Explaining heparin’s varying effects
The study did not specifically sort out why moderately ill patients fared better on heparin than their critically ill counterparts, but Dr. Lawler speculated on possible reasons. “One might be that the extent of illness severity is too extreme in the ICU-level population for heparin to have a beneficial extent,” he said.
He acknowledged that higher rates of macrovascular thrombosis, such as venous thromboembolism, in ICU patients would suggest that heparin would have a greater beneficial effect, but, he added, “it may also suggest how advanced that process is, and perhaps heparin is not adequate to reverse the course at that point given relatively extensive thrombosis and associate organ failure.”
As clinicians have gained experience dealing with COVID-19, they’ve learned that infected patients carry a high burden of macro- and microthrombosis, Dr. Berger said, which may explain why critically ill patients didn’t respond as well to therapeutic levels of heparin. “I think the cat is out of the bag; patients who are severe are too ill to benefit,” he said. “I would think there’s too much microthrombosis that is already in their bodies.”
However, this doesn’t completely rule out therapeutic levels of heparin in critically ill COVID-19 patients. There are some scenarios where it’s needed, said Dr. Berger, associate professor of medicine and surgery and director of the Center for the Prevention of Cardiovascular Disease at New York University Langone Health. “Anyone who has a known clot already, like a known macrothrombosis in their leg or lung, needs to be on full-dose heparin,” he said.
That rationale can help reconcile the different outcomes in the critically and non–critically ill COVID-19 patients, wrote, of Maastricht University in the Netherlands, wrote in an accompanying . But differences in the study populations may also explain the divergent outcomes, Dr. ten Cate noted.
The studies suggest that critically ill patients may need hon-heparin antithrombotic approaches “or even profibrinolytic strategies,” Dr. Cate wrote, and that the safety and effectiveness of thromboprophylaxis “remains an important question.” Nonetheless, he added, treating physicians must deal with the bleeding risk when using heparin or low-molecular-weight heparin in moderately ill COVID-19 patients.
, of Brigham and Women’s Hospital Heart & Vascular Center, Boston, said in an interview that reconciling the two studies was “a bit challenging,” because effective therapies tend to have a greater impact in sicker patients.
“Of course, with antithrombotic therapies, bleeding side effects can sometimes overwhelm benefits in patients who are at high risk of both bleeding and ischemic complications, though that does not seem to be the explanation here,” Dr. Bhatt said. “I do think we need more data to clarify exactly which COVID patients benefit from various antithrombotic regimens, and fortunately, there are other ongoing studies, some of which will report relatively soon.”
He concurred with Dr. Berger that patients who need anticoagulation should receive it “apart from their COVID status,” Dr. Bhatt said. “Sick, hospitalized patients with or without COVID should receive appropriate prophylactic doses of anticoagulation.” However, he added, “Whether we should routinely go beyond that in COVID-positive inpatients, I think we need more data.”
The ATTACC platform received grants from the Canadian Institutes of Health Research and several other research foundations. The ACTIV-4a platform received funding from the National Heart, Lung, and Blood Institute. REMAP-CAP received funding from the European Union and several international research foundations, as well as Amgen and Eisai.
Dr. Lawler had no relationships to disclose. Dr. Berger disclosed receiving grants from the NHLBI, and financial relationships with AstraZeneca, Janssen, and Amgen outside the submitted work. Dr. ten Cate reported relationships with Alveron, Coagulation Profile, Portola/Alexion, Bayer, Pfizer, Stago, Leo Pharma, Daiichi, and Gilead/Galapagos. Dr. Bhatt is chair of the data safety and monitoring board of the FREEDOM COVID anticoagulation clinical trial.