Color Atlas and Synopsis of Electrophysiology, 1st Ed.

49. THE IMPLANTABLE LOOP RECORDER

Blair P. Grubb, MD, FACC

CASE PRESENTATION

A 71-year-old woman presents with complaints of multiple syncopal episodes. She describes these events as sudden in onset with little or no prodrone, accompanied by a rapid fall to the ground. She has suffered multiple traumas during falls. The loss of consciousness lasts anywhere from a few seconds to 5 minutes. Several episodes have been associated with urinary incontinence, and she is often confused afterwards. The patient has undergone electroencephalography, magnetic resonance imaging of the brain, echocardiography, a 12-lead electrocardiogram, coronary angiography, and electrophysiology study, all of which have been unremarkable. Multiple attempts at recording episodes by both Holter monitor and external event monitor have been unsuccessful. She therefore underwent placement of an implantable loop recorder. Five weeks later she suffered another syncopal episode, and a download of the event disclosed an episode of asystole that coincided with the syncope (Figure 49-1). She thereafter underwent dual chamber pacemaker implantation and has had no further syncopal episodes.

Images

FIGURE 49-1 ILR recorded asystole.

EPIDEMIOLOGY

Syncope, defined as the transient loss of postural tone and consciousness and spontaneous recovery, is a common clinical problem.1 Approximately 3% of all emergency department visits and 1% to 6% of hospital admissions are for syncope. While a complete history and physical examination combined with direct laboratory testing can adequately establish a diagnosis in many patients, there are nonetheless patients who experience episodic cardiac arrhythmias that are not apparent on initial evaluation. They are often intermittent and transient and therefore difficult to detect. In these patients prolonged ambulatory monitoring using both external and now implantable electrodiagnostic recorders has been of great use in establishing a diagnosis. Indeed, by allowing for prolonged electrocardiographic monitoring, the implantable loop recorder (ILR) is able to provide a more certain correlation between observed rhythm experiences and the patient’s symptoms. While external monitoring is only practical for relatively short periods of time, the ILR is capable of monitoring for up to 3 years. In addition, the ILR has the ability to auto-activate when a rhythm disturbance is present, thereby allowing episodes to be recorded independent of the patient having to activate the device. There are two ILRS that are presently available in the United States.2 These are the Reveal (DX and XT) made by Medtronic (Minneapolis, MN) and the Confirm by St. Jude Medical (St. Paul, MN). Each of these is a small rectangular device that measures roughly 62 × 19 × 8 mm and weighs approximately 17 grams. Two built-in sensing leads are located in the shell of the device, allowing for the recording of a single-lead, bipolar electrogram. These recordings can be stored and downloaded by means of a radiofrequency signal through a special programmer. The unit is usually implanted in the left pectoral area under local anesthesia. A study conducted at our institution evaluated the utility of an anatomic-based implant location based on a modified ECG lead II access.3Placement was determined by drawing an imaginary line between the substernal notch and the approximate area of the left nipple. An area in the inferior middle segment of the line was prepped and draped and anesthetized with 1% zylocaine solution. A 2-cm incision was made with a #15 scalpel along the lower one-third of the aforementioned line. Meticulous blunt dissection was used to create a subcutaneous pocket into which was inserted one of the aforementioned ILR devices. A telemetry wand (in a sterile cover) was then used to determine adequate signal size and strength. Very clearly visible P and QRS complexes were seen in all 63 patients at the time of initial placement. In none of the patients was it necessary to change the location or shape of the pocket. The average P-wave amplitude was 0.12 ± 0.2 mV and the mean peak-to-peak QRS amplitude was 0.48 ± 0.15 mV. Over a mean follow-up period of 10 ± 4 months, only 2 patients were noted to have a loss of P-wave amplitude (3.2%) while 1 patient had QRS under sensing (1.6%). We did not stitch the ILR in place as we found that this increased the amount of artifact present; rather, the subcutaneous pocket was made purposefully small to hold the device in place. (This also facilitates later removal.)

CLINICAL EXPERIENCE

A number of clinical trials have demonstrated the utility of the ILR in determining the etiology of syncope. Krahn et al found that in a group of 16 patients with syncope of unknown case (despite extensive evaluation) the ILR showed that in 60% of them syncope occurred due to an arrhythmic event.4 Additional studies have shown that the device is equally effective in patients who had not undergone as extensive an amount of preimplant testing.5 The recent ISSUE studies have clearly demonstrated the utility of the ILR in not only the diagnosis of syncope but also in guiding its treatment.6 The recent ISSUE-3 trial showed that in patients with recurrent neurocardiogenic syncope associated with ILR documented asystole that permanent pacemaker implantation significantly reduced the recurrence rate of syncope.7The ILR has also been shown to be an effective means of detecting paroxysmal atrial fibrillation in patients with cryptogenic stroke.

REFERENCES

1. Grubb BP. Clinical Practice. Neurocardiogenic syncope. N Engl J Med. 2005;352(10);1004-1010.

2. Kanjwal K, Figueredo V, Karabin B, Grubb BP. The implantable loop recorder: current uses, future directions. J Innov Card Rhythm Manage. 2011;2:215-222.

3. Grubb BP, Welch M, Kanjwal K, Karabin B, Kanjwal Y. An anatomic-based approach for the placement of implantable loop recorders. Pacing Clin Electrophysiol. 2010;33(9):1149-1152.

4. Krahn AD, Klein GJ, Norris C, Yee R. The etiology of syncope in patients with a negative tilt table test and electrophysiologic testing. Circulation. 1995;92:1819-1824.

5. Krahn AD, Klein GJ, Yee R, Hoch JS, Skanes AC. Cost implications of testing strategy in patients with syncope: randomized assessment of syncope trial. J Am Coll Cardiol. 2003;42:495-501.

6. Brignole M, Sutton R, Menozzi C, et al. Early application of an implantable loop recorder allows effective specific therapy in patients with recurrent suspected neurally mediated syncope. Eur Heart J. 2006;27:1085-1092.

7. Brignole M, Menozzi C, Moya A, et al. Pacemaker therapy in patients with neurally-medicated syncope and documented asystole. Third International Study on Syncope of Uncertain Etiology (ISSUE-3): a randomized trial. Circulation. 2012;125: 2566-2571.