20 P waveRepresent the electrical activity of both atria ( atrial depolarization)The depolarization slow within the AV node, there is a brief delay or PAUSE before the depolarization conducted to the ventricles
21 Normal duration <0.12 sec Absent P wave: Atrial fibrillation SA Block AV Rhythm Peak P wave: Atrial hypertrophy
22 PR interval Normally :0.12-0.2sec Prolonged in : heart block. Short in : W-P-W syndrome.
23 QRS Complex Represent the electrical activity of both ventricles. Ventricular depolarization( initiation of the ventricular contraction
24 QRS Complex Q wave R wave: S wave : : Normal QRS duration < 0.12 sec
30 ST - SegmentST segment: the plateau phase of ventricular repolarization.Isoelectric or> or<1mm.If the ST segment elevated or depressed beyond the normal baseline this usually sign of serious pathology. (MI)
31 T- Wave T-wave :represent rapid phase of ventricular repolarization. peaked T wave:early MIhyperkalemiaBlack racesInverted :MI .Ventricular hypertrophy.HypokalemiaDigoxin
32 Q-T interval 0.4 sec in HR 70 Prolonged in : Hypocalcemia hypomagnesemia
33 U wave repolarization of the interventricular septum. low amplitude Prominent: suspect hypokalemia, hypercalcemia or hyperthyroidism
34 J waverepresents the approximate end of depolarization and the beginning of repolarizationcamel-hump sign .Hypothermiahypocalcemia.
35 Low voltage ECGObesityEmphysemaCOPDSevere hypothyroidism
36 Rate Normal heart rate 60-100/ min < 60 called bradycardia >100 called tachycardia
44 AXISAt any point during depolarization and repolarization electrical potential are being propagated in different directions. Most of these cancel each other out and only the net force is recorded. This net is called AXIS or cardiac VECTOR