SUDDEN CEREBRAL VASOCONSTRICTION DURING INDUCED POLYMORPHIC VENTRICULAR-TACHYCARDIA AND FIBRILLATION - FURTHER OBSERVATIONS OF A PARADOXIC RESPONSE

To determine the effect of induced polymorphic VT/VF on the cerebral c irculation, transcranial Doppler (TCD) ultrasonography was used to pro spectively assess changes in cerebral blood flow velocity during ICD i mplantation. Fourteen patients (13 men, 1 woman, mean age 58 +/- 20 ye ars, range 34-74 years) who were survivors of an out of hospital cardi ac arrest, were evaluated during routine ICD implantation. TCD ultraso nography was used to assess middle cerebral artery systolic velocity ( V-s), diastolic velocity (V-d), pulsatility index (PI = V-s - V-d/V-me an) and resistance index (RI = V-s-V-d/V-s) before, during, and after DFT testing with alternating current induction of polymorphic VT/VF. I n each of the 14 patients studied, concomitant with the abrupt onset o f hypotension, TCD sonography demonstrated a 33% +/- 28% decrease in d iastolic velocity, a 42% +/- 28% increase in systolic velocity, a 190% +/- 141% increase in PI, and a 44% +/- 19% increase in RI. These find ings reflect an increase in cerebrovascular resistance secondary to ar teriolar vasoconstriction distal to the point of insonation of the mid dle cerebral artery. This response is paradoxic, as the expected respo nse of the cerebral circulation to hypotension is vasodilation, but it is consistent with observation made in other acute hypotensive settin gs, such as tilt induced neurocardiogenic syncope.