The effectiveness of rivaroxaban, a direct oral anticoagulant, in resolving acute left ventricular thrombus in patients with ST-segment elevation myocardial infarction (STEMI) was similar to that of warfarin in the RIVAWAR trial.
“We saw complete resolution of thrombus in more than 95% of patients in both groups, with no significant increase in deaths, ischemic stroke, or major bleeding,” said principal study investigator Jehangir Ali Shah, MBBS, from the National Institute of Cardiovascular Diseases in Karachi, Pakistan.
“Our findings support rivaroxaban as a viable alternative to warfarin, offering predictable dosing and eliminating the need for routine monitoring in patients with post-MI left ventricular thrombus,” he explained during his presentation of the RIVAWAR results at the American College of Cardiology (ACC) Scientific Session 2025 in Chicago.
Left ventricular thrombus, a serious complication of MI, occurs in 2%-3% of all patients with STEMI and in around 9% of patients with anterior STEMI, and increases the risk for embolic events, such as ischemic stroke and death.
The recommended first-line therapy for the treatment of left ventricular thrombus is a vitamin K antagonist, such as warfarin, which requires regular monitoring to achieve optimum anticoagulant levels and can interact with various foods and other frequently used drugs.
Direct oral anticoagulants have several advantages over warfarin and are increasingly used to treat left ventricular thrombus, but data comparing outcomes with these drugs and warfarin for this indication are limited. The investigator-initiated RIVAWAR study was designed to assess the comparative effectiveness of direct oral anticoagulants.
The RIVAWAR Trial
The study enrolled 261 patients with MI (90% STEMI) who had developed a left ventricular thrombus. They were randomized to treatment with either rivaroxaban or warfarin for 3 months. Patients also received oral dual antiplatelet therapy for 1 month followed by single antiplatelet therapy for the remaining 2 months.
The primary end point was the resolution of left ventricular thrombosis at 3 months.
At 4 weeks, left ventricular thrombus had resolved in significantly more patients in the rivaroxaban group than in the warfarin group (20.1% vs 8.3%; P = .017).
At 3 months, the clot resolution rate was 95.8% in the rivaroxaban group and 96.6% in the warfarin group, which was a nonsignificant difference.
For safety outcomes, there was a slight increase in the rate of ischemic stroke in the rivaroxaban and warfarin groups (3.5% vs 1.1%), but this was not statistically different. Rates of all-cause mortality were not significantly different in the rivaroxaban and warfarin groups (3.5% vs 3.3%), nor were rates of major bleeding (2.3% vs 1.1%).
The open-label design of the study and the fact that it was conducted at a single center — the National Institute of Cardiovascular Diseases — were limitations of the study. Because of a lack of funding, follow-up ended after 3 months, so longer-term follow-up to assess the recurrence of left ventricular thrombus has not been possible.
This is “a very nice investigator-initiated trial,” said Thomas Lüscher, MD, from the Royal Brompton & Harefield Hospitals in London, England, during a discussion at the ACC session.
In addition, it “is an important study because, although since the introduction of primary PCI, left ventricular thrombus has become less common, these patients are still at increased risk of having an ischemic stroke after they suffered a severe MI,” he said.
The international normalized ratio (INR) takes a while to reach a target level with warfarin, whereas with a direct oral anticoagulant, anticoagulation action will occur right away, he pointed out.
In the warfarin group in the RIVAWAR trial, the target INR was 2.1-2.8 (mean INR, 2.4) and was controlled at the second week, Lüscher reported.
In the study, echocardiography was used to detect thrombus, but MRI has a higher specificity and sensitivity, so would have been better, he added.
The numerical increase in ischemic stroke in the rivaroxaban group may be “a little safety glimpse,” and it would be desirable to have another larger trial, he said.
Rivaroxaban ‘Pop and Go’ Strategy
A larger trial with longer follow-up is needed to look at longer-term recurrent events, said Shah.
The RIVAWAR trial provides evidence to support the idea of using rivaroxaban to treat left ventricular thrombus in patients with MI, said Anna Bortnick MD, PhD, associate professor in the Division of Cardiology at the Montefiore Medical Center and Albert Einstein College of Medicine in New York City.
Treatment with a direct oral anticoagulant is a “pop and go” strategy that eliminates the need to deal with all the monitoring required with warfarin, she said. The results provided more confidence in this easier approach, and helps to answer “a burning question for us, as interventionalists, on how to manage these patients.”
The RIVAWAR trial was an investigator-initiated trial, funded by the National Institute of Cardiovascular Diseases in Karachi. Shah reported no disclosures.