T95. The off-label use of external cardiac pacemaker electrode for d-wave intra-operative monitoring: Reliability of a common practice in Brazil

Abstract

Introduction Considered a neurophysiologic biomarker of the motor spinal tract function, D-wave recording is accessed by an epidural electrode (EE) which resembles the external cardiac pacemaker electrode (ECPE). Due to their apparent similarity, ECPE is being largely used instead of EE in economically developing countries due to its lower cost. The aim of our study is to present our D-wave data obtained with the off-label use of ECPE in cases of spinal cord tumor surgeries comparing with the existing data from the literature, discussing its safety and reliability. Methods The ECPE properties were compared with the EE and also the D-wave data of our patients recorded with ECPE and the reported D-wave data from the literature with the EE. Being more rigid them the EE, we decided to use the ECPE only when positioned under direct view. After signing a consent form, 28 patients were submitted to spinal cord tumor resection under total intravenous anesthesia and our standard intraoperative monitoring protocol which consists of upper and lower limbs sensory (SEP) and muscle recorded transcranial motor (mTcMEP) evoked potentials, continuous EMG (cEMG), and epidural recorded transcranial motor evoked potential (epTCMEP) with the ECPE instead of the EE. Results There were a great similarity between the ECPE and the EE, both for technical properties and recorded data. There were no complications regarding the use of the ECPE, despite of being more rigid. Easy-to-identify distal D-waves were recorded in 21 out of 28 patients. There were no distal D-waves in 3 patients which the ECPE were positioned bellow T10 and in additional 4 cases which the ECPE were positioned at upper levels, but proximal D-waves were observed in all of these patients. Proximal D-waves were recorded in 20 patients, because in 8 cases the tumors were too high in the cervical spine or at the spinomedullary junction, preventing the correct positioning of the electrode. From 21 patients with distal D-waves monitored, mTcMEP warnings were reported in 4, but only in one case D-wave amplitude was significantly reduced by the end of the surgery. These patients showed immediate postoperative motor deficit followed by complete restoration of the motor function, despite the one with D-wave amplitude reduction that remained with a partial motor deficit. In 3 patients SEP waves were lost above the level of the surgery at the moment of the myelotomy. Transient postoperative sensory symptoms were observed in 2. The other case with SEP warning was the one with mTcMEP and D-wave warnings that remained with permanent partial motor deficit. Conclusion ECPE is more rigid but has similar properties compared to EE. Recording D-waves with ECPE or EE is comparable and safe. We believe that the ECPE could be approved for D-wave recording in spinal tumor surgeries were the electrode can be placed under direct vision.