Safety Risk of Multislice CT Angiogram Compared to Cardiac Catheterization
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May 9, 2006 -- Two articles in the recent Journal
of the American College of Cardiology, published online on April 17,
address
the debate
of how non-invasive MultiSlice Computed
Tomography (MSCT) imaging compares to standard angiography (cardiac catheterization)
on the issue of safety.
One of the
few drawbacks of MSCT has been the higher dose of radiation involved.
This is
discussed
in article 1 below in a
study done at the Bristol Heart Institute in the U.K., showing
that the radiation
dose "was
significantly higher" for MSCT. The concern, of course, is that higher
radiation doses have been shown to increase the incidence of cancer later on.
This finding has been questioned by at least one researcher who commented that
the amount of radiation used in the U.K. study was more than usual, and that
newer methods, such as ECG gating, have reduced that amount by almost half.
(ECG gating synchronizes the X-ray emitter to the patient's heartbeat, so that
the only one part of the heartbeat cycle gets the full radiation
dose).
However,
radiation dose is not the whole safety story. Article
2, "Risk
Has Its Reward",
was written by researchers at New York's famed Memorial Sloan
Kettering
Cancer
Center, and their interpretation
is that MSCT is safer when taking into account the "overall risk" of
both procedures. The risk of radiation-related cancer fatality over a partient's
lifetime for standard angiography is 2 in 10,000; for MSCT it's 7 in 10,000
(again, this higher figure is disputed by many imaging specialists).
But
the non-radiation risk of mortality in angiography is an additional 11
in 10,000, so (2 + 11 = 13) the actual "overall risk" for standard
angiography is 13 in 10,000 -- almost double that of MSCT. If one uses
the lower estimates of radiation for MSCT, then the safety factor is two,
three or more in favor of CT angiography. Additionally this study did not
take into account the various major and minor complications
experienced with the more invasive cardiac catheterization angiography
(around 2-3%) that can occur (access site complications, nerve trauma,
hematoma,
pseudoaneurysm,
etc.).
The study concludes:
"For an equivalent
clinical diagnostic efficacy of MSCT angiography and CCA
[Conventional Coronary Angiography] (25–33),
MSCT angiography emerges as the safer of these two alternatives,
despite its higher radiation dose."
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