Cardiovascular shunts

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Cardiovascular (cardiac) shunts are abnormal connections between the pulmonary and systemic circulations. Most commonly they are the result of congenital heart disease.

Pathology

Blood can either be shunted from the systemic circulation to pulmonary circulation ~~(left~~(i.e. 'left-to-right shunt') or between the pulmonary circulation and systemic circulation ~~(right~~(i.e. 'right-to-left shunt')^1-4. Rarely, the shunted blood returns to the same cardiac chamber without traversing a capillary bed, termed a 'circular shunt' ^5-7.

Left-to-right shunt

In a left-to-right shunt oxygenated blood flows directly from the systemic circulation to the pulmonary circulation, which results in decreased tissue oxygenation through reduced cardiac output^1-4. Causes include^1-4:

cardiac
- ventricular septal defect (VSD)
- atrial septal defect (ASD)
- atrioventricular septal defect
- patent ductus arteriosus (PDA)
- Gerbode defect
vascular pulmonary shunts
- total/partial anomalous pulmonary venous return (TAPVR/PAPVR)

Right-to-left shunt

In a right-to-left shunt deoxygenated blood flows directly from the pulmonary circulation to the systemic circulation, decreasing tissue oxygenation by reducing the oxygen content of systemic arterial blood^1-4. Causes include^1-4:

cardiac
vascular pulmonary shunts
- pulmonary arteriovenous malformations
- hepatopulmonary syndrome
parenchymal intrapulmonary shunts

Circular shunt

In most left-to-right or right-to-left cardiovascular shunts, shunted blood returns to the same chamber after traversing a capillary bed (either pulmonary or peripheral), if this does not occur then the term 'circular shunt' can be employed ⁵. Such shunts are generally present in complex congenital heart defects ^5-7.

Examples that have been described in the literature include:

a ventricular septal defect, pulmonary stenosis, tricuspid regurgitation, and a patent foramen ovale⁵: some blood moves from the left atrium to the left ventricle, shunts to the right ventricle, regurgitates into the right atrium, and shunts back to the left atrium without traversing a capillary bed
a patent foramen ovale, pulmonary atresia, and a Gerbode defect⁶: some blood shunts from the right atrium to the left atrium, to the left ventricle, and shunts back to the right atrium without traversing a capillary bed
a communication between a pulmonary artery and the right atrium⁷: some blood moves from the right atrium to the right ventricle, to the pulmonary artery, and communicates back to the right atrium without traversing a capillary bed

Radiographic features

Imaging findings vary depending on the underlying aetiology, please see articles listed above for further details.

-<p><strong>Cardiovascular (cardiac) shunts</strong> are abnormal connections between the pulmonary and systemic circulations. Most commonly they are the result of <a href="/articles/congenital-cardiovascular-anomalies">congenital heart disease</a>.</p><h4>Pathology</h4><p>Blood can either be shunted from the systemic circulation to pulmonary circulation (left-to-right shunt) or between the pulmonary circulation and systemic circulation (right-to-left shunt).</p><h5>Left-to-right shunt</h5><p>In a left-to-right shunt oxygenated blood flows directly from the systemic circulation to the pulmonary circulation, which results in decreased tissue oxygenation through reduced cardiac output. Causes include:</p><ul>
+<p><strong>Cardiovascular (cardiac) shunts</strong> are abnormal connections between the pulmonary and systemic circulations. Most commonly they are the result of <a href="/articles/congenital-cardiovascular-anomalies">congenital heart disease</a>.</p><h4>Pathology</h4><p>Blood can either be shunted from the systemic circulation to pulmonary circulation (i.e. 'left-to-right shunt') or between the pulmonary circulation and systemic circulation (i.e. 'right-to-left shunt') <sup>1-4</sup>. Rarely, the shunted blood returns to the same cardiac chamber without traversing a capillary bed, termed a 'circular shunt' <sup>5-7</sup>.</p><h5>Left-to-right shunt</h5><p>In a left-to-right shunt oxygenated blood flows directly from the systemic circulation to the pulmonary circulation, which results in decreased tissue oxygenation through reduced cardiac output <sup>1-4</sup>. Causes include <sup>1-4</sup>:</p><ul>
-</ul><h5>Right-to-left shunt</h5><p>In a right-to-left shunt deoxygenated blood flows directly from the pulmonary circulation to the systemic circulation, decreasing tissue oxygenation by reducing the oxygen content of systemic arterial blood. Causes include:</p><ul>
+</ul><h5>Right-to-left shunt</h5><p>In a right-to-left shunt deoxygenated blood flows directly from the pulmonary circulation to the systemic circulation, decreasing tissue oxygenation by reducing the oxygen content of systemic arterial blood <sup>1-4</sup>. Causes include <sup>1-4</sup>:</p><ul>
~~-<li><a title="Eisenmenger syndrome" href="/articles/eisenmenger-syndrome-1">Eisenmenger syndrome</a></li>~~
+<li><a href="/articles/eisenmenger-syndrome-1">Eisenmenger syndrome</a></li>
-</ul><h4>Radiographic features</h4><p>Imaging findings vary depending on the underlying aetiology, please see articles listed above for further details.</p><h4>See also</h4><ul><li><a href="/articles/extracardiac-shunts">extracardiac shunts</a></li></ul>
+</ul><h5>Circular shunt</h5><p>In most left-to-right or right-to-left cardiovascular shunts, shunted blood returns to the same chamber after traversing a capillary bed (either pulmonary or peripheral), if this does not occur then the term 'circular shunt' can be employed <sup>5</sup>. Such shunts are generally present in complex congenital heart defects <sup>5-7</sup>.</p><p>Examples that have been described in the literature include:</p><ul>
+<li>a <a href="/articles/ventricular-septal-defect-1">ventricular septal defect</a>, <a href="/articles/pulmonary-valve-stenosis">pulmonary stenosis</a>, <a href="/articles/tricuspid-valve-regurgitation-1">tricuspid regurgitation</a>, and a <a href="/articles/patent-foramen-ovale">patent foramen ovale</a> <sup>5</sup>: some blood moves from the <a href="/articles/left-atrium-1">left atrium</a> to the <a href="/articles/left-ventricle">left ventricle</a>, shunts to the <a href="/articles/right-ventricle">right ventricle</a>, regurgitates into the <a href="/articles/right-atrium">right atrium</a>, and shunts back to the <a href="/articles/left-atrium-1">left atrium</a> without traversing a capillary bed</li>
+<li>a <a href="/articles/patent-foramen-ovale">patent foramen ovale</a>, <a href="/articles/pulmonary-artery-atresia">pulmonary atresia</a>, and a <a href="/articles/gerbode-defect">Gerbode defect</a> <sup>6</sup>: some blood shunts from the <a href="/articles/right-atrium">right atrium</a> to the <a href="/articles/left-atrium-1">left atrium</a>, to the <a href="/articles/left-ventricle">left ventricle</a>, and shunts back to the <a href="/articles/right-atrium">right atrium</a> without traversing a capillary bed</li>
+<li>a communication between a <a href="/articles/pulmonary-trunk">pulmonary artery</a> and the <a href="/articles/right-atrium">right atrium</a> <sup>7</sup>: some blood moves from the <a href="/articles/right-atrium">right atrium</a> to the <a href="/articles/right-ventricle">right ventricle</a>, to the <a href="/articles/pulmonary-trunk">pulmonary artery</a>, and communicates back to the <a href="/articles/right-atrium">right atrium</a> without traversing a capillary bed</li>
+</ul><h4>Radiographic features</h4><p>Imaging findings vary depending on the underlying aetiology, please see articles listed above for further details.</p><h4>See also</h4><ul>
+<li><a href="/articles/extracardiac-shunts">extracardiac shunts</a></li>
+<li>
+<a href="/articles/paediatric-cardiovascular-procedures">paediatric cardiovascular procedures</a> (many of which are mechanical shunts)</li>
+</ul>

References changed:

5. Shone JD, Anderson RC, Elliott LP, Amplatz K, Lillehei CW, Edwards JE. “Circular” shunt resulting from co-existent ventricular septal defect, pulmonary valvular stenosis, congenital tricuspid insufficiency, and patent foramen ovale. (1962) Am Heart J. 64:547–55.
6. Jue KL, Noren G, Edwards JE. Pulmonary atresia with left ventricular-right atrial communication: basis for circular shunt. (1966) Thorax. 21 (1): 83-90. <a href="https://www.ncbi.nlm.nih.gov/pubmed/5934846">Pubmed</a> <span class="ref_v4"></span>
7. Singhi AK, Sivakumar K. Circular shunt in a pulmonary artery to right atrial tunnel, an anomaly unreported so far. (2014) Annals of Pediatric Cardiology. 7 (2): 155. <a href="https://doi.org/10.4103/0974-2069.132504">doi:10.4103/0974-2069.132504</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/24987267">Pubmed</a> <span class="ref_v4"></span>