12th Zoology

ECG Electrocardiogram

ECG Electrocardiogram

The electrocardiogram (ECG) is a record of the electric potential
changes that occur in the heart during the cardiac cycle. It is recorded from
the surface of the body. The instrument used to record the ECG is called
Electrocardiogram. The waves of the ECG are due to depolarization and not
due to contraction of the heart. This wave of depolarization occurs first
before the contraction of the cardiac muscle begins.

The electrical activity of the heart was first recorded by Waller in
1887 with a capillary electrometer. But the work of Einthoven who recorded
the ECG with a strong galvanometer only lead to the development of modern
electrocardiography. Einthovan was awarded Nobel Prize in 1924.
A normal ECG is composed of five waves designated from left to
right with the letters P,Q,R,S and T. P,R and T are normally upward or
positive waves while Q and S are downward or negative waves.
ECG-’PQRST’ wave

When the cardiac impulse (originating in sinus node which is the
primary pace maker) passes through the heart, electrical currents spread in
the tissues surrounding the heart. A small amount of this current spreads to
the surface of the body. If electrodes are placed on the skin on opposite
sides of the heart, electric potentials generated by these currents can be
recorded. This recording is known as electrocardiogram (ECGorEKG).
P.Wave: It occurs in the auricles. It is an atrial wave. It is due to the
spread of depolarisation in the atria (auricles). Its duration is 0.1 second and
it occurs just before the atrial systole. Its amplitude is about 0.1 to 0.3 mv.The
cardiac impulse reaches the sinu-auricular node at about the summit of the
Pwave. The P wave is a guide to the activity of atria.
Q,R, and S Waves

After the completion of P wave, the isoelectric interval occurs.
Following this, QR and S waves begin. Q wave is a small negative
downward deflection. It is mostly indistinct. It represents atrial septal
depolarization. R wave is a prominent positive wave and S wave is a small
negative wave. R and S are due to depolarization of the ventricular muscle.
The duration of the QRS complex is about 0.08 second and usually does not
exceed 0.1second. The average amplitude to R wave is about 1 mv. Lot of
diagnostic information can be gained from alteration in the QRS complex.
T wave

Following S wave there is an isoelectric interval. T wave begins after
that. It is due to ventricular repolarization. It is a broad wave. Its average
duration is about 0.27 second and amplitude 0.15 to 0.5 mv.

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Livestock and Management

  2. Important cattle breeds and their characteristics

  3. Milch breeds (or) Dairy breeds

  4. Dual purpose breeds & Draught breeds

  5. Exotic breeds of cattle

  6. Common diseases and control in Cattle – Contagious diseases

  7. Non-contagious diseases – Cattle

  8. Techniques adopted in cattle breeding

  9. Poultry Breeds

  10. Farming methods

  11. Poultry byproducts

  12. Fish Pond

  13. Edible Fishes Of Tamilnadu

  14. Medical Lab Techniques – Stethoscope

  15. Sphygmomanometer

  16. Haemocytometer

  17. Urine Sugar analysis

  18. ECG Electrocardiogram

  19. Computed Tomography CT

  20. Endoscopy (Laproscopy) techniques , Artificial Pacemaker

  21. Autoanalyser

Unit 7. THEORIES OF EVOLUTION Topic List Zoology

  1. Theories Of Evolution Introduction

  2. Lamarck Laws

  3. Neo Lamarckism

  4. Darwinism

  5. Theory of Natural Selection

  6. Objections to Darwinism

  7. Modern concept of Natural Selection

Leave a Reply

Your email address will not be published. Required fields are marked *