The Evaluation and Monitoring of Volume Status ... - Wiley Online Library

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Review Paper

The Evaluation and Monitoring of Volume Status in Congestive Heart Failure

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y definition, congestive heart failure (CHF) is a fluid problem. Thus, congestion defined the diagnosis of heart failure (HF) until the latest set of guidelines. The large number of patients with HF dictates that physicians effectively assess and treat congestion. There are currently an estimated 5 million people in the United States with HF, resulting in approximately 1 million hospital admissions each year. The economic impact of HF is tremendous, consuming 1% to 2% of total health care expenditures domestically. Readmission for repeat episodes of exacerbation is frequent, possibly due to the difficulties associated with assessment of volume status. Based on the Acute Decompensated Heart Failure National Registry (ADHERE) database, one-half of hospitalized patients lose 2 to 3 cm being abnormal. Hepatojugular reflux is appreciated with palpation of the liver and adds to the sensitivity of examination of the jugular veins. When noted by the clinician, the presence of jugular venous distention is highly sensitive for elevated pulmonary capillary wedge pressure (PCWP).5,7 Edema is an important finding, particularly from the patient’s perspective. In HF, it is usually symmetric, 136

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beginning with the feet and ascending to the abdomen. Diseases of the liver, kidneys, or vascular system and obesity may confound the critical assessment of edema. In such cases, using the presence of edema alone without other signs of volume excess can lead to inaccuracies in therapy, which can be dangerous for the patient. Other challenges include the position of patients, who, if immobile, redistribute edema such that it is underestimated. Rales, when present, are an obvious indicator of hypervolemia. Frequently, they are absent even in the face of obvious exacerbation. Rales can be absent in the majority of patients with systolic HF because of increased lymphatic drainage and chronic perivascular compensation. For instance, Stevenson and Perloff4 found that in patients with significantly elevated PCWP, only 20% had rales.

be attributed to the use of a PAC. The difficulty in comparing these study findings with current practice is that any patient felt by the investigator to require a PAC was excluded. An additional difficulty in the use of the PAC lies in the absence of explicit guidelines or definitions of optimum PAC numbers or how to adjust medications in response to these data. Even in the ESCAPE trial, the utilization of data to manage patients was left up to individual physicians. This variation may account for the difficulty in proving the PAC utility. Thus, the PAC likely has a role in the management of the most critically ill HF patients, but its role in more routine inpatient volume and hemodynamic management is still not clearly defined. Unfortunately, PACs can only be used in patients already decompensated and cannot prevent decompensations.

Beyond Physical Examination: Current Methods Available for Assessing Volume Status

Brain Natriuretic Peptide. The laboratory measurement of brain natriuretic peptide (BNP) assay was found to correlate with the severity of HF and there was thought to be great promise in using BNP to monitor fluid. BNP values have been shown to decrease with the use of b-blockers,12 but no study has shown consistent and statistically significant decreases in wedge pressure with decreased BNP. Improved BNP does correlate with improved New York Heart Association (NYHA) classification,13 and the measurement has a role in chronic HF management but, as with other physical examination and symptoms, it is not a stand-alone measurement to follow volume status because individual patients may vary greatly.

Pulmonary Artery Catheter. The pulmonary artery catheter (PAC) has had a tumultuous history, now with an unclear role in the intensive management of HF, except in critically ill patients in whom its use is thought to be essential. Multiple trials have failed to demonstrate a superiority of this method of care with regard to mortality or more immediate care outcomes.8,9 The Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE)10 enrolled more than 400 patients admitted with severe HF who were randomized to therapy guided by clinical assessment and PAC or clinical assessment alone. No difference was noted in overall mortality or hospitalization rates. Results have been consistent in smaller trials and in examination of combined data. A meta-analysis that consisted of 13 randomized clinical trials of more than 5000 patients was recently performed.11 Neither an increase in mortality nor improved length of hospital stay could

Echocardiography. Echocardiography, although representing only a snapshot in time, can provide important information on the fluid status in HF. Estimated right ventricular or pulmonary artery pressures may be used to estimate filling pressures in HF, and mitral inflow Doppler imaging provides information about diastolic function, including the volume overload may . june 2008

Figure 1. Latitude weight monitoring system (Boston Scientific Corporation, Natick, MA). Weight measurements, along with other device data, are automatically transmitted to the Internet database for physician monitoring.

of restrictive physiology. The utility of these measures over the course of clinical treatment, however, is unpredictable.14 Tissue Doppler–derived mitral E/Ea has been compared with BNP and was found to have a higher accuracy in predicting elevated PCWPs.15 Impedance Cardiography. Impedance cardiography (ICG) is a cardiac monitoring technology that provides a beat-by-beat estimate of hemodynamic parameters based on noninvasive measurement. The proprietary measurement BioZ (CardioDynamics, San Diego, CA) is one such method that can estimate parameters such as stroke volume, cardiac output, contractility, systemic vascular resistance, and thoracic fluid content in outpatient and inpatient settings. ICG is a conceptually old technology, dating back to 1940,16 and has been described during its development.17 ICG is relatively easy to use and is used in clinics and intensive care unit settings where it can be a useful surrogate for a PAC,18 assisting in medical decision making, without necessitating the invasive nature of the PAC. A meta-analysis of studies correlating cardiac output measurements using ICG with other standard techniques shows good correlation.19 fluid monitoring in CHF

The recently completed Prospective Evaluation and Identification of Cardiac Decompensation by ICG Test (PREDICT)20 showed the predictive power of ICG in identifying HF patients at risk for recurrent decompensation. Three hemodynamic parameters (velocity index, thoracic fluid content index, and left ventricular ejection time) from the BioZ ICG monitor independently predicted an event within 14 days of assessment (P=.0002). While this technology is exciting, it still necessitates that the patient be physically present in the clinic to be used and has not been prospectively evaluated in large treatment trials. Radiographic Methods. Radiographic findings of CHF may be present during exacerbation. The typical findings of perivascular congestion, Kerley B lines, effusions, and fulminant edema are definitive in their diagnosis of congestion. Their absence, however, is not a reliable method for assessing volume status. Even in patients with markedly elevated PCWP, radiographic evidence of congestion may be absent in one-half of patients.6 Daily Weights. The most common avenue for the evaluation of fluid

status is the use of scales to monitor weight changes. This can be done by the patient but requires that the patient call with changes. There are now several methods of weight monitoring that utilize the remote monitoring paradigm either with implantable devices (Latitude patient management system; Boston Scientific Corporation, Natick, MA; see Figure 1 for an example of report) or nonimplantable device monitoring systems. The data behind the use of these systems is surprisingly robust, with demonstrable improvements in mortality rates seen with the simple reporting of weight increases to health care professionals.21 A recently published European trial (The Trans-European Network Homecare Monitoring Study [TENHMS])22 demonstrated that patients randomized to home telemonitoring of weight, blood pressure, heart rate and rhythm had lower mortality rates than usual care patients. While extremely helpful, weight measurements can lead to inaccurate fluid assessment due to variations of percentage of body fat. In end-stage HF, cardiac cachexia and edema can occur, allowing for stable weight with worsening symptoms and fluid overload. As the patient improves, they may become may . june 2008

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dehydrated due to working to maintain a specific weight as they are actually putting on body fat.

Newer Methods Currently Under Evaluation: Monitoring Fluid With Implantable Devices

Figure 2. Thoracic impedance monitor (Medtronic, Minneapolis, MN). This report highlights the importance of consideration of all aspects of the patient’s condition, including arrhythmia data. This is an 87-year-old woman with New York Heart Association class III congestive heart failure who presented to the clinic with increased leg swelling. Review of her impedance reports shows a precipitous decline in her impedance.

Figure 3. Cardiac compass report (Medtronic, Minneapolis, MN). A further look at this patient shows that the decline occurred in proximity to the start of atrial fibrillation. In this case, onset of atrial fibrillation preceded weight gain, and the patient may benefit from restoration of sinus rhythm or better rate control.

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Intracardiac devices are almost inevitably the future method for monitoring volume status. There has been a dramatic increase in the number of data available to manage patients based on real-time physiologic data. Devices can provide data about arrhythmias, activity levels, and now markers for volume overload. Devices have the capacity to transmit data to the Internet for potentially specialized management by physicians. These features allow the patient to be monitored without a face-to-face interaction. Their integration into health care is in its infancy but will likely become very significant. Intrathoracic Impedance. A feature that measures intrathoracic impedance, now included in several devices, was recently released to the market (OptiVol; Medtronic, Inc, Minneapolis, MN, see Figure 3). The idea is similar to bioimpedance; however, the device measures impedance from implanted leads from the tip of the lead to the can or generator multiple times per day. Impedance can be tracked over time, giving an indication of intrathoracic fluid content, establishing normal values for the patient (Figure 2). The initial publication describing the use of the feature showed significant impedance reduction, which can indicate fluid accumulation, occurring 15 days before onset of symptoms.23 There are limited data on the use of this device, although larger studies are forthcoming. A prospective unblinded study in Europe looked at the utility of this device using an alarm to alert the patient when the thoracic impedance significantly dropped.24 The sensitivity of the device was 62%, with 1.5 false-positive results per patient-year.

Even in the case of false-positives, 55% of events had an identifiable reason for decreased impedance, including atrial fibrillation, pneumonia, and lead dislodgement. Another study has found that the feature is very sensitive but may benefit from a higher threshold to balance sensitivity and specificity.25 The intriguing aspect of this device is its ability to offer providers with information about the patient’s status when they are not in the clinic or at home via the use of remote monitoring. Care pathways have been described to help integrate this data into the clinic.26 This is the first device on the market to allow invasive fluid monitoring without the patient’s presence in the clinic. Implantable Hemodynamic Monitor. A device under investigation (Chronicle implantable hemodynamic monitor; Medtronic, Inc, Minneapolis, MN) provides information similar to that obtained from a PAC. The device has been validated with regard to reproducibility of data obtained compared with right-sided heart catheterization over time27 and reproducibility of implant (similar to standard pacemaker implant with regard to duration, complications, and safety).28 The device monitors right ventricular systolic and diastolic pressures, maximum change in pressure over time (dp/dt), estimated pulmonary diastolic pressure (a surrogate that correlates with PCWP), heart rate, and patient activity (Figure 4). These measures may be used to monitor intracardiac pressures in the outpatient setting or even during acute exacerbations. Pressure increases were noted before exacerbations leading to hospitalization, often several days before clinical events.29 The Chronicle Offers Management to Patients With Advanced Signs and Symptoms of Heart Failure (COMPASS-HF) trial,30 a prospective evaluation of this technology, showed a 22% decrease in hospitalizations while using the device but failed to meet the primary end point may . june 2008

of HF hospitalizations, emergency department visits, and urgent clinic visits. This was thought to be due to the lower than expected event rate in both groups. These findings led the US Food and Drug Administration to deny initial approval of the device. In subgroup analysis, however, the number of hospitalizations was significantly decreased and, in NYHA class III patients, the primary end point was achieved. The use of this device in monitoring volume status has been described during withdrawal of diuretics during a 2-week course.31 Increases in intracardiac pressures were noted upon withdrawal of medications in NYHA class II patients. This finding highlights the potential of this technology in both the management of the “usual” disease state and concurrent illnesses. Research on the utilization of this device in the management of HF is ongoing. Currently, the device is being evaluated in combination with an implantable cardioverter-defibrillator. This, however, excludes patients with diastolic dysfunction. These 2 devices herald a new era in volume management. The technology is promising, and the integration of this information may revolutionize HF management by finding changes in volume status before decompensation. Physicians may choose to manage patients with fewer visits, although this has not yet been evaluated in any of the current studies. Additional novel systems are being developed, including permanently implanted left atrial pressure monitors and pulmonary venous monitors. These devices will continue to change the way that we monitor volume status in the coming years.

Conclusions

HF patients are complex to treat, and adequate assessments of fluid status by physical examination alone can be difficult, especially in the growing population of obese patients and patients with lung disease. Today, physical examination remains the fluid monitoring in CHF

Figure 4. Example of implantable hemodynamic monitoring tracing (Medtronic, Minneapolis, MN). This report shows an example of the pressure tracing seen in the right ventricular (RV) outflow tract of an implantable hemodynamic monitor.

primary means of assessment of HF. This, however, requires the patient to make frequent trips to the physician’s office for volume assessment. Currently, daily weight measurements function as the primary outpatient management tool. As newer methods for remotely following volume status become available and prospectively validated, the hope is that these data, along with weight, can complement our current practices and allow us to be notified of problems between visits, before patients require hospitalization. This information will not negate the need for HF physicians, but will hopefully allow us to help manage a growing number of HF patients with a limited number of HF physicians. It is likely that the workload can

be addressed by training physician extenders to interpret the growing number of data remotely obtained between visits. In this way, the data that are supposed to help streamline these complicated issues will not overwhelm us. The management of volume status in these patients is crucial. We have progressed from the days of inserting tubes into the legs of patients. The challenge ahead lies in ensuring that we harness available technology to treat patients in a manner that benefits them and their providers in the most effective ways. Disclosures: Dr Germany has received research grants and honoraria and is a consultant for Medtronic, Inc. Dr Murray is a consultant for Medtronic, Inc. may . june 2008

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