NT-proBNP May Help Hone AF Screening With Implantable Loop Recorder

Using an implantable loop recorder (ILR) to screen older individuals for atrial fibrillation (AF) may be more beneficial when NT-proBNP levels are high, according to a post hoc analysis of the LOOP study.

Such screening was associated with lower risks of stroke/systemic embolism and stroke/systemic embolism/CV death through several years of follow-up among study participants with higher, but not lower, NT-proBNP levels, researchers report.

“So if we bother screening for A-fib, we should probably think about screening the part of the population that has a higher proBNP and not worry about the population with a lower proBNP,” according to Søren Zöga Diederichsen, MD, PhD (Copenhagen University Hospital – Rigshospitalet, Denmark), who presented the findings at the recent European Heart Rhythm Association (EHRA) 2023 congress in Barcelona, Spain. “That is what this study tells me.”

But the study, published simultaneously online in Circulation, with Lucas Yixi Xing, MD (Copenhagen University Hospital – Rigshospitalet), and Diederichsen as lead authors, should be considered exploratory and hypothesis-generating. Diederichsen noted that the ongoing STROKESTOP II trial is exploring whether NT-proBNP can be used to identify a population of older patients who will benefit from AF screening.

NT-proBNP as a Risk Marker

Though multiple trials, including the LOOP study and STROKESTOP, have tested the impact of screening for AF, there is no definitive proof yet that the strategy can prevent strokes, Diederichsen noted. Researchers have begun searching for ways to identify populations that may derive more benefits from screening.

NT-proBNP, Diederichsen said, was originally identified as a risk marker in heart failure, but in recent years, it’s become increasingly recognized as a marker for AF and stroke risk. The current analysis of the LOOP study, which was not prespecified, explored the impact of NT-proBNP levels on the effects of screening for AF.

The LOOP study included 6,004 individuals 70 or older who had at least one additional risk factor for stroke. They were randomized 1:3 to usual care of continuous screening with an ILR. Anticoagulation was initiated in the ILR group when an AF episode lasting 6 minutes or longer was detected.

This post hoc analysis included the 5,819 study participants (mean age 74.7 years; 47.5% women) who had a baseline NT-proBNP measurement. The median level was 15 pmol/L (125 pg/mL).

An NT-proBNP level above the median was associated with a greater likelihood of AF diagnosis both in the control group (HR 2.79; 95% CI 2.30-3.40) and in the screening group (HR 1.84; 95% CI 1.51-2.25). In addition, high NT-proBNP was associated with greater detection by ILR of episodes lasting 24 hours or more (HR 2.45; 95% CI 1.46-4.10).

So if we bother screening for A-fib, we should probably think about screening the part of the population that has a higher proBNP and not worry about the population with a lower proBNP. Søren Zöga Diederichsen

During a median follow-up of 5.4 years, 5.3% of participants had a stroke or systemic embolism and 8.1% had one of those events or died from a cardiovascular cause. An NT-proBNP level above the median was associated with a nonsignificantly greater risk of stroke/systemic embolism (HR 1.21; 95% CI 0.96-1.54) and a significantly greater risk of stroke/systemic embolism/CV death (HR 1.60; 95% CI 1.32-1.95).

NT-proBNP level significantly influenced the relationship between AF screening and clinical outcomes. Compared with usual care, screening was associated with a lower risk of stroke/systemic embolism when NT-proBNP levels were high (HR 0.60; 95% CI 0.40-0.90), but not when they were below the median (HR 1.11; 95% CI 0.76-1.62). Findings were similar for the outcome of stroke/systemic embolism/CV death.

An analysis looking at NT-proBNP level as a continuous measured provided similar results.

Not Yet Ready to Change Practice

Though the findings suggest that measuring NT-proBNP can identify a group of individuals more likely to benefit from AF screening, Diederichsen said the approach is not yet ready for widespread clinical use.

“We are not saying that now everybody in America should have a proBNP measured if they are a certain age and then that proBNP should be used as an argument for implanting a loop recorder to screen for A-fib,” he said. “But at least this is actually very, very interesting, and the results are pretty convincing, I think, that this is something that could be important.”

He added, however, that “if you have a patient and you are thinking about atrial fibrillation and stroke risk, maybe proBNP could be used to guide you a little bit in the direction towards if you want to screen this patient a little bit more for atrial fibrillation or not.” And on the flip side, he said, if a patient has a low NT-proBNP level, it might push the decision away from AF screening.

The study comes at a time when screening for AF, either formally in a clinic setting or with consumer wearable devices, is becoming increasingly common, and it’s important to determine which types of AF are most clinically relevant, Diederichsen noted, indicating that NT-proBNP may provide a means to do that. “We have to figure out what kind of A-fib is actually meaningful to diagnose and to treat, and tools such as proBNP, but also other risk factors, could probably help us refine this a little bit more.”

And not to be lost in this discussion of AF-related stroke is the role of other key risk factors for stroke, like hypertension, Diederichsen said. “I think it’s important to remember to treat the risk factors that we are used to managing already and that we know what to do about.”