Mechanical cardiopulmonary support in children and young adults: Extracorporeal membrane oxygenation, ventricular assist devices, and long-term support devices

Director, Pediatric Cardiac Intensive Care Program, Chief, Critical Care Cardiology, Associate Professor, Department of Pediatrics, Texas Children's Hospital and Baylor College of Medicine, Houston, Texas, USA
Anthony C. Chang

1. ICU management of children with chronic heart failure: New strategies
Chronic heart failure is accompanied by incessant stimulation of the sympathetic nervous system as well as the renin-angiotensin system. To counterbalance these systems, the neurohumoral system acts via the natriuretic peptides to ameliorate the deleterious effects observed in heart failure.
　The atrial and B-type natriuretic peptides are produced by the atria and ventricles in heart failure when there is atrial and ventricular stretch, respectively. Serial measurements of BNP have been useful in assessing degree of heart failure. Human recombinant BNP (neseritide) can be used to achieve natriuresis and vasodilation in addition to possibly improve inotropic and lusitropic effects.
　With the current successes of extracorporeal membrane oxygenation and ventricular assist devices, there is a dire need for longer-term mechanical assist devices such as the pulsatile VAD and the axial type VAD. The axial type VAD, with its miniaturized impeller systems at high rotational speeds, holds promise as a future implantable pediatric ventricular assist device.

2. Cardiopulmonary interaction and mechanical ventilation in patients with heart disease
There is a wide range of cardiopulmonary interactions in congenital heart disease. In tetralogy of Fallot with absent pulmonary valve, for example, the cardiopulmonary interaction is not simply at the level of the major airways but continues to the vasculobronchial level. Positive pressure ventilation decreases preload and increases afterload on the right ventricle while it increases preload and decreases afterload on the left ventricle.
　Pulmonary vascular resistance is affected by total lung volume such that pulmonary vascular resistance is at its lowest when total lung volume is at functional residual capacity. At lung volumes above and below functional residual capacity, the pulmonary vascular resistance is increased.
　End-tidal CO₂ is a reflection of lung ventilation while arterial and venous CO2 an indicator for cardiac output and pulmonary blood flow. A discrepancy between the CO2 values contributes to understanding of the pathophysiology in critically ill cardiac patients.

3. Overview of lesion specific intensive care: Diagnosis of residual cardiac lesions after congenital heart surgery
While many potential postoperative residua can occur, it is essential for cardiac intensivists to fully comprehend the steps of the relevant surgeries as well as physiologic alterations after surgery to be proactively cognizant of these issues.
　While two-dimensional echocardiography with color Doppler is adequate for intracardiac delineation of anatomy and physiology, certain extracardiac issues (such as aortopulmonary shunts, cavopulmonary anastomoses, and pulmonary venous obstruction) are not always well visualized with echocardiography.
　The determination of the best timing for reoperation can be complex, but coronary ischemia secondary to surgery is most critical and warrants immediate attention and correction. Interventional catheterization can be an interventional strategy in selected cases.

4. Perioperative management of Ebstein's anomaly in infants and children
In Ebstein's anomaly, multiple interactions are important, including right-left atrial interaction (with right atrium more compliant than the left atrium) and right-left ventricular interaction, in which the dilated right ventricle can negatively impact on left ventricular performance (altered septal elastance).
　The strategy for positive pressure ventilation in these patients should take into account possible pulmonary hypoplasia that can be associated with this lesion.
　Inhaled nitric oxide can be used to lower pulmonary vascular resistance in order to encourage antegrade pulmonary blood flow. Ductal supply of pulmonary blood flow or surgically created shunts can often lead to hemodynamic instability. Interventional catheterization can be performed to create an antegrade flow to the pulmonary arteries from the right ventricle.

5. Postoperative management of the patient after bidirectional Glenn procedure
Objectives:
1) To understand the changes after this surgery of the ventricle (its size and morphology) and of ventriculoarterial coupling
2) To be able to delineate the possible etiologies of cyanosis after the bidirectional Glenn procedure
3) To appreciate the influence of cerebral blood flow and circulation in bidirectional Glenn procedure

The ventricular size is decreased after the bidirectional cavopulmonary anastomosis as the pulmonary blood flow is decreased. This results in an unfavorable mass/volume relationship and in addition, ventriculoarterial coupling is altered unfavorably after this surgery.
　Etiologies in cyanosis include not only pulmonary etiological factors such as pleural effusion, pneumothorax, etc but also venous decompression via a number of vestigial veins. A contrast echocardiogram can often lead to a screening of this potential diagnosis, and elevated pulmonary vascular resistance as well anastomotic problems need to be considered as an etiology for these decompressing veins to appear.
　To maximize pulmonary blood flow after the bidirectional Glenn procedure, adequate paCO₂ will ensure sufficient cerebral blood flow and thus pulmonary blood flow. Excessive hyperventilation to lower paCO₂ may lower pulmonary vascular resistance, but lead to cerebral vasoconstriction and eventually less pulmonary blood flow.

6. Evaluation and management of postoperative arrhythmias: Interactive case presentations
Objectives:
1) To be able to diagnose and treat ectopic tachydysrhythmias such as atrial and junctional ectopic tachycardias in the postoperative setting
2) To appreciate that intra-atrial reentrant tachycardia can be associated with Fontan surgery
3) To appreciate the serious implication of a new onset ventricular arrhythmia in the postoperative setting

It appears that the risk factors for junctional ectopic tachycardia, a narrow complex tachydysrhythmia that may be related to injury or edema of the AV node, include infants and VSD repair. Higher risk lesions include tetralogy of Fallot. Atrial ectopic tachycardia is often underdiagnosed as the manifestations could be subtle, but should be monitored in infants, especially those with heterotaxy syndrome.
　Intra-atrial reentrant tachycardia can be associated with Fontan surgery and intraoperative cryoablation or radio-frequency ablation can be part of the Maze procedure to minimize postoperative atrial tachydysrhythmias after the Fontan or Fontan conversion operations.
　Ventricular tachycardia can be an ominous sign for myocardial ischemia and/or coronary insufficiency. Surgeries that have an increased risk of coronary insufficiency include arterial switch operation, Ross and/or Konno operations, anomalous left coronary artery from the pulmonary artery and reimplantation of the coronary artery, and others (RV-PA homograft and Ebstein's valve repair).

7. Management of the low birth weight infants with congenital heart disease: Intensivists' perspective
Objectives:
1) To appreciate the implication of low pulmonary vascular resistance in these neonates on cardiopulmonary pathophysiology
2) To delineate the differences in cardiopulmonary physiology between low birth weight and normal neonates
3) To understand that extracardiac issues that warrant diagnostic and therapeutic strategies

An important cardiopulmonary variable in the pathophysiology of congenital heart disease in these low birth weight neonates is the low pulmonary vascular resistance, which leads to imbalance of Qp/Qs in certain lesions such as hypoplastic left heart syndrome.
　There are various differences between the smaller heart of the low birth weight neonate and the heart of the normal neonate. Compliances as well as tolerance of acute changes in preload and afterload in the smaller and less mature heart can be essential to understand.
　These neonates can have extracardiac issues in the perioperative period, such as intraventricular hemorrhage, pulmonary disease, and necrotizing enterocolitis. These issues affect timing of surgery and interventional options. Genetic aberrations are common in low birth weight neonates and workup should include a full genetic analysis.