Use of an Extended Monitoring Strategy in Patients with Problematic Syncope

ABSTRACT & COMMENTARY

Synopsis: Prolonged monitoring using an implantable loop recorder is an effective means for evaluating patients with recurrent symptoms.

Source: Krahn AD, et al., for the Reveal Investigators. Circulation 1999;99:406-410.

Krahn and colleagues report on the use of implantable loop recorders in 85 patients with recurrent syncope. Patients with recurrent syncope were eligible for inclusion in the trial. All had undergone at least one 24-hour period of conventional ECG monitoring. Head-up tilt studies, electrophysiologic studies, and external loop recordings had been performed in 49%, 43%, and 24% of the patients, respectively. The implantable loop recorder used in this study (Reveal, Medtronic) is a 61 × 19 × 8-mm recording device with two sensing bipoles. The device can store 21 minutes of uncompressed ECG signals or 42 minutes of compressed signals in 1,3 divided parts. The data are stored in a circular buffer that can be frozen with a handheld activator provided to the patient. The data obtained from symptomatic episodes of syncope or presyncope can then be downloaded on a standard pacemaker programmer. The device is implanted in a procedure analogous to a pacemaker implantation, usually in a left infraclavicular subcutaneous pocket.

The patients enrolled were 59 ± 18 years of age and 62% had structural heart disease. They had experienced 5.1 ± 5.5 episodes of syncope within the prior year. Symptoms had been present for more than two years in 71% of the patients. During 10.5 ± 4 months of follow-up, symptoms recurred in 58 of 85 patients. The median time to recurrence was 51 days. Adequate data that allowed evaluation of symptoms and rhythm were obtained during 128 episodes of syncope or presyncope in 50 patients. On 24 occasions in 14 patients, the patient failed to appropriately activate ECG storage. Arrhythmias were recorded in 21 of 50 (42%) patients with symptoms and an adequate recording. Of this, 18 had bradycardia and three had a tachycardia. The remaining 29 patients in this group had sinus rhythm documented at the time of recurrence. Episodes of syncope were more likely to be associated with an arrhythmia (70%) than episodes of presyncope (24%). Complications associated with the device included two local infections, one erosion plus infection, and one pocket revision due to pain at the initial implant site. Krahn et al conclude that prolonged monitoring using an implantable loop recorder is an effective means for evaluating patients with recurrent symptoms.

Comment by John DiMarco, MD, PhD

Patients with recurrent syncope are difficult to manage since the cause of their symptoms often remains obscure. By definition, episodes of syncope are transient and the patient usually has a stable rhythm and blood pressure when he presents for evaluation. Standard ambulatory ECG monitoring is of limited value unless the patient has frequent episodes. Available patient activated external loop recorders require rapid activation due to limited memory and are inconvenient for the patient to wear or carry. Tilt table studies or electrophysiologic studies are provocative tests that have frequent false-negative and false-positive results.

In this study, implantation of a small subcutaneous recorder allowed symptom-rhythm correlation in about 60% of a group of patients with recurrent syncope. It is interesting to note that sinus rhythm was the most common rhythm documented. Unfortunately, the device does not monitor blood pressure so episodes of severe hypotension without arrhythmia were not excluded. However, even in these cases, the devices provided reliable information to exclude arrhythmias and prevented fruitless therapeutic trials to treat possible brady- or tachyarrhythmias.

We can expect to see further advances in these devices. The model used in this study is easy to implant, produces no unsightly scar or bulge, and can be easily removed. Algorithms to automatically activate recording in response to high- or low-rate episodes would eliminate the absolute need for patient activation even though the latter feature would not store episodes where the rhythm remained stable.

The data presented here suggest that implantable loop recorders should become an important part of the diagnostic approach to patients with recurrent, unexplained syncope. Patients at high risk for a life-threatening arrhythmia that is usually reproducible at electrophysiologic study should still undergo that procedure first. Neurocardiac syncope is usually diagnosed on clinical grounds and tilt table studies used, when necessary, to support that impression. In other patients, the implantable loop recorder will be an attractive diagnostic option. The major limiting factors with these devices will be their cost and the need for an invasive procedure.