Bethesda, MD - Hemodynamic measures obtained by transthoracic impedance cardiography (ICG) can independently predict the short-term risk of decompensation in patients with chronic HF, according to a prospective pilot study that helps validate the technique's use in identifying patients who might benefit from intensified therapy [1].

The study suggests that a combination of ICG measurements add to the independent prognostic strength of several clinical parameters, write the investigators, Dr Milton Packer (University of Texas Southwestern Medical Center, Dallas) and associates. And, they speculate, ICG "may complement rather than replicate the information provided by right-heart catheterization," which is too invasive for regular use. The group's preliminary report on the Prospective Evaluation and Identification of Cardiac Decompensation by ICG Test (PREDICT) study appears in June 6, 2006 issue of the Journal of the American College of Cardiology.

This study is really a first attempt to confirm what many people believe clinically.

As explained in the report, the transthoracic ICG system (CardioDynamics, San Diego, CA) used in PREDICT requires that the patient be connected by leads to a device that sends an alternating current across the chest to measure fluid-related impedance. Based on the magnitude and duration of impedance changes over time compared with baseline, several hemodynamic measures can be directly measured and others estimated.

Coauthor Dr William T Abraham (Ohio State University, Columbus) told heartwire, "This study is really a first attempt to confirm what many people believe clinically, that one can use these measurements to help determine which heart-failure patient is getting sicker and which is not." The device is currently used in many university and community hospitals, he said, especially those with heart-failure clinics.

"I think it has the potential to substantially reduce the risk of worsening heart failure that requires hospitalization," according to Abraham. Information from the device, although it can't replace clinical evaluations, he said, could also possibly sharpen clinically based identification of HF patients who need more frequent and intensive follow-up.

In PREVENT, investigators at 21 institutions performed ICG on an outpatient basis every two weeks for 26 weeks in 212 patients with chronic HF and least one prior hospital or clinic visit for exacerbations. They were overwhelmingly in NYHA class 2-3, with either ischemic or nonischemic disease; LVEF averaged 27%. "Throughout the study, patients were managed according to the judgment of their usual physicians, who had no knowledge of the ICG test results," they write.

These three variables provided powerful short-term prognostic information that was incremental to that available from a physician's clinical evaluation.

Of a combined total of 2316 office visits, 77 (3.3%) preceded a decompensation event within two weeks. The events, which struck an average of six days after ICG, were the study's primary end point and prospectively defined as death or a hospitalization or emergency-department visit for worsening HF that led to intensified therapy.

In multivariate analysis, independently significant clinical predictors of a decompensation event included NYHA class, heart rate, systolic blood pressure, and patient clinical self-assessment. Three ICG parameters measured at the most recent test emerged as independent event predictors. They were thoracic fluid content index, hemodynamic velocity index, and LV ejection time, which were then integrated into a composite score based on a scale ranging from zero to 10. Importantly, according to the authors, the composite's individual parameters are directly taken, not estimated, from the ICG measurements

"When combined into a single composite score, these three [ICG] variables provided powerful short-term prognostic information that was incremental to that available from a physician's clinical evaluation," according to the authors. Moreover, they write, in a second multivariate analysis that included the composite ICG score and the three independently significant clinical variables, the ICG-based score emerged as the most statistically powerful predictor.

"Neither clinical nor ICG variables measured at the start of the study identified patients who deteriorated," the PREVENT report states, "suggesting that the predictive value of both clinical and ICG measurements may wane over time. This observation underscores the need for periodic reassessment and close follow-up for the optimal management of patients."

Abraham said that PREDICT is being followed up by a prospective, randomized, controlled trial called PREVENT, which is exploring whether transthoracic impedance monitoring can help prevent hospitalization for worsening HF.

ICD-based impedance monitoring: A guide for preventive intensified therapy? Boston, MA - Implantable cardioverter-defibrillators (ICDs) that can detect changes in intrathoracic impedance that signal rising pulmonary fluid volume have been on the market for a while, yet there are few prospective data showing that they make a substantial clinical difference. But recently, a small case-control study suggested that the device's warnings of impending decompensation, although sometimes inaccurate, "can result in early treatment during the preclinical stage of HF decompensation and in a significant reduction of hospital admissions for congestive heart failure," Dr Massimiliano Maines (S Maria del Carmine Hospital, Rovereto, Italy) said at the recent Heart Rhythm Society 2006 Scientific Sessions [2]. Maines and his colleagues followed 54 consecutive patients with newly implanted biventricular pacer-ICD devices every three months for an average of 359 days. Half the patients, the controls, had received a Medtronic InSync III Marquis device, with the remainder receiving an otherwise-similar Medtronic InSync Sentry unit with integrated intrathoracic-impedance-monitoring capability. The two groups were similar with respect to a wide variety of clinical and other features, including age, LVEF, QRS duration, prevalence of ischemic vs nonischemic cardiomyopathy, NYHA, and history of HF admissions. Patients with impedance-monitoring ICDs were instructed to report for evaluation and possible therapy whenever the device sounded the appropriate warning of increasing fluid volume. That happened 18 times, including four in which the alarm was inappropriate. One of the group's patients required hospitalization for acute decompensation after "ignoring" the device's alarm for 13 days, Maines said. Outcomes in HF patients and ICDs with, without intrathoracic fluid monitoring Primary-end-point* outcomes Impedance monitoring, n=27 No impedance monitoring, n=27 Incidence 1 8 Rate (%) 3.7 29.6† *Hospital admissions for acute decompensated HF †p<0.05 vs impedance-monitoring group To download table as a slide, click on slide logo below After his presentation, session moderator Dr J Graeme Sloman (Epworth Hospital, Richmond, Victoria, Australia) was optimistic about what the results might mean for patients with HF and an indication for biventricular pacemaker-ICD devices, but he cautioned that the monitoring technique's clinical potential needs further exploration in larger trials.