Cardiac Shunt: Symptoms, Causes, Diagnosis and Treatment
Table of Contents
Key takeaways
- A cardiac shunt means blood is moving through an abnormal opening or connection in the heart or nearby great vessels.
- Many shunts are congenital, but the effect on health depends on the size, direction of blood flow, pressure in the lungs and whether other heart defects are present.
- Symptoms can include breathlessness, poor exercise tolerance, blue lips or fingers, fatigue, palpitations, recurrent chest infections or poor growth in babies.
- Assessment usually involves echocardiography and specialist cardiology review; treatment may include monitoring, medicines, catheter closure or surgery.
- Use NHS 111 for urgent advice or call 999 in a life-threatening emergency, especially with severe breathlessness, chest pain, fainting or blue discolouration.
Overview
A cardiac shunt is an abnormal route for blood flow through the heart or between the heart and major blood vessels. Instead of following the usual path from the right side of the heart to the lungs, then to the left side of the heart and out to the body, some blood crosses through a hole or abnormal vessel connection. The word shunt describes the direction and effect of this flow, not one single diagnosis.
The most familiar shunts include atrial septal defect, ventricular septal defect, atrioventricular septal defect and patent ductus arteriosus. Some are found in infancy after a murmur, poor feeding or blue colouring. Others are small and discovered later during an echocardiogram for breathlessness, palpitations or an unrelated check.
The clinical importance depends on physiology. A left-to-right shunt sends extra oxygen-rich blood back to the lungs, which can overload the right side of the heart and pulmonary circulation over time. A right-to-left shunt allows oxygen-poor blood to bypass the lungs and enter the body, which can cause cyanosis, low oxygen levels and exercise limitation. Long-standing high-flow shunts can contribute to pulmonary hypertension and, in severe cases, irreversible changes in the lung blood vessels.
Types of cardiac shunt
Atrial septal defect (ASD) is an opening between the two upper chambers of the heart. Small ASDs may cause few symptoms, while larger defects can lead to right-sided heart enlargement, palpitations, breathlessness or reduced stamina in adulthood.
Ventricular septal defect (VSD) is an opening between the two lower pumping chambers. A small VSD may only cause a murmur. A larger VSD can increase blood flow to the lungs, making babies breathe fast, sweat during feeds, gain weight slowly or develop signs of heart failure.
Atrioventricular septal defect involves the centre of the heart and the valves between the upper and lower chambers. It is often diagnosed in infancy and is more common in babies with Down syndrome. Because both septal tissue and valve function may be affected, early specialist assessment is important.
Patent ductus arteriosus is a persistent connection between the aorta and pulmonary artery after birth. It can be small and monitored or large enough to cause extra lung blood flow and heart strain. Some complex congenital heart conditions also involve deliberately maintained or surgically created shunts as part of staged treatment, which is different from an untreated defect.
Symptoms
Symptoms vary widely. Some people have no obvious symptoms and the shunt is found because a clinician hears a heart murmur. Others notice breathlessness on exertion, tiredness, reduced exercise capacity, frequent respiratory infections, palpitations or swelling of the ankles. Babies may breathe quickly, tire during feeds, sweat, have poor weight gain or appear blue around the lips and fingers.
Symptoms are shaped by the shunt size and direction. Extra blood flow to the lungs can make the heart work harder and cause breathlessness or poor feeding. Low oxygen levels may cause blue discolouration, dizziness or fatigue. Rhythm disturbances can occur when chambers stretch or after previous heart surgery. Pregnancy can place additional strain on the heart, so anyone with known congenital heart disease should have pre-pregnancy and antenatal cardiology advice.
Causes and risk factors
Most cardiac shunts are congenital, meaning they arise while the heart forms during pregnancy. Often there is no single identifiable cause. Risk can be influenced by genetic conditions, family history of congenital heart disease, some maternal infections, poorly controlled diabetes, some medicines, alcohol exposure and smoking during pregnancy. These factors do not explain every case, and parents should not assume blame without a clinician explaining the likely cause.
Acquired shunts are less common but can happen after a heart attack, trauma, infection, previous surgery or certain catheter-based procedures. For example, a ventricular septal rupture after myocardial infarction is a medical emergency because blood suddenly crosses between the ventricles and the heart may fail to maintain circulation.
Diagnosis
Diagnosis starts with a history, examination, oxygen saturation measurement and listening for murmurs. Echocardiography is usually the key test because it shows heart structure, chamber size, valve function, flow direction and pressure clues. An ECG may assess rhythm and chamber strain. A chest X-ray can show heart size or lung congestion. Cardiac MRI, CT or catheterisation may be used when anatomy is complex, when pressure measurements are needed or when a closure procedure is being planned.
Specialist interpretation matters. A small shunt that is harmless for one person may need treatment in another because of symptoms, chamber enlargement, pulmonary pressures, arrhythmia or pregnancy plans. Self-diagnosis is not reliable because breathlessness, chest discomfort and fatigue have many possible causes.
Treatment and management
Treatment is personalised after cardiology assessment. Small defects with no chamber enlargement may need observation, periodic echocardiograms and advice about symptoms to report. Medicines do not close most structural shunts, but they may be used to manage heart failure symptoms, rhythm problems, blood pressure or fluid overload while a plan is made.
Closure may be recommended when the shunt is large enough to cause symptoms, right-heart enlargement, excess lung blood flow or other complications. Some ASDs, VSDs and patent ductus arteriosus defects can be closed using a catheter device passed through a blood vessel. Others need open-heart surgery, especially if the anatomy is complex or valve repair is required. The choice depends on age, size and position of the defect, pulmonary pressures, associated heart problems and procedural risk.
For advanced pulmonary hypertension or Eisenmenger physiology, closure may be unsafe because the shunt can be part of how the circulation has adapted. These cases need specialist congenital heart disease and pulmonary hypertension care.
Self-care and prevention
There are no home remedies that close a cardiac shunt. Practical self-care means attending follow-up, taking prescribed medicines as directed, keeping vaccinations current, avoiding smoking, seeking advice before pregnancy and asking the cardiology team about exercise limits, dental care and endocarditis prevention. People with repaired or unrepaired congenital heart disease should know who to contact if symptoms change.
Not all congenital shunts can be prevented. General pregnancy health measures, such as avoiding smoking and alcohol, managing diabetes, taking recommended folic acid and reviewing medicines before conception, may reduce some risks but cannot remove all congenital heart disease risk.
When to seek medical advice
Seek medical advice promptly for new breathlessness, reduced exercise tolerance, palpitations, fainting, swelling, chest discomfort, blue lips or fingers, poor feeding in a baby or unexplained poor growth. Use NHS 111 for urgent advice if symptoms are concerning but not immediately life-threatening.
Call 999 if there is severe breathlessness, crushing chest pain, collapse, severe blue discolouration, confusion, or a baby is struggling to breathe or is difficult to rouse.
Sources
- NHS: Congenital heart disease: https://www.nhs.uk/conditions/congenital-heart-disease/
Relevance: Explains congenital heart disease symptoms, causes, diagnosis and treatment pathways for a UK audience. - Mayo Clinic: Atrial septal defect: mayoclinic.org guidance page link unavailable during validation (mayoclinic.org guidance page, link unavailable during validation)
Relevance: Provides benchmark condition-page coverage for one common cardiac shunt. - Mayo Clinic: Ventricular septal defect: mayoclinic.org guidance page link unavailable during validation (mayoclinic.org guidance page, link unavailable during validation)
Relevance: Supports symptom, cause and treatment discussion for ventricular shunts. - NHLBI: Congenital heart defects: https://www.nhlbi.nih.gov/health/congenital-heart-defects
Relevance: Gives additional authoritative detail on types, diagnosis and treatment of congenital heart defects.
Disclaimer
Educational only. Results vary. Not a cure.
Details that must be confirmed before publishing: confirm whether WHM wants this article to focus on congenital shunts only or include acquired and surgically created shunts.