1. Field of the Invention
This invention relates to medical instrumentation and, more particularly, to electrocardiographic and cardiocirculatory monitoring equipment.
2. Prior Art
Every muscle can perform only one movement; the shortening of its fibers by contraction. This also applies to the heart muscle. Every action of a muscle has associated with it an electrical activity which changes in the course of the contraction. The electrical signal thus associated with the muscle action is transmitted through various tissues and ultimately reaches the surface of the body. There such electrical signals can be detected by electrodes applied to the skin. Thus, such signals that are being detected by the electrodes can be recorded with the aid of suitable electrocardiographic equipment or can be observed in/or recorded with a monitor/recording unit. The record thus obtained is called an electrocardiogram or a rhythm-monitoring strip.
As early as 1855 action currents from the heart were recorded, as measurements were being made of a beating frog heart. The first actual recording of a frog electrocardiogram was made by A. D. Waller in 1887. The first recording of a human heart electrical action signal (hereinafter the "heart-signal") was made by A. D. Waller in 1889. Modern electrocardiograph, however, started with Einthoven, who invented the string galvanometer (and is credited with the bipolar lead triangle setting for recordings of standard limb leads I, II, III) and applied it to recording small voltages of short duration, which is the category into which heart-signals fall. His recording techniques have not been improved upon very much since they were first published many years ago. Here it should be noted that the term "lead" as used herein is being used in the medical sense and not the electronic sense (i.e., "lead" is a spatial position at which the heart-signal is viewed, not a wire).
After Einthoven's work, the entire field of research stagnated for nearly 30 years until the introduction by Wilson of upper and lower extremities' local leads and the zero electrode used in unipolar recordings. The entire 12-lead system is fed by unipolar and bipolar signals. Unipolar leads are divided into unipolar extremity or limb leads and unipolar precordial or chest leads.
In unipolar limb leads the three extremity leads are;
aVR -- the unipolar right arm lead, (R designating the right arm); PA0 aVL -- unipolar left arm lead (L designating left arm); and, PA0 aVF -- unipolar left leg lead,
in all of which the "a" stands for "augmented".
The unipolar chest leads are designated by the letter V followed by a subscript numeral which represents the exact location on the chest. In a standard setting there are six precordial leads V1-V6.
In standard limb bipolar leads, lead I is the potential difference between the arms, i.e. left arm potential minus right arm potential. Lead II is the potential difference between the left leg potential and the right arm potential. Lead III is the potential difference between the left leg and the left arm. If the leads are diagrammed on the body they inscribe, essentially, an equilateral triangle. The electrocardiograph generates the lead voltages from the potentials applied to it from the bipolar electrodes. The term "lead" as used in electrocardiography means "view" of the heart's electrical impulse. That "view" varies between leads.
The electrocardiograph is widely used by the medical profession. The standard electrocardiograph requires at least 10 wires to be attached to the body of the patient at one end, and to the electrocardiograph at the other end to detect heart-signals and transform them into a 12 lead electrocardiogram evaluation. This involves attaching six electrodes to the chest or precordial area to obtain recordings of leads V1-V6 as well as attaching 4 electrodes, the arms and legs of the patient to obtain recordings of leads I, II, III, AVR, AVL, AVF. Only three electrodes and three terminal wires are applied to the chest for heart rhythm monitoring. After the ten electrodes are attached to the patient, ten specific wires must be connected between each specific electrocardiograph terminal and the related electrode of predetermined position.
Many and frequent difficulties exist and cumbersome operation of the conventional system arises because of the following factors:
1. Terminal wires from the electrocardiograph have to be connected to the distal electrodes in a pre-determined order. (Defined limb and side to defined wire, as well as specific precordial points to defined precordial wires.) In practice there are relatively frequent errors of connection between a specifically positioned electrode and the specifically associated wire from the electrocardiograph.
2. Often, the 10 terminal wires become intertangled with each other and it takes precious time to get them untangled.
3. When the electrocardiograph is to be operated by an Intensive Coronary Care Mobile Unit, which operates in relatively abnormal conditions, often speed of utilization of the system is crucial since life-threatening situations are involved. In this environment the existing electrocardiographic system exhibits low efficiency and low effectiveness.
4. Since the terminal wires are re-used, if they have any manufacturing defects inherent in them or develop such defects with use throughout their long extent (defects often difficult to detect), operation of the system, (the electrocardiograph or monitor), is unsatisfactory.
5. During surgical procedures the patient is monitored for arrhythmias. Often the wires which extend beneath or beside the sterile field become disconnected from the electrodes during the procedure and it is difficult, out of the sterile surgical field, to reconnect the necessary wires. It is also time consuming and interruptive of the procedure.
6. During hospitalization, rhythm-monitored patients occasionally are permitted to ambulate within the department area. Often the patient disconnects the wires connected from the bedside monitor to the electrodes in order to take a walk or visit the restroom in the area. During this period no rhythm monitoring is possible.
Therefore, it is an object of this invention to overcome the problems previously experienced in connection with application of electrocardiographs in the taking of electrocardiograms and in connection with the rhythm monitoring of patients.
It is a further object of this invention to provide electrocardiographic and rhythm monitoring systems in which the physical wires between the patient and the electrocardiograph or monitor are eliminated.