Rapid ventricular pacing (RVP) is a technique to obtain flow arrest for short periods of time during dissection or rupture of the aneurysm. RVP results in an adequate fall in blood pressure which presents as an on-off phenomenon. However it is not clear whether repetitive periods of pacing are harmless for the patient. Silent cardiac and cerebral infarcts may be undetected. The investigators will study the safety of RVP, particularly for the heart and the brain.