Cerebral autoregulation appeared to be initially intact in all patients. This effect, at times, may be profound, as illustrated in Figure 2. A representative real time tracing of trancerebral Doppler flow during an episode of VT, terminated by ICD shock. 2 Cerebral blood flow recording during VT . There was no consistent relationship between cycle length and CBF decrease, however.
Autoregulation is achieved by momentary regional adjustments in cerebrovascular tone.
During episodes of VT, systemic pressure typically falls transiently below the lower limit of autoregulation. In this situation, cerebral vasodilatation and diminished cerebrovascular resistance lose their ability to offset the effects of the profound decrease in cerebral perfusion pressure. At this stage CBF becomes dependent on systemic pressure. The results of the present study are consistent with these concepts. Therefore, those with higher set points appear to be inordinately sensitive to transient episodes of hypotension.