Initial Clinical Experience with Implantable Loop Recorders

Syncope is responsible for 5% of emergency department visits and 1% of hospital admissions.1 Syncopal episodes are often too infrequent and unpredictable for detection with conventional ambulatory monitoring techniques. Electrophysiologic testing is performed when noninvasive tests and neurologic work-ups are negative. Nonetheless, electrophysiological testing is negative in 14–70% of patients.1–3 The purpose of this study was to review our initial experience of a university hospital with a first-generation implantable loop recorder (ILR) for diagnosis of recurrent unexplained syncope or presyncope. METHODS Patients with syncope or presyncope of unknown etiology (who had a negative tilt table test, electrophysiologic study, and neurologic work-up) underwent implantation of ILR. Ten patients received Reveal™ (Medtronic AVE, Santa Rosa, California), a first-generation device that is manually activated by magnet, while 2 patients received Reveal-Plus™, a second-generation device with automatic telemetry and programmable triggers (Figures 1 and 2). The Reveal is an 8 cc device, which is 61 mm long, 19 mm wide, 8 mm thick and weighs 17 grams. It has 18 months of battery life and has 2 electrodes with 38.5 mm spacing. The device is nonvascular and is implanted approximately 2 fingerbreadths below the clavicle in a subcutaneous pocket (1.5 inches long) and is secured via polydacron suture to the pre-pectoral fascia/pectoralis muscle.4 RESULTS Twelve patients with a mean age of 61 ± 22 years received the ILR (Tables 1 and 2). Ten patients received the Reveal device, and 2 received Reveal-Plus. Ten patients had syncope and 2 had presyncope. Three patients had coronary artery disease and 2 had dilated cardiomyopathy. ILRs were implanted for a mean follow-up period of 7.2 ± 5.8 months (range, 1 day to 18 months).4 The mean number of events prior to ILR implantation was 6.0 ± 5.4. Eight patients (66%) had recurrent syncope after implantation. One patient was not available for follow-up, because he left the country. There were no significant complications from the implant. In 5/12 patients (42%), the ILR helped to diagnose the etiology of the syncopal episode (Tables 1 and 2). Syncope was secondary to asystole in 3 patients, junctional bradycardia in another patient, and seizure activity in an additional patient (high-frequency noise was recorded on the electrocardiogram during sinus rhythm). The 4 patients with ILR-documented bradyarrhythmias underwent permanent pacemaker implantation and are alive and well. Both patient who received the Reveal-Plus device had a diagnosis made with automatically detected arrhythmias by the device. Two patients still continue to be monitored at the time of this report. It is possible that with the passage of time the yield from this device will, in fact, increase to an even higher percentage of patients. DISCUSSION The etiology of syncope is often difficult to determine if the diagnosis is not evident after initial investigations, e.g., Holter monitor, tilt table test, electrophysiologic test and neurologic work-up.5,6 The cause of syncope is often not determined after a standardized diagnostic evaluation in 38–47% of patients.3 The correlation of infrequent symptoms to clinical arrhythmias is often difficult due to the inability to monitor and record these sporadic events. Recent advances in long-term monitoring using an ILR may enhance the diagnostic yield in patients with infrequent symptoms. In our study, we demonstrated that both first-generation (Reveal) and second generation (Reveal-Plus) ILRs were effective in helping to define the etiology of syncope of unknown etiology. Importantly, both patients who received the second-generation device had rapid detection of critical arrhythmia events triggered automatically by the device. Three out of 10 patients had manual detection using the Reveal first-generation device. In summary, ILR implantation is a simple, useful and safe method in assisting with the diagnosis of recurrent unexplained syncope or presyncope after an inconclusive electrophysiologic and neurologic evaluation. This device can help elucidate infrequent episodes of syncope and presyncope. In our study, it helped diagnose the etiology of syncope in 5/12 patients (42%). The determination of the etiology of syncope has obvious therapeutic significance. All diagnoses were amenable to treatment, with resolution of syncope after etiology was determined. Further larger studies are necessary to significantly document what appears to be an obvious advantage of the second-generation, automatic and programmable ILR device.

1. Krahn AD, Klein GJ, Yee R, Manda V. The high cost of syncope: Cost implications of a new insertable loop recorder in the investigation of recurrent syncope. Am Heart J 1999;137:870–877. 2. Krahn AD, Klein GJ, Norris C, et al. The etiology of syncope in patients with negative tilt table and electrophysiologic testing. Circulation 1995;92:1819–1824. 3. Krahn AD, Klein GJ, Yee R, et al. Use of an extended monitoring strategy in patients with problematic syncope. The REVEAL Investigators. Circulation 1999;99:406–410. 4. Cohen T, Ibrahim B, Sassower M. Revealing: Data retrieved from an implantable loop recorder. J Invas Cardiol 2000;12:174–175. 5. Hammill SC. Value and limitations of noninvasive assessment of syncope. Cardiol Clin 1997;2:195–218. 6. Krahn AD, Klein GJ, Yee R. Recurrent unexplained syncope: Diagnostic and therapeutic approach. Can J Cardiol 1996;10:989–994.