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

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

AFRICA

Possible deleterious effects of ionising radiation include (1)

genetic consequences, the risks of which can be assessed only

from animal studies; (2) carcinogenesis, which can be assessed

from survivors of nuclear bombings and patients exposed for

medical reasons; and (3) teratogenic effects on the developing

embryo or foetus.

Most cardiovascular diagnostic procedures

expose the embryo and foetus to less than 50 mSv,

which

does not increase reproductive risks (either birth defects or

miscarriage).

The reported dose of radiation with consequent increased

incidence of birth defects or miscarriage is above 200 mSv.

Termination of pregnancy on the grounds of ionising radiation

exposure is not recommended unless there is sufficient

documentation that the estimated foetal dose exceeds 15 rad

(150 mSv).

An important determinant of the consequence of radiation

exposure in pregnancy is the stage in which the radiation

exposure occurs.

1,9

In the first two weeks following conception

or the second two weeks from the last menstrual period, the

developing embryo is resistant to the malforming effects of

X-rays. However, the developing embryo is sensitive to the

lethal effects of X-rays, although doses much higher than

5 rad (50 mSv) are necessary to cause a miscarriage.

From the

third to the eighth week of pregnancy, in the period of early

embryonic development, the embryo is hardly affected, in terms

of birth defects, pregnancy loss, or growth retardation, unless the

exposure is substantially above 200 mSv.

From the eighth to the

15th week of pregnancy, the embryo or foetus is sensitive to the

effects of radiation, particularly on the central nervous system

(CNS). However, for the development of microcephaly and other

CNS malformations, the radiation exposure has to be sufficiently

high. The threshold for an observed effect on intelligence

quotient is estimated to be greater than 30 rad (300 mSv).

Cardiovascular diagnostic studies do not reach these levels

and, therefore, these effects are rarely of concern for patients.

The most sensitive period for CNS teratogenesis is between eight

and 15 weeks of gestation, therefore non-urgent radiological

testing should be avoided during this time. Rare consequences

of prenatal radiation exposure include a slight increase in the

incidence of childhood leukaemia and, possibly, a small change

in the frequency of genetic mutations.

Such exposure is not an

indication for pregnancy termination, however.

Appropriate counselling of patients before radiological

studies are performed is critical. After 20 weeks of gestation,

the foetus is fully developed and it again becomes resistant to

the effects of radiation exposure. At this late stage, there is no

evidence of increased risk of birth defects or miscarriage from

radiological diagnostic studies.

Deleterious effects of ionising radiation

Radiation-induced teratogenesis

CNS malformations, in particular microcephaly and mental

retardation, are the most commonly seen non-stochastic

complications following high-dose radiation exposure.

Following Hiroshima, many Japanese bomb victims who were

exposed

in utero

to doses greater than 10 to 150 rad developed

Table 1. Rationale for use and indications for

imaging of CVD in pregnancy

Evaluation of biventricular structure, size and function

Evaluation of native and prosthetic valve disease

Evaluation of pregnancy-induced hypertension and hypertensive heart

failure of pregnancy

Evaluation of congenital heart disease

Evaluation of myocarditis

Evaluation of specific cardiomyopathies

• Dilated cardiomyopathy

• Peripartum cardiomyopathy

• Hypertrophic cardiomyopathy

• Arrhythmogenic right ventricular cardiomyopathy

• Iron-overload cardiomyopathy

• Restrictive cardiomyopathy

• Myocardial infiltration (e.g. sarcoidosis)

• Left ventricular non-compaction

• Systemic rheumatic diseases (e.g. rheumatoid arthritis, systemic lupus

erythematosus, systemic sclerosis)

• Other less-common diseases (e.g. Chagas disease, Churg-Strauss

syndrome)

Evaluation of pericardial disease

• Pericarditis

• Pericardial effusions

• Pericardial tumours

• Pericardial effusive-constrictive syndrome

• Pericardial constriction

Evaluation of great vessels and pulmonary veins

Evaluation of cardiac masses (differentiation of tumour from thrombus)

Evaluation of infective endocarditis

Evaluation of ischaemic heart disease

• Diagnosis of myocardial infarction and its sequelae

• Assessment of myocardial viability

• Assessment for inducible ischaemia

• Coronary imaging

• Assessment of suspected coronary artery fistula

• Assessment of suspected anomalous coronary origins

Differentiation of ischaemic versus non-ischaemic cardiomyopathy

Evaluation of mechanical dyssynchrony

Evaluation of unexplained heart failure or stroke

Table 2. Measures of ionising radiation

Measure

Definition

Conventional units

SI units

Exposure

Number of ions produced by X-rays per kg of air

Roentgen (R)

Coulombs/kg (C/kg)

Absorbed dose Amount of energy deposited per kg of tissue

Radiation absorbed dose (rad) Gray (Gy)

1 Gy = 100 rad

KERMA

Kinetic energy released per unit mass

Radiation-absorbed dose (rad) Gray (Gy)

1 Gy = 100 rad

Dose equivalent A measure of radiation-specific biological damage in humans

Roentgen equivalents man (rem) Sievert (Sv)

1 Sv = 100 rem

Relative effective

dose

Amount of energy deposited per kg of tissue normalised for biological

effectiveness

Roentgen equivalents man (rem)

(1 rem = 1 rad for X-rays)

Sievert (Sv)

1 Sv = 100 rem

(1 Sv = 100 rad for X-rays)

Activity

Amount of radioactivity expressed as the nuclear transformation rate

Curie (Ci)

Bequerel (Bq)

1 Ci = 3.7 × 10