Automatic Remote Monitoring of Implantable Cardiac Devices in Heart Failure: the TRUST Trial

DOI: 10.19102/icrm.2010.010904

NIRAJ VARMA, MA, DM, FRCP

Cardiac Pacing and Electrophysiology, Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, OH

ABSTRACT. Cardiac implantable electronic devices are increasing in prevalence. Post-implant follow-up is important for monitoring both device function and patient condition. However, practice is inconsistent. For example, implantable cardiac device follow-up schedules vary, e.g. from 3-monthly to yearly according to facility and physician preference and availability of resources. Importantly, no surveillance occurs between follow-up visits. In contrast, implantable devices with automatic remote monitoring capability provide a means for performing constant surveillance, with the ability to identify salient problems rapidly. Recent trials demonstrated that remote home monitoring reduced clinic burden and permitted early detection of patient and/or system problems, i.e. enabling efficient monitoring and an opportunity to enhance patient safety. This has significant implications for management of patients receiving all forms of cardiac implantable electronic devices.

KEYWORDS. cardiac implantable electronic devices, early detection, follow-up, ICD, recall management, remote monitoring.

Dr. Varma reports being Principal Investigator of the TRUST Trial.
Manuscript submitted August 9, 2010, final version accepted August 19, 2010.
Address correspondence to: Niraj Varma, MA, DM, FRCP, Cardiac Electrophysiology, Cleveland Clinic, Cleveland, OH 44195. E-mail: varman@ccf.org

Introduction

The implantation of cardiac electronic devices has increased exponentially over the last decade in response to widening indications.¹ Subsequent monitoring is an integral part of both device and patient but remains unguided by any prospectively derived data. Consensus suggests that patients with implantable cardiac devices (ICDs) should report for routine face-to-face clinic checks every 3–6 months. This generates a huge clinical burden.² Symptomatic events (e.g. shock therapy) prompt additional encounters including unscheduled office/emergency room (ER) visits or even hospitalization. The volume of unscheduled encounters periodically increases, for example, when a device reaches elective replacement indicator or in response to product advisories. A major limitation of this conventional follow-up method based on patient presentation is that there is no monitoring at other times, i.e. the majority of the time. Hence, important diagnostic data such as system problems and onset of atrial fibrillation (AF), particularly if asymptomatic, may remain concealed for extended periods. Remote monitoring may be a mechanism for performing intensive device surveillance and reporting important information rapidly, without over-burdening device clinics.

Remote monitoring

Available technologies have different operating philosophies. Wand-based systems require patient-driven downloads relayed via telephone connections to following facilities.^3,4 This time-consuming process may be cumbersome to use, challenges compliance, and remains vulnerable to overlooking asymptomatic events. This technology may fail to reduce cardiac-related resource utilization.⁵ In contrast, an automatic transmission mechanism fully independent of patient or physician interaction has considerable advantages. It implements the use of automatic (wireless or landline-based) data transmissions, which may be reviewed securely via the internet (Figure 1). This form of technology was pioneered by Biotronik (Berlin, Germany; home monitoring: HM, FDA approved 2002). Reliability, data fidelity, and early notification ability of this communication system were excellent.⁶ System operation is not energy costly. Remote monitoring with instantaneous event transmission, without any patient or nurse involvement, has the ability to maintain surveillance and rapidly bring to attention significant data, enabling clinically appropriate intervention. This capability has been tested in recent trials.

Figure 1: Home monitoring technology.

Top: Transmission steps. A very low-power radiofrequency transmitter circuitry is integrated within the pulse generator, wirelessly transmitting stored data on a daily basis to a mobile communicator (typically placed bedside at night). The data are relayed wirelessly or via landline (automatically seeking the first path available) to a service center. The wireless transmission ability is especially useful as almost 20% (and increasing) of US households are currently estimated to have no landline facility. The service center receives incoming data and generates a customized summary (Cardioreport) available to the physician online via secure internet access. Thus, daily patient monitoring occurs with trend analysis information of typical follow-up data, e.g. battery status, lead impedance, and sensing function. Service center processing and data upload on the home monitoring (HM) webpage is automatic, bypassing potential delays (and errors) associated with manual processing. Critical event data may be transmitted immediately and flagged for attention on the HM webpage (see also Figure 2). Automatic alerts occur for silent but potentially dangerous events and include transmission of intracardiac electrograms (IEGM-Online snapshots) similar to those available during office device interrogations. This provides the ability for early detection enabling prompt clinical intervention if necessary (compiled with permission from⁷).

Bottom Left: A feasibility study demonstrated that >90% of transmissions were received in <5 min with 100% preservation of data integrity (compiled with permission from⁶).

Bottom Right: Event notifications are programmable according to need, and reprogramming may be performed online without the need for patient attendance. For example, if atrial fibrillation becomes permanent, then this feature may be disabled, preventing unnecessary daily notifications. Although an event notification may be potentially triggered every day, in practice such messages occurred infrequently.^32,33

The TRUST (The Lumos-T Safely Reduces Routine Office Device Follow-Up) trial has been the only published prospective multicenter clinical study to assess follow-up, both conventionally and with remote monitoring using HM.^7,8 Patients (1,516) enrolled at 105 US sites were randomized to conventional care (HM off) or to remote monitoring (HM on) groups (Figure 2). The results demonstrated that:

HM reduced healthcare utilization by approximately 50% as measured by the total of scheduled and unscheduled (ER visits, patient- or physician-initiated checks) hospital evaluations. This is because the bulk of scheduled encounters involve collection of routine measurements only (e.g. battery status, lead impedance, and sensing function) requiring no clinical intervention (reprogramming, alteration of antiarrhythmic medications), and may be performed by online data review.
Importantly, the reduction in face-to-face visits was accomplished safely, as there were no differences between the two study arms for death, incidence of strokes, and events requiring surgical interventions (e.g. device explants or lead revision).
HM permitted earlier detection and physician evaluation (median <3 days) of cardiac and/or device problems (despite fewer face-to-face encounters) compared to >1 month with conventional care.
HM secured greater follow-up adherence to 3-monthly calendar-based checks. This is presumably because patient data may be monitored remotely anytime and from anywhere, as opposed to the conventional arm, which relies on patients to present themselves physically at their physician’s office.

Figure 2: The TRUST Trial.

Top: After randomization, all implantable cardiac device (ICD) patients had scheduled follow-ups at 3, 6, 9, 12 and 15 months post implant, and unscheduled (interim) evaluations as needed. Patients in conventional care were evaluated in-hospital only. Home monitoring (HM) patients had HM checks followed by office visits at 3 and 15 months. At 6, 9, and 12 months and for interim visits, data were remotely retrieved and evaluated. Between these periodic checks, automatic event notifications were evaluated online, and patients were brought in for office visits if deemed necessary by the investigator.

Bottom Left: HM reduced cardiac-resource utilization, i.e. scheduled and unscheduled clinic and hospital visits (including responses to HM event notifications), were reduced by 45% in 1 year.

Bottom Right: Time to physician evaluation of arrhythmias was <48 h in HM, including silent events (compiled from⁸).

These results indicate that remote monitoring may be adopted as an instrument for device management performing intensive surveillance, substituting for in-office follow-up but also fulfilling the important role of a mechanism for early detection. Management of unscheduled checks may be also facilitated. For example, with patient inquiries, shock data and online electrogram are available and may be used to determine best management confidently. An appropriate shock may require reassurance only without the need for a hospital visit. In contrast, a series of inappropriate shocks may be rapidly evaluated online and the patient would be asked to come in to the hospital promptly. The capacity for early detection is exceptionally valuable for detection of silent events. Potentially dangerous asymptomatic events that typically remain concealed in diagnostic memory and manifest only at formal interrogation may be revealed within hours by automatic HM and direct clinical intervention^6,9,10 (Figures 3 and 4).

Figure 3: Home monitoring generator coupled to a Medtronic (Minneapolis, MN) Fidelis (MDT 6949) lead. Two event notifications were transmitted immediately on occurrence of lead fracture, occurring silently during sleep at 4:43 am, 6 weeks after last clinic follow-up on November 14 (compiled with permission from¹⁰).

Left Panel: Two occurrences of detection in ventricular fibrillation (VF) zone are noted (top) and flagged (red exclamation mark on yellow background). The accompanying wirelessly transmitted electrogram demonstrated irregular sensed events (markers indicate coupling intervals as short as 78 ms) with VF detection (marked). No therapy was delivered, indicating spontaneous event termination. (Electrogram definition is modest in first generation devices with wireless intracardiac electrogram transmission (Lumos). Current generation devices transmit electrograms with improved resolution (1/128 s) and longer duration (e.g. Figure 5) including post-detection sequences⁹.

Right Panel: The second event report is a separate notification in response to the same event indicating a lead impedance alert. Lead impedance trend had been stable below 600 Ohms in prior weeks but then suddenly increased >500 Ohms, triggering an event notification (red), although this absolute value still remained within specifications. The clinic received these notices and informed the patient, who was then reviewed urgently within 24 h and treated with lead extraction and replacement. The case demonstrates the value of remote monitoring with daily automatic surveillance and rapid, automatic (i.e. without patient participation) event notification to the clinic of fault detection, which enabled prompt intervention. The addition of non-sustained ventricular tachycardia events to the impedance deviation improves the specificity of detection of lead failure³⁴. Without home monitoring, presentation may have occurred later with inappropriate shocks or catastrophically with failure of pacing or VF sensing.

Figure 4: Middle-aged male with ischemic cardiomyopathy and left bundle branch block treated with a cardiac resynchronization therapy device. He had had several bouts of atrial fibrillation (AF) requiring cardioversion and then had been maintained on dofetilide. The patient had felt lassitude and worsening shortness of breath in the face of unchanged daily weights or worsening edema for several weeks. However, he contacted providers late only when fluid congestion started to occur. At outpatient evaluation, he was found to have both AF and congestive heart failure (HF) and was admitted for treatment with diuretics.

Device interrogation revealed several notable features. The patient had developed persistent AF (AF h/day) prior to development of HF symptoms. Note initiation towards the end of June (first vertical blue dashed line) marked by withdrawal of atrial pacing, although presentation with clinical decompensation occurred 6 weeks later in August. A steeper rate of deterioration in parameters is marked by the second vertical blue dashed line in the 2–3 weeks preceding hospitalization. These were characterized by longer bursts of accelerated ventricular rates, greater loss of biventricular pacing to approximately 80% (arrow), diminished patient activity, and progressively increasing intrathoracic impedance (Optivol fluid index). This is derived from the difference between the daily and reference intrathoracic impedance (bottom graph) and may reflect accumulation of fluid in the thorax.

Prompt resolution in all these parameters occurred after treatment of AF. He was treated with diuretics and cardioverted. Subsequently, he relapsed with similar episodes of acute decompensated heart failure (ADHF) precipitated by AF and underwent ablative therapy for AF. His condition stabilized.

The TRUST management protocol received FDA approval in May 2009 and has been adopted by several large volume centers. (The follow-up scheme described is for device management and not intended to replace consultations with internists, cardiologists, or heart failure [HF] specialists, which may otherwise occur.) Reimbursement guidelines were instituted in January 2009 in the USA by the Centers for Medicare and Medicaid Services. Three-monthly checks performed remotely are reimbursed. Between these, additional remote interrogations performed within the 90-day “global period” are only reimbursed if the evaluation prompted an in-office evaluation and device reprogramming.

Emerging applications

Lead and device performance

Assessment of post-implant system performance is an important responsibility, but challenging in view of increasing volume, device complexity, and advisory notices. Management of components under advisory notices poses several daunting challenges. Intensive monitoring by increasing office visits (e.g. monthly) is impractical, onerous, and inefficient (as problem incidence is very low), and is likely to fail to detect potentially catastrophic problems occurring between interrogations.^11,12 Remote monitoring systems relying on patient-driven communication may be similarly limited in ability to detect asymptomatic failure.

In contrast, HM technology, which provides constant surveillance of system integrity with automatic alerts, eliminates the burden of patients having to monitor their own devices frequently and coordinate with clinic services. TRUST demonstrated that conventional monitoring methods under-reported device-related problems.¹³ HM, in contrast, enhanced discovery of system issues (even when asymptomatic) and enabled prompt clinical decisions regarding conservative versus surgical management. Performance problems were often asymptomatic. Figure 3 illustrates the benefit of HM in the management of recalled components.^10,14

Thus, the call for intensive and comprehensive monitoring of implantable devices may be met by remote monitoring technology.^14,15 The ability to collect detailed device-specific data, with component function assessed daily and automatic archiving, sets a precedent for longitudinal evaluation of lead and generator performance.

Monitoring disease progression

Recipients of ICD therapy commonly have HF, which is a dynamic condition. Hospitalizations for acute decompensated heart failure (ADHF) have more than doubled in the last 20 years, and continue to increase.¹⁶ Rehospitalization is an independent predictor of 1-year mortality, especially in elderly patients,^17,18 with significant fiscal repercussions for health-care services.

The development of ADHF is complex, involving several processes (e.g. hemodynamic, neurohumoral, electrophysiological, and vascular abnormalities) that converge to manifest with fluid congestion. After hospitalization, management is directed to identification and correction of precipitating factors and comorbidities, and management of fluid overload, arrhythmias, and any conduction system problems. Therapeutic strategies aimed at interrupting this train of events are potentially valuable. This may be possible as, in most cases, pathophysiologic processes progress over days to weeks prior to clinical presentation with a fluid-overloaded state. However, the initial inciting event(s) are varied and their early detection challenging as they are generally asymptomatic. Implantable devices that collect, quantify, and trend important data may permit identification of upstream factors, triggering HF deterioration, and facilitate diagnosis and direct appropriate treatment. Figure 4 illustrates how the interplay of asymptomatic events (AF and lack of biventricular pacing in this case) contributed to HF decompensation, and also the length of time taken from inciting events to clinical presentation.

As HF precipitants act to produce fluid congestion, which ultimately is the basis of clinical presentation with dyspnea or peripheral edema, attention has centered on identifying fluid excess itself. Intrathoracic impedance (illustrated in Figure 4) correlated inversely with pulmonary capillary wedge pressures¹⁹ and began to change approximately 2 weeks before hospitalization for ADHF. Early action taken in response to such data tended to reduce HF hospitalizations.²⁰ Further developments include miniature fully implantable devices for pulmonary artery pressure monitoring,²¹ direct left atrial pressure monitoring,²² and impedance vectors employing a left ventricular lead only.²³ To be effective, these sensors need to have a high predictive value for ADHF requiring hospitalization, and also enable implementation of a treatment algorithm that may prevent hospitalization. Application of stand-alone technology for long-term management of a large number of patients with HF in whom conventional devices are not currently indicated requires prospective evaluation.

All pre-emptive strategies designed to prevent ADHF hinge on early evaluation of deviation of studied parameter(s) from baseline values. Problem detection by an implanted device without concomitant physician notification is ineffective for enabling early therapeutic intervention. Intensive patient surveillance with increased frequency of physician–patient face-to-face encounters is generally not feasible, and in any case no monitoring takes place between hospital visits, i.e. most of the time. In this regard, the results of TRUST are important. TRUST demonstrated that remote monitoring may be adopted as an instrument for efficient management of a large patient volume with implanted devices, performing intensive surveillance and reducing unnecessary routine evaluation, while acting as an early detection mechanism to enable earlier evaluations of patients when necessary. These characteristics are suited to managing HF patients. The ability to generate individually based parameter trends and self-declare out-of-range asymptomatic events is critical to allow timely intervention. For instance, as illustrated in Figure 4, notification of AF, loss of cardiac resynchronization therapy (CRT), and deviation of fluid sensor index all occurred asymptomatically well in advance of ADHF presentation. All would have flagged immediate event notifications if the implanted device had been equipped with an automatic remote monitoring mechanism and had enabled early pre-emptive therapy. Alternatively, following physicians may have reviewed and quantified trended data in these higher-risk patients and identified important deviations of single or combined trends.¹⁰ Thus, remote monitoring may be the instrument to provide sentinel notification of conditions leading to decompensation and thus prompt rapid pre-emptive therapy to prevent hospitalizations. This is being assessed in prospective studies.²⁴

Arrhythmias

AF in HF patients may be associated with increased morbidity and mortality.^25,26 This is likely to be multifactorial, involving increased risk of stroke and of HF (Figure 4). Rapid ventricular conduction may diminish the intended beneficial effect of CRT (reduced when pacing is diminished to <92%²⁷) and also lead to inappropriate therapy. AF facilitates ventricular arrhythmias, and prompt termination of atrial tachyarrhythmia was found to significantly delay the time to the next episode of ventricular tachycardia (VT)/ventricular fibrillation (VF).²⁸ Early treatment of AF may be beneficial but is difficult because most AF is clinically silent. However, early detection of AF by HM was demonstrated in the TRUST trial (Figure 2). Automatic databasing permits evaluation of AF burden and frequency of episodes (Figure 5), which may have a bearing on risks posed by this arrhythmia. Non-sustained VT may indicate future sustained therapy, which may result in shock delivery.⁹ This is important because emerging data indicate that shock delivery may have deleterious long-term consequences.^29,30 Minimizing inappropriate therapy by early identification of atrial arrhythmias and non-sustained ventricular arrhythmias, and maximizing appropriate therapy by evaluating efficacy of drugs and other treatments are important potential benefits of remote monitoring.^6,9

Figure 5: Left Panels: Trend of cardiac resynchronization therapy (CRT) pacing. Loss of pacing is event notified (red dots), resulting in a clinic evaluation (FU) and therapy. CRT pacing resumes at >95% (black dots).

Right Panel Top: Event notification of atrial fibrillation (top) with accompanying wirelessly transmitted intracardiac electrograms.

Bottom: A patient’s AF history may be reviewed on the webpage (bottom). Frequency and duration of mode switches and simultaneous mean ventricular rate data are presented as graphic trends over time. Three paroxysmal AF episodes occurring over 29 days are illustrated. Although >50 mode switches (triangles) are recorded during each episode, the mode switch duration (circles) is <20%, indicating a light overall AF burden for these particular events. The three paroxysmal AF episodes are each accompanied by simultaneous increases in mean ventricular heart rates (compiled with permission from⁶).

Future

Remote monitoring provides the mechanism for accessing and delivering prioritized data collected by increasingly sophisticated implantable units. Access to internet-based information systems provides a framework for multidisciplinary communication and collaboration, such as electrophysiologists monitoring device function (e.g. arrhythmias, paced burden) and HF experts assessing diagnostic information regarding HF. Information sharing and multidisciplinary effort aided patient care when applied to a CRT optimization clinic.³¹ This practice may be facilitated by remote monitoring interfacing with electronic medical records, thus placing all relevant data in a single central database accessible by all treating physicians.

In summary, automatic remote HM fulfills the aims of post-implant device management. TRUST presents a device management model in which near continuous remote surveillance maintains continuity of follow-up and combines with automatic self-declaration of problems, identifying the exceptional group of patients requiring in-clinic attention. Thus, unnecessary in-office follow-up is avoided, and necessary face-to-face encounters facilitated. This reduces clinic load for the physician but permits earlier attention to actionable events. Patient safety and convenience are improved. Automatic data archiving provides a resource for monitoring system performance and disease progression. In congestive HF patients, there is high value to a mechanism providing early identification of problems that could, if managed expeditiously, prevent patient morbidity and hospitalization. The characteristics of remote HM demonstrated in the TRUST trial have significant ramifications for cardiac implantable electronic devices in general and patient care.

References

Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol 2008; 51:e1–e62. [CrossRef] [PubMed]
Wilkoff BL, Auricchio A, Brugada J, et al. HRS/EHRA expert consensus on the monitoring of cardiovascular implantable electronic devices (CIEDs): description of techniques, indications, personnel, frequency and ethical considerations. Heart Rhythm 2008; 5:907–925. [CrossRef] [PubMed]
Schoenfeld MH, Compton SJ, Mead RH, et al. Remote monitoring of implantable cardioverter defibrillators: a prospective analysis. Pacing Clin Electrophysiol 2004; 27:757–763. [CrossRef] [PubMed]
Joseph GK, Wilkoff BL, Dresing T, Burkhardt J, Khaykin Y. Remote interrogation and monitoring of implantable cardioverter defibrillators. J Interv Card Electrophysiol 2004; 11:161–166. [CrossRef] [PubMed]
Al-Khatib SM, Piccini JP, Knight D, Stewart M, Clapp-Channing N, Sanders GD. Remote monitoring of implantable cardioverter defibrillators versus quarterly device interrogations in clinic: results from a randomized pilot clinical trial. J Cardiovasc Electrophysiol 2010; 21:545–550. [CrossRef] [PubMed]
Varma N, Stambler B, Chun S. Detection of atrial fibrillation by implanted devices with wireless data transmission capability. Pacing Clin Electrophysiol 2005; 28 Suppl 1:S133–S136. [CrossRef] [PubMed]
Varma N. Rationale and design of a prospective study of the efficacy of a remote monitoring system used in implantable cardioverter defibrillator follow-up: the Lumos-T Reduces Routine Office Device Follow-Up Study (TRUST) study. Am Heart J 2007; 154:1029–1034. [CrossRef] [PubMed]
Varma N, Epstein A, Irimpen A, Schweikert R, Shah J, Love CJ. Efficacy and safety of automatic remote monitoring for ICD follow-up: the TRUST trial. Circulation 2010; 122:325–332. [CrossRef] [PubMed]
Varma N, Johnson MA. Prevalence of cancelled shock therapy and relationship to shock delivery in recipients of implantable cardioverter-defibrillators assessed by remote monitoring. Pacing Clin Electrophysiol 2009; 32 Suppl 1:S42–S46. [CrossRef] [PubMed]
Varma N. Remote monitoring for advisories: automatic early detection of silent lead failure. Pacing Clin Electrophysiol 2009; 32:525–527. [CrossRef] [PubMed]
Medtronic. Physician Advisory Letter: Urgent Medical Device Information Sprint Fidelis^® Lead Patient Management Recommendations. 2007.
Kallinen LM, Hauser RG, Lee KW, et al. Failure of impedance monitoring to prevent adverse clinical events caused by fracture of a recalled high-voltage implantable cardioverter-defibrillator lead. Heart Rhythm 2008; 5:775–779. [CrossRef] [PubMed]
Varma N, Michalski J, Epstein A, Schweikert R. Automatic remote monitoring of ICD lead and generator performance: The TRUST Trial. Circ Arrhythm Electrophysiol 2010; Epub ahead of print. [CrossRef] [PubMed]
Carlson MD, Wilkoff BL, Maisel WH, et al. Recommendations from the Heart Rhythm Society Task Force on device performance policies and guidelines endorsed by the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) and the International Coalition of Pacing and Electrophysiology Organizations (COPE). Heart Rhythm 2006; 3:1250–1273. [CrossRef] [PubMed]
Maisel WH, Hauser RG, Hammill SC, et al. Recommendations from the Heart Rhythm Society Task Force on lead performance policies and guidelines: developed in collaboration with the American College of Cardiology (ACC) and the American Heart Association (AHA). Heart Rhythm 2009; 6:869–885. [CrossRef] [PubMed]
Rosamond W, Flegal K, Friday G, et al. Heart disease and stroke statistics–2007 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation 2007; 115:e69–e171. [CrossRef] [PubMed]
Pulignano G, Del Sindaco D, Tavazzi L, et al. Clinical features and outcomes of elderly outpatients with heart failure followed up in hospital cardiology units: data from a large nationwide cardiology database (IN-CHF Registry). Am Heart J 2002; 143:45–55. [CrossRef] [PubMed]
Blackledge HM, Tomlinson J, Squire IB. Prognosis for patients newly admitted to hospital with heart failure: survival trends in 12 220 index admissions in Leicestershire 1993–2001. Heart 2003; 89:615–620. [CrossRef] [PubMed]
Yu CM, Wang L, Chau E, et al. Intrathoracic impedance monitoring in patients with heart failure: correlation with fluid status and feasibility of early warning preceding hospitalization. Circulation 2005; 112:841–848. [CrossRef] [PubMed]
Bourge RC, Abraham WT, Adamson PB, et al. Randomized controlled trial of an implantable continuous hemodynamic monitor in patients with advanced heart failure: the COMPASS-HF study. J Am Coll Cardiol 2008; 51:1073–1079. [CrossRef] [PubMed]
Hoppe UC, Vanderheyden M, Sievert H, et al. Chronic monitoring of pulmonary artery pressure in patients with severe heart failure: multicentre experience of the monitoring Pulmonary Artery Pressure by Implantable device Responding to Ultrasonic Signal (PAPIRUS) II study. Heart 2009; 95:1091–1097. [CrossRef] [PubMed]
Ritzema J, Melton IC, Richards AM, et al. Direct left atrial pressure monitoring in ambulatory heart failure patients: initial experience with a new permanent implantable device. Circulation 2007; 116:2952–2959. [CrossRef] [PubMed]
Khoury DS, Naware M, Siou J, et al. Ambulatory monitoring of congestive heart failure by multiple bioelectric impedance vectors. J Am Coll Cardiol 2009; 53:1075–1081. [CrossRef] [PubMed]
Arya A, Block M, Kautzner J, et al. Influence of home monitoring on the clinical status of heart failure patients: design and rationale of the IN-TIME study. Eur J Heart Fail 2008; 10:1143–1148. [CrossRef] [PubMed]
Ehrlich JR, Hohnloser SH. Milestones in the management of atrial fibrillation. Heart Rhythm 2009; 6:S62–S67. [CrossRef] [PubMed]
Bunch TJ, Day JD, Olshansky B, Stolen KQ, Mullin CM. Newly detected atrial fibrillation in patients with an implantable cardioverter-defibrillator is a strong risk marker of increased mortality. Heart Rhythm 2009; 6:2–8. [CrossRef] [PubMed]
Koplan BA, Kaplan AJ, Weiner S, Jones PW, Seth M, Christman SA. Heart failure decompensation and all-cause mortality in relation to percent biventricular pacing in patients with heart failure: is a goal of 100% biventricular pacing necessary? J Am Coll Cardiol 2009; 53:355–360. [CrossRef] [PubMed]
Stein KM, Euler DE, Mehra R, et al. Do atrial tachyarrhythmias beget ventricular tachyarrhythmias in defibrillator recipients? J Am Coll Cardiol 2002; 40:335–340. [CrossRef] [PubMed]
Poole JE, Johnson GW, Hellkamp AS, et al. Prognostic importance of defibrillator shocks in patients with heart failure. N Engl J Med 2008; 359:1009–1017. [CrossRef] [PubMed]
Sweeney MO, Sherfesee L, Degroot PJ, Wathen MS, Wilkoff BL. Differences in effects of electrical therapy type for ventricular arrhythmias on mortality in implantable cardioverter-defibrillator patients. Heart Rhythm 2010; 7:353–360. [CrossRef] [PubMed]
Mullens W, Grimm RA, Verga T, et al. Insights from a cardiac resynchronization optimization clinic as part of a heart failure disease management program. J Am Coll Cardiol 2009; 53:765–773. [CrossRef] [PubMed]
Varma N, Epstein A, Irimpen A, Gibson L, Love CJ. Event notifications by remote monitoring systems performing automatic daily checks: load, characteristics and clinical utility. Eur Heart J 2009; 30:1909.
Theuns DA, Rivero-Ayerza M, Knops P, Res JC, Jordaens L. Analysis of 57,148 transmissions by remote monitoring of implantable cardioverter defibrillators. Pacing Clin Electrophysiol 2009; 32 Suppl 1:S63–S65. [CrossRef] [PubMed]
Gunderson BD, Swerdlow CD, Wilcox JM, Hayman JE, Ousdigian KT, Ellenbogen KA. Causes of ventricular oversensing in implantable cardioverter-defibrillators: implications for diagnosis of lead fracture. Heart Rhythm 2010; 7:626–633. [CrossRef] [PubMed]