Flexible MEA for adult zebrafish ECG recording covering both ventricle and atrium

This paper presents a flexible parylene micro-electrode-array (MEA) that records Electrocardiograms (ECG) from the Zebrafish heart in-vivo, covering both the ventricle and atrium area. ECG is a powerful tool for monitoring the heart activity. While ECG technology for human has been well established, this is not true for zebrafish. Our previous work demonstrated baseline ECG recording from zebrafish using MEMS MEAs [1, 2]. However, due to the body structure and small size of the zebrafish (e.g., the heart is roughly 1mm in size and its atrium is buried deep in the thoracic cavity, Fig.1b.), all zebrafish ECGs to date were only recorded from the ventricular side, making it easy to miss important electrophysiological signals from the atrium. To our knowledge, ECG from the atrial angles in Zebrafish has not yet been demonstrated. This work describes a flexible MEA implant (i.e., specially designed according to zebrafish heart anatomy) that records from both the ventricular and the atrial angles. Furthermore, to demonstrate that this device is useful for heart regeneration monitoring, our work also includes ECG recording before and after laser damage on the ventricle (532nm green light, 32mJ/mm², 20mJ total). This chosen energy level of laser pulse is first calibrated using ablated heart histology by EthD-1 florescence staining. The post injury ECG data clearly show ST-wave depression, an indication of ventricular abnormal repolarization state. In addition, repeated missing T-wave is observed from the channels recorded from the atrial angles, which indicate abnormalities in atrial physiology. A hypothesis is that since absorption coefficient of 532nm light in body tissue is rather low, the laser beam penetrated deeply in the heart and created damage deep in the atrium as well as the ventricle. The MEA presented here shows potential for an effective tool to study long-term adult zebrafish heart development and regeneration.