (undersized) or absent right ventricle. This defect is contracted during prenatal development, when the heart does not finish developing. It causes the systemic circulation to be filled with relatively deoxygenated blood. The causes of tricuspid atresia are unknown.

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Pulmonic stenosis, is a dynamic or fixed obstruction of flow from the right ventricle of the heart to the pulmonary artery. It is usually first diagnosed in childhood.

In cardiology, a cardiac shunt is a pattern of blood flow in the heart that deviates from the normal circuit of the circulatory system. It may be described as right-left, left-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The direction may be controlled by left and/or right heart pressure, a biological or artificial heart valve or both. The presence of a shunt may also affect left and/or right heart pressure either beneficially or detrimentally.

<span class="mw-page-title-main">Aortopulmonary window</span> Medical condition

Aortopulmonary window (APW) is a faulty connection between the aorta and the main pulmonary artery that results in a significant left-to-right shunt. The aortopulmonary window is the rarest of septal defects, accounting for 0.15-0.6% of all congenital heart malformations. An aortopulmonary window can develop alone or in up to 50% of cases alongside other cardiac defects such as interrupted aortic arch, coarctation of the aorta, transposition of great vessels, and tetralogy of Fallot.

<span class="mw-page-title-main">Hypoplastic right heart syndrome</span> Type of congenital heart disease

Hypoplastic right heart syndrome (HRHS) is a congenital heart defect in which the structures on the right side of the heart, particularly the right ventricle, are underdeveloped. This defect causes inadequate blood flow to the lungs, and thus a cyanotic infant.

<span class="mw-page-title-main">Ventricular outflow tract obstruction</span> Medical condition

A ventricular outflow tract obstruction is a heart condition in which either the right or left ventricular outflow tract is blocked or obstructed. These obstructions represent a spectrum of disorders. Majority of these cases are congenital, but some are acquired throughout life.

References

  1. "right-to-left shunt" at Dorland's Medical Dictionary
  2. 1 2 Rao, PS (Aug 2013). "Consensus on timing of intervention for common congenital heart diseases: part II - cyanotic heart defects". Indian Journal of Pediatrics. 80 (8): 663–74. doi:10.1007/s12098-013-1039-2. PMID   23640699. S2CID   39106680.
  3. Krishnan, U; Rosenzweig, EB (Dec 2013). "Pulmonary arterial hypertension associated with congenital heart disease". Clinics in Chest Medicine. 34 (4): 707–17. doi:10.1016/j.ccm.2013.08.011. PMID   24267300.