FRCA Notes

Tetralogy of Fallot

This topic bridges the paediatric and cardiac anaesthetic curricula, but hasn't been a SAQ/CRQ question as of yet.

There's no dedicated curriculum item, but instead comes under: 'recalls the implications of paediatric medical problems including congenital heart disease'.

Resources

  • Tetralogy of Fallot is the commonest cyanotic congenital heart disease

  • As its name suggests, it comprises of four cardiac defects:
    1. RVOT obstruction: at the pulmonary valve (pulmonary stenosis) or proximally within the infundibulum
    2. Ventricular septal defect: a single, large, non-restrictive hole in the ventricular septum
    3. Over-riding aorta: an aortic valve with a bi-ventricular connection i.e. connected to both ventricles and situated above the VSD
    4. RV hypertrophy: as a consequence of RVOT obstruction

  • Incidence 3 in 10,000 births
  • Male gender
  • 1st degree family history of congenital heart disease
  • Presence of teratogens during pregnancy
  • Other genetic conditions:
    • Down's syndrome
    • DiGeorge syndrome
    • 22q11 chromosome deletion syndrome
    • Cleft lip/palate

  • There is right-to-left shunt across the VSD, with subsequent cyanosis dye to lack of pulmonary blood flow and deoxygenated blood entering the systemic circulation
  • The degree of shunt is determined by the pressure gradient between the RV and LV

  • The amount of pulmonary blood flow is determined by the degree of RVOT obstruction
  • RVOT obstruction has both fixed (e.g. pulmonary stenosis) and dynamic (infundibular spasms) components

  • Right ventricular hypertrophy leads to impaired RV diastolic function
  • Therere is raised RVEDP and a dependence on increased venous return for adequate RV filling

Hypercyanotic spells

  • Hypercyanotic (a.k.a 'Tet') spells are precipitated by acute increases in PVR (due to infundibular spasm) or decreases in SVR

    • Increased PVR Decreased SVR
    Crying Hot baths
    Defaecation Vasoplegia from infection
    Feeding Induction of anaesthesia
    Pain Other vasodilating drugs
    Anxiety
    Sympathetic stimulation

  • This increases right-to-left shunt across the VSD
  • There is therefore venous blood shunted into the arterial circulation, leading to:
    • Reduced PaO2
    • Increased PaCO2
    • Reduced pH
  • These changes further increase PVR, exacerbating the issue

  • Attempted compensation for this leads to:
    • Tachypnoea
    • Generation of more negative intrathoracic pressure
    • Increased venous return because of this
  • This causes an unhelpful increase in right-to-left shunting and therefore a vicious cycle

Management of Tet spells

  • Correct underlying cause or remove precipitant

    • Reduce PVR Increase SVR
    Administer 100% oxygen Squatting or knees-to-chest position
    Relieve distress with sedation e.g. BZD, opioids, ketamine Fluid bolus
    β-blockers to control infundibular spasm e.g. esmolol Vasopressors

  • Ultimately, patients may require I&V to correct hypoxaemia and hypercapnoea if there is no improvement

  • There is an excellent prognosis following surgical repair

Pre-repair

  • Prostaglandin infusions may be required to prevent closure of the ductus arteriosus in those with duct-dependent circulations
  • Patients will then go on to have a palliative procedure (see below)

  • Medical management may involve:
    • β-blockers to reduce infundibular spasm
    • Diuretics to manage acyanotic patients with large shunts causing cardiac failure

  • Cardiac catheter interventions
    • To improve pulmonary blood flow e.g. RVOT stenting, pulmonary valvotomy
    • To maintain a patent ductus arteriosus e.g. stenting of the DA

  • In patients with profound cyanosis, not yet suitable for full repair, a temporising (palliative) systemic-to-pulmonary shunt can be created
  • The most commmon is the modified Blalock-Taussig shunt, which connects the subclavian artery to the ipsilateral pulmonary artery via a prosthetic tube

Repair

  • The majority of cases are managed with a single, complete repair
  • Complete repair of TOF normally takes place prior to 6 months of age to reduce the pathophysiological adaptations in ToF
  • Early repair is associated with improved mortality
  • It involves:
    • VSD closure, separating the pulmonary & systemic circulation
    • RVOT enlargement, improving pulmonary blood flow
    • Septation of the overriding aorta
    • Repair of other abnormalities found at the time

Post-repair

  • Patients who have had their ToF repaired may still present for further surgery such as:
    • Pulmonary valve surgery
    • Cardiac arrhythmia ablations
    • ICD insertion

    • Any normal non-cardiac surgery
    • Obstetric interventions

Perioperative management of the patient with Tetralogy of Fallot


History and examination

  • Surgical intervention to date
  • Presence, frequency and severity of Tet spells
  • Features of cardiac insufficiency such as tachypnoea, tachycardia, sweating, cool peripheries, poor feeding, failure to thrive or hepatomegaly
  • Features associated with polycythaemia e.g. stroke, developmental delay, intracranial abscesses
  • Baseline oxygen saturations (if known)

  • History of associated syndromes and their relevant features

  • Drugs
    • Patients may be on propranolol to reduce risk of infundibular spasm
    • Those who have had palliative procedures tend to be on aspirin
    • May be on anticoagulants if prior valve repair has taken place

Investigations

  • Bloods
    • FBC - may be polycythaemic and required venesection if Hct >0.65
    • U&E - may be electrolyte deplete due to diuretic therapy
    • Clotting studies - coagulopathy often present

  • ECG
    • RBBB post-repair
    • QRS >180ms associated with malignant arrhythmia generation

  • TTE
    • Right ventricular function, size and severity of pulmonary regurgitation
    • Left ventricular function
    • Evidence of aortic regurgitation or aortic root dilatation
    • Residual VSD or RVOT obstruction

  • Cardiac CT or MRI, to elicit cardiac morphology and myocardial function
  • Holter monitoring, to check for arrhythmias which are common following ToF repair

Risk assessment

  • CPET or other functional capacity assessments can be performed
  • Overall patients are at high perioperative risk owing to the presence of pulmonary hypertension, arrhythmias and cardiac failure

Optimisation

  • Will generally be under the care of a Cardiologist
  • Should have surgery in a tertiary centre

  • Premedication to avoid sympathetic drive (and raised PVR) may be sensible, with your paediatric sedative of choice

Haemodynamic goals

  • There is a fine balance between PVR and SVR
    • Increased PVR ± decreased SVR = poor pulmonary blood flow and desaturation
    • Decreased PVR ± increased SVR = better pulmonary blood flow but decreased systemic blood flow
  • Want to strike the correct balance to avoid coronary ischaemia
  • Overall saturations 75-85% are ok

    • Factor Goal Notes
    Heart rate Avoid tachycardia Disproportional reduction in (RV) diastolic time, compromising filling and RV stroke volume
    Preload 'Full' Poor RV compliance
    Stents open RVOT
    Contractility Avoid excessive contractility
    Avoid decreases in contractility    		 Excessive contractility may ↑ dyanmic RVOT obstruction
    Poor RV contractility may worsen shunt
    PVR (RV afterload) Low Encourage pulmonary blood flow
    SVR High Reduce right-to-left shunting

Monitoring and access

  • AAGBI
  • Arterial line, although femoral site is preferred as subclavian artery may be needed for shunts
  • CVC, to facilitate use of inotropes or inodilators
  • Depending on the surgery:
    • TOE
    • NIRS

Anaesthetic technique

  • Prior to surgical repair, the need to maintain SVR and reduce PVR means regional anaesthesia is relatively contra-indicated
  • Following surgical repair, both GA and RA are generally acceptable
  • However, patients have residual cardiac issues (e.g. RV failure, arrhythmias) which may influence choice and conduct of anaesthesia

  • The particular drug or method of induction is probably a secondary consideration behind a carefully titrated induction technique in experienced hands
  • Options may include:
    • Inhalational induction
    • Ketamine, owing to its SVR-maintaining properties
    • Opioid-heavy techniques inc. remifentanil
    • Dexmedetomidine
  • Propofol is generally avoided due to its cardiodepressant and SVR-reducing effects

  • Anticipate difficult airway due to presence of other congenital syndromes or other tracheal abnormalities (11%)
  • Avoid excessive PPV or PEEP as may increase PVR

Haematological management

  • Haemostatic function is often compromised:
    • Raised PT or APTT
    • Low platelet number (or platelet dysfunction)
    • Low fibrinogen
    • Excess fibrinolysis
  • Therefore need to consider all children as high risk of bleeding

  • Be wary of high (>60%) haematocrit which can predispose to clots
  • If >60% (or [Hb]>18g/L) consider IV fluids
  • Avoid dehydration, iron deficiency and fever

Other considerations


  • ICU environment with continuous monitoring

Analgesia

  • Opioid-heavy techniques
  • Avoid NSAIDs due to existing coagulopathy, renal dysfunction and duct-dependent circulations requiring prostaglandins

Complications

  • Paradoxical air embolus - must ensure air-free lines or use air filters

  • Arrhythmias
    • Junctional ectopic tachycardia post-repair
    • Atrial flutter or AF
    • VT or VF

  • Tet spells

  • RV failure or congestive cardiac failure

  • Pleural effusions