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Different cardiac rhythms

What is sinus rhythm?
SA node is the pacemaker of heart. It generate impulse at a rate of 60 ot 100 per minute.
What is idioventricular rhythm? 
This rhythm is seen when the cardiac impulse arises from the ventricle at the rate of 36 per minute, hence the pulse rate at ventricular rhythm is 36 per minute, this is known as idioventricular rhythm;
What is nodal rhythm ?
When the SA node fails to generate impulse , often the AV node produce the impulse at the rate of 40-60 per minute resulting in a pulse rate of 40-60 per minute.
What are the irregularities in the rhythm ?
Rhvthm is the spacing of successive beats (pulse wave) in time. Normal pulse is regular in rhythm and it is known as sinus rhythm, because it is controlled by the SA node. Irregularities are of two types .
Regularly irregular - i.e. Irregularity comes at regular interval and is seen in extrasystoles. sinus arrhythmia  2nd degree heart block, etc.
Irregularly irregular or completely irregular - i.e. irregularity between two pulse beats in every aspect (volume, spacing etc that is totally chaotic).This is commonly seen in atrial fibrillation, multiple extrasystoles, atrial flutter with varying degrees ol heart block etc.
What is sinus arrhythmia?
Sinus arrhythmia is defined  as increase in pulse rate with inspiration and diminution in pulse rate with expiration. This is a physiological phenomenon commonly observed in children and athletes.
Mechanism of sinus arrhythmia is that the increased amount of blood which comes in the left ventricle in expiration increases the stroke volume. This will immediately stimulates the baroreceptors leading to slowing of the heart rale. Sinus arrhythmia may be absent in autonomic neuropathy and CCF