Heart rhythm is the beating of heart at regular intervals. Sinus rhythm is considered as the normal rhythm of the heart. It has SA node pacing the heart by initiating electric impulses at a constant rate. Hence, a normal heart rhythm is regular with heart rate of 60–100 beats per minute and is paced by SA node. On an electrocardiograph, a single beat of the heart in sinus rhythm is traced as a P wave, a QRS complex, a T wave and a U wave. They occur in a definite order, over definite time periods, with definite relative sizes.
Abnormal heart rhythms:
Nodal rhythm – When there is a block in conduction of impulses AV node takes over as the pacemaker. This abnormal heart rhythm is called junctional rhythm or nodal rhythm. The heart rate in such cases is 40 to 60 beats per minute.
Arrhythmia – An irregular heart rate and rhythm. Common types are premature atrial contractions, skipped heartbeat (premature ventricular contractions), sick sinus syndrome, atrial flutter, atrial fibrillation, ventricular fibrillation, bradycardia, heart block etc.