Jani Vivek, Aslam M Imran, Fenwick Axel J, Ma Weikang, Gong Henry, Milburn Gregory, Nissen Devin, Salazar Ilton Cubero, Hanselman Olivia, Mukherjee Monica, Halushka Marc K, Margulies Kenneth B, Campbell Kenneth, Irving Thomas C, Kass David A, Hsu Steven
bioRxiv. 2023 Mar 12:2023.03.09.531988. doi: 10.1101/2023.03.09.531988.
Right ventricular (RV) contractile dysfunction commonly occurs and worsens outcomes in heart failure patients with reduced ejection fraction and pulmonary hypertension (HFrEF-PH). However, such dysfunction often goes undetected by standard clinical RV indices, raising concerns that they may not reflect aspects of underlying myocyte dysfunction.
To determine components of myocyte contractile depression in HFrEF-PH, identify those reflected by clinical RV indices, and elucidate their underlying biophysical mechanisms.
Resting, calcium- and load-dependent mechanics were measured in permeabilized RV cardiomyocytes isolated from explanted hearts from 23 HFrEF-PH patients undergoing cardiac transplantation and 9 organ-donor controls. Unsupervised machine learning using myocyte mechanical data with the highest variance yielded two HFrEF-PH subgroups that in turn mapped to patients with depressed (RVd) or compensated (RVc) clinical RV function. This correspondence was driven by reduced calcium-activated isometric tension in RVd, while surprisingly, many other major myocyte contractile measures including peak power, maximum unloaded shortening velocity, and myocyte active stiffness were similarly depressed in both groups. Similar results were obtained when subgroups were first defined by clinical indices, and then myocyte mechanical properties in each group compared. To test the role of thick-filament defects, myofibrillar structure was assessed by X-ray diffraction of muscle fibers. This revealed more myosin heads associated with the thick filament backbone in RVd but not RVc, as compared to controls. This corresponded to reduced myosin ATP turnover in RVd myocytes, indicating less myosin in a cross-bridge ready disordered-relaxed (DRX) state. Altering DRX proportion (%DRX) affected peak calcium-activated tension in the patient groups differently, depending on their basal %DRX, highlighting potential roles for precision-guided therapeutics. Lastly, increasing myocyte preload (sarcomere length) increased %DRX 1.5-fold in controls but only 1.2-fold in both HFrEF-PH groups, revealing a novel mechanism for reduced myocyte active stiffness and by extension Frank-Starling reserve in human HF.
While there are multiple RV myocyte contractile deficits In HFrEF-PH, clinical indices primarily detect reduced isometric calcium-stimulated force related to deficits in basal and recruitable %DRX myosin. Our results support use of therapies to increase %DRX and enhance length-dependent recruitment of DRX myosin heads in such patients.
右心室（RV）收缩功能障碍在射血分数降低和肺动脉高压（HFrEF-PH）的心力衰竭患者中普遍存在，并会使预后恶化。然而，这种功能障碍通常无法通过标准临床右心室指标检测到，这引发了人们对这些指标可能无法反映潜在心肌细胞功能障碍方面的担忧。
确定HFrEF-PH中心肌细胞收缩抑制的组成部分，识别临床右心室指标所反映的部分，并阐明其潜在的生物物理机制。
对23例接受心脏移植的HFrEF-PH患者和9例器官捐献者对照的离体心脏中分离出的透化右心室心肌细胞进行静息、钙依赖性和负荷依赖性力学测量。使用方差最高的心肌细胞力学数据进行无监督机器学习，得出两个HFrEF-PH亚组，这两个亚组又分别对应临床右心室功能降低（RVd）或代偿（RVc）的患者。这种对应关系是由RVd组中钙激活等长张力降低驱动的，而令人惊讶的是，两组中许多其他主要的心肌细胞收缩指标，包括峰值功率、最大无负荷缩短速度和心肌细胞主动硬度，同样受到抑制。当首先通过临床指标定义亚组，然后比较每组的心肌细胞力学特性时，也得到了类似的结果。为了测试粗肌丝缺陷的作用，通过肌肉纤维的X射线衍射评估肌原纤维结构。结果显示，与对照组相比，RVd组中与粗肌丝主干相关的肌球蛋白头部更多，而RVc组则不然。这与RVd组心肌细胞中肌球蛋白ATP周转率降低相对应，表明处于横桥就绪无序-松弛（DRX）状态的肌球蛋白较少。改变DRX比例（%DRX）对患者组中峰值钙激活张力的影响不同，这取决于他们的基础%DRX，突出了精准导向治疗的潜在作用。最后，增加心肌细胞前负荷（肌节长度）使对照组中的%DRX增加了1.5倍，但在两个HFrEF-PH组中仅增加了1.2倍，揭示了人类心力衰竭中心肌细胞主动硬度降低进而Frank-Starling储备降低的新机制。
虽然HFrEF-PH中存在多种右心室心肌细胞收缩缺陷，但临床指标主要检测到与基础和可募集的%DRX肌球蛋白缺陷相关的等长钙刺激力降低。我们的结果支持在此类患者中使用增加%DRX并增强DRX肌球蛋白头部长度依赖性募集的治疗方法。
