CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 3, May/June 2010
AFRICA
145
higher on the stress studies when compared to the rest studies
(Fig. 5, Table 4).
For the purpose of validating the MYO:EXT ratio, the
absence or presence of interfering activity was considered to
be present when at least two or three physicians concurred. The
kappa statistic revealed fair to moderate inter-observer agree-
ment, with better agreement noted on the rest studies (
κ
=
0.42)
when compared to the stress studies (
κ
=
0.37). These values
were calculated independently of the intervention that was used.
The presence of interfering extra-cardiac activity was consist-
ently judged higher in the erythromycin group (55.56%) when
compared to the lemon juice group (46.15%) (
p
=
0.36). A
strong and statistically significant relationship was found with
the qualitative evaluation when using the rest MYO:EXT (
p
=
0.0002). Using the MYO:EXT ratio generated from the stress
images did not yield a statistically significant result (
p
=
0.0568).
Table 5 combines the results of all three observers and evaluates
the stress and rest studies separately. The presence or absence of
interfering activity was considered to be positive when at least
two or three physicians concurred.
A sub-group of 48 patients was selected from the study partic-
ipants in whom an additional MYO:EXT ratio was calculated on
the lateral images of both the stress and rest images. An average
value was generated for each of the 48 patients using both the
anterior and lateral images. This was calculated separately for
stress and rest studies and correlated with the qualitative results.
The results were similar to those provided in the table above
with only the ratios obtained from the rest images proving to be
statistically significant (
p
=
0.0002).
Discussion
SPECT myocardial perfusion imaging with sestamibi is a widely
used, non-invasive diagnostic method for assessing patients with
coronary artery disease with regard to severity, extent, prognosis
and therapeutic response. The initial myocardial uptake of sesta-
mibi is related to regional myocardial blood flow and is depend-
ent on a mitochondrial-derived membrane electrochemical gradi-
ent. Sestamibi is predominantly excreted by the hepatobilliary
system. Unfortunately, this mechanism of excretion is frequently
the source of artifacts due to abdominal activity, which affects
both observer interpretation and reconstruction. Various propos-
als have been made to overcome this problem in order to improve
diagnostic accuracy.
Recently, a prospective, randomised trial with 86 patients and
82 controls was conducted to evaluate the use of metoclopra-
mide. This study followed two previous studies with conflicting
results. Therefore the aim was to conclusively determine whether
metoclopramide was useful in reducing artifacts related to
abdominal activity in myocardial perfusion SPECT. In this study
metoclopramide showed neither a qualitative nor quantitative
impact on abdominal activity in myocardial perfusion imaging.
8
The use of metoclopramide is based on the rationale that it
is a prokinetic drug, which should enhance gastric clearance of
70%
60%
50%
40%
30%
20%
10%
0%
Obs 1
Obs 2
Obs 3
Fig. 5. Comparison of results from the two studies.
Lemon juice
Erythromycin
TABLE 5. RESULTS OF STRESSAND REST
STUDIES SEPARATELY
Stress
Rest
Y
N
Y
N
Number
57/96
39/96
48/96
48/96
Myo:Ext
1.12
1.22
1.08
1.24
±
SD
0.26
0.22
0.21
0.19
p
-value (difference
betweenY and N)
0.057
0.0002
95% CI
1.05-1.19 1.14-1.29 1.02-1.14 1.18-1.29
Myo:Ext
=
myocardium-to-extra-cardiac activity ratio; Y
=
presence
of interfering extra-cardiac activity; N
=
absence of interfering extra-
cardiac activity; CI
=
confidence interval.
Fig. 4. Circular semi-automatic ROI surrounding the
myocardium of the left ventricle and an irregular, manu-
ally drawn area starting from the infero-lateral aspect of
the myocardial ROI to the medial aspect thereof.
