CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 3, May/June 2010
Cardiovascular Topics
142
AFRICA
Erythromycin as an alternative to reduce interfering
extra-cardiac activity in myocardial perfusion imaging
MARIZA VORSTER, MM SATHEKGE, P RHEEDER
Summary
Objectives:
We sought to determine whether taking oral
erythromycin prior to SPECT myocardial perfusion imaging
with Tc99m-sestamibi would reduce the amount of interfer-
ing extra-cardiac activity and improve the image quality.
Methods:
A total of 96 patients who were routinely referred
for myocardial perfusion imaging were randomly assigned
to one of two groups. Patients in group A received 500 mg of
non-enterically coated erythromycin orally one hour prior to
image acquisition (45 patients). Patients in group B received
diluted lemon juice which comprises the current standard of
care in our department (51 patients). A two-day protocol was
followed and study participants received the same interven-
tion on both days. Planar images of both the stress and rest
images were assessed visually by three experienced nuclear
medicine physicians for the presence of interfering extra-
cardiac activity. Physicians were blinded to the detail of the
protocol and independently assessed the images.
Results:
The qualitative results favoured lemon juice in
reducing the amount of interfering extra-cardiac activity.
The overall incidence of interfering extra-cardiac activity
was 46.15% in the lemon juice group vs 55.56% in the eryth-
romycin group. However, this difference was not found to be
statistically significant (
p
=
0.36). The use of a MYO:EXT
ratio similar to the one described by Peace and Lloyd,
11
appeared promising in quantifying interfering extra-cardiac
activity.
Conclusion:
The difference between the effect of erythro-
mycin and lemon juice on interfering extra-cardiac activity
appears statistically insignificant and erythromycin could
therefore be considered as a suitable alternative to lemon
juice.
Keywords:
erythromyacin, myocardial perfusion imaging, arte-
facts, improving diagnostic accuracy
Submitted 16/4/09, accepted 11/9/09
Cardiovasc J Afr
2010;
21
: 142–147
Single-photon emission computed tomography (SPECT) myocar-
dial perfusion imaging is a means of providing functional infor-
mation about the left ventricle and myocardial perfusion.
Accurate and reliable determination of left ventricular func-
tion and perfusion are important to guide therapeutic manage-
ment, improve risk stratification, and provide prognostic infor-
mation in the cardiac evaluation of patients. Hence it is of
great importance that the results are reliable and reproducible.
However, artifacts related to abdominal activity frequently affect
the accuracy. This is due to the fact that the two most commonly
used radiopharmaceuticals: Tc99m methoxy isobutyl isonitrile
(sestamibi) and Tc-99m tetrofosmin are both excreted by the
hepatobilliary system.
1,2
Due to the fact that the heart lies on the diaphragm just above
the left lobe of the liver and in the vicinity of the bowel, attenu-
ation and scattered radioactivity from these organs can interfere
with both visual and quantitative interpretation and cause arti-
facts during reconstruction of SPECT images, especially in the
inferior and infero-septal walls of the left ventricle. This is most
commonly associated with rest or pharmacological stress studies
in which the hepatic uptake is most marked, and it is also seen
more frequently in women.
3
Since the introduction of sestamibi, it has been recommended
that a fatty meal be given to reduce interference from liver and
gall bladder activity.
4
The recent procedure guidelines adopted
by the British Cardiac Society, however, state that the value of
a fatty meal is uncertain and may be counter-productive if there
is gastro–duodenal reflux, or if the tracer reaches the transverse
colon.
5
Various proposals have been made to reduce extra-cardiac
activity and its unwanted effects, with mixed results. Some of
these include prone imaging, pixel truncation, ECG-gated acqui-
sition and supplemental exercise with pharmacological stress.
1,5,6
Pharmacological interventions have included the use of chole-
cystokinin and metoclopramide. Recently, the effect of lemon
juice has also been evaluated.
7-9
The latter comprises the current
protocol in our department.
To our knowledge, erythromycin has not been used in a
study to evaluate the effect on interfering extra-cardiac activity.
The rationale behind the use of erythromycin is the following.
Erythromycin has been shown to increase gastric emptying,
possibly by mimicking the effect of motilin after binding to the
Department Pharmacology, Steve Biko Academic Hospital,
University of Pretoria, South Africa
MARIZA VORSTER, MB ChB, FCNP (SA), MMed (Nucl Med),
MPharm Med,
Department of Nuclear Medicine, Steve Biko Academic
Hospital, University of Pretoria, South Africa
MARIZA VORSTER, MB ChB, FCNP (SA), MMed (Nucl Med),
MPharm Med
MM SATHEKGE, MB ChB, MMed (Nucl Med)
Department Clinical Epidemiology, Steve Biko Academic
Hospital, University of Pretoria, South Africa
P RHEEDER, MB ChB, PhD
