Cardiac MRI for Evaluation of Right Heart Function before and after Catheter-directed Therapy in Submassive Pulmonary Embolism: A Prospective Study of Feasibility and Potential Utility

Abstract

Cardiac MRI is clinically feasible in the setting of submassive pulmonary embolism and is able to demonstrate measurable differences of right heart function before and after catheter-directed therapy.

Keywords: Interventional-Vascular, Thrombolysis, MRI, Echocardiography, Cardiac, Pumonary Arteries, Right Ventricle, Embolism/Thrombosis, Experimental Investigations

Summary

Cardiac MRI is clinically feasible in the setting of submassive pulmonary embolism and is able to demonstrate measurable differences of right heart function before and after catheter-directed therapy.

Introduction

Cardiac MRI (CMR) is the standard of reference for quantifying right ventricular function and pulmonary flow dynamics but has not been used to study acute pulmonary embolism (PE) (1). The purpose of this study was to assess the feasibility and potential utility of CMR in patients with acute submassive PE treated with catheter-directed therapy (CDT).

Materials and Methods

This was a prospective, institutional review board–approved feasibility study. Written informed consent was obtained from all participants. Data were handled in a Health Insurance Portability and Accountability Act–compliant manner. Two coauthors (G.W. and C.H.) have received consulting fees and research funding from Penumbra. Coauthors (M.L., A.K., H.M.) had control of inclusion of any data and information that might present a conflict of interest for these authors. Between October 2017 and June 2019, five patients with acute submassive PE were enrolled and underwent CMR. Four patients subsequently underwent CDT and repeat CMR. CMR was performed with a 1.5-T scanner (Siemens Aera; Siemens Healthineers) using previously described acquisition parameters (2). Right ventricular (RV) ejection fraction (RVEF) and volume were determined after endocardial contours were manually drawn on short-axis cine steady-state free precession images. Quantification of flow through the main pulmonary artery (MPA) was performed after assigning a region of interest within the proximal MPA on phase-contrast images. CDT was performed using the Indigo CAT8 system (Penumbra). Seven to 15 mg of recombinant tissue plasminogen activator (Activase; Genentech) was injected into each pulmonary artery, and aspiration was performed in all lobar branches. Pre-CDT and post-CDT data were compared using a two-tailed paired t test. An RVEF less than 45%, tricuspid annular plane systolic excursion (TAPSE) of less than 15 mm, and indexed RV volume greater than 88 mL/m² in male patients or greater than 76 mL/m² in female patients were considered abnormal (3–5).

Results

Mean patient age was 49 years ± 18 (standard deviation). Mean heart rate and mean arterial pressure at presentation were 103 beats per minute ± 10 and 94 mm Hg ± 6. All patients had elevated troponin levels. Mean PE severity index was 83 ± 27. Mean RV-to–left ventricle ratio at preprocedure CT was 1.50 ± 0.2. Preprocedure CMR was performed 23 hours ± 2 after PE diagnosis. Mean CMR scan time was 32 minutes ± 14. No adverse events occurred. Postprocedural CMR was performed 60 hours ± 27 after CDT. Mean RVEF before CDT was 30% ± 18 versus 41% ± 22 after CDT (P = .016). Mean indexed RV end-diastolic volume before CDT was 99 mL/m² ± 28 versus 99 mL/m² ± 3 after CDT (P = .41). TAPSE was in agreement with the CMR-derived RVEF in three of nine cases. Qualitative assessment of RV size at transthoracic echocardiography (TTE) was in agreement with CMR in eight of nine cases (Table). Mean MPA systolic acceleration time before CDT was 89 msec ± 22 versus 139 msec ± 28 after CDT (P < .05). Mean MPA flow increased from 4250 mL/min ± 628 before CDT to 5223 mL/min ± 496 after CDT (P < .05) (Table and Figure).

Cardiac MRI Measures of Right Ventricular Size and Function and Pulmonary Arterial Flow before and after Catheter-directed Therapy

Main pulmonary artery flow data from patients 1, 2, 4, and 5 derived from velocity-encoded cardiac MRI sequences before catheter-directed therapy (CDT; blue lines) and after CDT (orange lines). Net flow (left column) and mean flow (right column) are plotted across the R-R interval. Note the late-systolic “notch” in the pre-CDT waveform in patients 1, 2, and 5, indicative of pulmonary vascular obstruction, which is not present on the post-CDT waveform.

Discussion

The SEATLEII and ULTIMA trials presented efficacy data for CDT in submassive PE using limited measures of RV dysfunction (6,7). RVEF is the reference measure of right heart function and is reliably quantified at CMR (1). TTE, while easy to obtain, does not reliably quantify RVEF and has only modest correlation with other modalities (2,8). This is highlighted in the current study, where RVEF that was based on TAPSE agreed with CMR in only three of nine cases. Additionally, in the current study, TTE was unable to detect improvement in RVEF following CDT, while CMR demonstrated a mean relative improvement in RVEF of greater than 30%. The main limitation of this study was the small number of patients, which precludes definitive conclusions on the value of CMR in acute PE. Future studies must expand on this data set to prove the clinical relevance of this modality. In conclusion, CMR use in submassive PE is feasible, and direct measures of RV function and pulmonary arterial flow may be of utility in assessing response to CDT.