Electrocardiogram| ECG| Why ECG done| ECG Leads| Einthoven's triangle| Procedure

Electrocardiogram

Electrocardiogram is the record or graphical representation of electrical activities of the heart which occur prior to the onset of mechanical activities. ECG tells about the electrical changes that occur extracellularly in heart during generation and propagation of action potentials (sequential depolarization and repolarization of cardiac muscle fibers) in the various regions of the heart.

Why ECG is done?

-To determine following ;

1. heart rate =300/no. of large box in RR interval
2. Rhythms of heartbeats =irregular regular or irregular irregular
3. to know PR interval
4. to know previous heart attack
5. to know problems in heart's valves

ECG Intervals

ECG Leads

• ECG leads refer to the two electrodes which are placed on the body surface and connected to ECG machine for measuring the potential fluctuations between only two points.
• ECG is recorded using two types of lead systems, the bipolar leads and unipolar leads.
• Bipolar leads
• Lead I
• Lead II
• Lead III
• Augmented unipolar limb leads
• aVL, aVF and aVR.
• Unipolar chest leads
• Leads V1, V2, V3, V4, V5, V6
• If electrograms are taken simultaneously with the three limb leads, at any given instant the potential in lead II is equal to the sum of the potentials in leads I and III.

Einthoven's triangle

• An equilateral triangle whose vertices lie at the left and right shoulders and the pubic region and whose center corresponds to the vector sum of all electric activity occurring in the heart at any given moment, allowing for the determination of the electrical axis.
• The center of the triangle offers a reference point for the unipolar ECG leads.
• This illustrates that the two arms and the left leg form apices of a triangle surrounding the heart. The two apices at the upper part of the triangle represent the points at which the two arms connect electrically with the fluids around the heart, and the lower apex is the point at which the left leg connects with the fluids.

                                                  

          

            

what happened during ECG?

• Patient should wear a gown.
• Patient need to lie still on a table.
• Technician attaches 12-15 soft electrodes with gel to patient's arm, chest and legs.
• Electrodes are attached to electrical leads (wires), which are then attached to the EKG machine.
• Machine records your heart’s electrical activity and places the information on a graph.
• After the procedure, the electrodes are removed and discarded.
• The entire procedure takes about 10 minutes.