Impact of high intensity transient signals on the choice of mechanical aortic valve substitutes.

Abstract

High intensity transient signals (HITS) observed during extracorporeal circulation and following mechanical valve replacement are suspected of causing cognitive dysfunction (deterioration of episodic and working memory). This study evaluates the role played by valve design (bileaflet versus tilting disc) and other parameters in the incidence of HITS. Thirty patients were selected for the study as follows: 18 males, 58-78 years of age; ten St. Jude Medical, ten CarboMedics, ten Medtronic Hall (MH); all size 23, in optimum orientation (Ann Thorac Surg 68 (1999) 1069); all in sinus rhythm; no coronary or carotid artery disease; all in sinus rhythm, international normalized ratio greater than 2.5 and all at least 9 months postoperative. All patients had bilateral HITS measurement in both middle cerebral arteries via transcranial doppler for 30 min. If five HITS or more were observed during the initial 10 min, patients were subjected to 100% oxygen breathing followed by 10 min of normal air breathing. Simultaneously, HITS were measured in the right radial and femoral arteries. Patients with bileaflet valve substitutes revealed HITS rates varying from 32 to 108 counts/h. There was only one HITS observed in the MH valve group during the 5h observation period (0.2 HITS/h). There were no HITS detected in either the radial or the femoral arteries in any patient. After breathing 100% oxygen, HITS significantly decreased or completely disappeared (0-30 HITS/h). When normal air breathing was resumed HITS reappeared or increased. With an intravenous infusion of 100 mg of lysine acetylsalicylate (Aspisol, Bayer Leverkusen, Germany), HITS decreased by 16 to 41%. We conclude that bileaflet mechanical valve prostheses produce HITS even in their optimum orientation. HITS following bileaflet valve replacement have an unstable nature and might be composed of nitrogen and platelets. Tilting disc valves in their optimum orientation provide almost physiological conditions with HITS measured in the same range as bioprosthesis.