Implantable Loop Recorder in Syncope Patients

Abstract & Commentary

By John P. DiMarco, MD, PhD Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.

Synopsis: In highly symptomatic patients with vasovagal syncope, the heart rhythm observed during spontaneous syncope does not correlate with the results of tilt table testing.

Source: Deharo JC, et al. An Implantable Loop Recorder Study of Highly Symptomatic Vasovagal Patients: The heart Rhythm Observed During a Spontaneous Syncope is Identical to the Recurrent Syncope But Not Correlated with the Head-Up Tilt Test or Adenosine Triphosphate Test. J Am Coll Cardiol. 2006;47:587-593.

In this report, deharo and colleagues correlate the tracings recorded by an implantable recorder during spontaneous episodes of syncope, with the results of provocative head-up tilt (HUT) and adenosine triphosphate (ATP) testing. Patients were included in the study if they met the following criteria: 1) a diagnosis of vasovagal syncope established by clinical criteria and provocative testing; 2) frequent episodes of spontaneous syncope; 3) an absence of structural heart disease; and 4) insertion of an implantable loop recorder (ILR—Medtronic Reveal or Reveal Plus). Baseline HUT was performed using a maximum of 45 minutes of tilt at a 60° angle. Nitroglycerine or isoproterenol challenge was used if the initial tilt was negative. The ATP test measured heart rate and blood pressure responses to a bolus intravenous injection of 20 mg of ATP.

The ILR was either patient activated only (3 patients) or set to automatically store heart rates below 40 beats per minute, above 165 beats per minute, or periods of asystole longer than 3 seconds.

Twenty-five patients met the study criteria. Their mean age was 60 years. They had a long history of syncope, with a mean of 7 episodes per year. All had a positive HUT, with a cardioinhibitory type response in 8 and a mixed response in 17. Seven patients had a positive response (> 6 seconds of asystole) during the ATP test. During follow-up after ILR insertion, 2 patients required early device removal. The other 23 completed the planned 18 months of follow-up. Eleven patients had no recurrent syncope. The remaining 12 patients experienced 31 episodes of recurrent syncope (2.6 ± 1.8 per patient). The ILR was activated by the patient during 23 episodes. In the other 8 episodes, automatic recordings were made during 2, but the remaining 6 did not trigger automatic activation excluding bradycardia in the latter. One patient experienced 6 episodes of recurrent syncope. One was associated with a 6-second pause after termination of an atrial arrhythmia, but recordings of the other 5 episodes, which were similar to her prior episodes, showed only sinus rhythm. The former episode was considered non-vasovagal and was not included in the rest of the analysis. A heart rate below 40 beats per minutes was recorded during 9 episodes in 5 patients. During these 9 episodes, sinus arrest (10.5 ± 6.2 seconds) was observed in 6, sinus bradycardia in 2, and sudden-onset atrioventricular block in one. Seven patients had more than one episode of vasovagal syncope. Each of these 7 had the same pattern of heart rate response during repeat episodes (heart rate > 40 beats per minute in 6 patients and < 40 beats per minute in 1 patient). Severe bradycardia during provocative testing did not predict bradycardia during clinical follow-up. Two of 4 patients with cardioinhibitory responses during HUT had bradycardia during spontaneous syncope. Two of 7 patients with vasodepressor/mixed responses during HUT had bradycardia. None of the 3 patients with asystole during ATP challenge manifested severe bradycardia during their clinical syncope, but 4 of 8 patients with a negative ATP test did.

Deharo et al conclude that in highly symptomatic patients with vasovagal syncope, heart rhythm responses during provocative HUT and ATP testing do not correlate well with observations made during spontaneous clinical episodes.


The value of provocative testing using either HUT or drug infusions in patients with recurrent, unexplained syncope remains controversial. When these tests were first introduced, they were enormously helpful in that they provided insights into the abnormal physiology associated with recurrent syncope. However, the value of these tests for making a diagnosis or for guiding therapy in an individual patient has proven to be disappointing. The diagnostic use of these tests is limited by a suboptimal sensitivity and specificity relationship. Day-to-day reproducibility of responses in individual patients is also poor, so that repeat testing is of little value. In this paper, we now see that hear rhythm responses during provocative tests in highly symptomatic patients with multiple episodes of syncope over many years do not predict the rhythm documented during later clinical episodes.

Patients with vasovagal syncope remain a challenge to clinicians. The diagnosis is best made on clinical grounds. If empiric therapy is not effective, the data in this paper suggest that ILR recordings rather than provocative test results should be used as guides to therapy.