拡張型心筋症における交感神経イメージングとその有用性

Myocardial Imaging With 123I-metaiodobenzylguanidine in Patients with Dilated Cardiomyopathy and its Usefuiness

　拡張型心筋症（DCM）15例，健常10例を対象に定量的¹²³I-MIBG（MIBG），²⁰¹Tl（Tl）心筋イメージングを行い，MIBGイメージングのDCM評価における有用性を検討した．MIBG,Tl各々の全注入量に対して心筋に集積した割合（％Up take，％UT）を計測した．また，心筋MIBGの3時間での減少率（WOR）の計測，欠損の広がりの定量化を行った．MIBGの心筋への取り込みをUptake Ratio（UR）（Tlの％UTで標準化したMIBGの％UT）で示した．URはDCMで健常例より有意に低く，ことに心不全例で低値であり，URは左室機能と正の相関を，血中ノルエピネフリンレベル（NE）と負の相関を示した．WORも左心機能やNEをよく反映した．MIBGでの欠損はDCM全例で存在したがTlの欠損は60％に存在し，かつMIBGの欠損の広がりはTlの欠損より大であった．DCMのうち，左心予備能不良群では左心予備能良好群に比し，MIBGの欠損が有意に大であった．心筋NEを反映するMIBGイメージングはDCMの病態を把握するうえで有用な方法であると考えられた。

To investigate the usefulness of myocardial imaging with ¹²³I metaiodobenzylguanidine (MIBU) in the assessment of dilated cardiomyopathy (DCM), we stud-ied 15 patients with DCM and 10 normal subjects.

Rest myocardial imaging (tomography and planar whole body imaging) with MIBG and ²⁰¹T1 (T1) was performed on separate days. From the whole body imaging, cardiac accumulation of the radionuclide in relation to the total injected dose was calculated (% Uptake). Uptake Ratio (%Uptake of MIBG divided by %Uptake of T1) was used as an index of myocardial MIBG uptake which was normalized by myocardial mass.

Uptake Ratio was significantly lower in patients with DCM (0.61±0.09) than in normal subjects (0.75±0.05) (p＜0.01). And Uptake Ratio corelated well with frac-tional shortening (%FS) (r=0.85, p＜0.01), left ventricular (LV) ejection fraction (r=0.87, p＜0.01) and plasma norepinephrine (NE) level (r=-0.74, p＜0.01). Decrease in myocardial MIBG within 3 hours (WOR) also reflected LV function and NE level. Although all patients with DCM showed defect in MIBG imaging, defect in T1 imaging was observed in 60% of them. It was also noted that the extent of MIBG defect was greater than that of T1 in every case.

From the results of exercise stress blood pool imaging with ^99mTc, 8 patients with DCM were divided into two groups: good LV functional reserve (n=4) and poor LV functional reserve (n=1). Although Uptake Ratio and WOR were similar in both groups, the extent of MIBG defect was significantly greater in patients with poor LV functional reserve than that in patients with good LV functional reserve.

It is supposed that MIBG myocardial imaging is a useful method to detect pathologic conditions in patients with DCM.