Like every heart disease, HLHS exists along a spectrum of severity. Regardless of severity, though, patients require lifelong medical attention and nearly all require multiple surgical palliations, even those who end up with a biventricular circulation.
Overview of HLHS spectrum
- Aortic arch obstruction (e.g. CoA) without significant aortic stenosis or mitral stenosis, and apex-forming LV. In this most favorable anatomy, the lungs are healthy at birth (no signs of LA HTN), and flow across the arch is all antegrade (pumped by the LV). In these cases, patients may undergo simple CoA repair and close monitoring for signs of LA HTN.
- Critical AS, apex forming LV, CoA. In these cases, the LV is thought to have (at least potentially so) sufficient capacity to sustain the systemic circulation without severe LA HTN. In these cases, we commonly balloon dilate the AV and monitor the circulation off PGE as the PDA closes. Again, antegrade flow across the arch is reassuring.
- In a subset of these cases, the AV remains limiting despite valvuloplasty, exhibiting a significant AS gradient (e.g. >40 mmHg). In these cases, if the LV is thought to be sufficient (which can be difficult to determine with confidence), a neonatal Ross procedure (with or without a Konno) can be performed.
- Hypoplastic left heart syndrome with mitral stenosis/aortic stenosis or mitral atresia/aortic atresia, CoA, unrestrictive atrial septum. Many neonates with HLHS fall into this category, in which left heart structures are thought to be inadequate to sustain circulation, at least in the neonatal period. When the atrial septum is unrestrictive, the lungs (and the baby) can be remarkably healthy. As PVR decreases, it is common for saturations to reach the mid- or high-90s with only mild resting tachypnea (though this would not persist indefinitely). These patients remain on PGE1 and may feed orally if WOB is minimal. Generally, they undergo stage 1 palliation in the first week of life.
- HLHS (any lesion) with the restrictive or intact atrial septum (see bottom image to right). These patients may be profoundly ill immediately after birth, including severe hypoxemia and/or cardiogenic shock. Typically undergo urgent cardiac cath for balloon dilation of the atrial septum. Even when effective in relieving acute LA HTN, patients often exhibit persistent lung disease, ventilator dependence, pulmonary vein disease, and lymphatic dysfunction (including chylous effusions and feeding intolerance). In some cases, pulmonary artery bands are placed and PGE continued while the patient stabilizes prior to S1P.
- Mitral stenosis/aortic atresia with left ventricular dependent coronary circulation. Coronary fistulae from the LV cavity are present, and in the most extreme cases, are the sole source of coronary flow (i.e. proximal coronary ostial atresia). This is rare but associated with high mortality. These patients may be palliated using a hybrid procedure as a bridge to OHT, or may be offered comfort care.
Importance of atrial septum in HLHS
Unrestrictive atrial septum
- Pulmonary venous return
passes freely from LA to RA
- Left atrial pressure low
- Pulmonary vein pressure low
- Alveoli normal
- Lymphatics normal
Restrictive/intact atrial septum
- Pulmonary venous return obstructed Left atrial pressure high
- Pulmonary vein pressure high
- Alveoli thickened and congested
- Lymphatics profoundly dilated Medial hypertrophy of pulmonary veins
Anatomy. Patients with MS/AS most commonly have a left ventricle that does not reach the apex (i.e. non-apex forming). The supporting structures of the MV are often displaced towards the base of the ventricle (basally displaced) and are narrowly spaced (sometimes parachute), meaning that the leaflets are unable to separate from each other and open widely towards the apex of the ventricle. This creates the substrate for mitral stenosis. Similarly, the AV may be bicuspid, small, and stenotic, although it is common at birth for there to be little to no AV gradient at birth due to diversion of pulmonary venous return through the RV. The endocardium may be lined with EFE, limiting diastolic excursion and exacerbating restrictive physiology.
Physiology. The systemic circulation is PGE dependent. As detailed on the prior page, patients with a restrictive atrial septum may exhibit LA HTN, diminished pulmonary blood flow, hypoxemia, dead space ventilation, chronic lung disease, and lymphatic dysfunction. Otherwise, most patients with MS/AS are stable after birth. Absent lung disease, most patients have saturations in the 80s shortly after birth, rising to the mid-high 90s by 2-3 days of life (high Qp/Qs + low VO2 –> high SvO2 + SaO2). In this anatomy, the LV also ejects into the aorta, such that there may be pre-post ductal SpO2 difference. In most cases, patients are not tachycardic or tachypneic and able to take some PO. The timing of surgery is typically elective within the first week of life. Rarely, complications (e.g. IVH or prematurity) may require delay of S1P, in which case branch PAB is necessary.
HLHS (MA/AA or MS/AA)
Anatomy. Patients with AA and either MS or MA do not have the possibility of antegrade aortic flow. The LV is anatomically prohibited from contributing to the circulation and the circulation is PGE dependent. In most cases, the LV is extremely diminuitive. In the unique case of MS/AA, there is inflow and no egress of LV preload from the LV. This maintains a high ventricular pressure throughout the cardiac cycle such that fistulae between the LV cavity and the coronary circulation persist (normally they are present early in gestation and regress over time). In a subset of these cases, there is ‘dependence’ of the coronary circulation on the LV, at times even definitive proximal coronary ostial atresia.
Physiology. The systemic circulation is PGE dependent due to aortic atresia. Most patients with MA/AA are stable after birth and follow a similar pattern of saturations in the mid-high 90s by 2-3 days of life with excellent peripheral perfusion (see prior page). The timing of S1P is typically elective within the first week of life. Patients with MS/ AA, however, may have LV-coronary fistulae or even coronary ostial atresia. In the latter case, the LV cannot be depressurized (e.g. by atrial septostomy) without causing coronary ischemia and the circulation may be quite unstable with increased troponin, EKG changes, or cardiac arrest. Rescue with VA ECMO may be ineffective in cases of coronary ostial atresia. Initial palliation on these cases is typically with a hybrid procedure, though in the absence of LV-dependent coronary circulation S1P may be pursued.