Aims Many factors cause left ventricular outflow tract obstruction (LVOTO) in hypertrophic cardiomyopathy (HCM). Previous studies reported that left ventricular basal muscle bundle (BMB) may be associated with LVOTO. We aimed to evaluate the role of BMB in LVOTO by echocardiography. Methods and results Two hundred fifty-six patients diagnosed with HCM were recruited. The morphologic characteristics of left ventricular outflow tract (LVOT) were analysed. BMB was detected in 178 (69.5%) patients by echocardiography. Patients were separated by a resting or provocative LVOT gradient ≥30 mmHg or not. Compared to patients without LVOTO, patients with LVOTO had a significantly thicker basal septum, elongated anterior mitral leaflet (AML), shorter distance between the AML-free margin and the septum or BMB (M-sept/bundle), larger angle between the plane of the mitral valvular orifice and the ascending aorta (MV-AO angle), and higher prevalence of BMB (P < 0.05). According to multivariate analysis, the independent predictors of LVOTO were the presence of BMB, a large basal septum thickness, a short M-sept/bundle, a large MV-AO angle, and a large AML [odds ratio (95% confidence interval): 5.207 (1.381–19.633), 1.386(1.141–1.683), 0.615(0.499–0.756), 1.113(1.054–1.176), and 1.343(1.076–1.677), respectively, P < 0.05]. Of the 256 included patients, 139 underwent surgical myectomy. The transthoracic echocardiography, compared with surgical specimen, showed: sensitivity 98.3%, specificity 82.3%, positive predictive value 97.6%, negative predictive value 87.5%, and accuracy 96.4% to detect BMB. Conclusions BMB is common in HCM. BMB is a risk factor for LVOTO.

中文翻译：

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肥厚型心肌病左心室基底肌束：对左心室流出道梗阻机制的认识

目的 许多因素导致肥厚型心肌病 (HCM) 中的左心室流出道梗阻 (LVOTO)。以前的研究报道，左心室基底肌束 (BMB) 可能与 LVOTO 相关。我们旨在通过超声心动图评估 BMB 在 LVOTO 中的作用。方法和结果 招募了 256 名诊断为 HCM 的患者。分析左心室流出道（LVOT）的形态学特征。通过超声心动图在 178 名 (69.5%) 患者中检测到 BMB。患者通过静息或激发 LVOT 梯度≥30 mmHg 或不分开。与没有 LVOTO 的患者相比，LVOTO 患者的基底隔膜明显增厚，二尖瓣前叶 (AML) 拉长，无 AML 边缘与隔膜或 BMB 之间的距离更短（M-sept/束），二尖瓣口平面与升主动脉的夹角（MV-AO 角）越大，BMB 患病率越高（P < 0.05）。根据多变量分析，LVOTO 的独立预测因子是 BMB 的存在、大的基底间隔厚度、短的 M 间隔/束、大的 MV-AO 角和大的 AML [优势比（95% 置信区间） : 分别为 5.207 (1.381–19.633)、1.386(1.141–1.683)、0.615(0.499–0.756)、1.113(1.054–1.176) 和 1.343(1.076–1.677)，P < 0.05]。在纳入的 256 名患者中，139 名接受了肌切除术。经胸超声心动图与手术标本相比，检测BMB的敏感性为98.3%，特异性为82.3%，阳性预测值为97.6%，阴性预测值为87.5%，准确率为96.4%。结论 BMB 在 HCM 中很常见。BMB 是 LVOTO 的危险因素。