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

描述（由申请人提供）：房颤（AF）影响超过220万美国人，预计到2050年将达到1200万人。中风是AF最严重的并发症，占AF患者所有中风的15 - 20%，由左心房（LA）血栓形成和随后的栓塞引起。房颤卒中预防的重点是在选定的高风险患者中使用华法林抑制血栓形成。虽然华法林可以有效降低中风风险，但它也与每年3.4%的大出血风险相关。临床医生利用风险评分来识别受益于warfarn的患者。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平庸的。 这意味着许多未接受华法林治疗的患者将发生中风，而许多接受华法林治疗的患者则不必要地暴露于大出血的风险中。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> 75岁、高血压）组成，这些因素在人群基础上与卒中相关，但在生理学原则上与个体中的血栓形成无关。导致血栓形成的关键因素之一是左心房内的血瘀。使用超声的研究已经将左心房低血流标志物与中风风险联系起来。然而，这种技术不适合广泛的筛选，并且不能映射3D流。结合时间分辨3D解剖结构和3D血流速度信息的功能性4D心血管磁共振成像（4DcMRI）的新技术可以评估3D血流特征，并且特别适合于评价LA和右心房（RA）内的血液淤滞。我们将应用这项技术来评估左心房和右心房附件的淤滞或流动模式的差异是否可以解释左心房附件血栓形成的风险比右心房附件血栓形成的风险高10倍，以及左心房和右心房附件血栓形成的风险比右心房附件血栓形成的风险高10倍。AF患者全身栓塞的风险比肺栓塞高一倍。我们假设，在有心房内栓塞风险的AF患者中，左心房附件的淤滞和血流模式改变的区域比右心房附件更常见。血栓形成 我们将a）优化AF患者血流表征的4DcMRI设置; B）开发半自动分析工具以计算停滞指数并评估3D血流模式;以及c）比较两组的血流模式：1）持续性AF患者和记录的既往心房血栓或血栓栓塞性卒中患者; 2）持续性AF>4年未接受华法林治疗且无左心房血栓或血栓栓塞事件史的患者。假设第1组与第2组的左心房与右心房附件的淤滞和流动模式改变指数存在显著差异。该项目将有助于确定4DcMRI是否可用于提供有关血栓形成风险的生理信息。长期目标是评估淤滞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AF患者需要华法林治疗，从而减少卒中和出血并发症。

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.