OptiVol Fluid Status Trend Feature

The OptiVol™ fluid trend tracks intrathoracic impedance changes over time. The impedance is monitored for 14 months, allowing the clinician to better understand how the patient’s fluid status compares with changes in medications, clinical events and outcomes, and overall patient status. 

Clinical data suggest that changes in intrathoracic impedance and fluid accumulation in the thoracic cavity or lungs are inversely correlated.1 As the patient’s lungs become congested, intrathoracic impedance tends to decrease. Similarly, an increase in intrathoracic impedance may indicate the patient’s lungs are becoming drier. OptiVol monitoring to predict worsening heart failure is not intended to replace assessments which are part of standard clinical practice.

This feature can be found in some Medtronic ICD, CRT-P, and CRT-D devices. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.

No programming is required to begin the collection of OptiVol data. Starting 34 days after implant (to account for pocket maturation), the device begins storing data. The OptiVol index is then available for viewing on the Cardiac Compass or Heart Failure Management Report printout upon device interrogation or CareLink transmission. To access the OptiVol fluid index, select Reports -> Heart Failure… .

Note that beginning with Viva™ and Evera™ XT devices, Cardiac Compass trends can also be viewed on the programmer in two ways:

  1. Cardiac Compass [>>] button on the Quick Look™ II screen
  2. Data > Clinical Diagnostics -> Cardiac Compass Trends -> [Open Data]

Cardiac Compass trends can be printed for Viva and Evera devices from these locations or as mentioned above.

Additionally, a clinical status observation appears on the Quick Look™ II screen and on the Heart Failure Management Report when the OptiVol fluid index has reached or exceeded the OptiVol threshold since the last session.

There are two programmable parameters for OptiVol. These parameters only need to be accessed in specific patient case situations. OptiVol operates and collects data without any programming.

  1. OptiVol threshold – The OptiVol threshold is a value above which the device will display an observation to notify the clinician that the patient’s OptiVol index has increased significantly. The nominal threshold is 60. Medtronic recommends that you use this setting until you have clinical experience using OptiVol Fluid Status Monitoring with individual patients. The threshold is only used to provide a diagnostic observation. You can change the threshold, if needed, by going to Alerts -> OptiVol 2.0 Fluid Settings -> OptiVol Threshold.
  2. Reference impedance (OptiVol 2.0 only) – Under appropriate circumstances, you can adjust the reference impedance so it more closely matches the patient’s daily impedance measurements. This should be done only in rare cases such as after a lead revision or a pocket revision. Wait until the patient has a stable pulmonary fluid status to adjust the reference impedance. The adjustment process takes several days. Adjust the reference impedance by going to Alerts -> OptiVol 2.0 Fluid Settings -> Additional Settings.
Intrathoracic impedance measurements are made at 20-minute intervals between 12:00 pm and 5:00 pm using the RV Coil to Can pathway (RV pace sense tip to Can in Consulta™ CRT-P), which passes through the tissue within the thoracic cavity. After all of the impedance measurements for a day have been made, the average impedance value is calculated for that day. The thoracic impedance graph, which is the lower graph, plots the average daily impedance value trend data. This daily impedance value is used to update a slowly adapting trend known as the reference impedance, which is calculated by the device. In this way, a control value for each individual patient is calculated. The device uses this control value to assess impedance variations. 
If the daily impedance falls below the reference impedance, this may indicate that fluid is accumulating in the patient’s thoracic cavity. If the daily impedance remains below the reference impedance, the difference between the daily impedance and reference impedance values, adjusted for individual patient variation, is added to the OptiVol fluid index. While there is a difference between the daily impedance and the reference impedance, the fluid index may continue to increase. If the daily impedance begins to rise, this may be an indication that the thoracic fluid accumulation is resolving and the fluid index may decrease. When the daily impedance returns to the reference impedance, the fluid event is considered to have ended and the OptiVol fluid index resets to 0.
The sample OptiVol report below identifies different aspects of the measurement:
1. OptiVol threshold – Value above which the device will display an observation (in the Quick Look ll screen) to notify the clinician that the patient’s OptiVol index has increased significantly.
2. OptiVol fluid index – Accumulation of the difference between the daily impedance and the reference impedance, adjusted for individual patient variation.
3. Reference impedance – Average impedance which is calculated per patient. It adapts slowly to daily impedance changes.
4. Daily impedance – The average of each day’s multiple impedance measurements.
OptiVol 2.0 provides a diagnostic plot that may indicate a patient’s fluid status over time.  It can be used as an additional tool in managing heart failure patients with Medtronic CRT-D devices.  


  • CRT-P devices utilize OptiVol and CRT-P MRI devices have the OptiVol 2.0 enhancements.
  • The OptiVol Fluid Status Monitoring feature has been updated to OptiVol 2.0 (beginning with the Protecta device models) to account for individual patient variation. OptiVol 2.0 allows the fluid index to update more frequently based on recent intrathoracic impedance measurements.
  • The OptiVol 2.0 Fluid Status Monitoring feature may not provide early warning for all fluid-related decompensations. Therefore, patients should be instructed to seek medical attention immediately any time they feel ill and need help, even if the OptiVol fluid monitoring features of their device or monitor indicate acceptable pulmonary fluid status conditions.
  • The OptiVol 2.0 Fluid Status Monitoring feature is an additional source of information for patient management and does not replace assessments that are part of standard clinical practice.

Below is an example of a patient whose intrathoracic impedance decreased significantly about four months after the device implant. The decrease in the impedance can also be viewed as a sudden increase on the OptiVol fluid index graph. By viewing the patient’s Cardiac Compass  report, the clinician discovered that this trend of fluid increase was most likely triggered by a sudden onset of AF. The AF caused an increase in the patient’s ventricular rate, which caused a decrease in biventricular pacing and a decrease in overall patient activity. Taking all of the device diagnostics and patient clinical status indicators into account can aid in managing the patient’s heart failure.

Although the OptiVol fluid index is normalized based on the reference and daily thoracic impedances, each patient’s clinical status is unique. Therefore, the OptiVol fluid index trends should be evaluated specifically for each patient.

Many trials have looked at the clinical utility of OptiVol as a tool in managing heart failure patients.

Topic Clinical Evidence Main Supporting Trials*
Impedance monitoring Intrathoracic impedance:
  • Declines with increased ventricular volumes and pressures.1-12
  • Is inversely correlated with PCWP, fluid balance and NT-pro BNP.13-14
  • Precedes patient’s symptoms and heart failure hospitalizations by two weeks.1
  • Decreases as fluid retention increases.15
MID-HeFT Trial1
Heart failure hospitalization OptiVol fluid index threshold crossings:
  • Patients with crossings are twice as likely to have a heart failure adverse event.16
  • Frequent or sustained events identified patients at risk for acute decompensated heart failure hospitalizations.17
Combined/integrated diagnostics:
  • Use of multiple device diagnostic parameters increased the ability to identify patients at risk of heart failure events beyond the use of impedance alone.16
  • Patients with two or more diagnostics observations were 5.5 times more likely to have heart failure hospitalization in next 30 days.17
Weight monitoring, 6-MHW, BNP marker
  • OptiVol detects 3 times more heart failure events than weight monitoring alone.18
  • OptiVol Fluid Index increases are associated with worsening 6-MHW and BNP.19
Heart failure readmissions
  • Device-derived heart failure diagnostic criteria identified patients at significantly higher risk of a heart failure event within 30 days post discharge.16-18, 20-22
  • Device diagnostics may help identify the patients at greatest risk of heart failure re-admission.21,22
  • Intrathoracic impedance changes can precede VT/VF episodes.23
  • Decreases in intrathoracic impedance can precede storms of VT.24
  • AT episodes preceded (43%) or occurred almost simultaneously (22%) with the threshold crossing in greater than half the patients.25
See references for supporting studies and case studies
Mortality risk
  • Diagnostic data was analyzed from 21,217 patients who were remotely monitored for > 6 months.26
  • Patients who experienced threshold crossings within the initial 6 months of remote monitoring had a 2.15-fold increased long-term mortality risk.26
Study by the Heart and Vascular Institute at the Cleveland Clinic26
*Additional trials support these statements, see references for additional information.


  1. Yu CM, Wang L, Chau E, et al. Intrathoracic Impedance Monitoring in Patients With Heart Failure. Circulation. 2005; 112: 841–848.
  2. Germany R, Murray C. Use of device diagnostics in the outpatient management of heart failure. Am J Cardiol. May 21, 2007;99(10A):11G-16G.
  3. Small RS. Integrating device-based monitoring into clinical practice: insights from a large heart failure clinic.Am J Cardiol. May 21, 2007;99(10A):17G-22G.
  4. Vollmann D, Nägele H, Schauerte P, et al. Clinical utility of intrathoracic impedance monitoring to alert patients with an implanted device of deteriorating chronic heart failure. Eur Heart J. August 2007;28(15):1835-1840.
  5. Repoley J, Dukes-Graves D, Kiser C. Surgical revision of implantable device “pocket” or lead can alter thoracic impedance-based indices of worsening heart failure. J Card Fail. 2006;12(6)(suppl): S66.
  6. Patient Case: LV Lead Dislodgement and Pocket Revision. Courtesy of R. Ward Pulliam and Jill Repoley, NP. The Heart Group and Lancaster General Hospital, Lancaster, PA. 2006 Medtronic Inc., data on file, UC200602091 EN.
  7. Small R, Tang W, Wickemeyer R, et al. Managing heart failure patients with intra-thoracic impedance monitoring: a multi-center US evaluation. J Card Fail. 2007;13(6)(suppl):S113-S114.
  8. Tang W, Germany J, Andriulli J, et al. Weekly and seasonal variations in daily activity and intrathoracic impedance in heart failure patients. J Card Fail. 2007;13(6)(suppl):S182.
  9. Braunschweig F, Mortensen PT, Gras D, et al. Monitoring of physical activity and heart rate variability in patients with chronic heart failure using cardiac resynchronization devices. Am J Cardiol. May 1, 2005;95(9):1104-1107.
  10. Rathman L. Use of device diagnostics as an educational tool to improve patient adherence. Am J Cardiol. May 21, 2007;99(10A):29G-33G.
  11. Wang L. Fundamentals of intrathoracic impedance monitoring in heart failure. Am J Cardiol. May 21, 2007;99(10A):3G-10G.
  12. Wang L, Lahtinen S, Lentz L. Feasibility of using an implantable system to measure thoracic fluid congestion in an ambulatory chronic heart failure canine model. Pacing Clin Electrophysiol. 2005;28:404Y411.
  13. Abraham W, Foreman B, Fishel R, Hass G, Moe B. Fluid accumulation status trial (FAST). Heart Rhythm. May 2005;2(5):S65-S66.
  14. Lüthje L, Vollmann D, Drescher T, et al. Intrathoracic impedance monitoring to detect chronic heart failure deterioration: relationship to changes in NT-proBNP. Eur J Heart Fail. June-July 2007;9(6-7):716-722.
  15. Medtronic Viva XT CRT-D System Reference Guides.
  16. Whellan DJ, Ousdigian KT, Al-Khatib SM, et al. Combined heart failure device diagnostics identify patients at higher risk of subsequent heart failure hospitalizations: results from PARTNERS HF (Program to Access and Review Trending Information and Evaluate Correlation to Symptoms in Patients with Heart Failure) study. J Am Coll Cardiol. April 27, 2010;55(17):1803-1810.
  17. Small RS, Wickemeyer W, Germany R, et al. Changes in intrathoracic impedance are associated with subsequent risk of hospitalizations for acute decompensated heart failure: clinical utility of implanted device monitoring without a patient alert. J Card Fail. August 2009;15(6):475-481. [OFISSER]
  18. Abraham WT, Compton S, Haas G, et al. Superior performance of intrathoracic impedance-derived fluid index versus daily weight monitoring in heart failure patients. Results of the Fluid Accumulation Status Trial. Late Breaking Clinical Trials. Congest Heart Fail. 2011;17:51-55.
  19. Gulati, Sanjeev K., John McKenzie, George H. Crossley, Mary Anne Papp, Jason Sims, and John Andriulli. "Relationship between Intrathoracic Impedance, BNP and Six-Minute Hall Walk." Journal of Cardiac Failure16, no. 8 (2010): S65.
  20. Crossley GH, Boyle A, Vitense H, Chang Y, Mead RH, and the CONNECT Investigators. The CONNECT (Clinical Evaluation of Remote Notification to Reduce Time to Clinical Decision) Trial: the value of wireless remote monitoring with automatic clinician alerts. J Am Coll Cardiol. 2011;57(10):1181-1190.
  21. Whellan DJ, Sarkar S, Koehler J, Small RS, Boyle A, Warman EN, Abraham WT. Development of a Method to Risk Stratify Patients With Heart Failure for 30-Day Readmission Using Implantable Device Diagnostics. 10 Am J Cardiol. 2012 Oct 2. pii: S0002-9149(12)02067-X. doi: 10.1016/j.amjcard.2012.08.050. [Epub ahead of print]
  22. Small RS, Whellan DJ, Boyle A, Koehler J, Sarkar S, Warman EN, Abraham WT. Implantable Device Diagnostics on the Day of Discharge from a Heart Failure Hospitalization Can Predict 30 Day Readmission Risk. J Card Fail. August 2012, Vol 18 (8 Suppl): S50. (abstract HFSA)
  23. Moore HJ, Peters MN, Franz MR, Karasik PE, Singh SN, Fletcher RD. Intrathoracic Impedance Preceding Ventricular Tachyarrhythmia Episodes. Pacing Clin Electrophysiol. 2010 Aug;33(8):960-6.
  24. Andriulli J, Coles J, Hetrick DA. Association between decreased intra-thoracic impedance and ventricular tachyarrhythmias. Int J Cardiol. 2008; 123:333-334.
  25. Jhanjee R, Templeton GA, Sattiraju S, Nguyen J, Sakaguchi S, Lu F, Ermis C, Milstein S, Van Heel L, Lurie KG, Benditt DG. Relationship of paroxysmal atrial tachyarrhythmias to volume overload: assessment by implanted transpulmonary impedance monitoring. Circ Arrhythm Electrophysiol. 2009 Oct;2(5):488-94.
  26. Tang, Wai Hong Wilson, Eduardo N. Warman, James W. Johnson, Roy S. Small, and James Thomas Heywood. "Threshold crossing of device-based intrathoracic impedance trends identifies relatively increased mortality risk." European Heart Journal 33, no. 17 (2012): 2189-2196.

Sources: Medtronic Consulta CRT-P Clinician Manual; Medtronic Protecta XT DR Clinician Manual; Medtronic Protecta XT CRT-D Clinician Manual

Last updated: 
21 Mar 2013