Evaluation of Left Ventricle Performance in Patients with Ischemic Heart Disease Using Single Photon Emission Computed Tomography (SPECT) in Comparison with Echocardiography

Background: Ischemic heart disease is a major cause of the diastolic heart failure. Risk of heart failures was increased with microvascular coronary disease, which is characterized by left ventricular stiffness with impaired relaxation and reduced compliance. Aim of this study is to estimate the effect of the severity of myocardium ischemia on the left ventricle ejection fraction and left ventricular volume using SPECT with 99m Tc MIBI and to compare the results with the echocardiography. The study included 117 subjects with ischemic heart disease were examined using SPECT and echocardiography techniques. The following parameters were measured: left ventricular end systolic volume (LVESV) , left ventricular end diastolic volume (LVEDV) , and left ventricular ejection fraction (LVEF). Results show that the change difference in EDV between the two technique was (98.79%) with insignificant (p > 0.05). While the change in the LVEF% between both groups was (105.40%) with significant (p <0.05). On the other hand, the difference in ESV and EDV/ESV ratio for both groups were (95.52%), and (103.61%) respectively with insignificant (p >0.05). It was concluded that SPECT with 99m Tc MIBI had a good relation with the echocardiography technique for evaluation of the left ventricular ejection fraction and the left ventricular volumes. The results showed that LVEF was decreased in patients with severe ischemic disease.


Introduction
Heart failure is a complex clinical syndrome caused by cardiovascular disease, resulting from any functional or structural impairment of ventricular ejection or filling of blood. Diastolic heart failure is characterized by abnormal left diastolic function [1]. Left ventricular diastolic function includes left ventricular function during relaxation and filling. The primary mechanisms of diastolic dysfunction are diastolic stiffness, and reduced relaxation. Many factors lead to impairment in diastolic function including hypertrophy, aging, and ischemia. The degree of left ventricular abnormalities permits to evaluate the myocardial performance [2] Left ventricular ejection fraction (LVEF) was used to measure the left ventricular systolic function and it is helpful in the management of the cardiovascular diseases. LVEF represents the percentage of blood volume ejected in each cardiac cycle . It is calculated from the (enddiastolic volume -end-systolic volumes)/ end-diastolic volume [3]. Recently , multiple diagnostic techniques have been used to measure left ventricular function, perfusion, and volumes including two-dimensional echocardiography, cardiac magnetic resonance imaging (cMRI), and radionuclide ventriculography (RNV) [4]. Single-photon emission computed tomography (SPECT) with 99m Tc MIBI has become one of the most clinical technique used to assess myocardial perfusion. Several studied have shown that this method is accurate and reproducible for measuring LVEF, regional wall motion and thickening [5]. The aim of this study is to assess the accuracy of SPECT for evaluation of left ventricular end-diastolic volume (EDV), end-systolic volume (ESV) and LVEF compared with echocardiography. patients and methods The study consisted of 117 patients (49 females and 68 males), their age range between 25 to 75 year old with mean age of 48.19 ± 10.02, The study was conducted according to the medical ethics rules. All the patients have given their consent. The study was carried out during the period between December 2019 and July 2020 , at Iraqi German Functional Imaging Clinic/Baghdad, and echocardiography unit at Baghdad Teaching Hospital/ Medical City/ Baghdad. All patients with coronary artery bypass graft surgery, acute myocardial infarction, arrhythmias, left bundle branch block, and implanted pacemakers were excluded from this study. In this study only ischemia severity patients were chosen whose clinical data were recorded along with history.
A dose of (370 -700) MBq 99m Tc methoxyisobutyl-isonitrile (MIBI) was given to the patients at least 3 ml of normal saline through the intravenous catheter, and rest SPECT was started (45-75)min following the injection. Myocardial SPECT images were obtained with a 90° configuration double-head gamma camera (Double-Head Gamma Camera, GE Medical Systems Millennium IPS, model ASM001145, SER . No. 1034 ). A total 64 of projections (step-and shoot mode) thirty two per each detector, matrix size (64 ×64) were acquired over a 180 0 anterior arc, divided into eight frames/ cardiac cycle. End systolic and diastolic volume, and left ventricular ejection fraction were assessed using available automated software program; Quantitative Gated SPECT (QGS) (XELERIS6200 SOFTWARE), used to estimate three dimensional image. Echocardiography examination was performed by the use 2-5 MHz probe of (SONOACE X8/ PS 3.1-3.18, 2007, South Korea made supplied by Medicine Company). M-mode recordings with 2 dimensional guided were taken from the standard parasternal, short-axis and apical (four and two chamber views), while end-systole, end-diastole, and LVEF were derived.

Statistical analysis
All the results were presented as mean values ± standard deviation (SD), and the difference as a percentage. Test for significance was carried out using t test, and p value less than 0.05 was statistically significant. All the results were collected and analyzed using Microsoft Excel 2010.

Result
Data of the 117 patients as shown in Table 1. The results showed change differences between two techniques in EDV and ESV of 98.79% and 95.52% respectively with insignificant (p >0.05). The difference in EF% was 105.40% with a highly statistically significant (p < 0.05), while the change difference in EDV/ESV ratio was 103.61% with insignificant (p >0.05), Table 2. The mean ± SD for EDV(ECHO)/EDV(SPECT) and ESV(ECHO)/ESV(SPECT) were 1.01 ± 0.06, and 1.06 ± 0.19, respectively, Table 2.

Discussion
Coronary arterial stenosis has possibility clinical importance when they produce an imbalance between myocardial oxygen supply and demand. Myocardial oxygen demand depends on the amount of blood oxygen that the heart requires. The balance between myocardial oxygen supply and demand is used to assess the ability of myocardial to contract provides a very useful functional measure of importance of coronary artery lesions [6]. Since flow limiting coronary lesions causes localized dysfunction of the regions of myocardium supplied by the vessel disease. Narrowed coronary arteries that carry sufficient oxygenated blood to supply myocardial demand and permit normal regional and global contractile function may be incapable of permitting of sufficient flow to support normal function during the increased oxygen demands imposed by any myocardial stress [7,8]. Therefore, to complete assessment of the physiologic importance of coronary artery lesions requires some type of intervention that will test the functional reserve capacity of coronary arteries [9]. The results showed that the change in the end systolic volume (ESV), and the end diastolic volume (EDV) appeared on the EDV/ESV ratio in two techniques , in addition to which parameter the change is more related, this may be indicate that the ischemia is related with structural changes, such as arterial dilatation, reduced LV diastolic distensibility, and an increase in the elastic stiffness of the myocardium. Results also showed that the reduction in EF% may be related to an increase in LVESV rather than an increase in LVEDV, because systolic dysfunction and may associated with an increase in the myocardial oxygen demand to the myocardium to perform an extra work including increased heart beats and increased blood pressure. The results showed a slight change between echocardiography and SPECT for assessment of LVEF, EDV ,and ESV. This study had good agreement with Choragudi et al. [10], they have calculated LVEF using echocardiography and GSPECT, reported showed that the two methods good correlation. Cwajg et al, showed highly significance between echocardiography technique and 99m sestamibi-gated SPECT [11]. Fatma Berk , et al., showed good correlations between LV volume measurements with gated SPECT and echocardiography [12]. The results also showed that SPECT technique had a good relation with echocardiography for assessment of LV volume and LVEF in patients with ischemic disease. Echocardiography is a safe, low cost, and easy to use method for evaluation of filling pressures and myocardial viability. We believe that both echocardiography and SPECT techniques complement each other. SPECT is used as an alternative for patients suffering from poor echocardiographic visualization. Furthermore, SPECT is able to distinguish between ischemic and non-ischemic dilated cardiomyopathy. The two techniques still show a good relation although some technical limitation in patients suffering perfusion defects. The gated SPECT technique is quick, mostly automated and highly reproducible, whereas echocardiography techniques that are widely used to evaluate LV volumes and LVEF depend on the operator