UNIPOLAR LIMB LEADS:

         The connection is these leads are (a) an exploring electrode and (b) an different electrode which is produced by joining the limbs leads together and hence through a resistance, so for all practical purposes this lead is neutral. These leads are termed 

  AVR--- The exploring electrode is placed on right arm. AVR stands for augmented voltage right arm. 

 AVL--- The exploring electrode is laced on left arm. AVL stands for augment voltage left arm.

 AVF --- The exploring electrode is placed on left leg against the right and left arm electrodes which from the neutral. AVF. stands for augmented voltage left foot.

       (c) UNIPOLAR CHEAT LEAD (WILSON CHEST LEAD ):

           These leads allow examination of the cardiaic vector in the horizontal plane, with the chest electrodes placed in position v1 to v6. 

                The E.C.G. instrument lead selector usually has' a position marked V or C referring to the chest leads. When the chest lead position is selected in the E.C.G. It records the potential between the chest electrode and an indifferent electrode formed by a resistance network connection of the three limb electrodes. 

              ROBERT, ZELENSKI, PROFESSIOR OF EMERGENCY MEDICINES, WAYNE STATE UNIVERSITY, DETROIT, AND COLLEAGUES in 1993 published an important article on the clinic use of the fifteen (15) lead E.C.G. which use v7, v8 and v9 in the diagnosis of acute coronary deseases, These additional leads increase the sensitivity of the electrocardiogram in the detection of myocardial infarction. 

                                                         THE E.C.G MACHINE 


 

               The E.C.G machines available, may be divided into single channel or three channel recorders. The single channel recorder, records only one E.C.G. leads on the paper at a time, hence the complete E.C.G. appears on a long and narrow strip of paper containing all the E.C.G. leads recorded in a sequential manner. The three channel recorder utilises a much wider. E.C.G. paper and have multiple pen system so as to enable three E.C.G. lead to be recorded simultaneously. Three channel recorder are commonly used in place where the work load id high.

                       The single channel recorders are the ones most commonly used by most medical practitioners because they are relatively cheap, simple and portable. 

               The majority of E.C.G. machines are now available with a rechargeable battery pack option which makes them more versatile as they are not dependent on mains supply. Now automatic E.C.G. machines are available which step through and record a predetermined sequence of E.C.G. leads.

           Most older E.C.G. machines have a write out system that utilises a heated stylus in contact with wax-coated or them sensitive E.C.G. paper. This is quite simple but the paper is expensive and the heated stylus drains the battery relativity quickly. other forms of right out machine including inkjet felt-tip stylus which can be used with low cost paper and digital thermographic system which produce a high resolution output. 

                                                                E.C.G. PAPER 

           E.C.G. paper is actually a graph paper having both horizontal and vertical lines. In both horizontal and vertical directions the lines are at a distance of 1 MM. The lines representing 5mm both in vertical and horizontal direction are thick and bold while the other lines in between are thin. The speed of paper movements is preadjust in the machine at 25 mm. per second. AT this speed each vertical line represents 0.04 sec. on the x-axis and thick line (thine 5 lines)represent 0.2 seconds. On standardistation by pressing the 'std button' in the machine a current of 1 mv. is released to the stylus of the E.C.G. machine which is recorded as 10 mm deflection in the 'y' axis. So 1 mm. Horizontal line represents a current of 0.1 mv. 1