Quantitative Assessment of RV Strain Using cMRI Following Catheter Intervention on PE
Quantitative Assessment of RV Strain Using cMRI Following Catheter Intervention on PE
Acute pulmonary embolism (PE) is a condition in which the vessels carrying blood to the lungs
 become suddenly blocked, usually by a blood clot. There are a number of adverse consequences
 that result, with one of the most significant being strain on the right side of the heart
 (which must push blood through the blocked arteries to the lungs). Although this strain on
 the right heart is very important, current methods for measuring it are flawed. The standard
 practice is to obtain an echocardiogram (ultrasound of the heart), from which indirect
 measurements of the size of the heart are used to make inferences about right heart strain.
 This method can help guide management in some patients, but it in not a sensitive test and
 does not provide detailed information.

 Patients with PE are treated with blood thinning medications. Some patients may be referred
 to the Interventional Radiology (IR) team for endovascular intervention, in which catheters
 are placed into the patient's vessels under radiologic guidance and advanced to the lungs to
 remove the clot entirely.

 Cardiac magnetic resonance imaging (MRI) is a well-established imaging technique that
 produces highly detailed images of the heart's structure and function, with no risks to
 patients of ionizing radiation or intravenous contrast. Cardiac MRI is far superior to
 echocardiogram in evaluation of the right side of the heart, however it has not been widely
 used in the evaluation of patients with PE. We propose that by using a fast MRI protocol, we
 will be able to detect right heart strain with more accuracy than echocardiogram.
 Furthermore, we hypothesize that MRI images obtained before and after IR catheter-directed
 therapy will demonstrate the degree to which strain is relieved with this treatment. Finally,
 we believe that using MRI may help to guide management of patients with PE by detecting early
 or mild heart strain before it progresses.

 In order to test these hypotheses, we plan to image PE patients who have been referred to the
 IR team with MRI. Patients recruited for this study will undergo two short MRI scans - one
 immediately before treatment, and one after completion of IR treatment (which lasts
 approximately 12-24 hours).
Pulmonary embolism occurs when embolic material (usually clot in the venous system) travels
 to the heart and lodges in the pulmonary vasculature. This obstruction, if significant, can
 lead to pulmonary arterial hypertension, which places increased demand on the right ventricle
 (RV), which must pump against the blockage. This can manifest as right ventricular
 dysfunction (RVD), which is characterized by dilatation of the RV, wall motion abnormalities
 and other structural and functional changes. There is a significant body of data
 demonstrating that function of the RV is an important prognostic indicator in patients with
 acute PE. In these studies, RVD allowed identification of patients who, although clinically
 stable on presentation, were at risk for hemodynamic instability and high
 morbidity/mortality. As a result, many authors have suggested that RVD represents an
 important indication for more aggressive therapy in patients with submassive PE.

 Currently, echocardiography is the most commonly used method for evaluating the RV in acute
 PE. However, obtaining quality imaging of the RV using echocardiography is technically
 difficult, and determining a reliable indicator of RV function has proved challenging. A
 number of markers of right ventricular function have been described, including size criteria,
 ejection fraction, wall motion, tricuspid regurgitation, paradoxical septal motion, and
 others. However, there is no general consensus on which methodology or measurements produce
 the most clinically meaningful data. The American Heart Association guidelines for submassive
 pulmonary embolism use the ratio of the right ventricle to left ventricle at end diastole
 (RV:LV ratio), which is defined as greater than 0.9 in patients with RVD. However, there is a
 large degree of heterogeneity in echocardiographic criteria for RVD used in the literature.

 Additionally, the quantitative data provided by echocardiography is suspect, as they show
 only modest correlation with cardiac magnetic resonance imaging (cMRI) or computed tomography
 (CT) in evaluation of the RV. Even when specifically utilizing the American Society of
 Echocardiography guidelines, echocardiography proves to be significantly less accurate than
 cMRI for evaluation of the RV, especially in patients with a dilated ventricle.

 Cardiac magnetic resonance imaging is considered the reference standard for accurate
 evaluation of ventricular structure and function. It has proven its accuracy, reliability,
 and prognostic value in the setting of other pathologies that result in RV dysfunction, such
 as pulmonary hypertension. However, to date, this modality has not been used to provide
 detailed information about the structure and function of the RV in patients with acute PE.

 Recently, new therapies for acute PE have come into use that allow more precise treatment of
 the embolus itself through the use of endovascular catheters. These catheter-directed
 therapies (CDTs) deliver thrombolytic medication or other treatment strategies directly to
 the pulmonary circulation. There is a strong body of evidence supporting the use of these
 therapies, and some devices have been FDA-approved for this indication. Despite this, there
 is a lack of definitive markers for the patients who would benefit most from this therapy.
 Additionally, techniques currently used to attempt to quantify response to therapy (such as
 RV:LV ratio) are not ideal. There remains a need for a quantitative method for evaluating the
 structure and function of the RV in patients with acute PE in order to determine their risk
 for hemodynamic compromise, the need for CDT, and response after therapy is completed.
Inclusion Criteria:

 -  Participants will be patients who present to the emergency department or are
 inpatients in the hospital, who are found to have a diagnosis of acute pulmonary
 embolism (confirmed by computed tomography pulmonary angiography), and who have been
 referred to Interventional Radiology for evaluation for CDT. Patients appropriate for
 recruitment into this study will have large PEs involving lobar branches or more
 central segments of the pulmonary arteries.

 Exclusion Criteria:

 -  Exclusion criteria will be limited to prisoners, pregnant women, patients for whom
 English or Spanish is not a first language, severe claustrophobia, and other routine
 contraindications for MRI. Patients with massive PE (resulting in hemodynamic
 instability) will not be appropriate participants for this study.