Truncus Arteriosus

Definition: single arterial trunk and overriding VSD, arising from normally formed ventricles. Absent or diminutive PDA. 100% mortality within the first year if untreated.

Prevalence 3% in CHD.

Incidence 5-15:100.000.

Physiology:

Parallel circulation.

With decreasing PVR there is  increased PBF and increased flow to LA and LV, leading to CCF.

Diagnosis:

Presents usually 1-2 weeks postnatally (decreasing PVR) and subsequently CCF with failure to thrive, dyspnea, diaphoresis.

Diagnosis is by echo and in selected cases, cardiac catheterisation.

Preoperative management:

• Balanced circulation (aim for SpO2 75-85%).
• Hypoventilation to increase the PVR and to reduce the SVR.  SNP (0.5-4 mcg/kg/min) to lower SVR.
• Aim for a MAP >35 mmHg in neonates.
• Intubate and sedate to lower oxygen consumption.

Preoperative preparation:

ECG, CXR, CUS, FBE, clotting, UECs, FISH, PRBC (4), FFP (2), platelets (2), cryoprecipitate (2).

Methylprednisolone 10mg/kg 12hrs and 6hrs pre surgery in neonates.

Surgery:

Detaching of the PAs, ventriculotomy to close the VSD, valved RV-PA conduit.

In severe truncal valve insufficiency there may be aortic homograft with reimplantation of the coronary arteries.

Postoperative management:

• Keep intubated, ventilated, sedated and paralysed for 24 hours
• Inotropes: milrinone plus dopamine or norepinephrine, aim for MAP >40mmHg in neonates
• Haemodynamics: age adjusted in neonates: SBP >60 mmHg, MAP >40 mmHg (increasing over time), LAP 8-12 mmHg, CVP 8-12 mmHg
• Respiratory: normoxaemia, normocapnea
• Fluid restriction: 1 ml/kg/hr, trophic feeds
• Haemostasis
• Keep normothermic

Specific problems:

• Low cardiac output state: expect 6-12 hrs post bypass
• Pulmonary hypertension crisis: especially in neonates
  
• Arrthymias: JET – decrease inotropes, overdrive pacing, add noradrenaline, cooling, amiodarone
• Diastolic RV dysfunction: restrictive physiology, usually transient phenomena lasting 48-72 hrs
• Residual truncal valve insufficiency: mild to moderate is usually well tolerated, however if severe may need reinvestigation

Outcome:

Perioperative mortality: 10%

Long term survival after 5, 10, 15 years: 90%, 85%, 83%

References:

[1] Critical Heart Disease in Infants and Children; 2nd ed, Nichols et al: Peristent Truncus arteriosus

[2] Surg Clin North Am. 1949 Aug;29(4):1245-70: Collett et al: Persistent truncus arteriosus; a classification according to anatomic types

[3] Am J Cardiol. 1965 Sep;16(3):406-25: Van Praagh et al: The anatomy of common aorticopulmonary trunk (truncus arteriosus communis) and its embryologic implications. A study of 57 necropsy cases

[4] Cardiol Young. 2005 Feb;15 Suppl 1:125-31: Backer et al: Techniques for repairing the aortic and truncal valves

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