Variable heart rate, also known as sinus arrhythmia
Sinus dysrhythmia can be a normal rhythm, but rather than having a steady rate, the rate varies by more than 10 beats per minute. In the above example, the heart rate varies from 75-94 beats per minute. All other measurements and aspects of the rhythm would be consistent with what is described under Normal Heart Rhythm.
Sinus dysrhythmia is divided into two categories, respiratory (related to breathing) and nonrespiratory. Respiratory sinus dysrhythmia is present when there is a gradual rate increase with inspiration (breathing in) and a gradual decrease with expiration (breathing out). Nonrespiratory sinus dysrhythmia is present when there is an irregularity not related to the respiratory cycle. Both types may occur in healthy or diseased hearts.
Sinus dysrhythmia is very common and usually normal in children and young adults with rate variations up to 30 beats in one minute not uncommon. Sinus dysrhythmias in the older population can frequently be associated with lung disease.