Technical aspects and clinical results of an esophageal pick-up for better recording of posteriorly generated heart sounds.

A miniature esophageal microphone has been constructed. It has a cylindrical shape with 5-mm outer diameter and 25-mm length. It is a type of accelerometer that detects vibration from the esophageal wall. It has a resonance frequency of 2.1 kHz and an acceleration charge sensitivity of 2.8 pCm-1s2. The upper limit of the useful frequency range is about 1 kHz. It has directional sensitivity which reaches a maximum perpendicular to the plane of the crystal. With the esophageal microphone cardiovascular sound is recorded simultaneously with other tracings: external phonocardiogram, E.C.G., carotid pulse and M-mode echocardiogram. The great advantage of the application of the esophageal microphone is that it can be positioned in the esophagus close to the mitral valve and the left atrium by use of fluoroscopy, so that sounds and murmurs originating from that part of the heart are recorded in detail. In a case of a shunt between aorta and pulmonary artery the microphone was used at different levels in the esophagus, showing different amplitudes of a continuous murmur. In all other cases the probe was situated in the esophagus just above the level of the mitral valve behind the left atrium. In 2 cases the advantage of the esophageal microphone (revealing signs of slight mitral incompetence) over the body surface microphone is shown. In 3 patients with artificial valves in the aortic and mitral orifices (where left heart catheterisation and left ventricular angiography is a considerable risk), the esophageal microphone also improved the postoperative evaluation and diagnosis of mitral valve regurgitation considerably.