Concordance between rest MIBG and exercise tetrofosmin defects: possible use of rest MIBG imaging as a marker of reversible ischaemia

Perfusion imaging combined with pharmacological stress is the study of choi ce in patients with ischaemic heart disease who are incapable of exercising . Some medical conditions, however, can preclude the use of pharmacological stress. In these particular situations, availability of a diagnostic test which allows for the assessment of ischaemic territory at rest would be des irable. With the purpose of providing a marker of reversible ischaemia, we evaluated myocardial iodine-123 metaiodobenzylguanidine (MIBG) uptake in re gions with fixed and reversible defects defined by exercise/rest perfusion study. Fifty-four male patients with ischaemic heart disease and previous m yocardial infarction were studied by means of exercise/rest tetrofosmin and MIBG single-photon emission tomography (SPET). Regional tracer uptake was quantified and expressed as a percentage of maximum peak activity. Areas wi th denervated but perfused myocardium and areas with ischaemic myocardium w ere calculated. Regions with <75% of peak activity in the exercise perfusio n study were divided into two groups according to whether the increase in p eak activity in the respective rest study was >10% (reversible regional def ect) or <10% (fixed regional defect). These percentages were compared with the percentages of the innervation study. The area of the innervation defec t was significantly larger when the perfusion defect was reversible than wh en it was fixed. In regions with reversible perfusion defects, the size of the area of denervated but perfused myocardium was similar to the size of t he area of ischaemic myocardium. In regions with reversible defects, the pe rcentage of myocardial MIBG uptake was not significantly different from the percentage of tetrofosmin uptake at exercise, while it was significantly l ower than the percentage of tetrofosmin uptake at rest. In regions with fix ed defects, the percentage of myocardial MIBG uptake was significantly lowe r than the percentage of tetrofosmin uptake at exercise and at rest. In pat ients who developed angina during exercise test, the area of denervated but perfused myocardium was significantly larger than in patients without angi na (4.1+/-2.4 vs 3.4+/-2.5, P=0.02). The same trend was observed with re ga rd to the size of the innervation defect (8.6+/-2.4 vs 5.7+/-2.2, P=0.02). It is concluded that when the use of pharmacological stress is not possible in patients incapable of exercising, rest studies with MIBG combined with rest myocardial perfusion studies may be useful as a marker of reversible i schaemia.