Oesophageal electrocardiography in healthy horses.

REASONS FOR PERFORMING STUDY: In human medicine, oesophageal electrocardiography (ECG) is a well-established technique that magnifies P waves with respect to the QRS complex.
OBJECTIVES: To investigate the feasibility of oesophageal ECG recording in horses and its ability to produce larger P waves compared with base-apex and unipolar recordings.
METHODS: Bipolar and unipolar ECG were performed using oesophageal and surface electrodes. Oesophageal ECG was obtained from 6 different recording configurations at different oesophageal depths. Amplitudes of P, Q, R, S and T waves were measured from 3 different cardiac cycles for each recording configuration and depth.
RESULTS: Oesophageal ECG was feasible in all horses. For all oesophageal recording configurations, significantly larger P waves were recorded from a depth that equalled 'height of the withers + 10 cm' (HW(+10) ) than from any other depth. P/QRS(magn), the ratio between the P wave and QRS complex magnitudes, was largest for intraoesophageal 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/QRS(magn) ratios than all other recording configurations except one combined oesophageal-surface recording (E/S(low)).
CONCLUSIONS: Oesophageal 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.