202406292351

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Tags: cardiology, CTS

Congenital heart disease

Background

around 1% of all live births having CHD
up to 90% surviving into adulthood
30% of CHD patients have non-cardiac congenital anomalies

Classification

• #By structure
• #By physiology

By structure

• Normal
• Balanced
• #completed single ventricular circulation

normal = ‘in series’

• predominant path of blood flow follows that of a structurally normal heart

Examples

• small septal defects, w/ simple shunts
• surgically corrected CHD

balanced = ‘in parallel’

Large cardiac defects lead to mixing of deoxygenated and oxygenated blood, and consequently a parallel or ‘balanced’ circulation

Flow to the systemic and pulmonary vasculature depends upon the relative resistances (i.e. the balance) of PVR vs SVR. Excessive blood flow to one area compromises blood flow to the other.

Chronic hypoxia can lead to abnormal clotting and hyperviscosity

Table 1. Factors affecting pulmonary blood flow

completed single ventricular circulation

When patients are born with a hypoplastic ventricle, surgery is palliative and leads to a single ventricular circulation. This is usually a three-stage process

Hypoplastic left heart anatomy showing features of

• a hypoplastic left ventricle (LV)
• hypoplastic aortic arch (Ao)
• an atrial septal defect (ASD)
  

Stage 1: Norwood procedure:

• atrial septostomy,
• anastomosis of Ao → PA
  • → 'neo-aorta'
• formation of a modified Blalock–Taussig shunt (mBTS)
  • Sano modification
    • RV-PA conduit
    • • PDA ligation
  • to supply pulmonary blood flow
    For illustrative purposes, both mBTS and Sano shunt are included in this diagram.
    

Stage 2: Glenn shunt / bidirectional Glenn / Hemi-Fontan:

at age 3-5mo

• mBTS or Sano shunt is ligated
• anastomosis of SVC → right PA
• post-op remains cyanosed
  • Sat 75-85%
    

Stage 3: Fontan procedure / total cavopulmonary circulation (TCPC):

age 3-5y

• completing the separation of systemic & pulmonary circulations
  • IVC + SVC connected to right PA
    • pulmonary blood flows passively
    • pressure gradient affected by PVR & intrathoracic pressure
      • ∴ Avoiding ↑ PVR + optimizing ventilation strategies important
    • fenestration can be created to decompress high pulmonary venous pressure
  • systemic circulation pumped by a single ventricle
    Shown here is an extracardiac conduit, the current favoured technique.

Although spontaneous ventilation increases blood flow through the lungs, positive pressure ventilation may allow better control of oxygenation and minute volume

If controlled ventilation is necessary, pulmonary blood flow can be optimized by

• ↓ peak insp time
• ↓ peak insp pressure
• ↓ PEEP

By physiology

by the shunt and direction of flow.

• L to R shunt (simple)
  • ↑ pulmonary blood flow
  • e.g.
    • atrial septal defect
    • ventricular septal defect
    • AVSD
    • patent ductus arteriosus
• R to L shunt (simple)
  • ↓ pulmonary blood flow
  • cyanosis
  • e.g.
    • Tetralogy of Fallot
    • pulmonary atresia
    • tricuspid atresia
    • Ebstein's anomaly
• complex shunts
  • mixed pulmonary / systemic blood flow
  • cyanosis
    • e.g.
      • Transposition of great arteries
      • truncus arteriosus
      • total anomalous pulmonary venous drainage
      • double outlet right ventricle
      • hypoplastic left heart syndrome
      • large septal defects
• obstructive lesions
  • high pressure gradients
    • e.g.
      • coarctation of aorta
      • interrupted aortic arch
      • aortic stenosis
      • pulmonary stenosis
        In some complex cases of CHD, such as complex shunts and obstructive lesions, oxygenation is dependent on a patent ductus arteriosus (PDA) to allow mixing of pulmonary and systemic circulations. Neonatal patients are often on prostaglandin therapy to keep the duct open, therefore any prostaglandin inhibitors, such as non-steroidal anti-inflammatory drugs, are contraindicated.

Cardiomyopathy

dilated cardiomyopathy
hypertrophic cardiomyopathy
LV non-compaction CMP
restrictive cardiomyopathy
ARVD

non-cardiac surgery

Pre-op assessment

Compensated vs compromised - Big 4

1) Heart failure

• very high risk
  • 10% arrest
  • 96% inotrope requirement
• s/s
  • tachpnoea
  • tachycardia
  • diaphoresis
  • failure to thrive

2) Pulmonary hypertension

• PAP >25mmHg at rest
• PAP >30mmHg on exercise
• chest infection poorly tolerated

3) arrhythmia

• RBBB common on pre-op ECG
• ventricular ectopics could be ominous sign
  • esp in pt w/ univentricular circulations

4) cyanosis

• usually w/ concomitant heart failure / PHTN / arrhythmia
• often polycythaemic
  • ↑ risk of cerebral vein & sinus thrombosis
• often young (<5yo)
• abnormal coagulation profiles
  • PT, APTT
  • platelet dysfunction
  • ↓ factor concentrations

History

resting SpO2
assess need x premed
non-cardiac anomalies

• e.g. risk of bradycardia on sevoflurane induction in trisomy 21
  chest infection → delay OT
  Details of previous intensive care admissions should be obtained, as a period of prolonged ventilation ↑ risk of tracheal stenosis & difficult intubation
  A history of DIVA may be an indication for an inhalational induction.

Drug Hx

• ACEi
  • ↑ likelihood of hypotension on induction
  • often withheld on morning of surgery
• Aspirin:
  • low-dose aspirin is often continued
• PHTN therapy:
  • if the degree of PHTN requires treatment → likely need specialist involvement

Exam

look for signs of heart failure

Ix

Echo

• pressure gradients across valves
• obstructive lesions
• PAP
• RV & LV function

ECG

look for arrhythmia

CXR

• chest infection
• cardiomegaly
• pulmonary oedema

Bloods:

• ↑ HCT if cyanotic
• check urea & lytes if on diuretics

Risk stratification + tertiary referral

children stratified as ‘low risk’ may have a similar risk of death as children without CHD

Conduct of anaesthesia

Pre-op

Clear instructions on fasting

• ∵ important to avoid dehydration
  • especially if cyanotic

Premed

• neither psychologically or physiologically desirable for children with CHD to be stressed
  • → lower threshold for premed
• e.g. midazolam 0.5 mg/kg 20–30 minutes prior to induction

Induction

if DIVA / inhalational induction → preferable to have 2nd experienced anaes

Inhalational induction

• possible w/ sevoflurane
  • should be slow w/ lower concentrations
  • avoid prolonged inspiration of 8% sevoflurane
    • ∵ ↓ SVR & coronary perfusion
  • caution w/ trisomy 21
    • ∵ risk of bradyarrhythmias.

IV induction

Propofol reduces SVR and mean arterial pressure
ketamine has less effect on these variables

Maintenance

volatile or IV

Analgesia

opioid commonly used
neuraxial: need vasopressor to counteract ↓SVR

Peri-op complications

Sudden complications

• arrhythmias / ectopics
• bleeding
  • esp patient on anticoagulation
• cardiac arrest
  • high risk features a/w peri-op arrest
    • Cardiomyopathy
    • cardiac failure
    • balanced or single circulation
    • arrhythmias
• hypoxia
  • DDx of unexpected intra-op hypoxia
    • pulmonary hypertensive crisis
    • reversal of shunt
    • ↓ SVR
    • ↑ PVR
      Complications relate to heart function
• cardiomyopathy
• poorly functioning Fontan
• ventricular failure requiring transplant

infective endocarditis prophylaxis

Patients with structural congenital heart disease, including surgically corrected or palliated structural conditions are at increased risk of infective endocarditis.
However, NICE no longer recommends prophylactic antibiotics for gastrointestinal, genitourinary and dental procedures.
Instead, the emphasis is on education regarding good oral hygiene and symptoms of infective endocarditis.

Pacemakers / defibrillators

Pacemaker

• type of device
• reason for insertion
• backup mode
• response to diathermy
• consider A line

ICD

• disable before induction
• external defibrillator pads applied
  • remote from the ICD
    Pacemakers & ICDs should be checked + reactivated in theatre recovery.

References

Anaesthetic Implications of Congenital Heart Disease for Children Undergoing Non-Cardiac Surgery
242. ACHD — Atrial Septal Defects With Dr. Richard Krasuski
245. ACHD — Ventricular Septal Defects With Dr. Keri Shafer