CEREBRAL AUTOREGULATION AS A MAJOR DETERMINANT OF TOLERANCE TO VENTRICULAR-TACHYCARDIA IN PATIENTS WITH IMPLANTED CARDIOVERTER-DEFIBRILLATOR

Background. ICD therapy is based on the results of supine electrophysi ologic (EP) testing. However, EP testing does not provide information about tolerance to ventricular tachycardia (VT) during upright posture . Transcranial Doppler (TCD) and cerebral venous oxygen saturation (rC VOS) may be used to assess cerebral blood flow and metabolism. Methods and results. Twenty patients (age 64 '' 8 yrs.) with implanted ICD an d pace-terminable VT, underwent supine and upright tilt (UT) ICD testi ng with continuous TCD and rCVOS monitoring. A bimodal distribution wa s noted, with 15 patients exhibiting NORMAL response (intact cerebral autoregulation) and 5 patients SENSITIVE (abnormal cerebral autoregula tion) resulting in neurologic symptoms during UT. The differences in t he extent of cortical desaturation during VT was significant for SENSI TIVE ( supine 8 '' 4% vs. upright 22 '' 5%, P=.02) but not for NORMAL (supine 6 '' 3% vs. upright 10 '' 4%, P=.1). In the supine position at baseline, cerebral blood flow (CBF) remained independent of mean arte rial pressure (MAP) in both groups. However, during VT the peak system ic pressure transiently fell below the lower limit of autoregulation a nd CBF became dependent on MAP. Upright testing accentuated the impare ment in autoregulation. The linear relationship between CBF and MAP st rengthened in the NORMAL group (r=.70, P=.003), but remained less seve re than the near total loss seen in the SENSITIVE patients (r=.78, P=. 07). There was no consistent relationship between VT cycle length and CBF decrease. Conclusions. (1) Supine ICD testing is insufficient to p redict individual patient tolerance to VT and ICD therapy, (2) UT test ing better predicts tolerance to VT and ICD therapy, (3) Cerebral auto regulation is a significant determinant of tolerance to VT in patients with implanted ICDs.