1.
|
What are some of the
technical pitfalls in the first stage palliative procedure for hypoplastic left heart
syndrome as described by Norwood?
|
|
| The majority of children who require mechanical circulatory support do so
following cardiac surgery. The indications are most often poor contractile function or low
cardiac output, inadequate to maintain kidney or other organ function. It is important in
this setting to search actively for residual defects that may explain the low cardiac
output, since complete correction offers the best chance for successful weaning from
mechanical support. If cardiac function does not recover, then circulatory support can be
continued while awaiting transplantation in those children deemed candidates. Less
frequently, the indication for circulatory assistance is pulmonary dysfunction with
inadequate ventilation or oxygenation despite mechanical ventilatory support. In this
situation, a complete extracorporeal membrane oxygenation (ECMO) circuit including an
oxygenator is required. Another important indication for mechanic al circulatory support
is resuscitation following cardiac arrest not responsive to conventional CPR. If the
arrest is witnessed, and effective CPR started promptly, circulatory support as part of
the resuscitation has resulted in relatively high survival probability (50% to 70%)
despite periods of CPR lasting up to 90 minutes. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
2.
|
What are the most important
sequelae or events that can occur following successful initial palliation and before
subsequent reconstructive surgery?
|
|
| Because long-term circulatory support (beyond one to two weeks)
without a high incidence of complications is not yet possible in children, the primary
goals of mechanical support are to maintain organ perfusion while the heart recovers or
while awaiting a heart transplant. Experience with mechanical support in children has
shown that the majority of patients who eventually are weaned successfully from support
have significant recovery of cardiac function 4 8 to 72 hours after extracorporeal
circulation is started. If little or not recovery of cardiac function has been observed by
72 hours, then transplantation should be considered for children who are deemed
candidates. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
3.
|
What are the relative
advantages of the bi-directional Glenn anastomosis and the hemi-Fontan procedure?
|
|
| Adults frequently require mechanical circulatory support as a
consequence of coronary artery disease. Whether support is required after myocardial
infarction or after coronary artery bypass grafting, left ventricular dysfunction is the
predominant physiologic abnormality. Because of this, intraaortic balloon counterpulsation
(IABP) or left ventricular assist devices (LVAD) are frequently successful in treating
adult patients that require mechanical circulatory support. Children with complex heart
disease more often have biventricular cardiac failure, pulmonary hypertension, and
hypoxemia as predominant features. For adequate support, biventricular assist devices
(BVAD) or extracorporeal membrane oxygenation (ECMO) are often required. Some pediatric
patients with cardiac defects such as anomalous left coronary artery from the pulmonary
artery and cardiomyopathy with predominant left ventricular dysfunction a re well
supported with LVAD. Size considerations are also important in pediatric patients
requiring mechanical circulatory support. Both ECMO and VAD can be used to support even
the smallest neonates. Priming volumes for ECMO tend to be somewhat larger with the
smallest circuits requiring approximately 350 mm, while the smallest VAD priming is less
than 150 mm. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
4.
|
What are the currently
available options for mechanical circulatory support in children?
|
|
| ECMO and VAD are both used successfully in pediatric patients. A
typical ECMO circuit employs a roller pump, a membrane oxygenator, a heating element, and
a servo-regulatory mechanism for controlling circuit flow and preventing collapse of the
cardiac structures against the venous cannulae. VAD circuits do not contain an oxygenator.
Cannulation can be performed for right ventricular (RVAD), left ventricular (LVAD), or
biventricular support (BVAD). The absence of an oxygenator simplifies the circuit, and
reduces the required priming volumes. On the other hand, the absence of an oxygenator
makes VAD somewhat less flexible. The occurrence of biventricular failure or pulmonary
failure might necessitate changing the type of VAD or converting support to ECMO. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
5.
|
What type of ventricular
assist devices exist for pediatric patients?
|
|
| The majority of published experience with VAD in children has involved
the use of a centrifugal non-pulsatile pump with a variety of pump head sizes. The circuit
is simple, with an intake port, an arterial perfusion port, and the appropriate tubing to
complete the circuit. There is a flow probe in the input tubing to monitor flow, and since
these pumps are not occlusive, to detect flow reversal when weaning from support.
Heparin-bonded tubing to decrease t he risk of thrombus formation has also been advocated.
There are currently no approved devices available in the United States that use a
pulsatile perfusion pump. Pulsatile systems are used in Europe and are under investigation
in the United States. One of the major obstacles in pediatric patients has been the
requirement for a variety of stroke volumes that would serve patients ranging in size from
infants to young adults. Adult-size pulsatile systems have been used in the United States
to support children as young as ten years of age in the 40-50 kg range. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
6.
|
How long can circulatory
support be continued?
|
|
| The main limitation to long-term circulatory support in children is
the need for immobilization and the onset of complications related to extracorporeal
circulation, including bleeding and infection. In most series using either ECMO circuits
or VADs for cardiac support, the incidence of serious complications requiring
discontinuation of support begins to rise after one week of support. There are reports of
successful support of children with cardiac failure for periods up to four to five weeks,
however, these are rare cases and in most instances, cardiac transplantation was required
to wean off mechanical circulatory support. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
7.
|
What are the outcomes and
complications for mechanical circulatory support in children with cardiac disease?
|
|
| The results for ECMO for all indications are maintained by the
Extracorporeal Life Support Organization (ELSO). ELSO maintains a large database that
covers a variety of features for each ECMO case that is performed by participating
institution. A similar database for VAD in children is currently being developed at the
Royal Children's Hospital in Melbourne, Australia. Extracorporeal membrane oxygenation
(ECMO) has been the most widely-used method of circulatory support in children with
cardiac dysfunction. For pediatric cardiac patients, the probability of survival with ECMO
support has consistently been in the 40-50% range. The group with the worst outcome are
patients that are unable to be weaned from bypass following cardiac surgery, with the
exception of infants who have the best survival chances because of an anomalous left
coronary artery from the pulmonary artery. Children placed on ECMO support emergently for
cardiac arrest also have a better outlook, with reported survival probability of 50-70%.
The results for children supported with VAD are similar to those in children supported
with ECMO, in the 40-50% range. The most frequent complication in pediatric patients is
hemorrhage related to the need for ongoing anticoagulation in patients in the immediate
postoperative period. Pulmonary edema from left ventricular distension and high left a
trial pressures can also occur if left ventricular decompression is not achieved. Although
the incidence is relatively low, central nervous system complications including stroke and
cerebral hemorrhage can also occur. One of the most common late complications is sepsis,
frequently from gram negative enteric bacteria, which increases in incidence by seven to
ten days of support. Mechanical complications related to malfunction of the circuit are
relatively rare. |
| NEXT Question | TOP
of Page | FAQs HOME | CTSNet HOME
|
8.
|
What are the future
directions of mechanical circulatory support in children?
|
|
| The development of pulsatile VAD systems for children is ongoing and a
system is likely to become available in the next two to three years in the United States.
Some devices currently available in Europe provide pumps with a variety of stroke volumes
with a minimum volume as low as 9 mm. Such pulsatile systems may provide an advantage in
the maintenance of end organ function over non-pulsatile systems during prolonged periods
of support. Another evolving area is in the development of totally implantable systems for
chronic support in children, similar to currently available devices in adults such as the
TCI Heartmate. These devices use an electrical pump in which energy is provided by an
external induction coil. New devices will also have to address features that are unique to
pediatric circulatory support such as size constraints and the need to support chronic
circulatory failure in children with univentricular physiology after the Fontan procedure. |
| TOP of Page | FAQs HOME |
CTSNet HOME
|
Additional Pediatric Cardiac Surgery FAQs
|
|
|
|
