Biotechnology Update:
Looking Deeper into the Heart with Multidetector CT
Spotlight on Heart Attacks
According to the American Heart Association, this year
an estimated 1.2 million Americans will have a new or recurrent
coronary
attack, 700,000 will have a new coronary attack, and
about 500,000 will have a recurrent attack. It is also estimated
that an additional 175,000 silent first heart attacks
occur
each year while the incidence of myocardial infarction
is 565,000 new attacks and 300,000 recurrent attacks annually.
Presently, 13.2 million Americans have a history of heart
attack, angina pectoris or both (7.2 million males and
6
million females). About 330,000 people per year die of
coronary attack either in a hospital emergency department
or without
hospitalization. Most of these are sudden deaths caused
by cardiac arrest, usually resulting from ventricular fibrillation.
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Doctors from the departments of cardiology and radiology at Rambam
Medical Center in Haifa, Israel, are using multidetector computed
tomography (CT) to predict myocardial recovery after acute myocardial
infarction. A study on the research was reported at the American
Roentgen Ray Society annual meeting this month. Multidetector CT
is lauded for its ability to image the coronary arterial tree,
which is useful in patients with stable angina or those with chest
pains who present at emergency departments unsure if their symptoms
are actually heart related. However, based on these findings, this
technology could also provide valuable prediction of future myocardial
viability.
Instead of simply viewing patients’ coronary arteries on
CT, the clinicians in this study also examined the myocardium for
functional abnormalities if coronary stenosis was detected. This
was achieved by analyzing the contrast enhancement of the myocardium.
Consecutive gated 16-slice CT coronary angiography was performed
on 34 patients, all of whom had echocardiography examinations upon
initiation and at follow-up. The researchers sought to view the
heart muscle at the time of the patient’s heart attack and
then compare this to the muscle’s functional recovery on
the follow-up echocardiogram two to four months later. Myocardial-perfusion
defects were detected in 24 of these patients and 8 showed no defects
with the multidetector CT. Regions of the heart muscle that had
reduced blood flow resulting from heart attack appeared as dark
spots on the CT. During the follow-up echocardiograms, 7 of the
8 patients with no defects at baseline had completely recovered,
while only 12 of the 24 patients with myocardial-perfusion defects
had recovered.
When the physicians in this study performed the CT coronary angiography
on each patient, they expanded their analysis beyond the normal
criteria to also include coloration, density, and enhancement
of the myocardium. The advantage to the technique used by the physicians
is that it did not require an additional scan or put the patients
through any additional radiation exposure. This significantly
amplifies
the future use of cardiac multidetector CT, and also equates
to cost efficiencies from minimizing the use of additional radiation.
The physicians concluded that cardiac multidetector CT was able
to efficiently predict which patients would have reduced myocardial
viability on follow-up echocardiography.
Cardiac CT machines are evolving rapidly, with scanners capable
of ever-increasing slices, ranging from 64- to 256-slice scanners
either available or being developed. However, larger number
of slices will not provide an advantage for the purpose of detecting
myocardial viability after heart attack because the dark spots
are very visible and easy to detect on the 16-slice scans.
In
addition, multidetector CT scans have a distinct advantage
over the standard
angiography, which misses the vessel wall or the myocardium.
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