元山 貞子

Sudden cardiac death and acute myocardial infarction often occur as the first manifestation of coronary artery disease. Otherwise asymptomatic individuals with subclinical atherosclerosis almost always have a classic risk-factor profile and it is essential that they are identified before the occurrence of an acute coronary event. The ability to recognize such individuals requires the development of strategies that can localize unstable atherosclerotic lesions. Plaques that are vulnerable to rupture demonstrate distinct histological characteristics, including large plaque and necrotic core volumes, extensive remodeling of the vessel at the lesion site, and attenuated fibrous caps. Precise metrics of typical vulnerable atherosclerotic plaque dimensions will need to be defined to facilitate their identification by noninvasive imaging modalities.

The optimal cardiac phases for coronary CT angiography (CTA) are end-systole and mid-diastole, in which cardiac movement is slow. In conventional methods, these cardiac phases are determined by visual selection. We have compared the images in the optimal cardiac phases that were selected by the conventional method and cardiac-phase search software (Phase Navi), and examined the clinical usefulness of Phase Navi in patients with atrial fibrillation. The subjects were 38 patients (regular rhythm: 20, atrial fibrillation: 18). The continuity scores of patients with regular rhythm (Phase Navi, conventional methods) were 2.4±0.3–2.5±0.3 in end-systole and 2.4±0.5–2.4±0.4 in mid-diastole. The scores of patients with atrial fibrillation (Phase Navi, conventional methods) were 2.3±0.4–2.3±0.4 in end-systole, and 2.2±0.5–2.1±0.6 in mid-diastole. Because the continuity scores of the optimal images from Phase Navi were similar to those from the conventional method, Phase Navi had clinical usefulness in patients with atrial fibrillation.

Background It has been proposed that 0.5-mm-slice multislice computed tomography (MSCT) is a noninvasive tool for the detection of atherosclerotic plaque, but the validity of such an assessinent has not been demonstrated by an invasive investigation. The present study was performed to compare the 0.5-mm-slice NISCT density of plaques with intravascular ultrasound (IVUS) findings. Methods and Results Atherosclerotic plaques were characterized in 37 consecutive patients undergoing percutaneous interventions. Based on the IVUS echogenecity, the plaques were classified as soft (n= 18), fibrous (n= 40) or calcified (n=40). In these 98 plaques, 0.5-mm-slice MSCT plaque density was calculated in 443 regions-of-interest, including 331 lesional foci and 112 luminal cross-sections, and represented as Hounsfield units (HU). MSCT density of the 3 types of plaque was 11 +/- 12 HU, 78 +/- 21 HU, and 516 +/- 198 HU respectively. Computed tomography density of the (contrast-filled) lumen was 258 +/- 43HU. There were statistically highly significant differences in the densitometric characteristics among the 4 groups (soft, fibrous, calcified plaque and lumen) by nonparametric Kruskal-Wallis test (p < 0.0001). Conclusions The IVUS-based coronary plaque configuration can be accurately identified by 0.5-mm slice MSCT. Noninvasive assessment of plaque characterization will ensure emphasis on the vessel wall beyond the vascular lumen.

反応性充血の評価には,超音波法により上腕動脈の拡張反応を利用したり,前腕のプレチスモグラフィーを用いて検討されることが多いが,これらの方法は再現性が低いことが問題点として指摘されている.そこで,簡便かつ定量的であると考えられる駆血負荷下肢タリウムシンチグラフィを考案し,核医学的反応性充血指標(radioisotopic reactive hyperemiai ndex=RIRHI)を算出した.すなわち,一側の大腿を5分間駆血し,タリウム静注後に駆血を解除し,駆血側と対側下肢との平均カウントの比をRIRHIとした.基礎的検討としてRIRHIと超音波による反応性充血指標(ultrasonic reactive hyperemia index=USRHI)を10症例で比較したところ,RIRHIは駆血解除10秒後のUSRHIと有意(p=0.031)に相関(r=0.678)した.また,RIRHIの検者間での再現性を最近の連続25例で検討したところ,有意(p<0.0001)な高い再現性(r=0.997)を示した.そこで,現在治療中の種々の循環器疾患107例(男78名,女29名,平均年齢64.1±13.0歳)について,RIRHIと冠動脈危険因子との関連を検討した.その結果,単回帰解析ではRIRHIは年齢(r=-0.286,p=0.003),性(r=0.262,p=0.006)のみが有意な相関を示し,ステップワイズ多変量解析でも年齢,性のみが選ばれた.従来から血管内皮機能と関連すると考えられている指標が選ばれたことから,駆血負荷下肢タリウムシンチグラフィから得られたRIRHIは反応性充血を臨床的に評価できる有用な指標と考えられた.

To study whether thrombolytic therapy affects Gd-DTPA-enhanced pattern and whether its pattern indicates myocardial viability, Gd-DTPA-enhanced magnetic resonance imaging (MRI) was performed in 43 patients with reperfused acute myocardial infarction 14.8 ± 5.0 days after onset with breathhold scanning on a 1.5T whole body system. The hypoenhanced area at 90 sec after contrast injection was defined as a perfusion defect (PD). Patients were divided into PD(+) and PD(-) groups. The PD was detected in 77.8% of patients treated with direct percutaneous transluminal coronary angioplasty (PTCA) and in 28.6% of patients treated by thrombolytic therapy with or without PTCA in the thrombolysis in myocardial infarction grade 3 group (p &gt 0.05). The myocardial wall was divided into seven segments based on the American Heart Association committee report. Wall motion of each segment was classified by one of six patterns (wall motion score [WMS]: dyskinesis, -1 akinesis, 0 severe hypokinesis, 1 hypokinesis, 2 slight hypokinesis, 3 normal, 4). By echocardiography, the average WMS and ejection fraction were similar between the PD(+) group and the PD(-) group on admission. Those parameters were significantly worse in the PD(+) group than in PD(-) group 1 month after onset. The change in WMS was significantly lower in the PD(+) group than in the PD(-) group. The number of patients and segments with more than two grades of improvement of WMS in the PD(+) group was significantly lower than that in the PD(-) group. Angiographically, left ventricular ejection fraction and WMS of the PD(+) group were significantly lower than those of the PD(-) group 3 months later. PDs were detected significantly less frequently in patients treated with thrombolytic therapy, suggesting that microvascular embolization related to formation of the no-reflow phenomenon.

Abnormal interventricular septal wall motion has been observed in various heart diseases. To assess the regional contractility of interventricular septum precisely, DANTE tagging cine MRI of septal slices parallel to the vertical long axis of left ventricle were acquired in 6normal volunteers and in 12 patients with a variety of heart diseases. DANTE tags were generated at end diastole with a 8 mm grid with about 60 intersection points on septal slice. Quadrangle area as a basic unit was calculated at end systole (S_ES) and end diastole (S_ES). Percent area contraction (PAC) was derived from the following formula: PAC= [(S_ES-S_ES)/S_ED]×100%. In addition, a quantitative map of the PAC was made to estimate regional contractility easily by visual inspection. The PAC was 29.4±1.3% in normal volunteers and the map of the PAC showed a homogeneous pattern. In patient with anteroseptal myocardial infarction reduced PAC units were localized at anterior site of interventricular septum, and in patients with inferior myocardial infarction, decreased PAC units were observed in inferoposterior site of interventricular septum. In a patient with dilated cardiomyopathy, the map demonstrated a diffused focal distribution of decreased PAC units. In conclusion, the PAC derived from DANTE-tagging cine MRI is a very useful index to evaluate regional contractility of interventricular septum, and the map of PAC can reflect regional abnormal contractility in accordance with clinical settings.