Oesophageal electrocardiography in healthy horses

Reasons for performing study: In human medicine, esophageal electrocardiography (ECG) is a well-established technique that magnifies P waves with respect to the QRS complex. Objectives: To investigate the feasibility of esophageal ECG recording and its ability to produce larger P waves compared to base-apex and unipolar recordings. Methods: Bipolar and unipolar ECG were performed using esophageal and surface electrodes. Esophageal ECG was obtained from six different recording configurations at different esophageal depths. Amplitudes of P, Q, R, S and T waves were measured from three different cardiac cycles for each recording configuration and depth. Results: Esophageal ECG was feasible in all horses. For all esophageal recording configurations, significantly larger P waves were recorded from a depth that equaled ‘height of the withers +10 cm’ (HW+10) than from any other depth. P/QRSmagn, the ratio between the P wave and QRS complex magnitudes, was largest for intra-esophageal recordings with an interelectrode distance of 10 cm, at HW+10, where it was significantly larger than base-apex and unipolar recordings. Base-apex recording resulted in significantly smaller P waves than all other recording configurations and significantly smaller P/QRSmagn ratios than all other recording configurations except one combined esophageal-surface recording (E/Slow). Conclusions: Esophageal ECG recording is feasible in horses and effective in magnifying P wave amplitude. Potential relevance: The procedure is promising for diagnosis of supraventricular tachydysrhythmias and might be used in electrophysiological studies and for cardiac pacing