LESSON STRUCTURE 

7.1 INTRODUCTION 

7.2 ELECTROCADIOGRAPHY ELECTRODES.

7.3 THE C.C.G LEADS.

7.4 THE E.C.G MACHINE 

7.5 E.C.G PAPER 

7.6 C.C.G WAVE RECORDING TECHNIQUE.

7.7 E.C.G WAVE FORM 

7.8 ARTIFACTS IN E.C.G RECORDING.

7.9 QUESTION FOR EXERCISE 

       

                 7.1 INTRODUCTION:  The action exciteable tissues in the body is associated with electrical activity. The contraction of the heart is also associated with electrical activities within it. Though these electrical activities can not be record directly from the heart surface, but they are transmitted to the body surface, though in a reduced magnitude. These small bioelectrical signals can be recorded from the body surface. The main purpose of the E.C.G machine is to record these small bioelectrical signals present on the skin surface as result of electrical activities within the heart. The process of recording is known as Electrocardiography and the record thus obtained is known as Electrocardiogram or E.C.G.

     5.2 ELECTRO CARDIOGRAPHY ELECTRODES:

     5.2.1 DESCRIPTION OF E.C.G ELECTRODE:


           Most E.C. equipments have plate type electrodes for the limp leads and suction type electrodes for the chest leads. The electrodes have hole and screw to accomodate the tip of the patient cables Some new type of electrodes have crocodile clip for holding the tip of the patient cable. These electrodes, after having been fixed on the patient's limbs and chest wall, as detailed below, are connected to the E.C.G machine through the patient cable which are either put in the holes in the electrodes and then tightened with the help of the screw in it (in the hole and screw type) or with the help of the crocodile clip.

     5.2.2 POSITIONING OF ELECTRODES:



          The idea of limb electrodes and the chest electrodes are as follows; 

 LIMB ELECTRODES :                                      POSITION 

* RIGHT LEG (R.L)                                            # Right leg inner side just above ankle 

* LEFT LEG (L.L)                                              # Left leg inner side just above ankle 

* RIGHT ARM (R.A)                                         #  Right forearm above wrist.

* LEFT ARM (L.A)                                            # Left forearm above wrist 

   N.B The recording  Electrodes are R.A , L. A and L.L while R.L is neutral Electrode.

                      **CHEST ELECTRODES:


   v1 -------------   FORTH INTERCOSTAL SPACE AT RIGHT STERNAL ANGLE. 

   v2------------- FOURTH INTERCOSTAL SPACE AT LEFT STERNAL ANGLE 

   v3------------- MIDWAY BETWEEN V2 AND V4.

   v4 ------------ LEFT FIFTH INTERCOSTAL SPACE IN MIDCLAVICULAR LINE.

   v5 ----------- ON SAME HORIZONTLY LINE AS V4 ON ANTERIOR AXILLARY LINE.

   v6 ------------ ON SAME HORIZONTAL LINE AS V4 MID AXILLARY LINE.                

             Error in Electrode placement can significantly affect both quality and the shape of the E.C.G wave from recording. Site on the limbs should avoid bony area and preferably be very closely adhered to.

                              5.2.3. CLECTRODE GEL



:

          The use of a little electrolyte between the skin and the electrode, in a form of a commercial electrode gel is essential. Commercial Electrode gels are usually slightly perfumed and are based on potassium chloride as the electrolyte with a frequent addition of a mild abrassive to help to reduce the skin resistance. A gel should not be spread over too wide an area in the chest since this may cause a short circuit between the various chest electrodes resulting in a distorting of the recording. 

            There must be two point of contact with the body skin to lead the electrical activity of the heart to be recorded in the galvanometer of the E.C.G. machine ; these connections are known as E.C.G. (electrocardiographic) leads. The leads in common use are ;

      (A).  BIPOLAR LIMBLIDES ;

LAED1 - Record Right arm and left arm.

LEAD2 - Record Right are  and left leg.

LEAD3 - Record Left arm and left leg.