Vectorcardiography

Introduction

This method is used for manual construction of the monocardiogram. It was applied to the waves of atrial depolarization (P waves), waves of ventricular depolarization (QRS complexes) and waves of ventricular repolarization (T waves). The resultant traces are loops of variable shapes and they are referred to as P loops, QRS loops and T loops. As this method follows the principals of spatial orientations of the vector quantities, these loops are projections of spatial loops upon the frontal plane. Many researchers have attempted to standardize nomenclature and symbolic representation of the spatially oriented loops. This is done by introducing sE into the symbols for the loops, the E to indicate electric quantities of vectorial nature and the “s” to indicate that these are spatial in orientation. Therefore, these loops indicate the loops as they appear oriented in space. This nomenclature can also indicate the frontal plane projections of the respective spatial loops.

It is important to mention that scientists using this method of vector analysis recognized the error in identification of right and left bundle branch currents at that time. These observations were confirmed later.

The manual method of obtaining the monocardiograms graphically was tedious and inaccurate.

It is important to mention that scientists using this method of vector analysis recognized the error in identification of right and left bundle branch currents at that time.

Therefore, the researchers attempted to employ the cathode ray oscilloscope to obtain monocardiograms directly. But the cathode ray tubes of that time were unsatisfactory for the purpose. Then an ingenious three-coil galvanometer was made which was capable of responding to the potential differences of the three standard leads at one time. Despite the obvious mechanical limitations of such instrument, it was successful in obtaining direct recordings. As a consequence of the difficulties involved in manual graphing and mechanical or automatic recording, the monocardiogram was ignored for many years by most observers. Then successful use of the cathode ray oscilloscope for automatic recording was reported in 1936. Wilson and Johnston suggested the scientific name vectorcardiogram as it was more specific and descriptive than the term monocardiogram.

Methods in vectorcardiography

Graphic construction of electrocardiographic leads and use of the cathode ray oscilloscope are the two main methods involved in the vectorcardiography. There is no doubt that the latter is the method of choice. Construction of vectors from leads of the electrocardiogram is subject to considerable errors, even when they are recorded accurately. It has been proved by oscilloscopic recordings that shifting the time phase of two electrocardiographic leads by even a few milliseconds may appreciably alter the contour of a normal vectorcardiogram. This can occur from the same set of potential differences and may actually changing the direction of inscription of a plane projection of a QRS loop. Since the time scale conventionally employed in electrocardiography from electrocardiograms are likely to have some errors. Vectorcardiograms derived from electrocardiographic leads which are not simultaneously recorded are subject to even greater error.

The use of precordial leads of the electrocardiogram to indicate the direction of spatial vectors, can be successively obtained by two methods. This can be done from a single complex to record a spatial vectorcardiogram or from average values of many complexes to obtain a spatial mean electric potential. This introduces possible errors related to the proximity of the exploring electrode. This also includes errors in construction described in the preceding discussion.

Methods of Recording

The preferred methods for recording vectorcardiography involve the use of the cathode ray oscilloscope as the recording galvanometer. Techniques can differ depending on the amplifier circuits, photographic equipment, reference frame, and special switching devices for automatic recording of selected aspects of the trace which are used. Although nearly accurate cathode ray oscilloscopes exist, there is room for considerable improvement in electric circuits. There is also scope for improvement in simplification of procedures of photography, and in interpretation of recordings. Detailed information of accomplishments existing today may be obtained by consulting the researchers.