GOALS •Brief overview of Basic Anatomy & Pathophysiology of HLHS. •Discuss surgical intervention. •Explain the LOGIC behind the management of HLHS. •DO not let you SNORE!
HYPOPLASTIC LEFT HEART SYNDROME EPIDEMIOLOGY: 2 to 3 percent of all CHD 2 to 3 cases per 1000 live births in the United States Male to female ratio about 1.5:1 Most common form of functional single ventricle heart disease Underestimated if left untreated, is responsible for 25 to 40 percent of all neonatal cardiac deaths
HYPOPLASTIC LEFT HEART SYNDROME History •First described by Maurice Lev in 1952. •Term used by Noonan & Nadas in 1958. •First successful 3-stage completion in 1983 (after multiple surgeries from 1979). •First successful cardiac transplant: Bailey, Nov. 1985
HYPOPLASTIC LEFT HEART SYNDROME MORPHOLOGY
“a spectrum of cardiac malformations with normally related great arteries… •a slit-like LV cavity - the “borderline LH” •characterized by underdevelopment of the LH with significant hypoplasia of the LV including atresia, stenosis or hypoplasia of the AV or MV, or both valves, and hypoplasia of the ascending aorta and arch.”
HYPOPLASTIC LEFT HEART SYNDROME Genetics: Occurs sporadically in otherwise clinically normal children. •Non-syndromic HLHS appears to be genetically heterogeneous, and multiple loci have been implicated including NKX2.5 on chromosome 5, and loci on 10q22 and 6q23 •Recurrence risk of LHD in first degree relatives of infants with this disease is 2 to 4% •Turner’s syndrome (XO), Jacobsen’s syndrome (deletion of distal 11q), trisomy 13, and trisomy 18
HYPOPLASTIC LEFT HEART SYNDROME PATHOGENESIS: •The underlying mechanism that causes HLHS is unknown •Intrauterine infarction, infection, and selective LV cardiomyopathy • “Flow begets growth.” Primary anatomic defects of isolated LH structures leading to altered blood flow through the left side of the heart, which results in secondary malformation of the LV and LVOT
HYPOPLASTIC LEFT HEART SYNDROME PATHOYSIOLOGY: RV supports both the pulmonary and systemic circulation. Survival is dependent on: a PDA a nonrestrictive ASD Resistance of the parallel circuit LV is unable to support SC therefore RV is used as the single ventricle.
HYPOPLASTIC LEFT HEART SYNDROME CLINICAL PRESENTATION: Cyanosis Respiratory distress “honeymoon” or asymptomatic period: DA is widely patent PVR is relatively high a nonrestrictive foramen ovale Cardiogenic shock and ventilatory insufficiency
HYPOPLASTIC LEFT HEART SYNDROME PHYSICAL EXAMINATION: No murmur S2 is single and loud Extremities are often cool Diminished peripheral pulses Hepatomegaly - RV dysfunction or TR Dysmorphic features
HYPOPLASTIC LEFT HEART SYNDROME DIAGNOSIS Echocardiographic imaging a diminutive LV, abnormal MV and AV and a hypoplastic AA Prenatal diagnosis â€”the 2nd trimester of pregnancy L to R flow at the level of the atrial septum (normally Rto-L in utero) and retrograde flow in the transverse arch No difference in mortality in prenatal vs. postnatal diagnosis Mahle WT, Clancy RR, McGaurn SP, et al. Impact of prenatal diagnosis on survival and early neurologic morbidity in neonates with the hypoplastic left heart syndrome. Pediatrics 2001; 107:1277. Kipps AK, Feuille C, Azakie A, et al. Prenatal diagnosis of hypoplastic left heart syndrome in current era. Am J Cardiol 2011; 108:421
HYPOPLASTIC LEFT HEART SYNDROME DIAGNOSIS Electrocardiography (ECG) Non-specific RAD and RVH difficult to distinguish from the typical RV predominance seen in the ECG of normal infants. Chest radiography Non-specific cardiomegaly and increased PV- increased PBF “white out”- restrictive ASD
HYPOPLASTIC LEFT HEART SYNDROME Fetal intervention Aortic valvuloplasty Second trimester Critical AS and preserved LV volume
Tworetzky W, Wilkins-Haug L, Jennings RW, et al. Balloon dilation of severe aortic stenosis in the fetus: potential for prevention of hypoplastic left heart syndrome: candidate selection, technique, and results of successful intervention. Circulation 2004; 110:2125. McElhinney DB, Marshall AC, Wilkins-Haug LE, et al. Predictors of technical success and postnatal biventricular outcome after in utero aortic valvuloplasty for aortic stenosis with evolving hypoplastic left heart syndrome. Circulation 2009; 120:1482.
HYPOPLASTIC LEFT HEART SYNDROME Initial Medical Management: •to maintain adequate systemic perfusion by preserving the patency of the DA (PGE1) •to establishing an adequate atrial defect for mixing of oxygenated and deoxygenated blood (+/-BAS) •to avoid measures that could decrease PVR and increase PBF (i.e., high FiO2) •Diuretic and inotropic agents, and possible mechanical ventilation in heart failure
HYPOPLASTIC LEFT HEART SYNDROME Surgical Management: •Primary cardiac transplantation •Staged palliative repair Staged repair has become preferred surgical approach •Scarcity of infant donors •Improving short term successes of SPR
HYPOPLASTIC LEFT HEART SYNDROME Three staged palliative procedures: Normal BV circulation is not restored •1st stage (Norwood procedure)- in neonates •2nd stage (bidirectional Glenn procedure) 4/12 to 6/12 •3rd stage (Fontan procedure) – 18/12 to 30/12
HYPOPLASTIC LEFT HEART SYNDROME Norwood Procedure Stage I: Goals •
Provide unobstructed blood flow from the RV to the SC
Establish a controlled source of PBF
• Ensure an unobstructed connection between the pulmonary venous return and the systemic RV
HYPOPLASTIC LEFT HEART SYNDROME Norwood Procedure Stage I: •Creation of a neoaorta : MPA divided; distally MPA closed with patch; hypoplastic aortic arch reconstructed and anastomosed to the proximal MPA with homograft augmentation. •Establishment of a source of PBF by placing a modified BT shunt •Resection of the atrial septum •Results in a functionally univentricular circulation maintained by the RV
HYPOPLASTIC LEFT HEART SYNDROME Patient-related variables identified as risk factors for mortality include: •Low gestational age •Weight < 2.5 kg •Concomitant noncardiac problems •Anatomic variants such as restriction of the atrial septum, MS with aortic atresia, and small size of the AA •Tricuspid regurgitation and RV dysfunction
SANO procedure Why? BT shunt results in diversion of flow from the systemic circulation including the coronary circulation
Modifies the Norwood procedure by creating RV to PA (RVPA) conduit to establish a source of PBF instead of the BT shunt
HYPOPLASTIC LEFT HEART SYNDROME Hybrid procedure
surgical + transcatheter approaches No Neonatal CPB and circulatory arrest and avoids: •Circulatory stressors imposed by the post bypass inflammatory state •Myocardial reperfusion effects •Recovery from extensive dissection through a median sternotomy The hybrid procedure entails the following: •intravascular stent in the DA •PA Band surgically •BAS or placement of a stent in the interatrial septum
HYPOPLASTIC LEFT HEART SYNDROME Norwood Procedure Stage II: Cavopulmonary shunt â€”also known as the bidirectional Glenn operation. The original shunt is removed and the SVC is anastomosed end-to-side to the (typically right) PA. Thus, systemic venous return from the SVC enters the PAs directly.
HYPOPLASTIC LEFT HEART SYNDROME Mortality 1-2 % Hospitalization for one week The post Glenn circulation is defined by a passive source of PBF, a volume-unloaded ventricle, and persistent cyanosis due to the obligate flow of IVC return to the RV, and which contributes to systemic arterial output.
HYPOPLASTIC LEFT HEART SYNDROME Norwood Procedure Stage III: Fontan Procedure •Creates a venous pathway (TCPC) that directs the IVC flow into the PA •Resulting in the entire systemic SR flowing passively into the PA •Creates a system with a SV pumping blood into separate, in-series systemic and pulmonary thereby relieving cyanosis for the first time •low mortality rate similar to stage II
HYPOPLASTIC LEFT HEART SYNDROME Anaesthetic Management Monitoring: •Standard cv, resp and temp monitoring. •UA lines are utilized whenever possible. •Direct thoracic atrial lines can be employed instead of percutaneous IJV or SCV CP catheters. •UVC positioned in the orifice of SVC at the time of surgery serves as a valuable monitor of SmvO2. •FA line is preferred. Right radial and FA lines are preferred in arch reconstruction and coarctation repair. •Both nasopharyngeal and rectal/bladder temp monitoring is mandatory when DHCA or low flow techniques are employed.
HYPOPLASTIC LEFT HEART SYNDROME Anaesthetic Management Induction: PGE1 infusion should be continued until CPB is established Any IV induction can be employed for induction with careful attention to the haemodynamics Total intraoperative fentanyl doses of 1020mcg/kg is employed with the target being extubation on the 1st Post Op day. Muscles relaxants such as pancronium help ETI without decreasing HR, especially in combination with higher doses of narcotics.
HYPOPLASTIC LEFT HEART SYNDROME Anaesthetic Management Pre CPB Management: •Maintenance of anaesthesia should aim at good analgesia and amnesia. •Methylprednisolone in 10-30 mg/kg •Maintaining a balance between the PVR and SVR and Qp/Qs •Ventilatory strategies with low FiO2, PaCO2 between 40-50 mm Hg, increasing dead space, and PEEP •Addition of 2-4% CO2 in inspired gas • use of vasodilators and/or ionotropes to maintain systemic perfusion.
HYPOPLASTIC LEFT HEART SYNDROME CPB management •Minimise the non-biological contact surface area of the CPB circuit. •Acid-base management on CPB is still a debatable issue. •Bicaval cannulation and hypothermic low flow techniques are employed in those situations where DHCA was the normal earlier.
CPB DHCA Management •Pre-CPB steroids •Hyper-oxygenation before DHCA. •Longer time for cooling (1-2 mins for each °C of cooling). •Using pH-stat tech during cooling and rewarming. •Maintaining a Hct of 30. •Intermittent cerebral perfusion for 2-3 mins at 15 20 mins interval. •MUF after CPB. •Postop cerebral protection strategies such as avoiding hyperthermia, hyper-glycaemia, and maintaining adequate CO
HYPOPLASTIC LEFT HEART SYNDROME Weaning from CPB: •Airway cleaned and lung expanded the terminal rewarming phase of on CPB •Trial opening of mBTS, if no widening of pulse pressure shunt inadequate or inadequate arch repair •Use of small doses of inotropes-Post stage I volume/pressure burden on RV is the same yet there is insult related to cessation of CBF , CPB and DHCA •If low SpvO2 secondary to atelectasis corrected by lung expansion and maintenance of FRC
HYPOPLASTIC LEFT HEART SYNDROME Weaning from CPB: •Secure heamostasis. Long suture lines as a result of neoaorta recreation •Use of fresh whole blood (less than 48 hr) or reconstituted whole blood, consisting of PRBC, FFP and Platelets from the same donor less than 7 days •Rapid administration of blood and blood products via a CV cath should be avoided, as they contain metabolites like lactic acid, K and Ca binding drugs that directly enter CBF •Consider ECMO and Mechanical Assisst Device
HYPOPLASTIC LEFT HEART SYNDROME Goal is balancing the flow to lungs and bodyâ€Ś Fick equations: Qs/Qp=(CaO2/CmvO2)/(CpvO2-CpaO2) where CaO2=arterial oxygen content = Hgb x 1.34 x SpO2 CmvO2=mixed venous oxygen content CpvO2=pulmonary venous oxygen content CpaO2=pulmonary artery oxygen content
Because PBF is supplied through the m-BTS from the aorta after Norwood Procedure CpaO2=CaO2 Qp/Qs = (SaO2 - SmvO2) / (SpvO2 - SaO2)
Assuming that SpvO2 = 95% (probably close to true in pre-op but NOT post-op care)
HYPOPLASTIC LEFT HEART SYNDROME After Norwood Procedure Stage I: •Leaves SV partitioning the CO to the SC and PC in a parallel fashion •Mixing of the systemic and pulmonary venous blood •Qp/Qs is determined by the resistance in either circulation- blood flow favoring the path of least resistance •The maximum DO2 occurs at a Qp/Qs of around 0.5 to 1 •DO2=COxCaO2
HYPOPLASTIC LEFT HEART SYNDROME Key here is that systemic saturation may be misleading SvO2 may drop, with more blood flow to lungs thereby preserving SaO2
HYPOPLASTIC LEFT HEART SYNDROME •SmvO2, Perfusion status, Acidosis, Lactic acidosis, Poor UO, High filling pressures, Poor function on Echo. •NIRS-Regional indicators for adequacy of O2 delivery •IN HLHS due to intra atrial mixing of venous blood, the best available estimation of SmvO2 is SVC venous saturation (SvO2) •Risk of anaerobic metabolism increased sharply when SvO2 fell below 30%-Hoffman et al •Targeting a SvO2 0f 50% after Norwood Procedure •CO difficult to measure in neonates
HYPOPLASTIC LEFT HEART SYNDROME Strategies for the management of PVR: •After Norwood Procedure PBF is controlled by the sum of resistances provided by B-T shunt (fixed resistance)and PVR •PVR can be increased by decreasing FiO2, inducing respiratory acidosis, decreased MV, increasing dead space and inhaled CO2) •A high PVR when Norwood Procedure is performed in older infants requires exactly the opposite measures
HYPOPLASTIC LEFT HEART SYNDROME Strategies for the management of SVR: •Promoting systemic flow by dropping SVR •Goal is to maximize DO2 (oxygen delivery) •Pharmacotherapy usual route •No universal therapy •Afterload reducing agents such as Milrinone, Nitroprusside, Phenoxybenzamine are commonly used
Phenoxybenzamine: •Commonly used in the post op management of HLHS across North American centers •Clear association with a reduction in SD •Nonselective, irreversible α adrenergic blocker •Prolonged half life of more than 24 h •Synthesis of new α adrenergic receptors is required to limit its duration of action •Conventional vcs epinephrine or norepinephrine have limited effect, infact may worsen the vasodilation due to unopposed β effect •In this situation vasopressin is effective as it works through a different mech (V1 receptors that are not blocked by POB) Tweddell JS et al: Circulation 106(12 Suppl. 1), 9 (2002)
Guzzetta NA: Anesthes. Analges. 105(2), 312-315 (2007)
HYPOPLASTIC LEFT HEART SYNDROME
Conclusion: •Significant progress has been made in neonatal cardiac surgery over the last two decades owing to major advances in paediatric cardiology, anaesthesia, cardiopulmonary bypass (CPB) techniques and perioperative cardiac intensive care. •The approach to the management of HLHS has changed from being a fatal diagnosis that may undergo fetal intervention in selected cases •Sound knowledge regarding the pathophysiology of HLHS and corrective interventional procedures is absolutely necessary for the appropriate anaesthetic management •Intraoperative anaesthetic management is part of a continuum in the perioperative care of neonates undergoing surgery for congenital cardiac defects.