Remote Follow-up of Cardiac Pacing Devices

No other emerging technology associated with implantable cardiac devices has the widespread ramifications that are associated with remote follow-up techniques. Traditionally, information from implanted cardiac devices has been available only to physicians specializing in cardiac devices. Improved technology allows one to think of devices as “health monitors” that can acquire and transfer information from the device itself to an accessible centralized location that could be used by all health care providers and, importantly, by the patient.

Currently, all commercially available cardiac pacemakers have some type of remote monitoring system.² Information stored in the memory of the pacemaker can be downloaded wirelessly to a receiver located in the patient’s home. Both patient-activated downloads and automatic downloads are possible, depending on the manufacturer. Information is transmitted via cell phone or over landlines to a central server that is maintained by the pacemaker manufacturer. This downloaded information can then be accessed via the Internet in a “two-way” manner, initiated by the physician as well as automatically, with automatic alerts sent from the server to the physician. Initial studies have suggested that remote monitoring can identify potential problems more quickly than can in-office or clinic visits.^2,3 In one study of patients with implantable defibrillators, remote monitoring identified lead failure (conductor wire break or insulation breach) 2 months earlier than can standard monitoring; consequently, lead failure–related inappropriate shocks were experienced by only 27% of patients with remote monitoring compared with 53% of patients with traditional follow-up.⁴

Identification of atrial arrhythmias in patients with bradycardia has been shown to provide important prognostic information. In a nested cohort of 312 patients from the Mode Selection Trial (MOST), the presence of a 5-minute or longer episode of atrial tachycardia was associated with an increased risk of death (heart rate [HR], 2.48; confidence interval [CI], 1.25 to 4.91) and development of atrial fibrillation (HR, 5.93; CI, 2.88 to 12.2).⁵ The usefulness of early identification of atrial arrhythmias by remote monitoring in improving clinical outcomes is the subject of several large multicenter trials. Preliminary results from the TRENDS study suggest that atrial fibrillation “burden” (>5.5 arrhythmia hours per day) is associated with a higher thromboembolic rate (2.4% per year) compared with that in patients without atrial arrhythmias identified by the device (1.1%).⁶ Another multicenter study, Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT), has completed its enrollment and will also evaluate whether atrial arrhythmias identified by and stored in the device can identify a group of patients at higher risk for stroke. Coupled with remote follow-up, early documentation of atrial arrhythmias may be beneficial in reducing the incidence of stroke by identifying patients who would benefit from anticoagulant therapy. Figure 38-1 shows an example of a patient with atrial fibrillation and an implanted pacemaker. Interrogation of the pacemaker after ablation of the atrial fibrillation confirms successful elimination of detected episodes of this arrhythmia.

Figure 38-1 A, Electrograms from a patient with episodes of atrial fibrillation. Atrial electrograms reveal rapid and irregular activity (arrows) consistent with atrial fibrillation that terminates at the end of the strip. B, Long-term continuous monitoring from the device confirms elimination of atrial arrhythmias after radiofrequency catheter ablation. AT/AF, Atrial tachycardia/atrial fibrillation; Abl, ablation.

(From Kusumoto FM, Goldschlager: Remote monitoring of cardiac devices, Clin Cardiol 25(2):89–90, 2009.)

Early studies have provided interesting data indicating that device-based hemodynamic monitoring may be beneficial in patients with heart failure. Devices currently in use can estimate patient activity via motion sensors and specific respiratory parameters and can estimate pulmonary venous congestion via intrathoracic impedance measurements.⁷ Fluid accumulation within pulmonary spaces decreases intrathoracic impedance, since fluid offers less resistance to electrical current than does air. In a small clinical study of 33 patients, a decrease in thoracic impedance was observed approximately 2 weeks before hospitalizations for heart failure. An example of the clinical use of intrathoracic impedance is shown in Figure 38-2. In the study, after remote monitoring was initiated, decreased impedance was used along with clinical variables to increase the diuretic dose of a patient with severe systolic dysfunction, which may have prevented rehospitalization.

Figure 38-2 Intrathoracic impedance monitoring in a patient with severe systolic dysfunction. After several hospitalizations for heart failure, remote monitoring (RM) was initiated. During follow-up, decreased intrathoracic impedance was detected via an algorithm as an increase in the “fluid index” during remote monitoring. The patient was contacted by telephone, and after a discussion with the patient, the diuretic dose was increased for 3 days and the fluid index returned to baseline.

(Modified from Kusumoto FM, Goldschlager: Remote monitoring of cardiac devices, Clin Cardiol 25[2]:89–90, 2009.)

Indirect estimates of volume status using technologies such as intrathoracic impedance can be incorporated into any lead-device system, but direct pressure measurements using specialized investigational leads may provide theoretical or real advantages. One lead system uses a specially designed pressure transducer that is placed in the right ventricular outflow tract; the transducer directly measures right ventricular pressure and uses an algorithm to estimate pulmonary artery diastolic pressure (Figure 38-3). Pulmonary artery diastolic pressure, as a correlate of pulmonary capillary wedge pressure, can be used as an estimate of left ventricular preload to guide heart failure management. In addition, the pressure monitor may also be useful in confirming the presence of ventricular arrhythmias by identifying accompanying hemodynamic compromise (Figure 38-4). In the largest study to date, the Chronicle Offers Management to Patients with Advanced Signs and Symptoms of Heart Failure (COMPASS-HF) trial, 274 patients with class III or IV heart failure were randomized to two groups: one in which information was available to clinicians and the other in which clinicians were blinded to hemodynamic data. After a 6-month follow-up, clinical use of a hemodynamic monitor resulted in a nonsignificant 21% reduction in heart failure–related events.⁸ Another specialized lead system under clinical investigation uses a pressure tip placed at the inter-atrial septum to directly measure left atrial pressure.

Figure 38-3 Fluoroscopy of a patient with an investigational single-chamber implantable cardiac device that uses a second lead (arrow) placed in the right ventricular outflow tract; the second lead uses a special sensor, which directly measures right ventricular pressure.

Figure 38-4 A significant drop in right ventricular (RV) pulse pressure (RV systolic – RV diastolic) readings during an episode of ventricular fibrillation (VF) (arrow) that confirms loss of RV pulse pressure caused by hemodynamic compromise during the event.

In addition to intracardiac pressures, new technologies that monitor other non-heart rate–related parameters such as ST-segment deviation and systemic blood pressure are being developed.^8–11 ST-segment changes can be monitored by analyzing the intracardiac electrogram from a tip electrode located in the right ventricle and the device “can.” The device continuously monitors the relationship between the ST segment and the P-Q segment. If a significant shift between the ST segment and the P-Q segment persists for a programmed number of beats, the device can either vibrate or provide an audio alert. In an animal study, changes in the ST segment recorded by implanted leads occurred earlier than in those recorded from surface electrocardiogram (ECG) leads; these changes therefore confer an ability to quickly detect myocardial ischemia in any of the three major coronary arteries. Initial data from experimental studies suggest that systemic blood pressure changes can be estimated by measuring bioimpedance between two electrodes placed in the subcutaneous tissue. Incorporation of this technology into implanted devices may provide a method for monitoring antihypertensive therapy.

It is hoped that freer and more widespread access to medical information by medical providers will improve healthcare outcomes and reduce costs. Implantation of devices will likely be the first clinical field where this information revolution will take place. Current devices provide simple audible alerts when the implanted device detects a potential problem, but it is an easy leap to imagine providing patients with access to information in a simplified and understandable format. In this way, implanted devices coupled with remote follow-up can initiate a major paradigm shift, with patients taking a more active role in their medical care, based on actual data rather than symptoms alone.¹²

Newer Cardiac Pacing System Algorithms

The development of specialized and complex algorithms for cardiac pacing systems has had a significant impact on pacemaker programming and thus on the delivery of more appropriate pacing therapy. Large randomized studies performed in the last decade of the twentieth century identified the deleterious effects of right ventricular pacing, especially if performed from the right ventricular apex.^13,14 Importantly, this deleterious effect occurs even when only moderate ventricular pacing is present. In a post hoc analysis of MOST, cumulative ventricular pacing greater than 40% of the time was associated with a 2.6-fold increased risk of hospitalization for heart failure.¹⁵

Several studies have shown that right ventricular pacing is also associated with an increased likelihood of developing persistent atrial fibrillation. For example, in MOST, a linear dose-response relationship was noted between ventricular pacing and the likelihood of developing atrial fibrillation, with a 20% increase in the likelihood of developing atrial fibrillation with each 10% increase in cumulative ventricular pacing.¹⁵ More recently, it has become apparent that specific algorithms that minimize right ventricular pacing can reduce the likelihood of atrial fibrillation in patients with sinus node dysfunction. In the Search AV Extension and Managed Ventricular Pacing for Promoting Atrioventricular Conduction (SAVE PACe) trial, 1065 patients with sinus node dysfunction and normal AV conduction were randomized either to an algorithm specifically designed to minimize ventricular pacing or to conventional dual-chamber pacing without this function.¹⁶ The algorithm resulted in a significant reduction in ventricular pacing (minimizing ventricular pacing algorithm: 9%; conventional programming: 99%) and after an almost 2-year follow-up, minimizing right ventricular pacing was associated with a 40% reduction in the relative risk for persistent atrial fibrillation (conventional DDD pacing: 12.7% versus minimizing pacing algorithm: 7.9%). The MINimizE Right Ventricular Pacing to Prevent Atrial Fibrillation and Heart Failure (MINERVA) trial is currently under way to evaluate whether algorithms that minimize ventricular pacing will reduce the burden of atrial fibrillation in those patients who already have an established diagnosis of atrial arrhythmias.¹⁷

The clinical benefits of other complex algorithms appear to have limited benefit in the aggregate; it is quite certain that these complex algorithms can be useful in selected individual patients.¹⁸ In the Advanced Elements of Pacing Randomized Controlled Trial (ADEPT), 872 patients who had a blunted heart rate response to exercise (chronotropic incompetence) were randomized to standard dual-chamber pacing or to dual-chamber pacing that modulated heart rate on the basis of input from an accelerometer and a minute ventilation sensor (rate adaptation).¹⁸ Although the use of rate-adaptation algorithms was associated with an increased heart rate in response to exercise, this did not translate into significant differences in quality-of-life and activity indices between the two groups. Initial unblinded trials had suggested that specialized pacing algorithms that provided higher pacing rates in response to sudden changes in heart rate could be useful for patients with severely symptomatic vasovagal syncope.¹⁹ However, a subsequent double-blind trial did not show any clinical benefit of pacing using specialized algorithms in patients with vasovagal syncope.²⁰

It is expected that in the next 5 years, pacemakers will be characterized by increased automatic functions. Automated algorithms for adjusting pacing output to minimize energy requirements and extend battery life have already been developed for atrial and ventricular pacing (e.g., the “autocapture” feature, St. Jude, Sylmar, CA).^21,22 In a multicenter randomized trial of 910 patients who underwent implantation of a dual-chamber pacing system, automatic threshold evaluation of ventricular capture was found to be reliable and comparable with manual threshold evaluation and led to a projected 16% increase in longevity from 8.9 to 10.3 years.²³ Large registry studies (ULTRA and Automaticity, both sponsored by Boston Scientific, St. Paul, MN) are currently under way to evaluate whether automatic algorithms will increase pacemaker longevity and reduce the use of health care resources.

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