Actual transtelephonic ICD interrogation was first reported in the early 1990s.

Camm and associates reported two patients receiving Medtronic ICDs using Medtronic transmitters connected by metal bracelets to the patients and employing interrogation heads placed over the implanted defibrillators;22 the telephone handsets were then placed on the transmitters which commenced automatic transmission to the device follow-up clinic. Interrogated information included data on currently programmed back-up pacing, VT/VF detection criteria and programmed VT/VF therapies, battery status, last charge time, episode counter, and therapy logs for VT/VF and the identity of the transmitting unit. Complete concordance was seen between data obtained transtelephonically and that obtained from the standard programmer interrogation in the clinic.

A total of 147 interrogations were performed, of which 47 failed, mostly due to stalling of the printer during printout (60%), incorrect placement of the interrogation head by the patient (30%) or transmitter battery depletion (4%). Testing of a similar Medtronic transmitter was subsequently evaluated in a larger series by Fetter et al.23 152 successful transmissions were obtained from 18 patients over a period of 23 months, with 42% indicating an arrhythmia and 16% prompted by presyncope/syncope. Episodes requiring treatment were effectively identified, both regarding the number of therapies delivered and their success in terminating the arrhythmia.

Most recently, a prospective study using the Medtronic CareLink Network was undertaken to analyze the feasibility of performing internet-based remote monitoring in the follow-up of patients with ICDs.24 The use of the Internet had previously been identified as an excellent means for registering and communicating pacemaker and ICD generator and lead failures among multiple implanting and follow-up centers.25 Timely communication of such failures has become particularly important in light of increasingly frequent ICD advisories coupled with a three-fold increase in number of devices affected per advisory .26 In this recent remote monitoring study of ICDs,24 10 investigational sites examined 59 patients who completed 119 transmissions (two per patient, scheduled roughly one week apart). Patients were given a portable monitor to self-interrogate their ICDs and transmitted data via a standard analog telephone line to a password protected clinician and patient website allowing clinicians to view and analyze patient device data stored on the computer server. Transmissions included all data within device memory, including stored episodes and device parameters, diagnostics including stored intracardiac electrograms and a 10 second presenting rhythm real-time electrogram. Aside from demonstrating ease of use by and satisfaction from both patients and physicians, clinically significant findings were identified early including: two cases of atrial undersensing, two cases of T wave oversensing, four cases of far-field R wave sensing, three cases of safety pacing, five patients in atrial fibrillation (one newly diagnosed leading to initiation of anticoagulation therapy) (see Fig. 2), two episodes of ventricular tachycardia, and six patients with significant changes in the percentage of pacing. The study was limited, by virtue of being a feasibility assessment, to a short follow-up period and did not allow for patient-initiated transmissions. Potential inabilities to communicate with and interrogate the ICD are still a reality just as is the case in an actual clinic exam.27 Furthermore, transtelephonic reprogramming is not a present reality.
This study did, nonetheless, demonstrate that all the data that can be interrogated during a patient clinic visit may be just as easily retrieved remotely. This technology can be used to facilitate communication with the patient on a number of issues, including battery longevity, the presence and appropriateness of device discharge, significance of an audible device alert, the development of new and often unsuspected arrhythmias and/or disease processes, and the need for an earlier office visit for device reprogramming and/or drug titration.

Two other manufacturers currently allow for remote monitoring.

The Biotronik home-monitoring system allows for radiofrequency transmission from a transmitter in the ICD via a cellular phone-like device to a service center. Transmission is initiated automatically once daily when no unusual events occur but may be transmitted immediately when therapy-relevant events take place. The physician then receives a report via fax or internet. Relevant data capable of being transmitted include impedance, paced/sensed percentages, arrhythmia detection and therapy delivered, and battery status; actual electrogram transmission whether stored or real-time is still under evaluation.15 Published data regarding follow-up are limited, though experience with this system particularly in Europe has been extensive. A case of twiddler's syndrome in an ICD patient detected by this home monitoring system was recently reported.28 Preliminary data suggesting important cost savings in ICD patient follow-up by reducing transportation expenses for clinic visits using the Biotronik system have recently been presented.29 The St. Jude Housecall Plus Remote Patient Monitoring System supports certain St. Jude model ICDs and allows for monitoring of parameters and settings, real-time electrograms, surface ECGs, delivered therapies and stored electrograms as well as clearing of diagnostics. Calls may be initiated by patient or follow-up center, and the system is not centralized, allowing for outsourcing of reception of patient data. In one prospective evaluation, 124 patients with single chamber St. Jude ICD's were monitored by remote interrogation and monitoring for a total of 570 transmissions (including 54 delivered and 22 aborted ICD therapies). As with the previously published Medtronic analysis, the St. Jude investigators demonstrated a high degree of patient satisfaction with the convenience and ease of use of remote ICD monitoring.30 Preliminary data from prospective analyses of the Medtronic, Biotronik and St. Jude remote ICD monitoring systems were presented at the late-breaking clinical trials of the NASPE-Heart Rhythm Society Annual Scientific Sessions in 2003. Though published data are limited to date,24,30 all three systems are commercially available in the United States and Europe, extending the worldwide experience with home monitoring.