Microembolic Signals and Serum Markers of Neuronal Damage During Transcatheter Aortic Valve Implantation.

Overview

Transcatheter Aortic Valve Implantation (TAVI) using femoral access is an option for definitive treatment of aortic stenosis when open-heart surgery is considered inappropriate. By avoiding the effects of cardiopulmonary bypass on cerebral hemodynamics and microembolic load, TAVI is assumed to be beneficial regarding risk for neurological complications. We anticipated that the extensive endovascular retrograde manipulation in ascending aorta and aortic root would generate a detectable cerebral microembolic load, and thus an increase in serological markers of neuronal injury postoperatively. Our hypothesis is that there is a positive correlation between the total amount of cerebral microembolic events during the TAVI procedure and the Area under curve (AUC24hrs) for the release pattern of two markers of neuronal injury. We also wish to describe the extent and distribution of microembolisms during the TAVI procedure using Transcranial Doppler (TCD).

Patients scheduled for TAVI at our institution are screened for inclusion into this prospective, observational study. A multidisciplinary expert committee evaluate all high-risk patients diagnosed with aortic stenosis. If rejected for open-heart surgery, and without contraindications for transcatheter approach, the patient is offered treatment with TAVI using the CoreValve ® (Medtronic, Inc., Minneapolis, Minnesota) system. The Human Ethics Committee of the University of Gothenburg, approved the study protocol, and all patients sign an informed, written consent. CoreValve ® is a TAVI system delivering a tri-leaflet bioprosthetic porcine pericardial tissue valve mounted and sutured in a self-expanding nitinol frame, using a trans-femoral or trans-subclavian artery access approach. Details regarding the TAVI procedure have been described previously . On the evening before surgery, the patients receive a loading dose of clopidogrel 300 mg. The morning of surgery an additional dose of clopidogrel 75 mg, together with acetylsalicylic acid 75 mg is given. No sedative premedication is given before the procedure. On arrival at OR, standard perioperative monitoring is established, including an Auditory Evoked Potential (AEP) monitor for anaesthetic depth measurements (AEP Monitor/2, Danmeter, Odense, Denmark) and radial arterial and central venous lines. General anaesthesia is induced with propofol 0.5-1 mg/kg and fentanyl 100-150 μg. Tracheal intubation facilitated using atracurium 0,5 mg/kg. A propofol infusion is used to maintain an anaesthetic depth adjusted to an AAI index of 15-30 as recorded by the AEP monitor. Hemodynamic stability is obtained by the use of colloidal solution administration, guided by the use of intra-operative transesophageal echocardiography, and norephineprine to maintain a mean arterial pressure above 75 mmHg. During the procedure, intravenous heparin is administered to achieve an activated clotting time \> 250 sec. Catheters and guide-wires are flushed and cleaned according to standard procedures at our laboratory. The preparation of the valve is performed according to the instructions of the manufacturer. The balloon valvuloplasty of the native aortic valve is performed under rapid right ventricular pacing (180 bpm) and the self-expandable prosthesis deployed stepwise without pacing. The same team of two interventional cardiologists and one cardiothoracic anaesthesiologist perform all procedures. A certified cardiologist or anaesthesiologist assess focal neurological impairment before and within 24 hours after the procedure.