Impedance Monitoring Helpful in Heart Failure

BOSTON — Monitoring fluid build-up in the chest by intrathoracic impedance is more predictive of events in heart failure patients compared with daily weight monitoring, according to the findings of a multicenter, prospective, double-blind investigation.

Still, experts agreed that the results do not suggest that impedance monitoring can replace daily weight monitoring of heart failure patients as a means for predicting events and guiding therapy.

Dr. William T. Abraham of Ohio State University in Columbus and his colleagues conducted the Fluid Accumulation Status Trial (FAST), comparing the results of intrathoracic impedance monitoring with those attained through daily weight monitoring—the current standard of care—in 156 heart failure patients.

The investigators used a drop in intrathoracic impedance as a surrogate for identifying presymptomatic, treatable fluid build-up. Changes in impedance were detected with the help of software that had been downloaded onto the patients' implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D) devices.

The participants all had heart failure symptoms for a mean of 18 months. At baseline, 85% were in New York Heart Association (NYHA) class II or III and most of the rest were in NYHA class I, he reported in a late-breaking abstract presented at the annual meeting of the Heart Failure Society of America.

The investigators compared the data collected by the impedance monitoring software with data collected by patient-completed daily weight diaries. While the impedance data were available for nearly every day of the trial, only 76% of the patients complied with daily weight monitoring, Dr. Abraham said.

Of the 65 heart failure events that occurred in 31 patients, intrathoracic impedance monitoring accurately predicted 48 of the events, compared with just 13 of the events predicted by daily weight monitoring. “The adjusted sensitivity for [impedance monitoring] was more than three times higher than with daily weight monitoring,” at 76% and 23%, respectively, he reported.

Of the predicted events, 40 of those detected by impedance monitoring were not detected by weight monitoring and 5 of those detected by weight monitoring were not detected by fluid monitoring, Dr. Abraham said.

Both impedance and weight monitoring set off many false alarms. The impedance monitoring system identified 417 “impedance crossings,” which are the signals predicting a heart failure event, while there were 890 changes in weight that met the warning level criteria (at least 3 pounds gained in 1 day or at least 5 pounds gained over 3 days), Dr. Abraham reported.

“With daily weight [monitoring], you have less sensitivity and more false alarms to respond to,” compared with impedance monitoring, suggesting that impedance status monitoring may be the better option and should be used in addition to the daily weight monitoring in patients with implanted devices that have this capability, he said.

Dr. Abraham didn't suggest doing away with daily weight monitoring as a heart failure maintenance strategy, as it has a proven role in helping predict heart failure progression and in guiding therapy. But he suggested that its reliability and effectiveness should be reevaluated and that other measurement systems be considered.

The FAST study was sponsored by Medtronic Inc., the manufacturer of the OptiVol Fluid Status Monitoring System used in the investigation. Dr. Abraham reported having received research grants and/or consulting fees from Medtronic, Biotronik Inc., Boston Scientific Corporation, and St. Jude Medical, Inc.

BOSTON — Monitoring fluid build-up in the chest by intrathoracic impedance is more predictive of events in heart failure patients compared with daily weight monitoring, according to the findings of a multicenter, prospective, double-blind investigation.

Still, experts agreed that the results do not suggest that impedance monitoring can replace daily weight monitoring of heart failure patients as a means for predicting events and guiding therapy.

Dr. William T. Abraham of Ohio State University in Columbus and his colleagues conducted the Fluid Accumulation Status Trial (FAST), comparing the results of intrathoracic impedance monitoring with those attained through daily weight monitoring—the current standard of care—in 156 heart failure patients.

The investigators used a drop in intrathoracic impedance as a surrogate for identifying presymptomatic, treatable fluid build-up. Changes in impedance were detected with the help of software that had been downloaded onto the patients' implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D) devices.

The participants all had heart failure symptoms for a mean of 18 months. At baseline, 85% were in New York Heart Association (NYHA) class II or III and most of the rest were in NYHA class I, he reported in a late-breaking abstract presented at the annual meeting of the Heart Failure Society of America.

The investigators compared the data collected by the impedance monitoring software with data collected by patient-completed daily weight diaries. While the impedance data were available for nearly every day of the trial, only 76% of the patients complied with daily weight monitoring, Dr. Abraham said.

Of the 65 heart failure events that occurred in 31 patients, intrathoracic impedance monitoring accurately predicted 48 of the events, compared with just 13 of the events predicted by daily weight monitoring. “The adjusted sensitivity for [impedance monitoring] was more than three times higher than with daily weight monitoring,” at 76% and 23%, respectively, he reported.

Of the predicted events, 40 of those detected by impedance monitoring were not detected by weight monitoring and 5 of those detected by weight monitoring were not detected by fluid monitoring, Dr. Abraham said.

Both impedance and weight monitoring set off many false alarms. The impedance monitoring system identified 417 “impedance crossings,” which are the signals predicting a heart failure event, while there were 890 changes in weight that met the warning level criteria (at least 3 pounds gained in 1 day or at least 5 pounds gained over 3 days), Dr. Abraham reported.

“With daily weight [monitoring], you have less sensitivity and more false alarms to respond to,” compared with impedance monitoring, suggesting that impedance status monitoring may be the better option and should be used in addition to the daily weight monitoring in patients with implanted devices that have this capability, he said.

Dr. Abraham didn't suggest doing away with daily weight monitoring as a heart failure maintenance strategy, as it has a proven role in helping predict heart failure progression and in guiding therapy. But he suggested that its reliability and effectiveness should be reevaluated and that other measurement systems be considered.

The FAST study was sponsored by Medtronic Inc., the manufacturer of the OptiVol Fluid Status Monitoring System used in the investigation. Dr. Abraham reported having received research grants and/or consulting fees from Medtronic, Biotronik Inc., Boston Scientific Corporation, and St. Jude Medical, Inc.

BOSTON — Monitoring fluid build-up in the chest by intrathoracic impedance is more predictive of events in heart failure patients compared with daily weight monitoring, according to the findings of a multicenter, prospective, double-blind investigation.

Still, experts agreed that the results do not suggest that impedance monitoring can replace daily weight monitoring of heart failure patients as a means for predicting events and guiding therapy.

Dr. William T. Abraham of Ohio State University in Columbus and his colleagues conducted the Fluid Accumulation Status Trial (FAST), comparing the results of intrathoracic impedance monitoring with those attained through daily weight monitoring—the current standard of care—in 156 heart failure patients.

The investigators used a drop in intrathoracic impedance as a surrogate for identifying presymptomatic, treatable fluid build-up. Changes in impedance were detected with the help of software that had been downloaded onto the patients' implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D) devices.

The participants all had heart failure symptoms for a mean of 18 months. At baseline, 85% were in New York Heart Association (NYHA) class II or III and most of the rest were in NYHA class I, he reported in a late-breaking abstract presented at the annual meeting of the Heart Failure Society of America.

The investigators compared the data collected by the impedance monitoring software with data collected by patient-completed daily weight diaries. While the impedance data were available for nearly every day of the trial, only 76% of the patients complied with daily weight monitoring, Dr. Abraham said.

Of the 65 heart failure events that occurred in 31 patients, intrathoracic impedance monitoring accurately predicted 48 of the events, compared with just 13 of the events predicted by daily weight monitoring. “The adjusted sensitivity for [impedance monitoring] was more than three times higher than with daily weight monitoring,” at 76% and 23%, respectively, he reported.

Of the predicted events, 40 of those detected by impedance monitoring were not detected by weight monitoring and 5 of those detected by weight monitoring were not detected by fluid monitoring, Dr. Abraham said.

Both impedance and weight monitoring set off many false alarms. The impedance monitoring system identified 417 “impedance crossings,” which are the signals predicting a heart failure event, while there were 890 changes in weight that met the warning level criteria (at least 3 pounds gained in 1 day or at least 5 pounds gained over 3 days), Dr. Abraham reported.

“With daily weight [monitoring], you have less sensitivity and more false alarms to respond to,” compared with impedance monitoring, suggesting that impedance status monitoring may be the better option and should be used in addition to the daily weight monitoring in patients with implanted devices that have this capability, he said.

Dr. Abraham didn't suggest doing away with daily weight monitoring as a heart failure maintenance strategy, as it has a proven role in helping predict heart failure progression and in guiding therapy. But he suggested that its reliability and effectiveness should be reevaluated and that other measurement systems be considered.

The FAST study was sponsored by Medtronic Inc., the manufacturer of the OptiVol Fluid Status Monitoring System used in the investigation. Dr. Abraham reported having received research grants and/or consulting fees from Medtronic, Biotronik Inc., Boston Scientific Corporation, and St. Jude Medical, Inc.