To the Editor:—

I recently saw a patient for a preanesthetic evaluation who had an Insertable Loop Recorder System (ILRS) (Reveal; Medtronic, Inc., Minneapolis, MN), which is used to continuously record a single lead electrocardiogram in patients with a history of syncopal or presyncopal episodes. The patient was a 43-yr-old woman scheduled to undergo an operative laparoscopy, and the only significant medical information was the presence of dizziness, which was being evaluated at an outside hospital. The patient stated that she had a Holter monitor (GE Marquette Medical Systems, Milwaukee, WI) implanted for 24 h on three separate occasions, and, because it had not revealed abnormalities, the decision was made 6 months previously to insert a more permanent monitoring device. During consultation with her cardiologist, I learned that this device was an internal Holter monitor used to detect arrhythmias. 1,2Nothing unusual was necessary before her proposed surgery, and results of her workup, including the readings from the ILRS, were normal. The team that performed the anesthetic and surgical procedures was informed of this device, and the surgery proceeded uneventfully.

The ILRS has been introduced to circumvent patient compliance and technical limitations. It is the size of a pacemaker and contains two sensing electrodes that are 32 mm apart within its shell. It continuously records a single-lead electrocardiogram that is stored in a circular buffer capable of either one 21- or 42-min segment or three 7- or 14-min segments of recorded rhythm. Using a magnet, the patient activates the device during a syncopal or presyncopal episode, storing the preceding 20- or 40-min segment (storage modes A and B) or 6- or 12-min segment (storage mode C and D). The ILRS stores 1 or 2 min of electrocardiography after activation and one to three events, depending on the storage mode chosen. The device is implanted in the left pectoral region in the subcutaneous fat and has a battery life of 2 yr. 3There are no absolute contraindications for the implantation of this device. 4There is no wiring between the device and the heart, and no treatment is provided by the ILRS.

There are several anesthetic implications in patients with an ILRS. Although there is no need to disable the device for surgery, it is important to discuss the patient’s history and workup with the cardiologist. It may be important to interrogate the device before the proposed surgery to determine whether the ILRS has recorded recent life-threatening arrhythmias.

The shell of the device is made of titanium, and the inside contains ferromagnetic components. Medtronic states that it is safe to use the device in the presence of a magnetic force (such as during magnetic resonance imaging), but that the patient should be warned that a pulling sensation may be perceived. Also, it is imperative to collect all data obtained in the ILRS beforehand because the magnetic forces may adversely affect the data collection. Electrocautery is safe, but may cause the device to reset, resulting in lost data. Lithotripsy may damage the device if it is at the focal point of the beam.

Krahn AD, Klein GJ, Norris C, Yee R: The etiology of syncope in patients with negative tilt table and electrophysiological testing. Circulation 1995; 92: 1819–24
Linzer M, Pritchett ELC, Pontinen M, McCarthy E, Divine GW: Incremental diagnostic yield of loop electrocardiographic recorders in unexplained syncope. Am J Cardiol 1990; 66: 214–9
Krahn AD, Klein GJ, Yee R: Recurrent unexplained syncope: Diagnostic and therapeutic approach. Can J Cardiol 1996; 12: 989–94
Reveal Insertable Loop Recorder [product information manual]. Minneapolis, MN: Medtronic, Inc., 1997:1–13