Mankad R, McCreery C J, Rogers W J, Weichmann R J, Savage E B, Reichek N, Kramer C M
Department of Medicine, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA.
J Cardiovasc Magn Reson. 2001;3(3):257-66. doi: 10.1081/jcmr-100107474.
Magnetic resonance tagging (MRI) can be used to study intramyocardial trains in human in vivo. We wished to determine whether patients with severe mitral regurgitation demonstrate subtle myocardial contractile dysfunction despite normal left ventricular (LV) ejection fraction (EF) and how, mitral valve repair (MVR) may preserve EF in such patients. MRI was performed on seven patients with severe mitral regurgitation (mean age +/- SD, 65+/-13 years) and normal EF day 1 (range, 0-8 days) before (Pre) and week 8+/-3 after (Post) MVR and on nine normal volunteers (mean age, 32+/-4). LV mass index (LVMI), end-diastolic and end systolic volume, mass/volume ratio, EF, and sphericity index were measured Pre and Post. Two-dimensional strain analysis of MR tagged images was performed and expressed as L1 (greatest systolic lengthening, radial in normal subjects), L2 (greatest systolic shortening, circumferential in normals), and beta (angular deviation of L1 from the radial direction). LVMI fell from 142+/-38 g/m2 Pre to 117+/-44 g/m2 Post (p < or = 0.008) as did LV end-diastolic volume (117+/-26 to 69+/-12 ml, p < or = 0.003), whereas EF remained unchanged (59+/-7% at both time points). LV mass/volume ratio increasedfrom 2.2+/-0.3 g/ml Pre to 3.1+/-0.4 g/ml Post (p < or = 0.02) and sphericity index fell from 0.86+/-0.10 to 0.71+/-0.13 (p = 0.02). In the short axis, L1 was greater in patients with mitral regurgitation than normal subjects (19+/-9% vs 16+/-6%, p < or = 0.003) and tended to increase further after MVR (21+/-8%, p < or = 0.06 vs. Pre). Beta was abnormal in mitral regurgitation (19+/-8 vs. 12+/-8 degrees in control subjects, p < 0.0001) and remained abnormal after MVR (19+/-9 degrees). L2 in the short axis was depressed in mitral regurgitation compared with control subjects (12+/-6% vs. 21+/-6%, p < or = 0.001) and was further depressed after MVR (9+/-7%, p < 0.001 vs. Pre). As detected by MRI, regional myocardial strains are abnormal in severe mitral regurgitation despite normal EF, characterized by increased short-axis systolic lengthening that is abnormally directed and by reduced shortening. After MVR, the further increase in short-axis lengthening may preserve EF despite its abnormal direction and a fall in shortening. The increase in short-axis lengthening may be due in part to the reduction in LV sphericity after MVR.
磁共振标记成像（MRI）可用于在体研究人体心肌束。我们希望确定重度二尖瓣反流患者尽管左心室（LV）射血分数（EF）正常是否仍存在细微的心肌收缩功能障碍，以及二尖瓣修复术（MVR）如何能在这类患者中维持EF。对7例重度二尖瓣反流患者（平均年龄±标准差，65±13岁）且EF正常，在MVR术前（Pre）第1天（范围0 - 8天）和术后第8±3周（Post）进行了MRI检查，并对9名正常志愿者（平均年龄，32±4岁）进行了检查。术前和术后测量了左心室质量指数（LVMI）、舒张末期和收缩末期容积、质量/容积比、EF以及球形指数。对MR标记图像进行二维应变分析，并表示为L1（最大收缩期延长，正常受试者为径向）、L2（最大收缩期缩短，正常受试者为圆周方向）和β（L1与径向方向的角度偏差）。LVMI从术前的142±38 g/m²降至术后的117±44 g/m²（p≤0.008），左心室舒张末期容积也如此（从117±26 ml降至69±12 ml，p≤0.003），而EF保持不变（两个时间点均为59±7%）。左心室质量/容积比从术前的2.2±0.3 g/ml增加到术后的3.1±0.4 g/ml（p≤0.02），球形指数从0.86±0.10降至0.71±0.13（p = 0.02）。在短轴方向，二尖瓣反流患者的L1大于正常受试者（19±9%对16±6%，p≤0.003），并且在MVR后有进一步增加的趋势（21±8%，与术前相比p≤0.06）。二尖瓣反流时β异常（与对照组受试者的12±8°相比为19±8°，p < 0.0001），MVR后仍异常（19±9°）。与对照组受试者相比，二尖瓣反流时短轴方向的L2降低（12±6%对21±6%，p≤0.001），MVR后进一步降低（9±7%，与术前相比p < 0.001）。通过MRI检测发现，尽管EF正常，但重度二尖瓣反流患者的局部心肌应变异常，其特征为短轴收缩期延长增加且方向异常以及缩短减少。MVR后，尽管短轴延长方向异常且缩短减少，但短轴延长的进一步增加可能维持了EF。短轴延长增加可能部分归因于MVR后左心室球形度的降低。
