Robert L. Kormos – Mechanical Circulatory Support. Braunwalds Heart Disease

Автор: Robert L. Kormos
Название книги: Mechanical Circulatory Support. Braunwalds Heart Disease
Формат: PDF
Жанр: Медицина
Страницы: 367
Качество: Изначально компьютерное, E-book

Mechanical Circulatory Support, by Drs. Robert L. Kormos and Leslie W. Miller, provides the clinically relevant information you need to effectively use this therapy to treat and manage end-stage cardiovascular disease. In this Companion to Braunwald’s Heart Disease, the world’s most prominent experts in mechanical circulatory support (MCS) cover basic science, device construction, clinical applications, socioeconomic implications, future directions, and more. Stay on top of hot topics – including innovative devices like continuous flow pumps, next-generation centrifugal pumps, and total artificial hearts; MCS for pediatric and congenital heart disease; cellular, molecular, genomic, and functional changes that occur in the failing heart in response to MCS; and Interagency Registry of Mechanically Assisted Circulatory Support (INTERMACS) as a tool to track and advance clinical practice. You’ll also have access the fully searchable text online at www.expertconsult.com.

The information in this textbook represents the most
contemporary
thinking in the field of mechanical circulatory
support. However, a short historical perspective is important
in understanding how quickly we moved to rapid adoption of
this technology. The therapy of mechanical circulatory support
began only 60 years ago, rooted in the concept of capitalizing
on the augmentative abilities of the skeletal muscle of the
hemi-diaphragm to support cardiac contractility. In 1959, the
pioneer, Adrian Kantrowicz, wrote extensively about using
the diaphragm in a counter pulsation mode long before his
development of the intra-aortic balloon pump. But limitations
caused by the challenges of chronic phrenic nerve stimulation
turned his team toward utilizing a mechanical prosthesis
as an auxiliary ventricle. A recently arrived Japanese research
partner, Yuki Nose, discovered that this prosthesis worked
more effectively the closer it was placed to the native heart.
Simultaneously, John Gibbon, Clarence Dennis, and Walt
Lillihei were developing the pump oxygenator
while Willem
Kolff, Frank Hastings, and Bret Kusserow pursued the total
artificial heart. Interestingly many of the early systems were
based on the concept of counterpulsation
with blood being
removed via one femoral artery and returned to the next. This
led Moulopoulis and others to further explore counterpulsation
using an intra-aortic balloon pump in 1962. In 1960 in a
second family of approaches, Salisbury showed the value of
left ventricular bypass, demonstrating its theoretical applications
in experimental heart failure. Dennis et al. reported a
technique for acute left heart failure, using a large-bore cannula
for transjugular/transseptal drainage of the left atrium,
which made left ventricular bypass possible without thoracotomy.
By 1964 they had used the procedure in 12 patients.
Potential application of left ventricular bypass for prolonged
left ventricular support began with Kusserow's report in 1961
of a paracorporeal pump located in juxtaposition to the outer
surface of the thoracic cage. Further experimentation was
carried
out by Domingo Liotta, Michael DeBakey, and their
colleagues. This led in 1966 to DeBakey's first clinical use of
such a pump in a 37-year-old woman who could not be weaned
from the pump oxygenator. The patient was supported on the
bypass pump for 10 days; she recovered and was discharged
from the hospital. In 1962, applying the principle of diastolic
augmentation, Kolff and Clauss had reported mock circulation
and canine studies with an intra-aortic balloon pump,
inflating the balloon with carbon dioxide and synchronizing
it to the electrocardiogram. But it was up to Kantrowicz and
his team in 1966 to design and fabricate balloon pumps in
the laboratory. They quickly learned the advantage of using
helium as the driving gas and by 1968, human studies were
being reported
Dr. Benjamin Eiseman, who was interested in organ
failure,
chaired a conference in the fall of 1964 that focused
on mechanical devices to assist the failing heart. It was cosponsored
by the Committee on Trauma, the Division of
Medical Sciences, the National Academy of Sciences, and the
National Research Council along with experts and pioneers
in the fields of engineering
and surgery who had an interest
in circulatory support. Dr Eiseman's opening comment was
that, “The heart is a set of pumps. Therefore there is no logical
reason
why it cannot be replaced by a mechanical equivalent.”
The challenges
for this development, although intimidating
in their engineering hurdles, he considered “mere details of
design.” Even at this early stage Dr. Eiseman had identified
two principle uses for such devices: reversible failure where
temporary use could lead to recovery and irreversible damage
where a more permanent substitute would be required for
one or both sides of the heart. The primary challenge Eiseman
identified was to have engineers and surgeons work closely
together to solve the issues of design.
An active participant in this meeting was Peter Salisbury,
mentioned above, who first introduced the concept of left
heart bypass for heart failure. But he also elaborated on the
characteristics of heart failure defined by Roy and Adam in
1888 as a syndrome of abnormally high left-sided diastolic
filling pressures, pulmonary hypertension, and a vicious
cycle of progressive hemodynamic and clinical deterioration
manifested by organ failure. He recommended, therefore,
that assisted circulation could have a major role when selfperpetuating
cardiac abnormalities due to low cardiac output
exists and when these are accompanied by ventricular
dilatation due to excess diastolic pressure and dilatation in a
failing ventricle and cannot be reversed by any other therapy.
These concepts for the indications for left ventricular support
have remained essentially unchanged in clinical practice
until 10 years ago when knowledge of patient selection
was modified. This will be explored later in the book. In his
presentation at this meeting in 1964, Salisbury goes on to distinguish
the acute hemodynamic collapse that occurs with
acute cardiogenic shock and its profound effects on the body
and how this situation may be less effectively corrected with
assisted circulation as compared to more chronic heart failure.
(Prophetic insight, given the struggles modern clinicians
have in accomplishing success with assisted circulation even
with more advanced and exotic technology in their hands.)
On a last note of interest, Salisbury predicts the current interest
in myocardial recovery using left ventricular assist devices
when he states, “A popular notion has it that 'tired' hearts
should be helped by ‘rest' and what could be more reposing
for the heart than having its 'work' taken over by an auxiliary
pump?”
The participants in this early meeting discussed in a
rather animated fashion their concerns with future pump
designs; the shortcomings and challenges of biocompatibility,
the effects of shear on the blood components, and ongoing
debate between proponents of pulsatile vs. non-pulsatile
pump designs. It was at this meeting that Michael DeBakey
and Domingo Liotta set forth their requirements for an ideal
implantable heart pump: (1) it should be capable of long-term
support (weeks or months); (2) it should be useable with or
without anticoagulants; (3) it should cause minimal blood
trauma; (4) it should make it possible to reduce mean left
atrial pressure to near normal; (5) it should maintain normal
aortic perfusion pressure; (6) it should enable function
to be discontinued for long intervals with normal resumption
of function (without the need for general heparinization
and without danger of pump thrombosis); (7) it should
enable synchronized pumping during any preselected time of
the cardiac cycle; and (8) it should be easy to implant. These
principles are interesting as the reader will see when outcomes
with devices and design principles of modern pumps
are reviewed.
At the conclusion of this meeting, the participants agreed
that certain challenges faced the field: (1) the engineers and
clinicians needed to work more closely together; (2) there
was a need to move from case reports to more populationbased
studies; (3) the need for pulsatile flow had not been
well-studied; (4) the field of biomaterials was not well-
developed;
(5) there were no clear guidelines or criteria for
the implementation of assisted circulation; and (6) the utility
of assisted circulation
for congenital heart disease in the setting
of pulmonary
artery hypertension was yet to be defined.
From an historical perspective, the field of mechanical circulatory
support has gone through several more recent decades
of change. The decade of the 1960's defined the problem and
cardiac assistance was limited to aortic counterpulsation,
direct cardiac compression, extensions of cardiopulmonary
bypass, left atrial to femoral bypass techniques, and primitive
pulsatile systems. The research goals during the 1970's
focused on myocardial recovery following post-cardiotomy
failure and shock and techniques of cannulation with further
refinement of timing of support. Research in the 1980's led to
the recognition and development of a need for more chronic
pulsatile devices. The optimal testing field for this new technology
would be those patients awaiting cardiac transplantation.
Again, patient selection and timing of implantation
issues were paramount. A large focus was on the determination
of the role of the total artificial heart in contrast to that
of the left ventricular assist device. This fact drove clinicians
to better define the role of the right ventricle during left ventricular
support. During the 1990's the use of a left ventricular
assist device as an alternative to cardiac transplantation
drove a number of clinical trials that were to be landmark in
their conclusions for long-term support. During this decade
clinicians moved to define the requirements for outpatient
LVAD management and began to acknowledge certain
instances of myocardial recovery on the LVAD. Perhaps the
strongest advances at this time came from the broader utilization
of the technology by more surgeons in more centers
resulting in more defined and structured protocols for device
implantation, early surgical management, and standards for
training.
In the past decade there has been a quantum change in
technology accompanied by major changes in clinical implementation.
From the technology perspective, there has been
a gradual reduction in size, making applicability wider and
reducing the invasiveness and complications of surgery. In
addition, we have seen the introduction and acceptance of
rotary blood pumps based first on axial flow technology and
soon followed by centrifugal designs. These devices have virtually
replaced the use of pulsatile systems except for the
more acute post-cardiotomy settings. There has been an introduction
of smaller and more portable peripheral components
such as the wearable controllers and batteries along with
smaller and more flexible external drivelines. Finally, a new
line of devices has been introduced as ultra-short term LVADs
for acute cardiogenic shock and even smaller devices for neonatal
and pediatric uses. We have seen evolution not only in
technology but also in utilization. Devices are now approved
or on the threshold of being approved for not only bridge to
transplantation but also for destination or permanent therapy.
Patient selection is now based on earlier risk assessment
scales that aim to identify those patients at risk who stand
to benefit from device utilization before the onset of preoperative
risks that further drive postoperative morbidity and
mortality. Thus the device application is seen to be moving
to earlier indications, in particular for those patients who are
looking at these devices as permanent solutions. Indeed there
is a gradual acceptance by clinicians that the intended use
of a LVAD device for chronic support may change during the
period of support from one indication to another. Recovery of
function after ventricular assist device support is being considered
more often for cases not only presenting
acutely, but
also in some instances following chronic support. Finally the
care of patients after implantation has moved from strictly
inpatient care to exclusively outpatient care, raising even
more challenges for the paradigms of care. Along with this has
been the gradual development of the specialty of advanced
heart failure cardiology that encompassed the understanding
and chronic management of ventricular assist devices. It is
for this reason that we have attempted to represent both surgical
and cardiologic perspectives in this textbook as the field
of mechanical circulatory support moves forward as a true
medical
and surgical collaboration.
There has been enormous progress in the field of MCS in
the past 5 years, including significant growth in the development
of a number of systems designed for temporary support
of severe HF and shock. Their use has been associated
with increasing success in reversing shock and improving
end organ and neurologic function in critically ill patients,
and has led to the concept of “Bridge to a Bridge or Bridge to
Decision,”
While the early days of pulsatile MCS were not based on
many controlled trials, especially randomized against medical
therapy (due to the critical nature of the HF/shock in these
patients who were largely awaiting a heart transplant), the
recent near total transition from pulsatile to rotary pumps has
been driven by large clinical controlled trial evidence. The
durability of the devices now in use or in clinical trials has
allowed a conversion from emergent to near totally elective
implantation. This change has been aided by development
of risk scores and profiles that help identify the highest risk
patient by co-morbidities associated with high risk of poor
outcome during the index hospitalization. There remains a
critical need to develop similar contemporary risk models for
predicting the outcome of HF patients with medical therapy
alone.
The future of MCS seems very promising based on the
progress of the last decade. With increased manufacturers in
the field, continued improvements and progressive miniaturization
of the devices is expected. This will then lead to
expanded indications into patients with less severe heart failure.
The new pumps will need to be free of an external drive
line and some type of transcutaneous energy transfer that will
greatly enhance patient satisfaction and reduce long-term risk
of infection. The number of patients, especially over 65 years
of age, with advanced heart failure will continue to increase,
leading to the overwhelming use as a long-term alternative to
heart transplantation. This expanded use in patients with less
critical heart failure will hopefully lead to reduction in cost
that will be associated with greater adoption of their use.
Finally, we salute not only the courageous pioneers mentioned
above, along with the engineers, surgeons, heart failure
cardiologists, and other clinicians and coordinators that now
make up the VAD team, but also the amazing patients whose
courage and sacrifices have helped to bring this technology to its
current state. They inspire all in the field to continue
the progress
seen in the past 60 years and help them enjoy prolonged life
with markedly improved function and quality
of life.
Robert L. Kormos