Maechler H, Lueger A, Huber S, Bergmann P, Rehak P, Stark G: The Internet Journal of Thoracic and Cardiovascular Surgery 1999; Vol2 (2), 1999. http://www.ispub.com/journals/IJTCVS/Vol2N2/esoecg.htm. Introduction: Because of suboptimized techniques, concerning leads and amplification methods, the esophageal ECG was thus only used to detect atrial arrhythmias. The esophageal ECG would be suitable for detecting intraoperative myocardial ischemia. Methods: The esophageal ECG signals are detected with a bipolar esophageal probe. The signals are passed to a new high-resolution preamplifier (frequency range 0.01-2000 Hz), further on to an analog-digital-board and finally are visualized on a PC for definite evaluation. Results: Compared with the surface ECG, the esophageal ECG could detect significantly more ischemic episodes in both, an animal comparison study (93% versus 47%) (n = 18), as well as in coronary artery bypass graft ( CABG) surgery. At the beginning of anesthesia 85 % of the high risk CABG patients showed ischemic episodes with the esophageal ECG (18% detection rate with the surface ECG), which were correlated with an adverse postoperative outcome (p<0.05). In addition to that, 8 of 18 CABG patients had a mean of 483 ± 119 high-amplitude, biphasic atrial components during cardioplegia (on the surface ECG, only one patient showed 26 P-potentials). Such atrial activities, visually not detectable, were correlated with postoperative supraventricular arrhythmias in 88 %. Conclusions: The clinical relevance is that the esophageal ECG represents a convenient technique with high sensitivity, to monitor intraoperative myocardial ischemia and to detect atrial activity during cardioplegia.