Cardiovascular Journal of Africa: Vol 27 No 2 (March/April 2016)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 27, No 2, March/April 2016

AFRICA

microcephaly.

A linear, dose-related association between severe

mental retardation and radiation was also found, with the

important caveat that most cases followed exposure during weeks

eight to 15 of gestation.

16,17

Radiation-induced malignancy

Exposure to as little as 1 or 2 rad has been associated with

an increase in childhood malignancies, especially leukaemia,

occurring in a stochastic fashion.

For example, the background

rate of leukaemia in children is about 3.6 per 10 000.

Exposure

to 1 or 2 rad increases this rate to five per 10 000.

While these

doses do fall within the range of some radiographic studies, the

absolute increase of risk (~ 1 in 10 000) is very small.

Therefore,

physicians should carefully weigh the risks and benefits of any

radiographic study and include the mother in the decision-

making process whenever possible.

Radiation-induced mutagenesis

Radiation can cause germ-line mutations, potentially affecting

future generations. Although radiation is commonly believed to

create bizarre new mutations, data show that it usually merely

increases the frequency of mutations occurring naturally in

the general population.

The dosage required to double this

baseline mutation rate is between 50 and 100 rad, far more

than the radiation doses occurring in common cardiovascular

radiographic studies.

The most important factor for physicians to remember is

that the currently accepted maximum limit of ionising radiation

exposure to the foetus during pregnancy is a cumulative dose of

5 rad (50 mSv or 50 mGy).

3,10,20,23

Non-ionising radiation and pregnancy

The reproductive risk of non-ionising radiation, which includes

electromagnetic fields from computers, microwave ovens,

microwave communication systems, cellular phones, power lines,

household appliances, heating pads and warming blankets,

airport metal screening devices and diagnostic ultrasound has

been studied extensively. Two national committees of scientists

in the US evaluated the risk from these non-ionising radiation

sources. The first report was published in 1993 from the Oak

Ridge Associated University panel

created by the White House,

while the second was the product of the committee of the

National Academy of Sciences.

Both of these groups concluded

that the reproductive risk of non-ionising radiation is minimal,

if even existent.

24,25

Chest radiography

The chest X-ray is the most commonly performed diagnostic

cardiovascular radiographic examination, and is able to produce

accurate images of the heart, lungs, airways, blood vessels and

the bones of the spine and chest. The chest X-ray utilises small

amounts of radiation (0.00002 to 0.00007 rad)

4,9

when a focused

beam of radiation is passed through the body, resulting in a

black-and-white image recorded on special film or a computer.

X-rays are able to differentiate tissues in the body because

of varying densities (each tissue allows a different amount of

radiation to pass through and expose the X-ray-sensitive film).

Dense bone absorbs much of the radiation while soft tissue,

such as heart muscle, allows more of the X-rays to pass through.

Consequently bones appear white on the X-ray, soft tissue shows

up in shades of grey and air appears black.

Medically indicated diagnostic chest radiographic studies

can be safely performed in pregnancy (Fig. 1), provided the

equipment works properly and the abdomen of the patient is

adequately shielded. The risk of not making the diagnosis often

far surpasses the risk of radiation in such instances.

Fluoroscopy and invasive angiography

Fluoroscopy is a type of medical imaging that shows a

continuous X-ray image on a monitor, much like an X-ray

movie. Fluoroscopy is routinely used to screen suspected stuck

prosthetic valves and for percutaneous transvenous mitral

commissurotomy (PTMC) in those with symptomatic mitral

stenosis in pregnancy. Furthermore, fluoroscopy is the basis

for imaging during invasive angiographic procedures (including

coronary angiography and haemodynamic studies). There

are many situations where the benefit of performing these

procedures is much greater than any small possible harm that

might arise from radiation exposure.

For a typical fluoroscopic

study, the amount of radiation occurring is in the range of 0.001

to 0.05 rad; dosage depends on duration of fluoroscopic time.

As always with any medical exposure, each particular

procedure must be clinically justified, including taking into

account when the procedure needs to occur and the anticipated

radiation dose to the foetus. Once justified, due diligence is

taken to optimise when and how the procedure is performed

to minimise radiation exposure to the foetus, consistent with

achieving the desired clinical outcome. The radiation exposure to

the foetus predominantly arises from scattered radiation within

the patient.

20,29

Some of the main methods for minimising the dose to the

foetus include: (1) restricting the X-ray beam size to as small

as is necessary; (2) choosing the direction of the primary

beam so that it is as far away from the foetus as possible; (3)

ensuring that the overall exposure time is as short as possible; (4)

selecting appropriate exposure factors; (5) calculating the dose

by a knowledgeable medical physicist, if there is concern; and (6)

using a lead apron on the table to shield any primary beam from

the X-ray tube reaching the foetus (Table 3).

Fig. 1.

Chest radiography of a pregnant woman with peripar-

tum cardiomyopathy. (A) posterior lateral projection, (B)

lateral projection.