Medical Policy: 02.02.18
Original Effective Date: January 2017
Reviewed: January 2017
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This Medical Policy document describes the status of medical technology at the time the document was developed. Since that time, new technology may have emerged or new medical literature may have been published. This Medical Policy will be reviewed regularly and be updated as scientific and medical literature becomes available.
Bioimpedance is defined as the electrical resistance of tissue to the flow of current. Cardiac bioimpedance, also referred to as thoracic electrical bioimpedance (TEB) or impedance cardiography (ICG), uses change in impedance by an alternating current applied across the thorax to determine various hemodynamic parameters, including stroke volume, cardiac output, and thoracic fluid content. The technology utilizes voltage changes in the flow of thoracic electrical impulses to estimate changes in the blood volume in the aorta and changes in fluid volume in the thorax. The current is introduced by electrodes placed on both sides of the neck and both sides of the lower thorax. When small electrical signals are transmitted through the thorax, the current travels along the blood filled aorta, which is the most conductive area. Changes in the bioimpedance, resulting from the pulsatile changes in volume and velocity of blood in the aorta, are inversely proportional to the stroke volume (cardiac output equals the stroke volume times the heart rate).
The noninvasive nature of cardiac bioimpedance has prompted interest in the use of this technology in a variety of outpatient applications. It has been proposed as a technique to: determine cardiac versus non-cardiac causes of dyspnea; promote optimization of drug therapy in patients with heart failure or hypertension; provide early detection of rejection in heart transplant recipients; monitor patients with pulmonary hypertension; or optimize the programming of pacemakers. Prognostic values have been studied in relationship to heart failure in profiling survivors versus non-survivors and in association with the need of hospitalization.
A number of early studies evaluated the accuracy of thoracic bioimpedance compared with other methods of cardiac output measurements, in both the outpatient and inpatient settings. In 2002, the Agency for Health Care Research and Quality (AHRQ) published a technology assessment on thoracic electrical bioimpedance (TEB) to evaluate data on the clinical effectiveness for several cardiovascular applications: patients with suspected or known cardiovascular disease; acute dyspnea; pacemakers; inotropic therapy; post-heart transplant evaluation; cardiac patients with a need for fluid management; and hypertension. A systematic review and meta-analysis of the TEB literature was conducted. The authors concluded that limitations in the available studies did not allow meaningful conclusions concerning the accuracy of thoracic electrical bioimpedance (TEB) compared with other hemodynamic parameters. There is also little conclusive evidence regarding TEB’s usefulness in the specific clinical areas addressed. This was largely due to the lack of focus on clinical outcomes by researchers in this area. The clinical reports on the use of TEB for a variety of clinical indications in reports published from 1991 onwards suggested that this non-invasive method is of interest and may potentially support some of these indications, but there is little evidence that directly addressed how this monitoring technique can affect patient outcomes.
A number of small case series have reported variable results regarding the relation between measurements of cardiac output determined by thoracic bioelectrical impedance and thermodilution techniques.
Several studies have assessed the association between thoracic bioimpedance measurements and heart failure-related outcomes:
In a sub-analysis of 170 subjects from the ESCAPE study, a multicenter randomized trial to assess pulmonary artery catheter guided therapy in patients with advanced heart failure, Kamath et. al. compared cardiac output estimated with the BioZ thoracic impedance plethysmography device with subsequent heart failure or hospitalization and to directly measured hemodynamics from right heart catheterization in a subset of patients (n=82). The results showed there was modest correlation between ICG (impedance cardiography) and invasively measured cardiac output (r=0.4 to 0.6 on serial measurement). Thoracic fluid content (TFC) measured by ICG was not a reliable measure of pulmonary capillary wedge pressure (PCWP). There was poor agreement between ICG and invasively measured hemodynamic profiles (kappa ≤ 0.1). No ICG variable alone or in combination was associated with outcome. The authors concluded in hospitalized patients with advanced heart failure, ICG provides some information about cardiac output but no left-sided filling pressures. ICG did not have prognostic utility in this patient population.
Packer et.al. reported on the use of the potential utility of impedance cardiography (ICG) in predicting clinical decompensation in ambulatory patients with heart failure (HF). This study prospectively evaluated 212 stable patients with HF and a recent episode of clinical decompensation who underwent serial clinical evaluation and blinded ICG testing every 2 weeks for 26 weeks and were followed up for the occurrence of death or worsening HF requiring hospitalization or emergent care. During the study 59 patients experienced 104 episodes of decompensated HF (16 deaths, 78 hospitalizations, and 10 emergency visits). Multivariate analysis identified 6 clinical and ICG variable that independently predicted an event within 14 days of assessment. These included three clinical variables (visual analog score, New York Heart Association functional class, and systolic blood pressure) and three ICG parameters (velocity index, thoracic fluid content index, and left ventricular ejection time). The composite score of 3 ICG parameters was a predictor of an event during the next 14 days (p=0.0002). Patients noted to have a high-risk composite score at a visit had a 2.5 times greater likelihood of a near-term event, and those with a low risk score had a 70% lower likelihood of a near-term event compared with patients at intermediate risk. The authors concluded that these results suggested that when performed at regular intervals in stable patients with HF with a recent episode of clinical decompensation, ICG can identify patients at increased near-term risk of recurrent decompensation.
In 2012, Anand et. al. reported results on the Multi-Sensor Monitoring in Congestive Heart Failure (MUSIC) Study, a non-randomized prospective study designed to develop and validate an algorithm for the prediction of acute heart failure decompensation using a clinical prototype of the MUSE system, multisensory system that includes intrathoracic bioimpedance measurements, along with electrocardiographic and accelerometry data. This study enrolled 543 heart failure patients (206 in the development phase, 337 in the validation phase) with an ejection fraction ≤ 40% and a recent heart failure admission. Patients were remotely monitored for 90 days using multisensory device. There was a high rate of study dropout: 229 (42% of the total) primarily due to withdrawal of consent or failure of the prototype device to function. 314 patients (114 in the development phase, 200 in the validation phase) were included in the analysis. Subjects were assessed for the development of an acute heart failure decompensation event (ADHF), which was defined as any of the following: (1) any heart failure related hospitalization, emergency department or urgent care visit that required administration of IV diuretics, inotropes, or ultrafiltration for fluid removal; (2) a change in diuretic directed by the health care provider that included 1 or more of the following: a change in the prescribed diuretic type; an increase in dose of an existing diuretic; or the addition of another diuretic; (3) an ADHF event for which death was the outcome. Development patient data were used to develop a multi-parameter heart failure detection algorithm. Algorithm performance in the development cohort had 65% sensitivity, 90% specificity, and a false positive rate of 0.7 per patient-year for detection of HF events. In the validation cohort, algorithm performance met the prespecified end points with 63% sensitivity, 92% specificity, and a false positive rate of 0.9 per patient-year. The overall rate of significant adverse skin response was 0.4%. The authors concluded using an external multisensory monitoring system, an HF decompensation prediction algorithm was developed that met the prespecified performance end point. Further studies are required to determine whether the use of this system will improve patient outcomes.
The evidence on cardiac bioimpedance (thoracic electrical bioimpedance (TEB) or impedance cardiography (ICG)) devices consists of nonrandomized studies that correlate measurements with other measures of cardiac function and studies that use bioimpedance measurement as part of an algorithm for predicting future heart failure events. No studies were identified that determined how cardiac bioimpedance measurements are associated with changes in patient management or in patient outcomes. Randomized clinical trials are needed that evaluate whether prediction of heart failure decompensation through cardiac bioimpedance allows earlier intervention or other management changes are needed to demonstrate that outcomes are improved.
For individuals who have heart failure in outpatient setting who receive hemodynamic monitoring with cardiac bioimpedance (thoracic electrical bioimpedance (TEB) or impedance cardiography (ICG)), there is lack of randomized clinical trial (RCT) evidence that evaluates whether the use of this technology improves health outcomes over standard active management of heart failure patient. The studies performed report physiologic measurement-related outcomes and/or associations between monitoring information and heart failure exacerbations, but do not provide definitive evidence on device efficacy. The evidence is insufficient to determine the effects on net health outcomes.
American College of Cardiology Foundation (ACCF) and American Heart Association (AHA) (H4)
In 2013, the American College of Cardiology Foundation (ACCF) and American Heart Association (AHA) issued a guideline for the management of heart failure which offers no recommendations for use of ambulatory monitoring devices.
Multiple thoracic impedance measurement devices that do not require invasive placement have been cleared for marketing by the U.S. Food and Drug Administration (FDA) through the 510(k) process because FDA determined that this device was substantially equivalent to existing devices for use of peripheral blood flow monitoring. The below list includes noninvasive thoracic impedance devices, this is not mean to be a comprehensive list.
|Device||Manufacturer||Year of FDA Clearance|
|BioZ Thoracic Impedance Plethysmograph||SonoSite (Bothell, WA)||1997|
|IQ System Cardiac Output Monitor||Renaissance Technology (Newtown, PA)||1998|
|Sorba Steorra Non-Invasive Impedance Cardiography||Sorba Medical Systems (Milwaukee, WI)||2002|
|Zoe Fluid Status Monitor||Noninvasive Medical Technologies (Las Vegas, NV)||2004|
|Cheetah NICOM System||Cheetah Medical (Tel Aviv, Israel)||2008|
|PhysioFlow Signal Morphology-based Impedance Cardiography (SM-ICG)||Vasocom, now NeuMeDx (Bristol, PA)||2008|
Cardiac bioimpedance (thoracic electrical bioimpedance (TEB) or impedance cardiography (ICG)) in the outpatient setting is considered investigational when utilized for cardiac hemodynamic monitoring for the management of heart failure.
For individuals who have heart failure in the outpatient setting who receive hemodynamic monitoring with cardiac bioimpedance (thoracic electrical bioimpedance (TEB) or impedance cardiography (ICG)), there is lack of randomized clinical trial (RCT) evidence that evaluates whether the use of this technology improves health outcomes over standard active management of heart failure patient. The studies performed report physiologic measurement-related outcomes and/or associations between monitoring information and heart failure exacerbations, but do not provide definitive evidence on device efficacy. The evidence is insufficient to determine the effects on net health outcomes.
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January 2017 - New Policy
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