Case Report

A 26-year-old woman with a history of migraines, syncope, palpitations, and heart murmur experienced visual disturbance and unilateral numbness (magnetic resonance imaging and brain CAT scan studies were negative). Neurologic evaluation honed in on multiple episodes of right sensory symptoms and identified one episode of a right-sided pronator drift consistent with a motor deficit. Her only medication, an oral contraception, was discontinued. The patient was referred for electrophysiology assessment.

Echocardiogram with bubble study ruled out patent foramen ovale. Upright tilt table testing was performed at 70 degrees for 10 minutes following weight-based infusion of isoproterenol at 2.7 micrograms per minute. She went into some form of supraventricular tachycardia (versus sinus tachycardia) at 160 beats per minute, but it did not become hypotensive.

Electrophysiology study showed normal baseline conduction with an HV interval of 35 ms, a normal corrected sinus node recovery time of 400 ms, and a normal AV block cycle length of 320 ms. Programmed electrical stimulation performed in the right atrium and right ventricle failed to induce supraventricular or ventricular tachycardia. An injectable loop recorder (Reveal LINQ^™ Insertable Cardiac Monitor, Medtronic, Inc.) was implanted (Figure 1). 

Figure 1 shows the small size of the device, which is inserted underneath the skin along the left sternal border. Figure 2 shows the device contained within the delivery tool and a nick/incision blade tool. Figure 3 shows a close-up of the Reveal LINQ in the delivery tool. The delivery procedure is quite simple. First, consent is obtained. It may also be preferable to give the patient some form of sedation and prophylactic antibiotics. The patient is then prepped and draped, revealing the site of insertion at the 4th intercostal space just left of the sternal border. The patient is anesthetized with a lidocaine-type preparation, where the insertion tool and device will be delivered. Figure 4A shows a nick being made at that site, and Figure 4B shows the delivery tool containing the device in a manner in which it is pushed from top to bottom into the subcutaneous tissue while avoiding any breast tissue. Figure 4C shows the injecting procedure: once the delivery tool is fully inserted, it is rotated 180 degrees, the device is injected under the skin by the tool, and the tool is then removed. The wound could be closed via holding pressure to stop the bleeding and then applying DERMABOND (Ethicon, Inc.), suture closure, or a combination thereof. Following insertion, the device is interrogated and the signal is checked to assure that it is sensing and recording appropriately. The procedure is very well tolerated; the main risks of the procedure are bleeding, discomfort, infection, erosion, and/or keloid formation. 

One week later, while the patient was showering, she felt rapid palpitations with pre-syncope. She transmitted a supraventricular tachycardia up to 150 beats per minute. Figure 5 demonstrates this tachycardia; the mechanism may be inappropriate sinus tachycardia versus an atrial tachycardia. However, rather than react to this first event, our general approach is to gather additional information, since other supraventricular tachycardias (including atrial fibrillation and atrial flutter) may be detected over time.

Discussion

This case highlights the potential applications of a novel, miniaturized, subcutaneous injectable loop recorder for the diagnosis and treatment of syncope of unknown etiology, potentially helping with a previously undiagnosed neurological condition. Although we cannot be certain of the diagnosis in this particular patient, transient ischemic attack is certainly a possibility, considering her multiple episodes of right sensory symptoms and one episode of motor deficit (right-sided pronator drift). Complicated migraines may cause neurological deficit, which is also vascular in origin. An implantable loop recorder has potential diagnostic value for both syncope of unknown etiology and in those with transient ischemic attack and/or cerebral vascular accident.^1,2 

The latest miniaturized injectable loop recording device (Reveal LINQ) records and stores ECG data and can remain implanted for up to three years. The device typically can be implanted in less than 60 seconds with very little morbidity and mortality associated with it. The risk of bleeding is extremely small and usually can be treated with pressure applied superficially. Rarely, erosion and/or infection at the site can occur; this can be treated with easy removal of the subcutaneous device and a short course of antibiotics. Lastly, scarring and/or keloid formation may occur at the incision site. Operator/electrophysiology expertise is helpful in analyzing the recorded signal and differentiating them from noise, loss of signal, and amplifier saturation (all reasons for interpretation error with this type of device). The ease of implication of the new injectable loop recorder (size of a paper clip) gives considerable advantage over implantation of the older, larger, and deeper implantable flash-drive sized loop recorder used in the recent Cryptogenic Stroke and Underlying Atrial Fibrillation (CRYSTAL AF) study.¹ That study demonstrated the utility of long-term monitoring implants with insertable cardiac monitors. In particular, they demonstrated a 6 month, 1 year, and 3 year atrial fibrillation detection yield with the older implantable loop recorder of 8.9 percent, 12.4 percent, and 30.0 percent respectively, as compared to the conventional following, which, even at 3 years, had atrial fibrillation detection yield of 3.0 percent.¹ 

Inamdar and colleagues demonstrated the advantages of the older implantable loop recorder in helping to diagnose syncope of unknown etiology in 100 consecutive patients.² Approximately half of the patients had cardiac arrhythmia diagnoses and many required permanent pacemakers.² 

We have found the newer injectable loop recording device to be very easy and quick to implant; the few barriers to implantation include patient acceptance of the implant and procedure, as well as the cost of the device (less than $5000) and procedure. Additional monitoring with the Reveal LINQ in our patient will help to determine the degree that supraventricular tachycardia plays a role in her symptoms. Most importantly, long-term monitoring will help correlate her disabling symptoms to clinical arrhythmic events from the ECG recordings captured on the device.

References

1. Sanna T, Diener HC, Passman RS, et al; CRYSTAL AF Investigators. Cryptogenic stroke and underlying atrial fibrillation. N Engl J Med. 2014;370(26):2478-2486. 
2. Inamdar V, Mehta S, Juang G, Cohen T. The utility of implantable loop recorders for diagnosing unexplained syncope in 100 consecutive patients: five-year, single-center experience. J Invasive Cardiol. 2006;18(7):313-315.

Disclosures: The authors have no conflicts of interest to report.