MYOCARDIAL PERFUSION SCINTIGRAPHY

Abstract

Background: Reduced septal uptake of myocardial perfusion agents is frequently observed in patients
having left bundle branch block (LBBB) without any significant coronary artery disease. Objective: To
evaluate the incremental value of gated SPECT myocardial perfusion scintigraphy (MRS) on apparent
regional perfusion and wall thickening, in order to standardize the protocol for reporting myocardial
perfusion scintigraphy in LBBB patients with the aim of avoiding false positive reports. Material &
Methods: Resting gated SPECT MPS was performed in 8 frames mode with intravenous injection of 740
MBq 99mTc-MIBI in 10 normal controls and 19 LBBB patients having low probability of coronary artery
disease (CAD). Visual analyses and quantitative analyses on non gated (NG), end diastolic (ED), end
systolic (ES), peak septal and peak lateral wall count frame images was carried out which include calculation
of septal to lateral wall ratio (SLR), end systolic myocardial thickening index (MTI) and peak MTI. Results:
Septal hypo perfusion was noted in 15 patients in NG and 19 in ES images, whereas only 1 patient showed
abnormalities on ED images. Fourteen patients demonstrated worsening of apparent perfusion on ES images
than that of NG. In NG study of LBBB group SLR (0.69 ± 0.08) was lower than that of control (0.89 ± 0.07)
group. Further worsening was observed in ES (0.61 ± 0.06), which markedly improved in ED (0.87 ± 0.07)
to reach near that of control (0.89 ± 0.08). End systolic MTI for septum was markedly lower in LBBB group
(22.821 ± 11.78) than that of control (65.02 ± 21.45). Lateral wall in LBBB group demonstrated values
(68.14 ± 15.8) similar to those of control (71.61 ± 22.06). Within the LBBB group septum demonstrated
much lower values than that of lateral wall. In all control subjects, frames showing peak lateral and peak septal wall counts were the same as their respective ES frame. Similar trend was noted for lateral wall of
LBBB patients. However time bin showing peak septal wall counts were different from ES frame in all
LBBB subjects. In controls, same value of SLR (0.86 ± 0.04) was found for ES frame and at peak
myocardial thickening. In LBBB patients, peak SLR ratio (0.73 ± 0.09) is significantly higher than that
observed in ES frame (0.61 ± 0.06), relatively higher than that in NG study, but still lower than that observed
in controls. Comparison of end systolic MTI with peak MTI shows same value for lateral wall (71.61 ±
22.06) and IVS (65.02 + 21.45) of control group and lateral wall (68.14 ± 15.8) of LBB group respectively.
However significantly higher value of septal peak MTI than end systolic MTI (42.6 ± 26 vs. 22.82 ± 11.78)
are observed due to out of phase contraction of septum. Conclusion: Smaller count increase in the septal
region during systole is basically responsible for apparent septal perfusion artefacts in NG images in LBBB
patients having low probability of CAD. Out of phase contraction of septum is responsible for apparent
worsening of septal perfusion from NG to ES. Septal hypoperfusion artefacts can be eliminated by
conducting gated myocardial perfusion scintigraphy in LBBB patients instead of nongated studies, and
reporting perfusion status on end diastolic images.