Stephen C. Brown

The Fontan circulation: who controls cardiac output?

In a Fontan circuit the mechanisms involved in control of cardiac output at rest and during exercise differ significantly from normal. The classical model presumes an unlimited preload which is not available in the Fontan circuit. This review critically analyses the role of contractility, heart rate, and afterload and highlights the importance of pulmonary vascular resistance (PVR) in determining adequate preload and, therefore, cardiac output in these patients. A conceptual model of the determinants of cardiac output in Fontan patients is presented.

Intravenous Amiodarone for Incessant Tachyarrhythmias in Children A Randomized, Double-Blind, Antiarrhythmic Drug Trial

Background— Intravenous (IV) amiodarone has proven efficacy in adults. However, its use in children is based on limited retrospective data. Methods and Results— A double-blind, randomized, multicenter, dose-response study of the safety and efficacy of IV amiodarone was conducted in 61 children (30 days to 14.9 years; median, 1.6 years). Children with incessant tachyarrhythmias (supraventricular arrhythmias [n=26], junctional ectopic tachycardia [JET, n=31], or ventricular arrhythmias [n=4]) were randomized to 1 of 3 dosing regimens (low, medium, or high: load plus 47-hour maintenance) with up to 5 open-label rescue doses. The primary efficacy end point was time to success. Of 229 patients screened, 61 were enrolled during 13 months by 27 of 48 centers in 7 countries. Median time to success was significantly related to dose (28.2, 2.6, and 2.1 hours for the low-, medium-, and high-dose groups, respectively; P=0.028). There was no significant association with dose for any arrhythmia subgroup, including JET, but the subgroups were too small for an accurate assessment. Adverse events (AEs) were common (87%), leading to withdrawal of 10 patients. There were 5 deaths in the 30-day follow-up period (2 possibly related to the study drug). Dose-related AEs included hypotension (36%), vomiting (20%), bradycardia (20%), atrioventricular block (15%) and nausea (10%). Conclusions— In children, the overall efficacy of IV amiodarone, as measured by time to success, was dose related but not significantly for any arrhythmia subgroup. AEs were common and appeared to be dose related. Although efficacious for critically ill patients, the dose-related risks of IV amiodarone should be taken into account when treating children with incessant arrhythmias. Prospective, placebo-controlled trials would be helpful in assessing antiarrhythmic drug efficacy in children, because their results may differ from retrospective series and adult studies.

The Fontan circulation after 45 years: update in physiology

The Fontan operation was first performed in 1968. Since then, this operation has been performed on thousands of patients worldwide. Results vary from very good for many decades to very bad with a pleiad of complications and early death. A good understanding of the physiology is necessary to further improve results. The Fontan connection creates a critical bottleneck with obligatory upstream congestion and downstream decreased flow; these two features are the basic cause of the majority of the physiologic impairments of this circulation. The ventricle, while still the engine of the circuit, cannot compensate for the major flow restriction of the Fontan bottleneck: the suction required to compensate for the barrier effect cannot be generated, specifically not in a deprived heart. Except for some extreme situations, the heart therefore no longer controls cardiac output nor can it significantly alter the degree of systemic venous congestion. Adequate growth and development of the pulmonary arteries is extremely important as pulmonary vascular impedance will become the major determinant of Fontan outcome. Key features of the Fontan ventricle are early volume overload and overgrowth, but currently chronic preload deprivation with increasing filling pressures. A functional decline of the Fontan circuit is expected and observed as pulmonary vascular resistance and ventricular filling pressure increase with time. Treatment strategies will only be successful if they open up or bypass the critical bottleneck or act on immediate surroundings (impedance of the Fontan neoportal system, fenestration, enhanced ventricular suction).

Premature foetal closure of the arterial duct: clinical presentations and outcome

AIMS The prevalence of intra-uterine ductal dysfunction is unknown and the clinical consequences are poorly understood. The aim of this study was to investigate the echocardiographic (ECHO) abnormalities and outcomes of this rare phenomenon. METHODS AND RESULTS Retrospective analysis of foetal (n = 602) and neonatal ECHO databases (n = 1477) between 1998 and 2007. Clinical and imaging studies were reviewed for pathology due to or associated with premature closure of the duct. Twelve cases were identified. Eight (1.3%) were diagnosed pre-natally at a median gestational age of 29.0 weeks (range: 20.0-37.5 weeks). Four neonates (0.3%) with significant cyanosis and absence of the arterial duct were also included. The most common ECHO features were: excessive right ventricular (RV) hypertrophy (100%), more than expected tricuspid and pulmonary regurgitation (100% and 92%, respectively), and right atrial dilation (75%). Premature induction of delivery was advised for five patients. Neonatal therapy consisted of observation and oxygen administration (n = 7), ventilation with pulmonary vasodilators (n = 5), and one required extracorporeal membrane oxygenation. There were three deaths due to respiratory failure with severe pulmonary hypertension. During follow-up, two children required additional right heart procedures and one developed a non-compaction cardiomyopathy. CONCLUSION Foetal premature closure of the arterial duct causes stress at different foetal ages and many different levels of the right heart and pulmonary circulation, resulting in a wide range of secondary pathology. Disproportionate RV hypertrophy is the most common finding. Clinical outcomes range from mild symptomatology to lethal respiratory insufficiency.

Transapical left ventricular access for difficult to reach interventional targets in the left heart

Objective: Interventional targets may be virtually “excluded” due to vascular access problems or complex previous surgical procedures. This study reviews our experience using transapical ventricular puncture to gain direct access to the systemic ventricle. Patients: Patient 1 (74 years, 2 previous sternotomies), patient 2 (66 years, 5 previous sternotomies), and patient 5 (69 years, 3 previous sternotomies) with prosthetic valves had paravalvular mitral valve leaks. Patient 3 (6.3 years, 2 previous sternotomies) with an extracardiac Fontan conduit, had a significant residual leak after two previous surgical attempts of patch closure of a severely regurgitant right atrioventricular valve. Patient 4 (10 months) had failure of standard ablation of the posteroseptal region of the mitral valve with persistent life‐threatening episodes of ventricular tachycardia. Methods: Procedures were performed under general anesthesia. Entry site was percutaneous in three patients and in two (and one conversion) a mini‐thoracotomy was used. Sheaths were placed (6 F) using standard Seldinger technique, followed by the procedure as required. Direct surgical closure of the puncture site was done in 4 patients and in patient 3, a percutaneous vascular occlusion device was used. Results: Easy and immediate access was obtained in all patients. The paravalvular leaks were crossed within seconds and completely closed with Amplatzer occluders. In patient 3 the valve was crossed using a Brokenbrough needle and a 12‐mm Amplatzer device was placed in the patch leak. Patient 4 was successfully ablated using a 7‐F irrigated catheter endo‐ and epicardially. Complications were in the percutaneous puncture group: in one patient a coronary artery was punctured and in one a hemothorax developed. Conclusion: Direct left ventricular puncture offers a very useful alternative access site in selected patients to reach “inaccessible” targets for certain percutaneous interventions in patients where standard approaches may be impossible or difficult.

The influence of pulmonary regurgitation on regional right ventricular function in children after surgical repair of tetralogy of Fallot

AIMS Pulmonary regurgitation after repair of tetralogy of Fallot (TOF) results in right ventricular (RV) dysfunction with significant late morbidity and mortality. The aim was to assess the influence of pulmonary regurgitation on regional RV function. METHODS AND RESULTS In 48 asymptomatic children (age 11.1 +/- 3.3 years) with repair of TOF, peak systolic strain rate (SR) and end-systolic strain (epsilon) were acquired using colour Doppler myocardial imaging. RV indices were quantified by magnetic resonance imaging. Echocardiography and exercise capacity was also performed. Forty complete data sets were analysed. An inverse linear relationship was demonstrated between the degree of pulmonary regurgitation and right ventricle end-systolic epsilon (r = -0.53, P < 0.01) as well as a correlation with peak systolic SR (r = -0.35, P < 0.01). A correlation existed between peak VO(2) and peak systolic SR (r = 0.51, P = 0.001) and end-systolic epsilon (r = 0.33, P < 0.05). CONCLUSION In asymptomatic children after repair of TOF, pulmonary regurgitation is associated with impaired regional systolic RV deformation indices. Regional strain and SR may be an early indicator of RV dysfunction in patients with post-TOF and pulmonary regurgitation.

Percutaneous treatment of stenosed major aortopulmonary collaterals with balloon dilatation and stenting: what can be achieved?

Background The natural history of major aortopulmonary collateral arteries (MAPCAs) in patients with pulmonary atresia and ventricular septal defect (PA-VSD) is frequently complicated by progressive stenosis, leading to pulmonary hypoperfusion and debilitating hypoxaemia. Objective To evaluate balloon dilatation and stenting for relief of stenoses and improvement of pulmonary flow in patients with PA-VSD. Design Retrospective analysis of all patients where dilatation of MAPCA stenoses was attempted. Patients Twelve patients with stenotic MAPCAs. Interventions Dilatation was attempted in 25 stenoses. Vessels were stented if elastic recoil was noticed (n = 3), in the presence of long segment stenosis (n = 4) or marked tortuosity (n = 1). Main outcome measures Diameter of stenoses before and after dilatation as well as arterial oxygen saturation data. Patients proceeding to surgical therapy. Results Two stenosed MAPCAs could not be crossed by a catheter. Four lesions were non-dilatable despite the use of high inflation pressures (18 atm). Six stenoses could be completely dilatated using angioplasty only; in five, only partial dilatation was obtained; eight stenoses needed stenting. In the group with partial expansion the mean (SD) diameter increased from 1.7 (0.8) to 3.5 (1.7) mm (p < 0.05); where full dilatation was achieved it increased from 2.1 (0.8) to 4.8 (1.9) mm (p < 0.05); and in the stented group it increased from 2.3 (0.9) to 5.0 (2.5) mm (p < 0.01). Percutaneous arterial oxygen saturation increased from 75(8)% to 82(8)% (p < 0.001). No complications were experienced during the procedures. Repeat dilatation was attempted in six stenoses, but only two procedures were successful. There were two episodes of vasospasm and in one an aneurysm had developed after redilatation. Two patients proceeded to outflow plasty and two subsequently had a unifocalisation procedure. Conclusions Pulmonary blood flow can be improved using balloon angioplasty or stents in patients with stenotic MAPCA; however, 17% of the lesions were not dilatable. Procedures are generally safe, but carry a small risk of vasospasm, dissection, occlusion or aneurysm formation.

Self expandable stents for relief of venous baffle obstruction after the Mustard operation

Objective Obstruction of the venous pathways after Mustard repair for transposition of the great arteries is associated with an increased risk of arrhythmia and sudden death. The purpose of this study was to assess the effectiveness of the largest (tracheal 22 × 40 mm) Wallstents in treating baffle obstructions. Design Retrospective analysis of patients with stented venous pathways. Subjects Eleven patients with baffle obstruction after Mustard repair for transposition of the great arteries. Interventions Stenoses were dilated with an 18 or 20 mm balloon. However, recoil was noticed in 11 patients: immediately (n = 7) or on repeat angiography (n = 4). Eighteen stents were implanted (mean (SD)) 18 (3.3) years postoperatively. After dilatation a tracheal Wallstent (11.5 F) was deployed. Main outcome measures Relief of obstruction, haemodynamic improvement. Results In the inferior vena cava, 10 stents were deployed in seven baffle obstructions with an increase in diameter from 9.8 (2.4) mm to 16.5 (1.4) mm (p < 0.01) and a mean (SD) pressure gradient decrease from 5.1 (3.6) mm Hg to 1.4 (2.0) mm Hg; in the superior vena cava, eight stents were implanted increasing the diameter from 9.1 (3.7) mm to 15.6 (3.8) mm (p < 0.001) with a decrease in mean pressure gradient from 5.1 (2.7) mm Hg to 1.9 (1.5) mm Hg. No complications were experienced during implantation. No anticoagulation was prescribed. During follow up (1.7 (0.6) years; range, 0.9–2.6) no problems were noted; five patients were re-catheterised without change in measurements. There was no evidence of peal formation in any of the stents. Conclusion It is concluded that Wallstents are safe, easy to use, and effective in relieving baffle obstruction. Anticoagulation does not seem neccessary.

Percutaneous pulmonary valve implantation for free pulmonary regurgitation following conduit-free surgery of the right ventricular outflow tract

INTRODUCTION Pulmonary regurgitation (PR) following surgery of the right ventricular outflow tract (RVOT) is not innocent and leads to significant right heart dysfunction over time. Recent studies have demonstrated that percutaneous valves can be implanted in conduit free outflow tracts with good outcomes. OBJECTIVES To evaluate in patients with severe PR--anticipated to require future pulmonary valve replacement--the feasibility and safety of pre-stenting dilated non-stenotic patched conduit-free right ventricular outflow tracts before excessive dilation occurs, followed by percutaneous pulmonary valve implantation (PPVI). PATIENTS AND METHODS Twenty seven patients were evaluated, but only 23 were deemed suitable based on the presence of an adequate retention zone ≤ 24 mm defined by semi-compliant balloon interrogation of the RVOT. A 2 step procedure was performed: first the landing zone was prepared by deploying a bare stent, followed 2 months later by valve implantation. RESULTS RVOT pre-stenting with an open cell bare metal stent (Andrastent XXL range) was performed at a median age of 13.0 years (range: 6.0-44.9) with a median weight of 44.3 kg (range: 20.0-88.0). Ninety six percent (22/23) of patients proceeded to PPVI a median of 2.4 months (range: 1.4-3.4) after initial pre-stent placement. Twenty one Melody valves and one 26 mm Edwards SAPIEN™ valve were implanted. Complications consisted of embolization of prestent (n = 1), scrunching (n = 4) and mild stent dislocation (n = 2). During follow-up, no stent fractures were observed and right ventricular dimensions decreased significantly. CONCLUSIONS Post-surgical conduit-free non-stenotic RVOT with free pulmonary regurgitation can be treated percutaneously with a valved stent if anatomical (predominantly size) criteria are met. In experienced hands, the technique is feasible with low morbidity.

Dilatable pulmonary artery banding in infants with low birth weight or complex congenital heart disease allows avoidance or postponement of subsequent surgery

OBJECTIVE This study evaluated the efficiency and feasibility of dilatable bands in selected patients. METHODS Two types of dilatable handmade bands were retrospectively evaluated and divided into two groups: main pulmonary artery bands and bilateral branch pulmonary artery bands (hybrid stage I palliation). Stepwise balloon angioplasty (BA) was performed, increasing the diameter either to completely dilate with total release of the band, or in others, to partially dilate the bands in order to improve flow and/or saturation. PATIENTS AND RESULTS Balloon angioplasty was performed in 20 patients (median birth weight 2.9 kg, range: 1.3-4.5 kg). Main pulmonary artery: Partial dilation: Six patients: Large ventricular septal defects (VSDs) and complex lesions requiring additional surgery. Progressive dilation allowed postponement of surgery in four children and allowed percutaneous VSD closure in one. Complete dilation: Eight patients: Spontaneous restriction of VSDs occurred in six patients; the bands were subsequently percutaneously completely released after a median of 39 weeks (7-91 weeks). The median gradient decreased from 90 to 38 mmHg (p<0.0001). Bilateral branch pulmonary artery: An average 8.5% increase in saturations was achieved in five patients, and in one patient, a hybrid procedure with borderline left ventricle, complete dilation allowed successful percutaneous biventricular repair. CONCLUSIONS Dilation of both main and bilateral branch pulmonary artery bands is possible, effective and safe. Dilatable main pulmonary artery bands allow for progressive dilation with postponement of surgery or complete release of the bands. Bilateral dilatable branch pulmonary bands offer palliative benefit, especially in hybrid cases where pulmonary blood flow may be limited by the bands before the ideal conditions for a stage II procedure exist.