The Role of Device Diagnostic Algorithms in the Assessment and Management of Patients with Systolic Heart Failure: A Review
Figure 1
OptiVol fluid index. The intrathoracic impedance is measured on a daily basis and is compared to the patient’s “reference” value, which is derived from the average of the last 4 daily measurements. Negative deviations from the reference value suggest a decrease in intrathoracic impedance, which may reflect pulmonary congestion. The difference between the measured intrathoracic impedance and the reference value is multiplied by time (measured in days) to generate the OptiVol fluid index, which has a unit measurement of ohms · days. The magnitude of the fluid index value is determined by (i) the absolute difference between the reference value and the measured intrathoracic impedance, and/or (ii) the time duration of the difference. The fluid index is plotted against time to graphically display the onset and duration of negative deviations of intrathoracic impedance. The nominal cut-off threshold is set as 60 ohms. The nominal cut-off threshold is set · days.
