4D Magnetic Resonance Imaging for Atrial Flow Assessment in Atrial Fibrillation

描述(由申请者提供)：房颤(AF)影响着超过220万美国人，预计到2050年将有1200万人。卒中是房颤最严重的并发症--15%-20%的卒中发生在房颤患者中--是左心房血栓形成和随后的栓塞术的结果。房颤的卒中预防侧重于在选定的高危患者中使用华法林来抑制血栓形成。虽然华法林在降低中风风险方面是有效的，但它也与每年3.4%的大出血风险有关。临床医生使用风险评分来确定哪些患者受益于华法林。然而，美国胸科医师学会的一个专家小组最近报告说，这些分数的预测价值充其量是一般的。这意味着许多没有接受华法林治疗的患者将患上中风，而许多接受华法林治疗的患者则面临着不必要的大出血风险。这些评分表现欠佳的一个原因是，它们由临床风险因素(例如年龄和75岁、高血压)组成，这些因素在人群中与中风有关，但根据生理学原理与个人血栓形成没有特殊关系。血栓形成的关键因素之一是LA血瘀证。使用超声波的研究已经将洛杉矶低血流的标志与中风的风险联系起来。然而，这种技术不适合广泛的筛查，也无法绘制3D流动图。功能4D心血管磁共振成像(4DcMRI)结合了时间分辨3D解剖和3D血流速度信息，可以评估3D血流特征，特别适合于评估LA和右心房(RA)内的血瘀症。我们将应用这项技术来评估LA和RA附件中淤血或血流模式的差异是否解释了在房颤中LA和RA附件血栓形成的风险是LA和RA的大约10倍，全身和肺血栓形成的风险是AF的10倍。我们假设房颤患者的左房与右房附件内有血栓形成风险的患者的左房与右房附件中更常见的是血流模式改变和停滞的区域。我们将a)针对房颤患者的血流特征优化4DcMRI设置；b)开发半自动分析工具来计算血栓指数和评估3D血流模式；以及c)比较两组患者的血流模式：1)有心房血栓或血栓栓塞史记录的持续性房颤患者；2)持续房颤患者&gt；4年未接受华法林治疗且没有LA血栓或血栓栓塞史的患者。假设在第1组和第2组的LA和RA附件中，停滞和血流模式改变的指数将显著不同。该项目将有助于确定是否可以使用4DcMRI来提供有关血栓形成风险的生理信息。长期目标是评估对血瘀证指数的个体化评估是否可以提供额外的有价值的信息，以建议哪些房颤患者需要华法林治疗，从而减少中风和出血并发症。

DESCRIPTION (provided by applicant): Atrial fibrillation (AF) affects over 2.2 million Americans, with projections of 12 million people by 2050. Stroke is the most serious complication of AF -15-20% of all strokes occurring in patients with AF - and results from thrombus formation in the left atrium (LA) and subsequent embolization. Stroke prevention in AF focuses on inhibiting thrombus formation with the use of warfarin in selected high risk patients. Although warfarin is effective at reducing stroke risk, it is also associated with a 3.4% annual risk of major bleeding. Clinicians utilize risk scores to identify patients who benefit from warfarn. However, an expert panel of the American College of Chest Physicians recently reported that the predictive value of these scores is mediocre, at best. This means that many patients who are not receiving warfarin will suffer a stroke while many patients who are treated with warfarin are being unnecessarily exposed to the risk of major bleeding. One reason for the subpar performance of these scores is that they are comprised of clinical risk factors (e.g. age > 75 years, high blood pressure) that are associated with stroke on a population basis but are not specifically related to thrombus formation in an individual based on physiologic principles. One of the key factors responsible for thrombus formation is blood stasis in the LA. Studies using ultrasound have linked markers of low flow in the LA to risk of stroke. However, this technique is not suitable for widespread screening and is unable to map 3D flow. The novel technique of functional 4D cardiovascular magnetic resonance imaging (4DcMRI) incorporating time- resolved 3D anatomy and 3D blood velocity information can assess 3D flow characteristics and is uniquely suited to evaluate blood stasis within the LA and right atrium (RA). We will apply thi technique to evaluate whether differences in stasis or flow patterns in the LA and RA appendages explain the approximately 10-fold greater risk of LA versus RA appendage thrombus formation and the 10-fold greater risk of systemic versus pulmonary embolism in AF. We hypothesize that stasis and regions with altered flow patterns are more common in the LA versus RA appendage in patients with AF at risk for intraatrial thrombus formation. We will a) optimize the 4DcMRI settings for flow characterization in AF patients; b) develop semi-automated analysis tools to calculate indices of stasis and assess 3D flow patterns; and c) compare flow patterns in two groups: 1) patients with persistent AF and documented prior atrial thrombus or thromboembolic stroke; 2) patients with persistent AF for >4 years not treated with warfarin and without history of LA thrombus or thromboembolic event. The hypothesis is that indices of stasis and flow pattern alterations will be significantly different in the LA versus RA appendage in Group 1 versus 2. This project will help determine whether 4DcMRI can be used to provide physiologic information regarding the risk for thrombus formation. The long-term goal is to evaluate whether individualized evaluation of indices of stasis can provide additional valuable information to advise which AF patients require warfarin therapy, thereby reducing both strokes and bleeding complications.