Electroencephalographic findings during presyncope and syncope induced by tilt table testing.

OBJECTIVE

To determine electroencephalographic (EEG) changes occurring during syncope induced by headup tilt table testing.

DESIGN

Prospective observational study.

SETTING

Calgary General Hospital Syncope Clinic, Calgary, Alberta.

PATIENTS

Eighteen patients with a history of recurrent syncope who developed syncope while undergoing diagnostic isoproterenol tilt table testing.

INTERVENTIONS

Continuous EEGs were recorded in 18 sequentially consenting patients while they underwent diagnostic headup tilt table testing.

MAIN RESULTS

Patients developed presyncope after 2.6 +/- 2.4 mins and syncope after 3.7 +/- 2.5 minutes. Systolic blood pressure dropped from 117 +/- 17 mmHg to 65 +/- 9 mmHg, and heart rate dropped from 124 +/- 26 beats/min to 65 +/- 27 beats/min. Fourteen patients developed presyncope, while five developed syncope without appreciable presyncope. Abnormal EEGs were recorded in 13 of 14 patients during presyncope and in 18 of 18 patients during syncope. No patients developed EEG abnormalities before the onset of presyncope, and the proportion of patients with EEG abnormalities gradually increased throughout presyncope. During presyncope, theta and delta wave slowing, and background suppression were noted in eight of 14, nine of 14 and one of 14 patients, respectively. During syncope, theta and delta wave slowing, and background suppression were noted in nine of 18, 11 of 18 and six of 18 patients, respectively (not significant versus presyncope). There were strikingly abrupt changes in the EEG rhythm within 15 s of the transition to syncope in 14 of 18 patients. Six patients developed new theta wave slowing, 11 developed new delta wave slowing, and seven developed background suppression. No epileptiform activity was recorded.

CONCLUSIONS

Both presyncope and syncope induced by tilt testing are associated with EEG abnormalities, and no single EEG pattern is pathognomonic of either. The transition from presyncope to syncope is marked by abrupt EEG changes.