Question

what is ECG?How is it performed?

Answer 1

Electrocardiograms — also called ECGs or EKGs — are often done in a doctor's office, a clinic or a hospital room. And they've become standard equipment in operating rooms and ambulances.
An electrocardiogram records the electrical signals in your heart. It's a common test used to detect heart problems and monitor the heart's status in many situations. 

Answer 2

Electrocardiogram (ECG):

 Electrocardiograph is a machine which gives electrocardiogram (ECG).

 Electrocardiogram is a graphical representation of electrical activity of heart during a cardiac cycle.

 To obtain an ECG, a patient is connected to the machine with three electrical leads (one to each wrist and one to left ankle).

 Wavy lines of ECG are called deflection waves.

 P-wave represents depolarization of atria which leads to contraction of both atria.

 QRS complex represents depolarization of ventricles which initiates ventricular contraction. The contraction starts shortly after Q and makes the beginning of ventricular systole.

 T–wave represents ventricular repolarisation (return of ventricles from excited to normal state).

Note:  

• End of T–wave marks the end of ventricular systole.

• By counting number of QRS complexes, one can determine the heart rate of an individual.

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