Question

please explain the steps and the different parts of an ekg (like the line)

Answer 1

EKG(ECG) Electrocardiogram is a Graphical representation of electrical activity of Heart.This can be used as a test to identify any Abnormality in the Heart.EKG Represents the different Electrical activity occuring in the Heart during Systole and diastole Graphically.

Electrical Activity of Heart Involves-Depolarization and Repolarization.

1.Atrial Depolarization

2.AV nodal Depolarization

3.Ventricular Depolarization

4.Atrial Reploarization

5.Ventricular repolarization.

Resting Membrane potential of myocardial cells=-90 mV

As stimulus reaches myocardial cells,Some positive ions enter the myocardial cell-----RMP changes from -90 mv to -70 mV(Threshold Potential)--At -70 mV Voltage gated Sodium Channels---Rapid Na+ Influx(+ve Charged Ion)-----This Causes further change in Membrane Potential from -70mV to Postive Voltage(approximately +30mV).

This is Called Depolarization.(Restinng membrane Potential which was Negatice(-90mv)Changes to postive voltage due to entry of Na + Ions.

Now,Depolarization sensitive Ca2+ and K+ Channel opens.

Ca2+ channel pump ca inward

K+ Channel pump K+ Outward.

So there is a Net Balance of charge as Positive charges are moving in and out of the cell---Plateu Phase

Later,Ca2+ channels stops,But K+ channels continue to Pump K+(Positive ion)out of the cell.This Changes RMP from nearly positive value back to -90 MV.

This is called Repolarisation(Here RMP is Changed from positive potential back to Resting Membrane Potential(-90mv) due to Efflux of K+ Ions.

This wave of depolarization and repolarization is transmitted from one myocardial cells to other.By this way,Action potenital spreads over Atria---AV node---Inter ventricular Septum--Ventricles.

The different Waves formed in the EKG according to Electrical Activity of Heart are-

1.P wave -This Corresponds to Atrial Depolarisation

(Small wave with Moderate Velocity-Because atrial tissue is less compaerd to ventricular Tissue and Lacks the fast conducting Purkinje System)

2.PR Segment:Isoelectric line corresponds to AV Node Depolarization.

Here SInce AV node depolarisation is very small,ECG machine cannot detect it so iso electric line is formed

3.QRS complex-Corresponds to Ventricular Depolarization-

a)Q-small but high velocity Negative wave,Corresponds to Depolarisation of interventricular Septum)

b)R-Large high velocity positive wave,Corresponds to Major Ventricular Depolarization

c)S wave-Small High velocity Negative Wave .Corresponds to Basal Ventricular Depolarization

4.ST Segment:Iso electric line,Time period between Complete Depolarization of Ventricles and Beginning Of Ventricular Repolarization

5.T wave:Corresponds to Ventricular Repolarization.Moderate velocity Positive Wave.

Atrail Repolariztion Occur during Ventricular depolarization ,Hence it is masked by Ventricular Depolarization So not detected In ECG as indepenedent.