Changes in cerebral perfusion during third-generation implantable cardioverter defibrillator testing.

Third-generation implantable cardioverter defibrillators (ICDs) are designed to provide tiered therapy for ventricular tachycardia and ventricular fibrillation. At present, however, therapy prescription does not take into account the hemodynamic consequences of ventricular dysrhythmias. Design of "intelligent" devices depends on their ability to assess hemodynamic consequences of tachyarrhythmias and end-organ perfusion. Quantitative electroencephalography (QEEG) and transcranial Doppler flow provide sensitive and specific measures of cerebral perfusion during ICD testing and programming. In response to prolonged hypotension (> 15 seconds), transient loss of alpha power (i.e., increase in delta power) in the EEG spectrum, accompanied by impaired cerebrovasomotor reactivity (CVR), was observed in 25 of 91 hypotensive episodes in 15 patients, ages 36 to 72 years, predicting intolerance to the programmed ICD therapy. Conversely, intact CVR prevented ischemia, slowing in the EEG, and predicted tolerance to the therapy prescription. These changes were exaggerated in the erect posture during tilt-table ICD testing. During ventricular tachycardia, signs of cerebral hypoxia detected by QEEG and Doppler techniques were accompanied by a fall in transcranial oxyhemoglobin saturation measured by near-infrared spectroscopy. We conclude that transcranial Doppler and QEEG are sensitive indicators of cerebral perfusion. These techniques could be used as indexes of perfusion against which hemodynamic sensors for future ICDs could be evaluated.