|Year : 2019 | Volume
| Issue : 1 | Page : 177-180
Assessment of viable myocardium by nitrate-augmented technetium-99m sestamibi myocardial perfusion imaging
Mahmoud A Solimana1, Awny G Shalabya1, Ahmed S Esawyb2
1 Department of Cardiology, Faculty of Medicine, Menoufia University, Egypt
2 Resident of Cardiology at Ministry of Health, Elshiekh Zayed Specialized Hospital, Giza Governorate, Egypt
|Date of Submission||06-Sep-2017|
|Date of Acceptance||19-Nov-2017|
|Date of Web Publication||17-Apr-2019|
Ahmed S Esawyb
Abdo Hamza St., Sirs Ellayan, Menoufia Governorate
Source of Support: None, Conflict of Interest: None
The aim of this study was to assess the role of nitrate-augmented technetium-99m (99mTc) sestamibi imaging in the evaluation of viable myocardium in patients who had ischemic heart disease with depressed left ventricle (LV) systolic function.
In the setting of acute myocardial infarction, stunning can occur, which is the persistent LV dysfunction following opening of the occluded coronary artery; recovery of function occurs usually within months. In the setting of chronic LV dysfunction, the pathophysiology underlying the dysfunction is referred to as myocardial hibernation. Various imaging techniques have been introduced to detect viability and discriminate this from scar tissue.
Patients and methods
Between November 2015 and November 2016, 100 patients with a history of myocardial infarction 'functional class II and III' or/and LV dysfunction were included in this multicenter prospective study. All patients underwent 99mTc sestamibi myocardial perfusion imaging under both rest and rest with nitrate conditions.
Nitrates improved viability detection by myocardial perfusion imaging in patients with depressed LV systolic function. There was significant decrease in the total perfusion defect in rest with nitrate study in comparison with the rest study (P = 0.006).
In patients with chronic ischemic heart disease with depressed LV systolic function, the use of nitrate-augmented Tc-99m sestamibi protocol in cardiac single photon emission computed tomography imaging results in improved detection of viable but hypoperfused segments. It is a good indicator for differentiating viable tissues from the scar.
Keywords: myocardial ischemia, myocardial perfusion imaging, nitrate augmented, technetium-99m sestamibi
|How to cite this article:|
Solimana MA, Shalabya AG, Esawyb AS. Assessment of viable myocardium by nitrate-augmented technetium-99m sestamibi myocardial perfusion imaging. Menoufia Med J 2019;32:177-80
|How to cite this URL:|
Solimana MA, Shalabya AG, Esawyb AS. Assessment of viable myocardium by nitrate-augmented technetium-99m sestamibi myocardial perfusion imaging. Menoufia Med J [serial online] 2019 [cited 2019 Aug 25];32:177-80. Available from: http://www.mmj.eg.net/text.asp?2019/32/1/177/256129
| Introduction|| |
The extent of myocardial viability in patients with chronic coronary artery disease (CAD), previous myocardial infarction (MI), and reduced left ventricular (LV) systolic function has both prognostic and therapeutic significance . Its assessment is therefore important in the clinical treatment of such patients, especially when a revascularization procedure is being considered.
The concept of myocardial hibernation was introduced by Rahimtoola to describe a condition of chronic sustained abnormal contraction attributable to chronic underperfusion in patients who have CAD and in whom revascularization causes the recovery of LV function .
Several imaging techniques have been developed for the detection of myocardial viability. Among them, positron emission tomography with 18 F-fluorodeoxyglucose seems to be the most accurate for the prediction of recovery of LV function after coronary revascularization. However, the decision for coronary revascularization in patients with ischemic LV dysfunction requires a more readily available, efficient, cost-effective, and noninvasive technique for viability assessment. Nitrate-augmented myocardial perfusion imaging was introduced for the detection of myocardial viability for more than 15 years, and this technique has been increasingly used in several laboratories .
Long-term outcome of patients with severe CAD and LV dysfunction may improve after coronary revascularization. However, this technique in such patients is limited by increased perioperative morbidity and mortality. It has been recognized that the presence and the extent of dysfunctional viable myocardium susceptible to ischemia (hibernating or stunned) is one of the most important determinants of recovery of LV function after coronary revascularization .
The aim of this study was to assess the role of nitrate-augmented technetium-99m (99m Tc)-sestamibi imaging in the evaluation of viable myocardium in patients who had ischemic heart disease with depressed LV systolic function.
| Patients and methods|| |
After approval of the study proposal by the Menoufia Ethics Committee, this prospective study was conducted between November 2015 and November 2016 in Menoufia University Hospitals and Alfa Radiology Center.
A total of 100 adult patients with history of MI 'functional class II and III' or/and LV dysfunction underwent 99m Tc sestamibi myocardial perfusion imaging under both rest and rest with nitrate conditions. All patients were older than 17 years (38–75 years). An informed consent was taken from each patient.
The criteria for exclusion from the study were recent MI less than 4 weeks, functional class IV heart failure, other significant cardiac conditions, systolic blood pressure less than 90 mmHg, and any patient who developed hemodynamic instability after sublingual nitrates.
All patients were investigated by history taking and 12-lead ECG. Then, they were encouraged to come off their β-blockers, calcium channel blockers, and nitrates 48 h before the test, and subsequently underwent single photon emission tomography (SPECT) study in 2 days.
On the first day of our study, all patients were injected intravenously with Tc-99m methoxyisobutylisonitrile (MIBI) under baseline resting conditions. On the second day, the same technique was used 15–20 min following sublingual nitrate administration, followed by having light fatty meal, and after 1 h, SPECT images were obtained.
Scintigraphic rest and rest with nitrate gated images were obtained quantitatively by a dedicated software (Auto QUANT 6.0; Philips Medical Systems, Cleveland, Ohio, USA) that employs a 17-segment LV model with a common five-point scoring system (0='normal perfusion'; 5='no perfusion').
Overall, 64 (32 frames by the dual-head camera) projection images were acquired using the stop-and-shoot method. An electrocardiogram R-wave detector provided a gate to acquire eighteen frames per cardiac cycle.
Three sets of SPECT slices representing summed, end-diastolic, and end-systolic images were formed for computer display. The summed stress scores (the rest study) and summed rest scores (the rest with nitrate study) of all segments were determined. The summed difference score was calculated as the difference between the summed stress scores and the summed rest scores.
The summed image set was normalized conventionally for comparison of rest and rest with nitrate images. The gated images were normalized to the region of highest activity on the end-systolic image set.
Data were collected, revised, coded, and entered to IBM SPSS software package (version 20.0; IBM Corp., Armonk, New York, USA). The qualitative data were presented as number and percentages, whereas quantitative data were presented as mean, SD, and ranges when their distribution was found to be parametric. The comparison between two paired groups with quantitative data and parametric distribution was done by using paired t-test.
| Results|| |
The studied group included 100 consecutive patients. The mean age was 56.69 ± 9.29 years. A total of 92 patients were male, representing 91% of our patients. Patients presented with other comorbidities, as 53 (53%) cases were hypertensive, 51 (51%) cases were diabetic, and 60 (60%) cases were dyslipidemic [Table 1].
There was significant decrease in the total perfusion defect in rest with nitrate study in comparison with the rest study (P = 0.006) [Table 2].
|Table 2: Comparison between rest and rest with nitrate regarding perfusion defect|
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Significant improvement of defect extension in rest with nitrate study in various walls was detected, with more detectable improvement in lateral and septal walls (P < 0.001) [Table 3].
|Table 3: Comparison between rest and rest with nitrate regarding defect extent in various walls|
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There was significant improvement in mean ejection fraction between rest and rest with nitrate study (P = 0.002) [Table 4].
|Table 4: Comparison between rest and rest with nitrate regarding function|
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Significant improvement in defect extent in septal wall of diabetic patients was recorded in rest with nitrate study (mean = 43.9) in comparison with rest study (mean = 49.45) [Figure 1].
|Figure 1: Comparison between rest and rest with nitrate regarding defect extent in septal wall in diabetic patients.|
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| Discussion|| |
In this study, we aimed to prove the effective role of adding sublingual nitrates to SPECT in patients with ischemic LV dysfunction. We observe that there was significant number of viable segments using nitrate in MIBI scan as compared with the resting study on both visual and semiquantitative analyses.
The role of Tc-99m MIBI imaging to identify severely ischemic but viable myocardium in patients with CAD has been established .
MIBI is a liposoluble cationic compound that is taken up by the myocardium through the transmembrane potential gradient and is fixed to the mitochondria. Its uptake is proportional to the coronary flow and therefore is a good perfusion tracer .
Accurate detection of viable myocardium predicts reversibility of regional wall motion after coronary revascularization ,.
Some studies have shown that Tc-99m MIBI may underestimate the presence of viable tissue when used alone ,, so in this study, we tried to improve viability detection of hypoperfused segments by adding nitrates to the test.
Similar results of improved Tc-99m MIBI uptake have been found using sublingual or intravenous nitrates in literature. Maurea et al.  have shown improvement in 27% of the perfusion defects after using nitroglycerine in 99m Tc MIBI imaging.
Galli et al.  demonstrated a significant decrease in mean perfusion defect in 54% of the patients after receiving sublingual nitroglycerine.
So adding nitrates to Tc-99m MIBI perfusion scan is important for detection of viable myocardium as proved by our study and previous studies.
| Conclusion|| |
In patients with chronic ischemic heart disease, use of nitrate-augmented Tc-99m MIBI protocol in cardiac SPECT imaging results in improved detection of viable but hypoperfused segments. It is a good indicator for differentiating viable tissues from the scar.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]