HUMAN ANATOMY AND PHYSIOLOGY

 NORMAL ECG::

When impulses are formed in SA node potential is not observed as soon as they reach atrial musculature within 0.04 sec potential rises by 0.2 mV and then fall to zero because of repolarization of the musculature the wave thus obtained is p wave 

            Next the impulses are picked up by AV node and spread through bundle of his and purkinje fibres there is no deflection so an isoelectric line is seen when impulses reach intermuscular septum a negative deflection is seen This is Q wave Immediately impulses spread in ventricular musculature and a big wave of 1.8 mV is seen this is R wave 

                    After this there is again a pause or isoelectric line and the ventricular repolarization occurs which give a deflection of 0.4 mV This is the QT wave 

The normal electrocardiogram(ECG)

Important events/intervals of electrocardiogram on bipolar leads

Wave/segment            Potential         Time                 Significance 

P                                    0.2mV            0.08 sec             atrial depolarization 

QRS                               1.8mV            0.06                    Ventricular depolarization

T                                    0.4mV            1.12sec                Ventricular repolarization 

P-R interval                     ---                0.12-0.2sec            Indicates the conduction of

                                                                                            impulse from SA node to

                                                                                               node to AV node

ST segment                     --                    0.12sec

QT interval                    --                        0.4sec