The univentricular heart encompasses a spectrum of rare and complex congenital cardiac malformations whereby both atria predominantly egress into one functionally single ventricular chamber, precluding biventricular repair. Population studies indicate an overall prevalence of approximately 2 per 10,000 live births. Subtypes include hypoplastic right or left ventricles, absence or atretic atrioventricular (AV) valves, common AV valves with only one well-developed ventricle, and heterotaxy syndromes (or isomerism), that is, disorders of lateralization whereby the arrangement of abdominal and thoracic viscera differ from normal and mirror-image of normal.
The general objectives of initial surgical palliation are to provide unobstructed systemic outflow, unobstructed systemic and pulmonary venous return, and controlled pulmonary blood flow. Most patients will be managed by a staged surgical approach in view of a Fontan procedure. A minority will not undergo Fontan palliation because of reasonably balanced systemic and pulmonary circulations or as a result of unfavorable hemodynamics. In patients with severe pulmonary obstruction or atresia, initial palliation may consist of aortopulmonary shunts ( Fig. 13.1A to D ) or a bidirectional cavopulmonary anastomosis (see Fig. 13.1E ). In contrast, in patients with unrestrictive pulmonary blood flow, pulmonary artery banding or division may afford initial protection.
Fontan procedures are typically completed between 18 months and 4 years of age, at an ideal weight of approximately 14 kg, and consist of directing systemic venous return to the pulmonary artery, characteristically without an interposed right ventricle (see Fig. 13.1F to H ). Multiple modifications and adaptations have been proposed since its original description in 1971. The classic Fontan involved a valved conduit between the right atrium and pulmonary artery. Older adults will have had a modified Fontan procedure, consisting of a direct anastomosis of the right atrium to a divided pulmonary artery (see Fig. 13.1F ). This technique has been supplanted by so-called total cavopulmonary connection Fontan procedures. The first iteration, proposed by De Leval, consists of an end-to-side anastomosis of the superior vena cava to the undivided right pulmonary artery, a composite intraatrial tunnel using the right atrial posterior wall, and a prosthetic patch to channel the inferior vena cava to the transected superior vena cava, which is anastomosed to the main pulmonary artery (see Fig. 13.1G ). A subsequent modification includes directing inferior vena caval flow to the pulmonary artery by means of an external conduit (see Fig. 13.1H ). In addition, Fontan pathways may be “fenestrated” by creating an atrial septal defect (ASD) as an escape valve for elevated Fontan pressures postoperatively. Such fenestrations may subsequently be closed, hemodynamic conditions permitting.
Patients with univentricular hearts and systemic outflow obstruction, the most severe form being hypoplastic left heart syndrome, constitute the most prevalent subtype. These patients typically undergo a variation of Norwood stages that culminate in a Fontan-type circulation.
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Objectives of the Norwood stage 1 procedure, performed within the first 2 weeks of life, are to provide unobstructed pulmonary venous return, permanent systemic outflow from the right ventricle, and temporary pulmonary blood supply to allow the pulmonary vasculature to develop and mature (see Fig. 13.1I and J ).
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The Norwood stage II procedure, performed prior to 6 months of age, consists of a bidirectional Glenn shunt or hemi-Fontan and closure of the Blalock-Taussig shunt.
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At 18 months to 3 years, the stage III procedure completes the total cavopulmonary Fontan by connecting the inferior vena cava to the pulmonary artery.
To understand long-term sequelae, the Fontan circulation may be viewed as a hemodynamic compromise. In normal biventricular hearts, caval pressures are typically less than 10 mm Hg, and mean pulmonary pressures exceed 12 to 15 mm Hg. Fontan physiology imposes systemic venous hypertension with concomitant pulmonary arterial hypotension. Long-term complications, the focus of the current chapter, are numerous, highly prevalent, and increasingly well characterized as the first Fontan recipients enter their fifth decade of follow-up. Lifelong surveillance in centers with expertise in adult congenital heart disease is recommended for all.
Clinical Evaluation
Routine follow-up typically involves one to two clinical visits per year. In addition to a thorough clinical history and physical examination, minimum testing includes resting oximetry, 12-lead electrocardiogram (ECG), chest x-ray, echocardiography with Doppler interrogation, complete blood count, biochemical analyses for liver function, serum protein, and albumin levels, and occasional cardiac rhythm monitoring. Testing for viral hepatitis should be considered, particularly in those exposed to blood products prior to universal screening for hepatitis C. Additional testing may include transesophageal echocardiography, cardiac catheterization, liver imaging, exercise spiroergometry, stool monitoring for enteroluminal protein loss, cardiac magnetic resonance (CMR) imaging, isotopic ventriculography, and electrophysiological study.
Physical Examination
After successful Fontan palliation, the physical examination typically reveals the following:
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Transcutaneous oxygen saturation greater than 94% in patients without fenestrations
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Nonpulsatile mild jugular venous distention; giant a-waves may be present in the classic Fontan
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A “beefy” or congested appearance may be present, often without overt edema.
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Single second heart sound that may be loud, depending on the position of the aorta
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No murmur or a soft systolic murmur (eg, mild AV valve regurgitation)
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Absence of a diastolic murmur
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Varicose veins are common, particularly in the lower limbs; may be evident on the trunk, especially when the circuit is obstructed
Common causes of hypoxemia include the following:
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Shunting through a baffle leak or residual interatrial communications
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Pulmonary vein compression by a giant right atrium ( Fig. 13.2 ) or aorta
Figure 13.2
Compression of right upper pulmonary vein. Transverse magnetic resonance image of a patient with a modified classic Fontan for tricuspid atresia and severe rotoscoliosis. The arrow designates the site where the massively enlarged right atrium (RA) compresses the right upper pulmonary vein (RUPV) .
(From Khairy P, Poirier N, Mercier L-A. Univentricular heart. Circulation . 2007;115:800-812.)
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Systemic venous collateralization (from systemic veins ultimately connecting to pulmonary veins or to the left atrium)
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Present in about 30% of patients with bidirectional cavopulmonary connections
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Between systemic or hepatic veins and pulmonary veins, left atrium, or coronary sinus
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Pulmonary arteriovenous malformations ( Fig. 13.3 )
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Particularly in patients with classic Glenn or Kawashima-type operations
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Also seen in patients with asymmetric distribution of inferior caval blood flow
Figure 13.3
Pulmonary arteriovenous malformations. Selective pulmonary angiography of the right lower lobe in a patient with tricuspid atresia and unidirectional Glenn shunt. In (A), multiple pulmonary arteriovenous malformations are seen. Following transcatheter coil occlusion, in (B), one residual pulmonary arteriovenous malformation is illustrated.
(From Khairy P, Poirier N, Mercier L-A. Univentricular heart. Circulation . 2007;115:800-812.)
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Pulmonary pathology including a restrictive pattern or diaphragmatic paresis
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Right-to-left interatrial shunting via small Thebesian veins
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Prior surgical unroofing of the coronary sinus to the left atrium
Markedly elevated jugular venous pressures may indicate Fontan obstruction, particularly if associated with hepatomegaly, mild cyanosis, and/or the presence of varicose veins. Loud systolic murmurs should raise suspicion for moderate or severe AV valve regurgitation, outflow tract obstruction of the systemic ventricle, or incomplete ligation of the main pulmonary artery, with forward flow. A diastolic murmur may indicate aortic regurgitation or pulmonary regurgitation in patients with particular variants that include pulmonary-to-aortic connections (eg, Damus-Kaye-Stansel).
Electrocardiogram
Given the heterogeneity of single ventricles, the ECG appearance is highly variable. It may be particularly helpful in detecting and characterizing rhythm disturbances. Patients with right atrial isomerism often have two separate sinus nodes, with a P-wave axis that fluctuates with the prevailing pacemaker. In contrast, most hearts with left atrial isomerism do not have a recognizable sinus node, with slow atrial or junctional escape rates.
In patients with tricuspid atresia, the following occur:
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The PR interval is usually normal with tall and broad P-waves.
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Left axis deviation is characteristic.
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Left ventricular forces are unopposed, as manifested by small r-waves and deep S-waves over right precordial leads and tall R-waves over left precordial leads.
In patients with univentricular hearts of right ventricular morphology, including hypoplastic left heart syndrome, typical ECG findings include right ventricular hypertrophy and a superior frontal QRS axis (in over 60%). In the most common subtype of double-inlet left ventricle, that is, with ventriculoarterial discordance, characteristic ECG findings include PR prolongation and possibly a higher-degree AV block, absence of Q-waves over left precordial leads, and Q-waves over right precordial leads and, occasionally, leads II, III, and aVF.
Radiologic Features
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The cardiac silhouette may be deviated if the heart is malposed, but is usually of normal size if hemodynamics are favorable.
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The pulmonary vasculature should be normal.
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Pleural effusions may indicate the need to rule out hemodynamic abnormalities or protein-losing enteropathy.
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Presence of a raised hemidiaphragm should be sought.
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Deformities of the spine, including scoliosis and kyphosis, should be noted.
Noninvasive Imaging
Echocardiography is considered the cornerstone of postoperative assessment. All patients should have periodic echocardiographic and/or CMR imaging by adult congenital heart disease specialists. Comprehensive echocardiographic examination is outlined in a previous chapter. In general, the underlying diagnosis and morphologic subtype may be fully characterized by a systematic and thorough appraisal that includes apical position; atrial situs; AV relationship; ventriculoarterial alignment; systemic and pulmonary venous anatomy and flow; atrial and ventricular shunts (including across a bulboventricular foramen); valvular stenosis and regurgitation; ventricular morphology, size, and function; and aortic and pulmonary artery size and abnormalities including aortic coarctation. In selected cases, CMR imaging may overcome limitations of echocardiography in demonstrating systemic and pulmonary venous anomalies, aortic arch malformations, and proximal pulmonary artery lesions.
History and Long-Term Sequelae
Long-Term Survival
Over the past few decades, improved survival in patients with congenital heart disease has been driven by a marked mortality reduction in those with the most complex forms of the disease. In a cohort of 261 patients with Fontan palliation (right atrium to pulmonary artery connection in 52%, right atrium to right ventricle variant in 10%, lateral tunnel in 38%, and extracardiac conduit in 1%), 29% died, and 2% had cardiac transplantation over a median follow-up of 12 years. Deaths were perioperative in 68%, sudden in 9%, thromboembolic in 8%, and secondary to heart failure in 7%. Perioperative mortality rates declined from 37% prior to 1982 to less than 2% in 1990 or later. Actuarial event-free survival at 1, 10, and 25 years was 80.1%, 74.8%, and 53.6%, respectively ( Fig. 13.4 ). Independent predictors of all-cause mortality or cardiac transplantation were protein-losing enteropathy, hypoplastic left heart syndrome, higher right atrial pressures, and diuretic therapy. Heart failure and thromboembolic deaths occurred a mean of 12 years and 9 years after Fontan surgery, respectively. Patients in whom thromboemboli were detected clinically and those without antiplatelet or anticoagulant therapy were at increased risk.
