PREDICTIVE ROLE OF CEREBRAL BLOOD FLOW STRESS-TEST WITH ADENOSINTRIPHOSPHATE QUANTIFIED WITH 99m TC-HMPAO SPECT IN PATIENTS WITH CAROTID ATHEROSCLEROSIS
Authors:   Cardiology Research Institute, Tomsk National Medical Research Center, Tomsk, Russia, Ussov W.Yu. ,   National Research Tomsk Polytechnic University, Tomsk, Russia, Yaroshevskii S.P. ,   National Research Tomsk Polytechnic University, Tomsk, Russia,   Loukh Central District Hospital, Karelia, Russia, Bobrikova E.E. ,   E.N. Meshalkin National Medical Research Center, Novosibirsk, Russia, Sinitsyn V.E. ,   M.V. Lomonosov Moscow State University, Moscow, Russia, Lishmanov Yu.B. ,   National Research Tomsk Polytechnic University, Tomsk, Russia
Published: October 2022

Introduction: Previously, a functional test with intravenous administration of adenosine triphosphate (ATP) was proposed to assess the reactivity of cerebral circulation and the functional significance of internal carotid artery stenoses, with evaluation by brain SPECT (neuroSPECT) with 99mTc-HMPAO. The types of the reaction of the cerebral blood flow during it were identified, with different ratios of internal carotid artery stenoses and the degree of ischemic brain damage assessed according to brain MRI data. However, the prognostic value of the results of the ATP test of cerebral blood flow in relation to disorders of cerebral circulation (NMC) remains unknown. Purpose: In a retrospective study, we tried to study the prognostic value of the ATP test of cerebral blood flow in relation to the risk of subsequent disorders of cerebral circulation. Material and methods: The retrospective study included 37 patients with atherosclerotic stenosis of the carotid arteries, who in 2002–2005 underwent functional studies of cerebral blood flow with a sample with intravenous administration of ATP solution. Brain damage was quantified according to MRI data (Magnetom Open, Siemens) in a T2-weighted mode, according to a previously developed technique. Denoting Iliq – the intensity of the T2 signal from the cerebrospinal fluid in the ventricles of the brain, Iinsult – in the area affected by ischemia, and Inorm – in the area of the unaffected brain, the volume of the damaged tissue (VDT) was calculated as the sum taken from all sections i, where the area of brain damage is visible: VDT=Σid·Si∙[(Iinsult ‒ Inorm)/(Iliq ‒ Inorm)]i, where d is the thickness of the slice, and Si is the area of the ischemia area on the slice i. The quota of damaged tissue in the physical volume of the lesion area is then obviously eqal to : QD={Σid·Si∙[(Iinsult ‒ Inorm)/(Iliq ‒ Inorm)]i}/{Σid·Si}. NeuroSPECT with 99mTc-HMPAO (540 MBq) in each patient was carried out at rest and with intravenous administration of ATP solution (100 μg / kg of weight, intravenously slowly for 1 min under ECG control). The asymmetry of the cerebral blood flow was evaluated at rest and in a sample with ATP as the 99mTc-HMPAO accumulation asymmetry index (AI) – the interhemispheric ratio of the average 99mTc-HMPAO absorption score in the middle cerebral artery basin. Results: In accordance with the previously presented classification, patients were assigned to one of three groups – with different types of brain blood flow reaction to a stress test with ATP. In 14 individuals (type 1), a symmetrical distribution of blood flow at rest was noted (AI=0.98±0.01), while the ATP test caused an asymmetry in the uptake of 99mTc-HMPAO (AI=0.91±0.04), due to a decrease on the side of the stenosis-dependent hemisphere (unilateral stenosis of the common and/or internal carotid arteries, exceeding 55 %), without signs of damage to the cerebral cortex. In 11 patients with previous ischemic brain injuries (type 2), proven by MRI, the carotid arteries were patent, including after carotid endarterectomy (5 patients) or after correction of stenosis with a stent (three). Rest asymmetry of blood flow was present (AI=0.92±0.03). The ATP test increased blood supply on the side of injury if, according to T2-weighted MRI in the ischemic area, QD<0.35. Due to this, in general, there was a significant decrease in the absorption asymmetry of 99mTc-HMPAO (AI=0.96±0.03) during the ATP test. In 12 patients (type 3) with predominantly unilateral 50‒90 % carotid artery stenosis and ischemic stroke on the same side (group III), the hemispheric asymmetry of blood supply to the brain, noted already at rest (AI=0.96±0.03), increased (AI=0.93±0.03) with an adenosine test. When analyzing the results of a two-year follow-up, it turned out that frequent transient ishemic attacs, minor strokes and strokes developed only in patients in whom the adenosine test induced or increased the interhemispheric asymmetry of 99mTc-HMPAO accumulation by more than 5 % – four with type 1 reactivity, and three with type 3 reactivity Conclusions: Thus, perfusion neuroSPECT with 99mTc-HMPAO and ATP stress-test can be employed to identify patients with a reduced reserve of cerebral perfusion, who have an increased risk of ischemic stroke. Quantitative analysis of T2-weighted MRI gives an estimate of the proportion of viable brain tissue in the focus of the past ischemia, in which reactivity is preserved.