Hypoplastic Left Heart Syndrome Flashcards
What are the lesions in HLHS?
Describe the route of pulmonary and systemic blood flow.
Hypoplastic left ventricle, aortic valve atresia, hypoplastic ascending aorta
The left ventricle is non-functional.
The RV provides blood flow for both the pulmonary and systemic systems.
SVC/IVC systemic venous return should be normal and blood will pass through the RA to the RV and out through the PA’s.
Pulmonary venous return enters the left atrium and crosses the foramen ovale or ASD into the right atrium and mixes there.
Systemic blood flow is propelled by the RV via the pulmonary artery and ductus arteriosis.
Blood flows retrograde from the ductus arteriosis to the ascending aorta and into the coronary arteries.
HLHS is dependent on the presence of the following two anatomic elements
- A duct (PDA)
- An inter-atrial communication
Closure of the duct will lead to a shock presentation
Imbalance of Qp:Qs will result in congestive heart failure or hypoxia
True or False:
HLHS is the most common cause of congestive heart failure in the first week of life.
True!
As PVR drops, there is ever-increasing pulmonary blood flow, thereby increasing the volume work the right ventricle must perform to preserve adequate systemic output.
The growing proportion of saturated blood entering the right atrium may give false reassurance, as the sats approach normal, despite clinical signs of congestive heart failure
Progressive imbalance in Qp:Qs will result in high output failure, acidemia reflecting inadequate systemic perfusion, and potentially death
Explain the importance of the interatrial communication in HLHS
In a restrictive interatrial communication, such as a foramen ovale, the pressure in the left atrium will exceed that of the right and blood will flow left to right at the foramen. There is a resultant increase in PVR that limits pulmonary blood flow.
If blood flows unrestricted across an ASD, or unrestricted FO, pulmonary blood flow increases dramatically as PVR drops.
If there is excessive narrowing or obliteration of the FO, this will impose severe restriction in pulmonary blood flow.
Overall, the systemic saturation reflects the mixture of systemic venous return with variable pulmonary venous return permitted by the interatrial communication
Describe the physical findings in a neonate with HLHS with a Qp:Qs of 1.
Blue (dusky in colour) from mixing, with adequate systemic perfusion: Normal systemic arterial blood pressure Warm extremities Good peripheral pulses Absence of metabolic acidemia Systolic ejection murmur Single second heart sound
How do patients with HLHS present if they have a marked imbalance in Qp:Qs?
Widely patent ASD -> Qp:Qs well in excess of 1
Once RV can no longer compensate with an increased output, systemic hypoperfusion develops. Results in shock and congestive heart failure
Conversely, if little or no interatrial communication, get severe impedance to pulmonary vascular return, resulting in increased PVR and inadequate pulmonary blood flow. These kids will be profoundly cyanotic -> myocardial performance will soon deteriorate, which could lead to a similar presentation of shock
What would you see on ECG in HLHS
Right atrial enlargement: Peaked p waves in II, III, avF
Right ventricle enlargement: qR pattern in right precordial leads
What are the goals of preoperative management in HLHS
- Maintain duct patency (PGE1 infusion)
2. Establish or maintain Qp:Qs ratio at unity
How can you estimate Qp:Qs?
The Fick equation
Qp:Qs = (Ao - SVC)/PV - PA)
What are the three goals of Stage I Reconstruction (Norwood)?
- To provide systemic perfusion independent of the ductus
- To offload the single ventricle (preserve the function of the single ventricle by minimizing excess pressure and volume work)
- To allow normal maturation of pulmonary vasculature
What is involved in a Norwood?
Creation of a neoaorta from the PA
Patch closure of distal PA
Atrial septectomy
Modified right Blalock-Taussig shunt connecting right innominate artery to the right PA
*Sano modification: RV to PA shunt in place of a systemic to PA shunt
What is a Fontan?
Fontan is not a specific operation, but rather a class of operations that separate the pulmonary and systemic circulations in patients with single ventricle physiology.
For HLHS, the goal of the Fontan is to have the systemic venous return routed directly to the pulmonary arteries. This changes the pulmonary and systemic circulations to be in series, rather than in parallel.
This is often accomplished by a superior cavopulmonary shunt (bidirectional Glenn anastomosis) at 4-6 months of age.
Fontan completion may be undertaken electively at 2 years of age (because kids can develop worsening cyanosis due to differential growth of the lower half of the body with a corresponding increase in the desaturated IVC return, as well as the development of venous collaterals and arteriovenous malformations).
Some kids will have a Fontan connection with fenestration - this allows some blood to shunt from the systemic venous system to the pulmonary venous system (RA) without passing through the lungs. This allows them to maintain systemic output even in the face of elevated pulmonary vascular resistance, albeit with a lower arterial O2 saturation.
What are the stages of surgical palliation?
Norwood
Superior cavopulmonary shunt (Bidirectional Glenn) @4-6 months of age
Completed Fontan @ 2 years of age
