Download Electrophysiologic Aspects of Cell Transplant

Electrophysiologic Aspects
of
Cell Transplant
Saeed Oraii MD, Cardiologist
Interventional electrophysiologist
Tehran Arrhythmia Clinic
Statistics
Cardiovascular disease affects approximately 58.8
million people in the United States.
About 400,000 new cases of congestive heart failure
occur each year.
More than 2,600 deaths occur each day from
cardiovascular disease -- 1 death every 33 seconds.
Currently the most effective treatment strategies
include lifestyle, medication and devices.
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Cell Transplant
The adult heart was once thought of as a post-mitotic and
terminally differentiated organ.
This dogma is being challenged by recent findings that the
adult heart contains cardiomyocytes that undergo proliferation.
“new paradigm sees heart as a highly dynamic organ in which
old, poorly functioning myocytes & vascular smooth muscle
cells replaced by activation & commitment of resident Cardiac
Stem Cells”
Limited cardiac regeneration through either recruitment of stem
cell populations from the bone marrow or through the
activation of resident cardiac progenitor cells has been
suggested.
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Regenerating Heart
Old dogma for last 30 years: “the heart is a post-mitotic organ
Incapable of regenerating parenchymal cells…
Cardiomyocytes can undergo cellular hypertrophy, but cannot
be replaced”
“… you have so many beats of your heart, so use it wisely”
In other words, the heart cells you have at birth is it!!
When they are damaged, or die – that’s it!!
Why the change?
•Observation of male cells in female hearts transplanted into
a male (progeny of primitive cells in the heart, or migrated from
elsewhere – bone)
Anversa P, Kajstura J, Leri A, Bolli R. Life and death of cardiac stem cells: a paradigm shift in cardiac
biology. Circulation. 2006 Mar 21;113(11):1451-63.
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New Paradigm
Heart is viewed as a self-renewing organ (cell # controlled by
stem cell compartment)
Primitive cells may represent 2% of cells
Clustered in atria, apex & throughout ventricular myocardium
Entire cell population of heart re-populated every 4.5 years

Old concept false - parenchymal cells do not live as long
as the organism (approx. 80 years)
Stem cells within infarcted area also die
Do not migrate from healthy myocardium to infarcted area to
replace dead cells
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New Paradigm
Intense myocyte formation in non-infarcted tissue, and
acute & chronic heart failure

11 fold higher than normal physiological turnover
Myocardial aging – telomere dysfunction, decrease pool of
competent stem cells.
View of aging & heart failure from perspective of stem cell
disorder.
“new paradigm sees heart as a highly dynamic organ in
which old, poorly functioning myocytes & vascular smooth
muscle cells replaced by activation & commitment of
resident Cardiac Stem Cells”
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Implications for Cardiac Rehabilitation
Awareness of trials for stem cell implantation

Potential for arrhythmias

Tracking other side effects
Sense of hope for CR patients

There is a healing capacity of the heart
What is the effect of our interventions (exercise, dietary, stress
management) on stem cell regeneration
Exercise – when to start and how much from the perspective of stem
cell health

e.g. effects of ischemia on stem cell health
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Arrhythmias in Heart Failure
The failing heart is prone to ventricular
tachyarrhythmias.
Ventricular arrhythmias are common in patients with
CHF.
During 24- to 48-hour period, 5% to 10% of patients
have runs of sustained (>30 seconds) VT and 40%
to 80% have nonsustained VT.
Of the annual mortality of up to 50% in severe heart
failure, about half the deaths are sudden and
presumably arrhythmic.
Zalmen Blanck, MD Nicholas D. Georgakopoulos, MD Marcie Berger, MD et al. Electrical Therapy in
Patients with Congestive Heart Failure. Current Problems in Cardiology Volume 27 Number 2 February
2002
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Mechanism of Arrhythmias
Reentry due to fibrosis
Myocardial ischemia
Enhanced automaticity
Dispersion of repolarization
Electrolyte abnormalities
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Transmural Heterogeneity
Normal cardiac cells exhibit significant
transmural heterogeneity of action potential
duration.
A delicate balance has to be maintained to
prevent arrhythmia.
When abnormal shortening or prolongation of
action potential duration in some, but not all, of
the myocardial cells, disturbs this balance, the
incidence of arrhythmia increases.
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Cell Regenerative Therapies
Many of the cell therapy strategies under
investigation will themselves be applied in
a patchy or regional distribution, which
may or may not be targeted to the areas
of greatest contractile dysfunction.
One important question that this raises is
whether this approach will suppress an
arrhythmic tendency, by restoring greater
uniformity of healthy tissue architecture
and function, or whether it will further add
to the heterogeneity, thereby enhancing
any arrhythmic tendency.
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EXAMPLES OF NATURALLY OCCURRING
STEM CELLS
TOTIPOTENT
CELL (ZYGOTE)
PLURIPOTENT
STEM CELLS
(EMBRYONIC STEM CELLS)
“ADULT”
STEM CELLS
BLOOD STEM CELLS
OTHER COMMITTED
STEM CELLS (Myoblast, ETC.)
SPECIALIZED
CELLS:
WHITE BLOOD
RED BLOOD
PLATELETS
CELLS
CELLS
ADAPTED FROM WWW.NIH.GOV/NEWS/STEMCELL/FIG2.GIF
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Which Cell Type?
Tissue-specific stem cells:
Germ-line
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Skeletal Myoblasts
Skeletal myoblasts are one of the
earliest cell types that have been
tested as a regenerative agent for
structural heart disease.
Myoblasts are derived from
skeletal muscle satellite cells that
normally lie quiescent under the
basal membrane of skeletal
muscle fibers.
They are harvested by muscle
biopsy, expanded in culture, and
then injected into the heart of the
same patient.
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Skeletal Myoblasts
From a clinical perspective, they are attractive for the
following reasons:
They are easily obtained by muscle biopsy
They are autologous, circumventing any
histocompatibility concerns
They have a high proliferative potential in vitro
They have commitment to a well-differentiated myogenic
lineage
They have high resistance to ischemia, which is an
advantage given the hypovascular nature of post-infarct
scars
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First Cell Transplants
Autologous myoblast transplantation was first performed
by Taylor et al in rabbit hearts following cryoinjury in
1996.
Skeletal myoblasts were the first cell type tested in
humans for cellular cardiomyoplasty by Menasche’s
group.
Menasche P, Hagege AA, Vilquin JT, et al. Autologous skeletal myoblast transplantation for
severe postinfarction left ventricular dysfunction. J Am Coll Cardiol 2003;41:1078–83.
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Gap Junctions
Although transplantation of skeletal myoblasts
was demonstrated to improve myocardial
performance in animal models, gap junctions
and functional coupling were not observed
between grafted and host tissues.
Yet even the presence of such gap junctions
between host and donor cardiomyocyte tissues,
as observed in some studies, does not
guarantee functional integration.
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Arrhythmogenic Risk
The second important electrophysiological
consideration relates to the possible
arrhythmogenic risk of these procedures.
In the skeletal myoblast trials, a disturbingly high
incidence of ventricular arrhythmias was noted
in the initial stages of clinical follow-up.
10 out of the first 22 patients undergoing skeletal
myoblast transplantation experienced ventricular
arrhythmias.
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Ventricular Arrhythmias
One of the five patients had sustained episodes of
ventricular tachycardia and required implantable
cardioverter-defibrillator placement.
The investigators also describe a subsequent unpublished
experience of two sudden deaths and three serious
ventricular arrhythmias in eight additional patients.
These data seem to correspond to the Menasche et al.
experience in which 4 of 10 patients required ICD
implantation for ventricular arrhythmias after open chest
autologous myoblast transplantation.
Smits PC, van Geuns R-J, Poldermans D, et al. Catheter-based intramyocardial injection of autologous
skeletal myoblasts as a primary treatment of ischemic heart failure: clinical experience with six-month followup. J Am Coll Cardiol 2003;42:2063–9.
Menasche P, Hagege AA, Scorsin M, et al. Myoblast transplantation for heart failure. Lancet
2001;357:279–80.
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Potential Hazards of Skeletal Myoblasts
Itsik Ben-Dor, Shmuel Fuchs and Ran Kornowski. Cell Transplantation Protocols for Ischemic Myocardial
Syndrome J. Am. Coll. Cardiol. 2006;48;1519-1526
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Time Course
The time course of these events appear to
show a peak at 11–30 days post cell
transplantation.
There is also a hint from the pooled
findings that there may be an early period
following cell transplantation, possibly
extending for the first 20–30 days, during
which there is enhanced arrhythmic
tendency.
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Why?
In the case of skeletal myoblasts, the generated
myotubes have completely different
physiological properties than host myocytes
(extremely short APD).
Moreover, due to their lack of gap junctions,
these myotubes are completely uncoupled to the
surrounding ventricular myocytes and may
therefore act as anatomical obstacles,
increasing tissue inhomogeneity, slowing
conduction, and increasing the likelihood for the
formation of reentrant arrhythmias.
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Cell Therapy Proarrhythmia
Proarrhythmia after stem cell therapy might be
attributed to one or more of the following
reasons:
Heterogeneity of action potentials between the
native and the transplanted stem cells
Intrinsic arrhythmic potential of injected cells
Increased nerve sprouting induced by stem cell
injection
Local injury or edema induced by
intramyocardial injection
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Slow Conduction Zones
This hypothesis was recently demonstrated
experimentally.
Co-culturing of human skeletal myoblasts with
primary rat cardiomyocyte cultures resulted in
the formation of slow conduction zones that led
to the generation of spiral (reentrant) wave in
this in vitro model.
Interestingly, genetic modification of the
myoblasts to express the major gap junction
protein, Cx43, improved conduction and
decreased the tendency for arrhythmias
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Different Cell Types
The nature of the injected cell may have the most impact on
arrhythmogenesis after transplantation.
Myoblasts and stem cells differ in their inherent
electrophysiologic properties and in their ability to couple
electromechanically both among themselves and with host
cardiomyocytes.
Limited clinical data available thus far suggest that arrhythmias
are more likely to occur after myoblast than after stem cell
transplantation.
Finally, limited clinical experience suggests that proarrhythmic
effects of cell therapy may be transient.
Nonetheless, because the occurrence of cardiac arrhythmia is
highly unpredictable, long-term follow-up studies of cell
transplant recipients would seem to be essential for
understanding the natural course of myoblast and stem cell
induced arrhythmogenesis.
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Potential Antiarrhythmic Effect
Although cell grafting could theoretically increase the
potential for arrhythmias, the opposite may also occur.
Cardiomyocyte transplantation in the infarct border zone
may facilitate the emergence of new reentrant ventricular
arrhythmias by generating slow conduction channels in
this area.
The same strategy, on the other hand, may also be
utilized as a novel antiarrhythmic strategy. Thus, if
cardiomyocyte transplantation will result in efficient
regeneration of the infarct, existing slow conduction
pathways within the scar may be eliminated, reducing
the arrhythmogenic risk in these patients.
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Border or Center
Soliman et reported more frequent and polymorphic
premature ventricular contractions, couplets, triplets,
longer post-PAC pauses, and bradycardiac death
following injection of myoblasts in the infarct border zone
compared with central scar injection in a rabbit model.
One might expect that myoblast injection into the border
zone, but not scar, may be proarrhythmic.
Because functional improvement is independent of
electrical integration of the injected myoblasts, injection
of myoblasts into regions of scar may improve
hemodynamics via a paracrine mechanism without the
potential proarrhythmic consequences.
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Cell Specificities
This mechanism may be specific for
transplanted myoblasts, because embryonic
stem cells have been reported to differentiate
into a spontaneously contracting functional
syncytium with gap junctions distributed along
the cell borders.
Kehat I, Gepstein A, Spira A, Itskovitz-Eldor J, Gepstein L. Highresolution
electrophysiological assessment of human embryonic stem cell-derived cardiomyocytes:
a novel in vitro model for the study of conduction. Circ Res 2002;91:659–61.
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Arrhythmias With Other Cell Types
Itsik Ben-Dor, Shmuel Fuchs and Ran Kornowski. Cell Transplantation Protocols for Ischemic Myocardial
Syndrome J. Am. Coll. Cardiol. 2006;48;1519-1526
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And we draw conclusions: what do we
learn by examining the evidence?
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Factors Affecting Risk
Current data suggest that the risk of arrhythmia occurring
after myocardial cell transplantation may be increased by
several factors:
The type of cell injected
The local myocardial milieu and electrical properties of
the recipient tissue
The presence of global and regional left ventricular
function;
The ex vivo cell expansion technique; and
The timing of the transplantation relative to the ischemic
or infarction events
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We Need More Basic Research on Stem Cells to Define
Antiarrhythmic or Proarrhythmic Potentials
?
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Conclusion
One implication of this clinical
observation may be a
requirement for a prophylactic
ICD implantation in all patients
participating in these trials.
Another implication is the need
for a clinical electrophysiologist
to be actively involved in the
designing and execution of
these trials.
This latter would allow better
patient selection and better
understanding of the nature,
prevention, and treatment of
the arrhythmia episodes.
1997: Dolly, a Cloned Mammal
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Cell Therapy for Cardiac Arrhythmias
Cardiac arrhythmias represent one of the
most common causes of worldwide
morbidity and mortality and result in a
major burden on the health care systems.
The possible applications of these
emerging technologies is establishing
novel antiarrhythmic therapeutic
paradigms.
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Cell Therapy for Cardiac Arrhythmias
LIOR YANKELSON and LIOR GEPSTEIN. From Gene Therapy and Stem Cells to Clinical Electrophysiology. PACE 2006;
29:996–1005
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Implanted Pacemakers
Implanted pacemakers have become a highly
effective and safe treatment modality.
Nevertheless, these devices are not without
limitations.



The need for a surgical procedure with its associated
small but existing risks
The requirement of repeated procedures for battery
replacement
The inability to adjust heart rate and the resulting
electrical activation sequence in the same
effectiveness as the native pacemaker and cardiac
conduction system.
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Biological Pacemakers
In recent years, a number of novel gene and cell therapy
approaches have emerged as experimental platforms for
the creation of biological pacemakers.
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Avenues for Creating Biological
Pacemakers
To manipulate autonomic control;
To manipulate ion channel number, structure,
and/or function in order to create a nidus of
pacemaker cells;
or
To create the SA or AV node “from scratch.”
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Cell Therapy
Both embryonic and adult mesenchymal stem cells have
been used in attempts to fabricate biological
pacemakers.
With embryonic stem cells (pluripotent), the general
strategy is to direct the cells down a lineage that will
incorporate pacemaker properties in its own right, couple
to adjacent myocytes, and be integrated as a new sinus
node cell.
With adult mesenchymal stem cells (multipotent), the
strategy is to use the cells as platforms to carry genes of
interest to regions of the heart where the cells would
need to couple with adjacent myocytes.
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Embryonic Stem Cells
Human embryonic stem cells provide a rich
source of material for regenerating myocardium
and initiating electrical activity in heart.
The possibility that their use requires
immunosuppressive treatment remains an issue.
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Human Embryonic Stem Cell Lines
LIOR YANKELSON and LIOR GEPSTEIN. From Gene Therapy and Stem Cells to Clinical Electrophysiology. PACE 2006;
29:996–1005
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Mesenchymal Stem Cells
Hyperpolarization-activated, Cyclic
Nucleotide-gated (HCN) channel
(If current)
Michael R. Rosen, MD. Biological pacemaking: In our lifetime? Heart Rhythm, Vol 2, No 4, April 2005
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Mesenchymal Stem Cells
Michael R. Rosen, MD. Biological pacemaking: In our
lifetime? Heart Rhythm, Vol 2, No 4, April 2005
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Limitations
In the case of the engineered Mesenchymal Stem Cells
it is not clear whether the transfected cells will eventually
discontinue expressing the channel or whether these
multipotent cells may differentiate into unwanted cell
types such as bone and cartilage.
The genetically engineered cells only partially
recapitulate the phenotype of the SA nodal cells.
In the case of the hESC-derived cells, it is not clear
whether these early stage cardiomyocytes, that display
some pacemaker like properties, will eventually mature
into adult ventricular-like cells and lose their capabilities
for spontaneous automaticity.
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Challenge: Knowledge Explosion
“We are drowning in
information but starved
for knowledge.”—Naisbitt, ‘82
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