Miokardiale perfusiebeelding met Tc-99m MIBI in pasiënte met linker bondeltakblok : die visuele en kwantitatiewe beoordeling van anteroseptale perfusie vir die diagnose van stenose van die linker afdalende arterie : cardiovascular topic
2005
lIgIntroduction:l/Ig The non-invasive detection of myocardial
ischaemia in patients with left bundle branch block
(LBBB) remains a challenge. It is often associated with
coronary artery disease or hypertension, but frequently
there is no indication of cardiovascular pathology at
presentation. Exercise-induced electrocardiographic ST
segment changes are non-diagnostic. Confirming coronary artery disease has obvious implications
for management. Several studies have shown
greater cardiac mortality in the presence of LBBB. Generally, a good prognosis has been found in patients
with LBBB and normal or near-normal myocardial
perfusion scintigraphy (MPS). Various investigators report frequent anteroseptal
defects with MPS in patients with LBBB in the absence
of significant left anterior descending (LAD) coronary
artery disease. Several mechanisms have been proposed
to explain this false-positive phenomenon. Various
interpretative methods and stress techniques have been
evaluated in an attempt to improve the specificity of noninvasive
studies for detecting LAD disease. A number of software packages for quantifying myocardial
perfusion are commercially available. Quantification
is recommended to improve diagnostic accuracy
and intra- and inter-observer reproducibility.
lbrglIgMethods:l/Ig Patients with LBBB on ECG, who were referred
to our institution (February 2002 to September 2003) for
myocardial perfusion scintigraphy, were included in the
study. Patients with previous myocardial infarction were
excluded, unless the location was confirmed to be not
anteroseptal before the onset of LBBB. Patients who did
not undergo coronary angiography within six months
were also excluded, unless a LAD lesion of luggl/ug 50% was
diagnosed more than six months prior to MPS without
subsequent intervention, or angiography more than six
months later showed a LAD lesion of lugll/ug 50%. Treadmill exercise, dipyridamole or dobutamine infusion
were used according to standard protocols and
imaging commenced 15-60 minutes later. QPSlsupgTMl/supg quantitative
software, used to reconstruct the images and
quantify perfusion, is described in detail elsewhere. Three experienced nuclear physicians interpreted the
studies. Stress and rest perfusion, as well as reversibility,
to the anteroseptal wall (excluding the apex),
anteroseptal wall and apex, and apex only, were graded
on a scale of 0 (normal) to 4 (absent perfusion), where
1 represents mild, 2 moderate, and 3 severe impairment
of perfusion. A final decision was made by consensus.
Using QPS TM , summed stress, rest and difference scores
were obtained for the same regions. Angiographic correlation was obtained by reviewing
the patients. records. Stenosis of the LAD or graft vessel
to the LAD of = 50% was regarded as significant. The Kruskal-Wallace non-parametric test was used
to compare the groups with and without significant
LAD stenosis. A Bonferroni correction was applied to
make provision for multiple testing. Receiver operating
characteristic (ROC) analysis was utilised to determine
the optimal threshold of the significant measurements to
distinguish between the two groups; for this threshold,
the sensitivity and specificity were calculated.
lbrglIgResults:l/Ig Nine men and nine women (42.78 years) satisfied
the inclusion criteria and were included in the study.
Dipyridamole was used in nine patients, exercise in
seven, dobutamine in one, and one patient was injected
during a period of typical chest pain. Ten patients had a
LAD stenosis of < 50% and eight = 50%. The only measurement that yielded a significant difference
between the groups was visual improvement in
perfusion to the anteroseptal wall and apex between
the stress and rest study (p < 0.0096). Even after applying
a Bonferroni correction, the value tended towards
significance (p = 0.16). A ROC curve was calculated and
an optimal threshold of 0.5 determined, which in turn
had a sensitivity of 88% and specificity of 67%.
lbrglIgDiscussion:l/Ig Our findings suggest that visual reversibility
in the anteroseptal wall and apex gives an indication of
significant LAD stenosis in patients with LBBB. This finding agrees with that of Mairesse et al.
Wackers argues that cardiomyopathic changes cause
anteroseptal perfusion defects in LBBB. It is possible
that irreversible perfusion defects in the anteroseptal
wall and apex are caused by a constant, stress-independent
mechanism, whereas reversible defects indicate
underlying ischaemia. Interestingly, quantitative analysis was not helpful in
predicting LAD disease. The quantitative software we
used is well validated. On the other hand, Svenssson
et al. compared three myocardial perfusion quantification
software packages and found considerable variation,
especially in the presence of perfusion defects. The state of perfusion to the apex was not helpful
to detect significant LAD disease. It is known that the
LAD usually supplies the apex. Matzer et al. found
that requiring the presence of an apical defect improved
specificity. This could not be confirmed by Lebtahi et
al. or Vaduganathan et al.
lbrglIgLimitations:l/Ig A definite limitation of our study was that
treadmill stress testing was performed in seven patients.
It is currently recommended by most authors that
pharmacological stress be performed in patients with
LBBB Selection bias is also a limitation because
only patients who also had angiography were included
in the study (18 out of 91).
lbrglIgConclusion:l/Ig A visual improvement in anteroseptal and
apical myocardial perfusion between stress and rest with
Tc-99m MIBI in patients with LBBB probably indicates
significant LAD stenosis. In our hands, quantitative
software did not aid in the diagnosis. A well-designed, prospective study using a standardised
stress protocol (probably dipyridamole or adenosine),
which specifically evaluates visual reversibility in
the anteroseptal wall and apex, will obviate the need
for a Bonferroni correction, and could confirm these
findings.
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