A new wearable monitor of lung impedance, a surrogate for congestion with fluid, was reported to reduce heart failure hospitalizations in a study presented at the annual American College of Cardiology meeting.
The study tested a device developed by an RSMM Company that uses wearable electrodes positioned around the chest to monitor lung impedance, isolated from the transthoracic impedance using an algorithm developed by the company. Given the growing burden of heart failure and high associated morbidity, this device is one of many that seek to use alternative markers for the disease where monitoring could facilitate early intervention and improved outcomes. The posterchild for that is the CardioMEMS device, a small sensor placed in the pulmonary artery that provides continuous pressure monitoring.
The lung impedance device studied here isn’t exactly a novel marker – many of Medtronic’s implantable cardiac devices have OptiVol which monitors transthoracic impedance. What does seem different is the claim here to somehow be able to isolate lung impedance by subtracting out chest wall impedance using left-right chest sensors rather than front-back, and an algorithm derived from preclinical data.
In this study, they randomized three hundred patients to either usual treatment or usual treatment plus lung impedance measurement. Aside from defining a decline of 18% in impedance as a warning sign, treatment decisions were all left to treating clinicians. All participants were scheduled for monthly visits, which helps standardize management intensity between the two arms.
Patients were enrolled over a nearly 10-year period but the study duration was only 12 months for each patient. Over the (HR 0.51, P<0.001) that they attributed to more frequent medication changes in the intervention group (P<0.001).
Having a noninvasive measure of pulmonary congestion is an intriguing possibility, even more so given these results. Looking specifically at the hospitalized patients, they report that declines in the measured impedance began about three weeks in advance which is an impressive head start. It also parallels data from the CardioMEMS studies suggesting that traditional clinical factors like weight gain or edema may be relatively late signs of worsening hemodynamics.
In the cardiology world, this was a pretty small study in terms of both enrollment and centers (2). It’s also critical to note that the lead author is a cofounder of the company that developed the device. For those reasons, we should retain some skepticism about the results reported here. Independent validation studies replicating these findings will be critical next steps before we put too much stock in these findings.
Source: MedPage Today