When the heart rate is greater than 100 beats per minute in adults, this is called sinus tachycardia. This rate may vary upto 160 beats per minute except in infants.

CAUSES OF SINUS TACHYCARDI

Physiological

1. Children.
2. Anxiety, emotional stress.
3. Exercise.
4. Pregnancy.
5. Menstruation.

Pathological

1. Fever.
2. Anaemia.
3. Cardiac failure.
4. Thyrotoxicasis.
5. Shock and collapse.
6. Haemorrhage.
7. Dehydration.
8. Drugs: Sympthomimetics, vagolytics.
9. Pheochromocytoma.
10. Alcohol intake.
11. Myocarditis.
12. Myocardical ischaemia with or without infarction.

When the heart rate is less than 60 beats per minute it is called sinus bradycardia.

CAUSES OF SINUS BRADYCARDIA

Physiogical

1. During deep sleep.
2. Athletes.

Pathological

1. Viral infection.
2. Obstructive jaundice.
3. Hypothyroidism.
4. Carotid sinus syncope.
5. Increased intracranial tension.
6. Sick sinus syndrome.
7. Hypothermia.
8. Myocardial infarction.
9. Gram negative sepsis.
10. Vasovagal fainting attack.
11. Some cases of severe anemia.
12. Aortic stenosis.
13. Mallory Weiss syndrome.
14. Boerhaave’s syndrome.
15. Drugs: Digitalis, Betablocker, Calcium Antagonists (Verapamil, Diltiazem), Amiodarone, Cimetidine, Clonidine.
16. Giant left atrium.