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Cardiac MRI Detects Thinned Heart Muscle Previously Deemed Unsalvageable

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Duke Health News 919-660-1306

ORLANDO – Duke University Medical Center researchers have
used cardiac magnetic resonance imaging (MRI) to demonstrate
that heart muscle that had been "thinned" by a heart attack
could indeed be "saved" by restoring blood flow to the affected
region.

In the past, physicians would typically write off such
thinned heart tissue as unsalvageable and would not pursue
revascularization therapy with coronary artery bypass surgery
or angioplasty. However, the Duke researchers said that the
cardiac MRI allows them to visualize the beating heart with a
precision and specificity that conventional methods cannot
match.

Although their study was based on a small sample of heart
patients seen at Duke University and Northwestern University,
Chicago, the researchers believe that as cardiac MRI is used
more routinely in the imaging of the heart, it could become the
new "gold standard" for determining heart muscle that while
damaged, is still viable given appropriate treatment.

The results of the Duke study were presented today (Nov. 12,
2003) at the 76th annual scientific session of the American
Heart Association, by cardiologist Dipan Shah, M.D., consulting
assistant professor of medicine at Duke

"Most cardiologists are beginning to recognize that MRI is
becoming the gold standard for viability testing, because with
its extremely high spatial resolution, it can detect details
not seen before," Shah said. "The ability to differentiate
between living and dead cells makes MRI a more direct measure
of tissue viability than any other method."

During a cardiac MRI examination, which is non-invasive and
radiation-free, a patient is guided through the cavity of a
large doughnut-shaped magnet. The magnet causes hydrogen nuclei
in cells to align, and when perturbed by radio waves, they give
off characteristic signals, which are then converted by
computers into three-dimensional images of the heart and its
structures. While MRI technology itself is 20 years old, only
in the past few years has technology improved to the point
where accurate images of moving tissues can be taken.

"Not only have we found thinned areas that could be saved by
revascularization, we have learned some new concepts that will
allow us to predict which of the thinned areas could be saved,"
said cardiologist Raymond Kim, M.D., co-director of the Duke
Cardiovascular Magnetic Resonance Center and member of the
research team. "It appears to depend on the ratio of viable
cells to scar tissue in the thinned area and not just the
absolute amount of viable cells.

"This is important since most other viability tests measure
only the amount of viable tissue and not the amount of scar,"
Kim continued. "Thus, thinned areas will generally be
interpreted as dead because the amount of viable tissue is
small by definition."

When a portion of heart muscle is deprived of blood flow, as
in a heart attack, those muscle cells are deprived of needed
oxygen and nutrients. As the muscle cells in the walls of the
heart die, they are replaced by collagen, which makes the walls
thinner and less effective in pumping.

For their study, the Duke team evaluated 30 patients with
chronic coronary artery disease who had large areas of thinned
myocardium, or heart muscle. Each patient received an initial
MRI scan to determine myocardial viability, and then another
after having a revascularization procedure.

Patients were then divided into two groups – 19 who had less
than 50 percent viability before revascularization, and 11 who
had greater than 50 percent.

"After revascularization, the patients in the first group
demonstrated minimal functional improvement in the thinned
region, while the second group had significant improvement not
only in contractile function but also wall thickness," Shah
said.

Specifically, the group with greater than 50 percent
alive-to-dead cells experienced an increase in diastolic wall
thickness from 4.4 mm to 7.4 mm, while the systolic wall
thickening increased from 4 percent to 32 percent. Systole is
that part of the heart's pumping cycle when it contracts and
pushes blood out to the body, while the diastole is when the
heart relaxes and fills with blood in preparation for the next
heart beat.

"Prior studies have suggested that myocardium which is
thinned to less than 5.5 mm is not viable and cannot improve in
contractile functioning even after revascularization," Shah
said. "However, our study has shown that there are some
patients with severely thinned myocardium who can be helped by
revascularization."

Kim said the larger studies need to be conducted to see how
often patients with thinned muscle actually have tissue that
can be saved, and what impact revascularization can have on
that tissue.

"But we have already proven that we can detect alive but
injured tissue and bring it back with revascularization," Kim
added.

Other members of the team were from Duke Robert Judd, Ph.D.,
Michael Elliott, M.D., Igor Klem, M.D., Louise Thomson, M.D.
and Michele Parker. From Northwestern, team members were Robert
Bonow, M.D., and Edwin Wu, M.D. Ham Kim, M.D., Cornell
University Medical Center, also participated in the study.

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