Intrathoracic Impedance Predicts Heart-Failure Events in PARTNERS-HF

September 24, 2008

September 24, 2008 (Toronto, ON) — Changes in intrathoracic impedance related to fluid buildup in the chest, monitored by technology included in an implantable electronic device, predict subsequent heart-failure–related adverse events, a new study has shown. Fluid indices crossing a predefined threshold significantly increased the risk of subsequent decompensation, shortness of breath, peripheral edema, and fatigue, suggesting impedance data can help stratify patients at risk for worsening heart failure, report investigators.

"The technology is going to help, we hope--studies are ongoing--identify patients earlier as they are decompensating so that it gives us time to intervene," lead investigator Dr David Whellan (Thomas Jefferson University Hospital, Philadelphia, PA) told heartwire . "Currently, many patients don't recognize they're getting worse, and they wait for their scheduled appointments. They then end up in the emergency department and are usually admitted to the hospital. We want to be able to identify patients earlier so that we have a window of opportunity to intervene and influence the natural course of the disease."

Presenting the findings of the Multisite Program to Access and Review Trending Information and Evaluate Co-Relation to Symptoms in Patients with Heart Failure (PARTNERS-HF) study here at the Heart Failure Society of America 2008 Scientific Meeting, Whellan said that despite medications, device therapies, and intensive follow-up shown to decrease morbidity and mortality in heart-failure patients, hospitalizations for heart-failure exacerbations remain high. Using intrathoracic-impedance monitoring, which works by measuring electrical pulses across the thoracic cavity to assess fluid in the chest, could identify patients with worsening heart failure.

In this observational 12-month study, 769 heart-failure patients with NYHA class 3 or 4 and left ventricular ejection fractions <35% were treated with cardiac resynchronization devices with defibrillators (CRT-D). The investigators performed two analyses: the first compared the risk of having a heart-failure–related adverse event based on whether or not the fluid index crossed a predefined threshold, in this case 100 {:Omega:}, in a 21-day evaluation period; the second analysis compared the risk of an adverse event based on whether the index crossed the threshold during a rolling a seven-day evaluation window.

Patients with a fluid index that crossed the predefined threshold in the 21-day evaluation period were twice as likely as those who did not cross the impedance threshold to have a subsequent heart-failure event. Similarly, more frequent monitoring of intrathoracic impedance, assessed in the second analysis, showed that patients with a fluid index that crossed 100-{:Omega:} threshold were 3.5 times more likely to have a subsequent heart-failure event.

"As we migrate to the technology, not only in terms of the device, but how to transmit the information, we think it'll be used more as an alert that will allow the patient to self-monitor or something that will allow us to intervene once we see the impedance cross a certain threshold," said Whellan. "We see it more, right now, as a clinic-based or provider-based intervention, but the more we can get patients involved in their care, they can recognize what the alert means and they can do something about it."

Does the Information Help Reduce Hard Clinical HF Events?

Commenting on the results of the study during the late-breaking clinical-trials session, Dr Marc Silver (Christ Hospital and Medical Center, Chicago, IL) said that smaller pilot studies have shown that intrathoracic impedance is a marker of fluid overload and future heart-failure events. The PARTNERS-HF study adds to the literature by increasing the number of patients exposed to the deviceand confirms previous results.

Discussing the study, Silver said the events--heart-failure decompensation, dyspnea/shortness of breath, peripheral edema, and fatigue--are subjective measures, and more information on the impact, cost, and effect on patient quality of life is needed.

"I think this clearly is an early look at the data," said Silver. "There is much analysis that needs to be done. . . . I think one of things that need to be done early on is define the end points because they are somewhat confusing. Signs and symptoms are more subjective and softer than things we're typically used to looking at, such as hospital or emergency-department admissions, IV diuretics, inotropes, or even death."

Speaking with heartwire , Whellan said the onus is on researchers to show clinicians and the community that seeing fluid information from these devices and acting on the impedance information with more intensive monitoring or increasing drug dosages will affect clinical events. "This is really going to be the next big step," said Whellan, "proving that acting on this information will improve outcomes."

Medtronic sponsored the PARTNERS-HF study, and its impedance-monitoring technology, called OptiVol, is available in the company's CRT-D device. Whellan reports receiving consultancy fees and honoraria from Medtronic.

The complete contents of Heartwire , a professional news service of WebMD, can be found at, a Web site for cardiovascular healthcare professionals.



Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.