Quantitative Assessment of RV Strain Using cMRI Following Catheter Intervention on PE (RVEF)

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.