Does myocardial viability detection improve using a novel combined 99mTc sestamibi infusion and low dose dobutamine infusion in high risk ischemic cardiomyopathy patients?

Abstract

Objective: Early identification of viable myocardium in ischemic cardiomyopathy (ICM) patients is essential for early intervention and better clinical outcome. 99mTechnetium (99mTc) sestamibi gated myocardial perfusion imaging (gMPI) is a well-established technique for myocardial viability evaluation. Detection of potentially viable segments is a predictor of hibernating myocardium. ICM patients with hibernation have a better prognosis after revascularization. We used a novel infusion technique to determine better viability detection preoperatively in challenging situations. Like thallium, does prolonged availability of sestamibi in circulation with additional low dose dobutamine steady infusion (DS Inf) facilitate improved myocardial viability?

Methods: A total of 58 ICM patients with infarct and left ventricular ejection fraction (LVEF) <45% underwent 99mTc sestamibi bolus injection followed by slow intravenous infusion single-photon emission computed tomography (SPECT) using a 2 day protocol. After acquiring the second set of 99mTc sestamibi infusion images, a third SPECT gMPI was performed during DS Inf.

Results: A 17-segment myocardial model was used; 52 of 58 patients (548/986 segments) demonstrated perfusion defects (nonviable myocardium) on bolus study. Only 24 patients demonstrated viable segments by standard bolus imaging protocol. The slow MIBI infusion study demonstrated 158 viable segments (12 ICM patients), while combined infusion (99mTc sestamibi+DS Inf) exhibited an additional 6 patients with improved myocardial viability. Thus, 18 high risk patients benefited by this novel infusion technique to demonstrate viable myocardium on SPECT. There was a significantly higher sensitivity (p=0.05) and positive predictive value (p=0.01) in viability identification with the combined DS Inf technique. In dysfunctional segments, the rate of concordance for detecting viability between infusion and bolus techniques was 65%. Paired t test showed statistically significant improvement in viability detection with combined infusion compared to the bolus study (p=0.001).

Conclusion: This novel infusion technique was shown to be feasible and incremental in viability detection in ICM patients with severe left ventricular dysfunction. It is a robust tool to guide revascularization, in high risk ICM patients. This study also showed that patients with large transmural MI demonstrated no significant improvement in myocardial perfusion status using either protocol.

Figure 1

Rest MPI SPECT (bolus and infusion) of 38-year-old male with NSTEMI (inferior wall) and LV dysfunction. Quantitative improvement noted in sestamibi uptake in the inferior segment from 40% to 50% to >60%

Figure 2

Comparative SPECT images of a 57-year-old patient with ICM. Perfusion defects noted in the apex, major part of anterior and entire septal LV segments. Infusion study shows overall improvement in left anterior descending (LAD) myocardial viability. Step 10 scale display shows improvement in score on WM and WT

Figure 3

Rest MPI SPECT images of a patient with inferolateral MI showing significant improvement in segmental viability on infusion highlighted on visual and 4D MSPECT quantitation

Figure 4

A 67-year-old diabetic man with known transmural MI (LAD territory). Comparative SPECT images show no improvement in LAD segmental viability by rest sestamibi bolus and DS Inf SPECT studies

Figure 5

Tabular columns comparing mean number of viable segments per patient by sestamibi infusion and infusion protocols

Figure 6

Graph depicts higher number of viable segments detected on dobutamine+sestamibi infusion SPECT when compared to sestamibi bolus myocardial perfusion SPECT study

Figure 7

Comparison of LVEF at baseline and 3-month followup echocardiogram