Implantable Hemodynamic Monitoring in Heart Failure

Implantable cardiac pacemakers were originally designed to support critical heart rate abnormalities. As this indication has successfully been realized, the number, type, diagnostic capability and complexity of these devices have been significantly expanded. Protection from sudden cardiac arrest is recognized with the advent of implantable cardioverter defibrillators (ICDs), and an increased survival rate has been proven with the introduction of a third lead with cardiac resynchronization (CRT). Physiological parameters that lend evidence to a patient’s fluid status can now be collected in patients who are receiving an ICD or CRT implant. Decompensated heart failure (HF) resulting in hospitalization is associated with significant morbidity, mortality and cost.¹ The American Heart Association (AHA) estimates that approximately 5 million people in the United States have heart failure, with >500,000 new cases each year.² Approximately $30 billion is spent in the US on the direct and indirect costs of managing heart failure. The average readmission rate within 60 days of a hospitalization for HF is 20–25%. Therefore, it is logical that early detection of symptoms, with subsequent early intervention and prevention of heart failure related hospitalizations, would reduce the economic burden of this chronic disease state on the US healthcare system while also improving the quality of life for those who suffer from this disease. As recommended in the current guidelines, careful surveillance of the fluid status is important in the chronic disease management of HF to maintain fluid balance and to avoid volume expansion.³ Monitoring body weight is the usual method recommended to patients to evaluate fluid changes, but this may have poor sensitivity for clinical deterioration, which can be determined by fluid redistribution rather than quantitative fluid overload.⁴ Lewin et al reported that weight gain has a sensitivity of less than 20% for detecting HF.⁵ Yet we recognize that a reliable method for the early detection and treatment of hemodynamic congestion in HF patients is essential to alleviate symptoms, prevent hospitalizations and halt disease progression, as well as improve functional capacity and quality of life. Moreover, observations suggest that diagnostic parameters such as heart rate variability or intrathoracic impedance change long before weight changes or symptoms worsen.⁶ One such method for detecting pulmonary congestion involves examining changes in transpulmonary electrical impedance. The measurement of impedance in the lung has been recognized for years as a relatively sensitive means for detecting pulmonary congestion. Currently, there are two US FDA-approved systems that are designed to aid clinicians in the detection of thoracic fluid accumulation. Impedance cardiography (ICG) measures thoracic impedance noninvasively by utilizing electrodes placed on the chest. The Prospective Evaluation and identification of Cardiac Decompensation in Patients with HF by ICG Test (PREDICT) study showed a reasonable correlation between changes in transthoracic impedance and clinical signs of pulmonary congestion.⁷ However, transthoracic impedance is greatly affected by different body positions, electrode placement and respiratory movement. OptiVol fluid status monitoring (Medtronic, Minneapolis, MN) represents the application of the concept of transthoracic impedance as a measure of pulmonary fluid status into implantable devices.⁸ Assessment of the intrathoracic impedance is achieved by measuring the device can, which is typically implanted in the left pectoral region, and the lead in the right ventricle. This vector represents much of the left thoracic cavity. The first human study looking at intrathoracic impedance with an implantable device was MIDHeFT (Medtronic Impedance Diagnostics in Heart Failure Trial).⁶ There was an inverse correlation between the intrathoracic impedance and pulmonary capillary wedge pressure or fluid balance (Figure 1; in print journal only). The OptiVol threshold, which is a physician-established measure of fluid accumulation, can be programmed at device implant or at follow-up device checks. If fluid accumulates in a patient’s lungs, the OptiVol fluid index increases. If this persists, the OptiVol fluid index crosses the OptiVol threshold and an observation will be triggered. The Heart Failure Management Report provides 14-month trended information on OptiVol fluid status monitoring as well as other pertinent parameters such as OptiVol fluid index and thoracic impedance, total daily AT/AF time, heart rate variability, average ventricular rate, patient activity, as well as the percentage of time pacing. There are several factors that may affect the reliability of the intrathoracic impedance monitoring. Conditions such as pneumonia, pleural effusions, or other intrathoracic issues can affect impedance measurements. Air volume can affect impedance because air itself is an insulator, and the more air in the lungs, the higher the impedance. Therefore, chronic obstructive pulmonary disease (COPD) patients may alter the impedance measurements. Current evidence indicates that remote surveillance of implanted devices in high-risk HF patients may be associated with a reduction in hospitalizations (29–43%) in comparison with conventional follow-up.^9,10 For more information about OptiVol, please see the example case study in Figure 2 of the print journal. Another implantable hemodynamic monitor, currently being investigated in the LAPTOP-HF (Left Atrial Pressure Monitoring to Optimize Heart Failure Therapy) study, is the HeartPOD™ System (St. Jude Medical, St. Paul, MN), which can be percutaneously implanted inside the left atrium, where it directly measures left atrial pressures (LAP) and can monitor impending decompensation as signaled by rapid increases in pulmonary capillary wedge pressure and left atrial pressure.¹¹ Clinician-directed, patient self-management, which has become standard in diabetes management, is a new approach for HF management. It may provide clinicians the ability to better personalize and optimize HF management on the basis of daily, objective measures of a patient's HF status. By providing patients with daily feedback on their LAP status and automated prescription instructions with a hand-held device, it may also encourage self-management and treatment adherence in a more efficient manner than possible with traditional heart failure management approaches. LAP is considered the “gold standard” for assessing HF status, providing the most objective measure of left-sided hemodynamics. Changes in LAP precede development of fluid in the lungs, and the study is aimed at showing the efficacy of frequent-dose titration on the basis of LAP variation. The CHAMPION (CardioMEMS Heart Sensor Allows Monitoring of Pressure to Improve Outcomes in NYHA Class III Patients) trial met its primary efficacy endpoint with a 30% reduction in heart failure hospitalization rates at 6 months (p 12 Access to the pertinent information, in a timely manner and in the right hands, is imperative to fully realize the clinical potential of using device-based data for heart failure monitoring purposes. A collaborative approach for the ongoing care of this patient population between the implanting electrophysiologist and heart failure specialist is crucial. The process and flow of this information needs to be seamless and fluent. Optimal multidisciplinary management of HF would reduce death and morbidity, and such management requires close monitoring of this patient population to prevent unnecessary decompensation. Implantable hemodynamic devices such as those discussed here can provide a tool to lend to this success.

Disclosures: Dr. Smart has no disclosures to report for the submitted work. Ms. Bonnet has no disclosures to report for the submitted work; she reports that honoraria and travel expenses were covered by Medtronic for a previous OptiVol summit.

References

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2. American Heart Association. Heart Disease and Stroke Statistics—2006 update. AHA, Dallas, Texas, USA.

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5. Lewin J, Ledwidge M, O’Loughlin C, et al. Clinical deterioration in established heart failure: what is the value of BNP and weight gain in aiding diagnosis? Eur J Heart Fail 2005;7:953-957.

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7. Packer M, Abraham WT, Mehra MR, et al. Utility of impedance cardiography for the identification of short term risk of clinical decompensation in stable patients with chronic heart failure. J Am Coll Cardiol 2006;47:2245-2252.

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10. Catanzariti D, Lunat M, Landolina M, et al. Monitoring intrathoracic impedance with an implantable defibrillator reduces hospitalizations in patients with heart failure. Pacing Clin Electrophysiol 2009;32:363-370.

11. Ritzema J, Troughton R, Melton I, et al. Physician-directed patient self-management of left atrial pressure in advanced chronic heart failure. Circulation 2010;121:1086-1095.

12. Donaho EK, Trupp RT. Hemodynamic monitoring in heart failure: A nursing perspective. Heart Failure Clin 2009;5:271-278.