The paediatric part of the curriculum asks for knowledge of 'the implications of paediatric medical and surgical problems including... congenital heart disease', without further specifying.
Further detail is in the applied science section, indicating knowledge of 'common congenital heart defects including PFO, ASD, bicuspid AV, VSD' is expected.
In terms of past questions on this topic, only atrial septal defect has come up as a CRQ.
Congenital heart disease is the most common birth defect
Incidence: 1 in 125 live births
Accounts for 1/3rd of all birth defects
May be associated with other diseases e.g. DiGeorge syndrome, Williams syndrome, Downs syndrome, VACTERL diseases
90% of children born with cardiac abnormalities will survive to adulthood
These so-called 'Grown-Up patients with Congenital Heart disease' (GUCH) patients pose an anaesthetic challenge
The commonest presentations are with arrhythmia, heart failure or endocarditis
Shunts
Shunts are described in terms of the direction of blood flow i.e. left-to-right or vice-versa
They can also be described in terms of the location of the shunt (intra-cardiac, vasculature)
The shunt fraction, or ratio of pulmonary to systemic blood flow (Qp:Qs), can be used to describe the degree of shunt
A shunt fraction >1 is indicative of left-to-right shunt, and a fraction >1.5 typically starts to manifest right heart changes (RA enlargement, RV dysfunction)
Conversely, a shunt fraction <1 is indicative of right-to-left shunt
Probably a blend of environmental and genetic factors
Some congenital cardiac defects occur more often in families, pointing to a genetic link
Various environmental factors implicated:
Maternal medications
Maternal conditions
Anti-epileptic drugs
Diabetes (type 1 or 2)
Alcohol
Rubella
Lithium
Influenza during first trimester
Ibuprofen
PKU
Isotretinoin
Organic solvents
The clinical features of congenital heart disease will ultimately depend on the underlying condition, though some generic signs may suggest congenital heart disease if present
Volume-overloaded hearts
Obstructive lesions
Cyanotic heart diseases
Failure to thrive
Collapse
Cyanosis, especially on crying
Recurrent infections
Acidosis
Dyspnoea
Tachycardia
Organ failure
Fatigue
Tachycardia or sweating whilst feeding
Pathological murmurs
Fainting
Tachypnoea
Radio-femoral delays
Stroke
Oedema (face, forearms, back, legs)
Hepatomegaly
These acynatoic lesions are the commonest pathophysiology seen in patients with congenital cardiac disease
The shunt causes progressive right heart volume overload and increased pulmonary blood flow
The relative degrees of SVR and PVR will determine the degree of shunt and its haemodynamic consequences
High PVR in utero limits pulmonary blood flow
At birth, PVR falls and SVR rises
This may cause the shunt to manifest as cardiac failure in the first few weeks of life
Factors reducing PVR will increase the degree of shunt and reduce cardiac output
The foramen ovale is formed from overlapping portions of the septum primum and secundum, creating a 1-way valve
Post-partum, the increased pulmonary blood flow and LA pressure should cause the flap to close
In 20-25% of people there is incomplete fusion of the foramen, leading to a persistent inter-atrial connection
The magnitude of shunt is rarely haemodynamically significant
It can cause paradoxical embolus formation and lead to stroke
It may contribute to hypoxia in the critically ill ventilated patient
PDA
The ductus arteriosus connects the pulmonary artery to the aorta in utero
Allows blood to bypass the pulmonary circulation and return to the placenta
Typically closes within 72hrs of birth
Incomplete obliteration of the ductus arteriosus results in a persistent connection between systemic and pulmonary circulations
The direction and magnitude of the shunt will depend on the relative PVR and SVR
In most patients SVR > PVR and there is left-to-right shunt
In large PDA's, the LVEDV must increase to achieve a normal cardiac output in the presence of the shunt, leading to pulmonary congestion and raised LA pressure
There is flow in both systole and diastole, the latter impairing coronary and splanchnic blood flow
Congenital narrowing of the normal outflow tracts from the heart causes:
Increased ventricular afterload and reduced downstream flow
Subsequent LV hypertrophy, with reduced compliance and higher filling pressures
Venous congestions on exertion, limiting cardiac output and exercise tolerance
Symptoms are generally related to the site of the obstruction and the side of the heart involved
Coarctation of the aorta
A congenital aortic narrowing, classically just distal to the origin of the left subclavian artery where the foetal ductus arteriosus inserted into the aorta
Represents 5-8% of all cases of congenital cardiac disease
Associated bicuspid aortic valve in 50-85% of cases
There is increased pressure proximal to the lesion
Over time, collateral arterial vessels form between the ascending and descending aorta
Leads to classic radiographic sign of rib notching
These collaterals 'mask' the extent of the obstruction
The most dramatic presentation occurs in neonates who are dependent on a patent ductus arteriosus for blood flow distal to the coarctation
After an period asymptomatic period of days - weeks, the duct closes
This immediately limits blood flow distal to the coarctation, causing both systemic hypoperfusion and cardiac failure from LV overload
Clinically this manifests as:
Respiratory distress
Cold & pale lower extremities
Markedly decreased/absent pulses
Mixed metabolic and respiratory acidosis
Pulmonary stenosis
Generally well tolerated until severe, owing to RV hypertrophy and increased RV systolic pressures in response to increased afterload
May be subvalvular, valvular or supravalvular
Isolated subvalvular pulmonary obstruction in adults is typically a residual effect of previous surgery e.g. to correct Tetralogy of Fallot
Isolated valvular pulmonary stenosis occurs in 8-10% of those with congenital heart disease
Mild disease is well tolerated
Moderate disease may be tolerated as a child, but then become more of an issue in adulthood owing to decreased RV compliance with ageing
Severe disease leads to RV hypertrophy
Tends to present with dysrhythmic events and exercise intolerance
Supravalvular pulmonary stenosis can occur:
In isolation
In association with other pathology e.g. ToF, Noonan's syn., Williams' syn., rubella, toxoplasmosis
Following previous surgery e.g. pulmonary artery banding or surgery for transposition of the great arteries
Certain lesions are only compatible with life if the ductus arteriosus remains open
If not recognised, they will present at 5 - 7 days of life when the duct closes
Duct-dependent pulmonary circulation
In these infants, pulmonary blood depends on left-to-right shunt from the aorta through the ductus arteriosus to the pulmonary arteries
Typically caused by right heart obstruction e.g. pulmonary or tricuspid atresia | pulmonary stenosis | Ebstein's anomaly | Tetralogy of Fallot
They lead to tachypnoea and cyanosis, yet there are normal femoral pulses as systemic circulation is unaffected
Duct-dependent systemic circulation
In these infants, systemic circulation depends on right-to-left shunt from the pulmonary artery, through the ductus arteriosus to the aorta
Typically caused by obstruction to blood flow through the left side of the heart e.g. critical AS | coarctation of the aorta | hypoplastic left heart
As the duct closes, there is hypoxia, respiratory distress, severe heart failure, metabolic acidosis and eventually cardiovascular collapse
Femoral pulses are typically absent
General management
In both cases, the initial step is to re-open the duct using prostaglandin infusions, in order to buy time for investigations and planning interventions
For example, dinoprostone (PGE2) infusion 5 - 50ng/kg/min
Side-effects include apnoea, bradycardia, hypotension and hyperthermia and are more common at doses >20ng/kg/min
Perioperative principles in the child with congenital cardiac disease
This section is not intended to be a complete guide on anaesthesia for complex congenital heart disease, but rather to give broad principles should you be unfortunate enough to be asked such a question in a viva
Pre-operative
Work out the anatomical and physiological differences, and how that will influence your desired balance of SVR, PVR and myocardial contractility
Requires:
Senior paediatric-specialist cardiac anaesthetist
Early involvement of paediatric cardiologists, ensuring not to stop drugs in the perioperative period without their input
Input from paediatric cardiothoracic surgeons ± PICU
Plan post-operative care in advance
Intra-operative
Anticipate difficult IV access
Consider invasive monitoring
Emergency drugs drawn up inc. phenylephrine and adrenaline 'lite'
Avoid hypothermia prior to going on bypass as hypothermia will raise PVR among other negative sequelae
Keep well hydrated but avoid overload
Maintain normal Hb
Meticulously avoid air injection, as may cause paradoxical right-to-left emboli and strokes
Need to ensure balance of PVR and SVR
Decreasing PVR ± increasing SVR will increase the degree of shunt
Increasing PVR ± decreasing SVR will reduce the degree of shunt but can lead to shunt reversal
In general need to have tight control over factors affecting pulmonary vascular resistance
Both inhalational and IV induction are safe if there's no pulmonary hypertension
Sevoflurane induction is often well tolerated although need to beware the myocardial depressant effects of inhalational anaesthesia
The degree of obstructive will determine the presentation
Critical lesions may lead to profound neonatal collapse requiring urgent resuscitation and intervention
Interventions may be medical, surgical or via IR
Anaesthetic conduct similar for adult stenotic lesions:
Maintain heart rate 60 - 90bpm
Maintain sinus rhythm and aggressive treatment of arrhythmia
Maintain SVR with vasoconstrictors e.g. phenylephrine (although prevent excessive increases in afterload)
Maintain coronary perfusion pressure by maintaining diastolic BP (Because CPP = AoDBP - LVEDP)
Maintain euvolemia without overload
Parallel circulations i.e. transposition of the great arteries
These are incompatible with life unless there is some pulmonary-systemic mixing e.g. an AVSD
Blood flow in each circuit depends on the relative resistance within them i.e. SVR and PVR
Typically accept saturations 75 - 80%; too high an FiO2 and PVR will drop, compromising systemic blood flow
Avoid dehydration, especially if polycythaemic
Single ventricle states
Both AV valves connect to a single ventricle, from which arises one great artery (aorta or pulmonary artery)
There is a rudimentary chamber, from which the other great artery arises
They are complex congenital defects which typically undergo a three-stage palliative repair:
Blalock-Taussig shunt, Sano shunt or Norwood Procedure for hypoplastic left heart syndrome
Glenn procedure
Fontan completion, which leads to total cavo-pulmonary connection
Need to ensure forward flow by:
Avoiding reductions in venous return e.g. high PEEP, tight tube ties, excessive PPV, raised intra-abdominal pressure
Aiming for a low-normal by controlling PCO2
Adequate inotropy
Carefully titrate induction agent to avoid myocardial suppression
Use of dopamine or milrinone
Maintaining sinus rhythm at an age-appropriate rate
Avoiding hypovolaemia, which is poorly tolerated
Patients should be kept euvolaemic, transfusing as necessary to maintain DO2
Quick surgery is better to avoid high insensible losses during cardiac surgery (up to 10ml/kg/hr)
Risk Factors
<2yrs old
Complex lesions e.g. single ventricle, AS, cardiomyopathy
Major surgery
Emergency surgery
Existing long-term sequelae
Arrhythmia
Some operations are at higher risk, especially those with extensive atrial suturing or ventriculotomy
Necrosis and fibrosis extends into the conducting system
Ventricular ectopic beats on pre-operative ECG is an ominous sign; 30% will die suddenly
The optimal anaesthesia for arrhythmia prevention is not well described
Avoid desflurane as it prolongs the QTc, even in normal children
Avoid arrhythmogenic factors e.g. hypoxia, hypercarbia, acidosis, LA with adrenaline
Cardiac failure
Cardiac failure is usually the end result of a persistently volume-loaded heart, although it can arrive de novo e.g. due to myocarditis or other cardiomyopathy
Patients are at high risk; both IV and inhalational induction agents are bad so one administered patiently at low dose is preferable
Could consider ketamine, although if there is a poor sympathomimetic response (e.g. patients with high resting sympathetic tone) then can cause myocardial compression too
May need early inotropic (dopamine, adrenaline) or vasopressor (phenylephrine) support
Need to be cautious with fluid shifts; exogenous IV fluids, Trendelenburg or even flat positioning can increase venous return and overload the heart
Pulmonary hypertension
Avoid factors which can increase PVR further
Need to involve PICU ± cardiac/pulmonary HTN centres