Background: Myocardial ischaemia (defined as an ST-segment depression on ECG) may occur during upper gastrointestinal endoscopy, but the mechanism is still unknown. The aim of our study was to evaluate the effect of oxygen therapy and tachycardia on the occurrence of ST-segment depression during routine diagnostic esophagogastroduodenoscopy.
Methods: Eighty-nine consecutive patients were randomized to receive either oxygen (21/min by nasal prongs) or nothing during endoscopy, in which arterial oxygen saturation was measured by continuous pulse oximetry, and ECG was measured continuously with a Holter tape recorder.
Results: A total of 28 patients (12 receiving oxygen) developed ST-segment depression ( > 0.1 mV) during endoscopy. In 22 patients (12 receiving oxygen) ST depression was related to tachycardia, and in 5 of these (none receiving oxygen) simultaneous episodic hypoxaemia was present during the event. Thus, in every case of ST depression related to episodic hypoxaemia there was simultaneous tachycardia. In six patients developing ST depression during endoscopy we did not find preendoscopy levels, and 63 patients (29 receiving oxygen) developed tachycardia during the procedure (rate > 100 min-1_.
Conclusions: Oxygen therapy had no significant effect on the occurrence of ST-segment depression during upper gastrointestinal endoscopy. The results suggest that tachycardia is more important than hypoxaemia in the pathogenesis of ST depression during gastroscopy.