Ventricular Septal Defect

Question 1

A 6-month-old male infant with a known ventricular septal defect (VSD) presents for elective repair of his cardiac lesion. You are asked to see the patient and his parents on the ward prior to his procedure.

What is a ventricular septal defect?

Answer 1

• A VSD is an abnormal communication between the left and right ventricles, due to a defect in the interventricular septal wall.
• It is the most commonly occurring congenital cardiac defect.

Question 2

How can you classify congenital cardiac defects?

Answer 2

• “Simple” left to right shunt, leading to increased pulmonary blood flow:
• Atrial septal defect (ASD).
• VSD.
• Atrioventricular septal defect (AVSD).
• Patent ductus arteriosus (PDA).
• “Simple” right to left shunt, leading to reduced pulmonary blood flow and cyanosis:
• Pulmonary atresia.
• Tetralogy of Fallot: right ventricular outflow tract obstruction, RV
  hypertrophy, VSD, and overriding aorta.
• Tricuspid atresia.
• “Complex” lesions, with mixing of pulmonary and systemic blood and resulting cyanosis:
• Hypoplastic left heart syndrome.
• Transposition of the great arteries (TGA).
• Truncus arteriosus.
• Obstructive defects:
• Coarctation of the aorta.
• Aortic stenosis.
• Pulmonary stenosis.

Question 3

What symptoms and signs may be seen in this patient?

Answer 3

Symptoms:
* If the VSD is small, patients may be asymptomatic.
* With moderate or large VSDs, patients can manifest with symptoms
related to the increased pulmonary blood flow, and development of CHF, including:
- Reduced growth and development or failure to thrive.
- Respiratory distress, which may be more apparent during, or can
limit, feeding.
- Recurrent respiratory tract infections.
- Sweating.
- Poor exercise tolerance.
- No cyanosis unless there has been the development of Eisenmenger syndrome and therefore shunt reversal.

Signs:
* Pansystolic murmur at the left sternal border.
* Precordial thrill.
* Tachypnoea, dyspnoea, respiratory distress.
* Hepatomegaly.

Question 4

What are the pathophysiological effects in a patient with a VSD?

Answer 4

• VSDs cause:
• Intracardiac shunting.
• Congestive cardiac failure.
• The development of pulmonary hypertension over time.
• Small VSDs that exhibit resistance to blood flow across the lesion, and therefore that limit shunting, are deemed “restrictive”. Large VSDs that exhibit no resistance to shunt flow across the lesion are deemed “non-restrictive”.
• A VSD produces a left to right shunt. Some oxygenated blood from the left ventricle passes through the VSD to the right ventricle, mainly during systole, instead of ejection into the systemic circulation.
• In order to maintain an adequate systemic cardiac output in the presence of a left to right shunt, compensatory mechanisms are activated such as the sympathetic nervous system and the renin-angiotensin-aldosterone system. (However, these mechanisms can actually worsen the pathophysiology and symptomatology.)

Question 5

What are the pathophysiological effects in a patient with a VSD?

Continued…

Answer 5

• The left to right shunt causes increased pulmonary blood flow, and pulmonary overcirculation, leading to:
• Increased left atrial and left ventricular blood volume, thereby
  leading to LV volume overload and dilatation, LV hypertrophy,
  and LA dilatation.
• Pulmonary oedema, and over time, reactive pulmonary vascular
  changes and an increased PVR, leading to pulmonary hypertension and RV failure.
• The RV can also be directly affected by the volume overload and particularly the high pressure from the LV transmitted through large non-restrictive VSDs.
• If large, non-restrictive VSDs remain unrepaired, over time pulmonary hypertension gradually worsens and RV pressures increase. Ultimately, if pulmonary arterial or RV pressures exceed systemic arterial or LV pressures, the shunt reverses, and blood flows right to left across the VSD, resulting in cyanosis.
• The development of fixed severe pulmonary hypertension, shunt reversal and cyanosis signifies the existence of Eisenmenger syndrome.

Question 6

What are the key considerations in the preoperative assessment of this patient?

1) History?

Answer 6

• Ask the parents about any symptoms of respiratory tract infections such as fever, cough, coryza, wheeze or shortness of breath. A recent infection can predispose the patient to increased comorbidities following cardiopulmonary bypass.
• Explore symptoms related to cyanosis, dysrhythmias, congestive cardiac failure and pulmonary hypertension.
• A full anaesthetic history should be taken including a full medical and birth history; any previous anaesthetics or stays on neonatal intensive care; regular medication including timings and known allergies. VSDs can be associated with congenital abnormalities such as Trisomy 13, 18 and 21, which may increase the risk of other systemic conditions/defects, in particular airway abnormalities.
• A discussion about the anaesthetic procedure, risks, and consent should be included in the preoperative assessment, including the insertion of invasive lines, PICU postoperative stay, and potential need for blood or blood product transfusion.

Question 7

What are the key considerations in the preoperative assessment of this patient?
2) Examination
3) Investigations

Answer 7

Examination:
* A full examination including an airway assessment should be done looking for the signs listed above.

• Venous access in these patients can be challenging. Look for potential sites during the preoperative examination.

Investigations:
* Baseline blood tests to include a full blood count, clotting screen, blood group and screen for antibodies, electrolytes and renal and liver function. Ensure appropriate blood has been ordered and is available.
* An ECG (for LA or LV/RV hypertrophy).
* Echo (for VSD location and size, shunt direction, ventricular chamber
size and function, estimates of pulmonary arterial pressure, and the
presence of any other anomalies or defects).
* Chest X-ray (for cardiomegaly, pulmonary oedema and pulmonary
vascular markings).

Question 8

The patient is anaesthetised for VSD repair. What ventilatory strategy would you adopt during the operative period prior to cardiopulmonary bypass, and why?

Answer 8

• Avoid high inspired concentrations of oxygen.
• Avoid hypocarbia. Aim for high-normal end tidal carbon dioxide.
• This patient has a left to right shunt. High oxygen concentrations
  and hypocapnia will decrease the pulmonary vascular resistance, thereby increasing the degree of left to right shunt. This will lead to an increase in pulmonary blood flow at the expense of systemic blood flow, thereby resulting in systemic hypotension, reduced coronary perfusion pressure, and reduced end-organ perfusion – all of which should be avoided.

Question 9

The patient undergoes uneventful surgical closure of the VSD. List some issues that could occur in the early postoperative period?

Answer 9

• SIRS response.
• Bleeding and coagulopathy.
• Cardiac tamponade.
• Low cardiac output state (other than due to tamponade).
• Tachy-dysrhythmias or heart block.
• Pulmonary hypertensive crisis.
• Presence of a residual defect.