Arterial pulse as a rare artifact observed on electronystagmography.

Abstract

We report a rare artifact observed during electronystagmography (ENG) in a 54-year-old-woman. Rhythmic waves were seen on ENG even though no corresponding movements of the eyes or eyelids were detected, even by infrared camera monitoring. The rhythmic waves corresponded to the patient's pulse and occurred after the appearance of each QRS complex on electrocardiography (ECG). The waves" were believed to have been generated by the pulse of the artery near the electrodes, which represented contamination of plethysmography at the temple. To the best of four knowledge, such an artifact has not been previously reported in the literature. When rhythmic waves unrelated to eye movements" are recorded during ENG, an artifact of cardiovascular origin should be ruled out, and ECG and direct observation of the eyes are necessary.

Introduction

Electronystagmography (ENG) enables otolaryngologists to make a quantitative assessment of eye movements and detect both peripheral and central vestibular disorders. (1-7) ENG measures corneorctinal potentials, so any kind of electrical "noise"--such as electrocardiography (ECG), myography, or electroencephalography--may cause artifacts.

In this article, we report a rare ENG artifact that corresponded with the patient's pulse. To the best of our knowledge, such an artifact has not been previously reported in the literature.

Case report

A 54-year-old woman with hereditary spinocerebellar degeneration was referred to our department for a neurootologic assessment. She was very thin. No abnormalities were found on blood biochemistry testing. No spontaneous nystagmus was found, but gaze nystagmus was observed during left and right gaze. ENG was performed. Horizontal electrodes were placed bitemporally, and vertical electrodes were placed above and below the right eye. Saccadic eye movement, dysmetria, and lateral gaze nystagnms were observed.

During this examination, rhythmic waves were recorded by the horizontal ENG leads, but no such wave was recorded by the vertical leads (figure 1). The waves were wide and left-beating, and the waveform changed during the examination (figure 2). No corresponding eye movements or blinks were seen during observation with Frenzel's goggles or with infrared camera monitoring. The rhythmic waves were synchronous with the radial and carotid pulses. Simultaneous electrocardiography (ECG) revealed that the waves occurred just after the appearance of the QRS complex (figure 3).

[FIGURE 1-3 OMITTED]

We concluded that these abnormal waves represented artifact that corresponded to the arterial pulse on the patient's face.

Discussion

In this case, no eye movements were observed during infrared camera monitoring, so the abnormal waves were believed to be artifact. The abnormal waves corresponded to the patient's pulse and occurred after the appearance of the QRS complex. The QRS complex rarely appears on ENG. (3) Only the T wave was believed to be a candidate for this abnormal wave from the viewpoint of timing. However, the abnormal waves changed form during the examination, even though the positions of the electrodes were fixed to the skin. T waves may change form in patients with hypo- or hyperkalemia, but our patient had no electrolyte imbalance. Moreover, the rhythmic waves themselves were not similar to the T waves or the QRS complex waves.

The rhythmic waves in this case might have represented the arterial pulse at the temple--that is, the ENG may have functioned as impedance plethysmography of the artery. Impedance plethysmography is a method of detecting blood volume changes, in part by measuring changes in electrical resistance. (80 Although the electrodes on our patient were fixed tightly to her skin, the position of the vessel beneath the skin might have changed slightly and the form of the wave might have changed during ENG.

Another interesting aspect of this case is that the artifact resembled a left-beating nystagmus on ENG. The increased resistance caused by the blood volume lowered the voltage, which might have appeared on ENG as a downward (i.e., left) shift.

We recommend that when rhythmic waves unrelated to eye movements are recorded during ENG, artifact of cardiovascular origin should be ruled out, and ECG and direct observation of the eyes should be performed.

References

(1.) Brookler KH. Fundamentals of electronystagrnography. Ear Nose Throat J 2000;79:14-15.

(2.) Simmons FB, Gillan SF, Mattox DE. An Atlas of Electronystagmography. New York: Grune and Stratton, 1979.

(3.) Barber HO, Stockwell CW. Manual of Electronystagmography. 2nd ed. St. Louis: Mosby, 1980.

(4.) Kayan A. Diagnostic tests of balance. In: Stephens D, ed. Adult Audiology. 5th ed. London: Butterworths, 1987:304-67.

(5.) Carl JR. Principles and techniques of electro oculography In: Jacobson GP, Newman CW, Kartush JM, eds. Handbook of Balance Function Testing. San Diego: Singular Publishing, 1997:69-79.

(6.) Dacies RA, Svundra PA. Diagnostic tests of the vestibular system. In: Stephens D, ed. Adult Audiology. 6th ed. Oxford: Buttelworths, 1997:14-18.

(7.) Tsunoda A, Komatsuzaki A, Muraoka H, Gou-Tsu K. A case with symptoms of vestibular neuronitis caused by an intramedullary lesion. J Laryngol Otol 1995;109:545-8.

(8.) Strandness DE, Langlois YE, Roederer G. Noninvasive evaluation of vascular disease. In: Hairnovici H, Callow AD, ed. Haimovici's Vascular Surgery. Principles and Technique. Norwalk, Conn.: Appleton and Lange, 1989:17-38.

From the Department of Otolaryngology, Tokyo Medical and Dental University.

Reprint requests: A. Tsunoda, MD, Department of Otolaryngology, Tokyo Medical and Dental University, Bunkyo-ku Yushima 1-5-45, Tokyo 113-8519, Japan. Phone: [phone]; fax: [phone]; e-mail: [e-mail]