Sudden Cerebral Vasoconstriction During Induced Polymorphic Ventricular Tachycardia and Fibrillation: Further Observations of a Paradoxic Response

Abstract

To determine the effect of induced polymorphic VT/VF on the cerebral circulation, transcranial Doppler (TCD) ultrasonography was used to prospectively assess changes in cerebral blood flow velocity during ICD implantation. Fourteen patients (13 men, 1 woman, mean age 58 +/- 20 years, range 34-74 years) who were survivors of an out of hospital cardiac arrest, were evaluated during routine ICD implantation. TCD ultrasonography was used to assess middle cerebral artery systolic velocity (Vs), diastolic velocity (Vd), pulsatility index (PI = Vs-Vd/Vmean) and resistance index (RI = Vs-Vd/Vs) before, during, and after DFT testing with alternating current induction of polymorphic VT/VF. In each of the 14 patients studied, concomitant with the abrupt onset of hypotension, TCD sonography demonstrated a 33% +/- 28% decrease in diastolic velocity, a 42% +/- 28% increase in systolic velocity, a 190% +/- 141% increase in PI, and a 44% +/- 19% increase in RI. These findings reflect an increase in cerebrovascular resistance secondary to arteriolar vasoconstriction distal to the point of insonation of the middle cerebral artery. This response is paradoxic, as the expected response of the cerebral circulation to hypotension is vasodilation, but it is consistent with observations made in other acute hypotensive settings, such as tilt induced neurocardiogenic syncope.

Cerebral Oxygenation During Defibrillator Threshold Testing of Implantable Cardioverter Defibrillators

“…The levels of HbO 2 , Hb, and MABP gradually recovered to baseline values following the restoration of sinus rhythm by device delivered or external rescue shocks. Transcranial Doppler studies have also shown a delayed recovery of cerebral blood flow after induced VT or VF 2,27,28 . Although our recovery times did not correlate with the duration of time in CA, they were similar to those detected by positron‐emission tomography following the restitution of sinus rhythm 29 .…”

“…Transcranial Doppler studies have also shown a delayed recovery of cerebral blood flow after induced VT or VF. 2,27,28 Although our recovery times did not correlate with the duration of time in CA, they were similar to those detected by positron-emission tomography following the restitution of sinus rhythm. 29 All parameters were restored to baseline levels by 30 seconds.…”

Wird die Hirndurchblutung durch Veränderungen des Herzzeitvolumens beeinträchtigt? Messungen der Hirndurchblutung an Normalpersonen während Volumenbelastung und an Herzschrittmacher- Patienten bei Veränderungen der Stimulationsfrequenz

“…Eine Reihe von Untersuchungen deuten darauf hin, dass Patienten mit Herzrhythmusstörungen -insbesondere Tachyarrhythmien -nicht nur eine chronisch erniedrigte Ruhedurchblutung, sondern auch eine Störung der zerebrovaskulären Autoregulationsfähigkeit haben (7,8,15,20). Dies ist zum einen auf einen Akuteffekt der kurzzeitigen Rhythmusstörungen auf den Blutdruck zurückzuführen bei dem die Mechanismen der Autoregulation nicht greifen, zum anderen über einen chronischen Effekt auf die Reaktivität der zerebralen Gefäße auf physikalisch-rheologische Veränderungen.…”