Listening to the electrocardiogram.

THE concept of listening to the electro-cardiogram brings up an interesting question and one that most cardiologists, even ones with long experience in electro-cardiography, have largely ignored. What would you expect to hear if any of the usual leads were amplified by a suitable electronic device and the output were connected to a loud speaker or to head phones? Since the QRS complexes are the only deflections in the electrocardiograms that are of high enough frequency to be in the audible range, one would expect to hear these complexes as short sounds, but the P and T waves, with their very low basic frequencies, would not in general be audible. Although there has been little interest in listening to QRS complexes, it is possible that with experience a physician might be able to suspect the presence of intra-ventricular block, especially if this is associated with an increase in high frequency components as often occurs in myocardial in-farction and some types of diffuse myocardial disease. The reader, at this point, will no doubt think the above is nonsense and suggest that we stop wasting time and get an electrocar-diogram. He is, of course, correct; but sometimes using another of our special senses (that of hearing) on a problem that was previously studied entirely in a visual fashion may lead to unexpected and valuable information. Suppose a technique could be developed which would make it possible to hear the atrial waves and the T waves, as well as the QRS complexes, and further that the instrument, capable of doing this, be relatively inexpensive and so simple that it can be put in operation in less than a minute. "The Electrocardio-phone" described by Dr. Henry L. Green in 810 this issue of Circulation is such an instrument. The principle on which the electrocardio-phone is based is simple and was employed several years ago by the writer to make low frequency (sub-audible) vibrations over the precordium audible. The instrument consists of an audio-frequency oscillator which produces a musical note which is heard from a small built-in speaker or with headphones. The electrocardiographic voltages are picked up by two knurled electrodes permanently fastened on the base of the device. A third electrode serves as a ground and provides stability when the instrument is placed on the precordium. The electrocardiographic voltages, after amplification, are used to modulate the audio-frequency oscillator, thus changing the pitch of the …