The oesophageal route in clinical electrocardiology
Abstract: The subject of this thesis is the clinical use of the oesophageal electrode in electrocardiology. The three areas covered are oesophageal electro- cardiography, the biophysics of transoesophageal atrial stimulation (TAS) and the clinical utility of TAS. The literature is reviewed with respect to these areas. TAS was performed in 64 patients with documented supraventricular tachycardia (SVT) or a clinical history suggesting this disease. A subgroup of the patients underwent an invasive electrophysiological study (EPS) as well. It is concluded that the inducibility of SVT by TAS is high and comparable with that obtained by EPS. The accuracy of conventional M-mode echocardio- graphy in locating the site of accessory pathways was assessed in 21 patients with overt WPW (Wolff-Parkinson-White) syndrome during sinus rhythm and during TAS and compared with the correspon- ding accuracy of a 12-lead ECG algorithm. Correct location of the accessory pathway during sinus rhythm could be attained in the majority of patients by both methods. TAS applied during echocardiography could amplify the precontraction but gave only limited diagnostic information. The influence of body position, interelectrode spacing, electrode surface area and stimulation waveform on pacing thresholds during TAS was assessed. Further, the effect of intra- oesophageal local anaesthesia and pacing waveform on the discomfort experienced during TAS was studied. Neither the interelectrode pole distance, the pole surface area nor the body position had any significant influence on pacing thresholds. Intra-oesophageal lidocaine did not affect the pacing discomfort. The peak pacing thresholds using the triangular waveform were significantly higher compared to thresholds using a square waveform. A new non-invasive method called "Frequency Analysis of Fibrillatory ECG" (FAF-ECG) for the assessment of the dominant atrial cycle length (DACL) during atrial fibrillation is introduced. The DACLs were derived from lead V1, the oesophageal lead and right and left atrial invasive recordings. The DACL may be useful as an index of atrial refractoriness. Spatial dispersion in DACL occurs in some patients.
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