Sinus arrhythmia

Arrhythmias are abnormal heartbeats.

To understand arrhythmias, let's look at what a normal heartbeat is. Normal sinus rhythm, or the rhythm of a healthy heart, is defined as the heart beating in a consistent rhythm.

One way to evaluate the quality of a heartbeat is by having an electrocardiogram (ECG). This test helps your healthcare provider see electrical impulses as they progress through the heart.

The electrical impulse is initiated by the sinoatrial node, a part of the heart that contains the pacemaker cells. On an ECG, the "P wave" is generated from the heart's upper chambers, or left and right atria. The heartbeat continues through the lower chambers or left and right ventricles with a "QRS wave." Finally, the heart returns to its resting state with the "T wave."

A single heartbeat with its electrical impulse sequence comprising P, QRS and T waves repeats about 100,000 times every day.

A sinus arrhythmia is an irregular variation of normal sinus rhythm, or an irregular heartbeat. It is more common in young adults and children. The sinus arrhythmia is seen when the measurement from one P wave to the next P wave has variations of greater than 0.12 seconds.

There are three types of sinus arrhythmia:

• Respiratory or phasic sinus arrhythmia. This is usually considered a normal heartbeat in children and young adults. Most people do not require a cardiac evaluation for this condition. It occurs less frequently and can disappear as people become older, potentially from age-related changes in the arterial muscle and diminished vagal responses. It has been associated with obesity, hypertension and diabetes.
  Respiratory sinus arrhythmia occurs when there are changes in the heart rate during breathing. The vagus nerve, a primary component of the parasympathetic nervous system, is responsible for regulating several bodily functions, including respiration. Breathing in can inhibit vagal tone and breathing out can cause the vagal tone to decrease; these changes can cause the heart rate to speed up and slow down depending on breathing patterns. Medications, such as morphine (a pain medication) and digitalis (a medicine used to treat heart conditions), can cause respiratory sinus arrhythmia by increasing vagal tone.
  A type of respiratory sinus arrhythmia is sinus bradycardia with sinus arrhythmia. It occurs when the heart rate falls below 60 beats a minute (bradycardia) with respiratory cycles that cause the heart rhythm to be irregular.
• Nonrespiratory or nonphasic sinus arrhythmia. This type of sinus arrhythmia is not related to the respiratory cycle. It can occur in a normal heart or after digitalis intoxication (too much digitalis) or in people with heart disease.
• Nonrespiratory or ventriculophasic sinus arrhythmia. This type of sinus arrhythmia is often found in third-degree atrioventricular block (AV block), a condition that occurs when there is a loss of communication between the atria and ventricles of the heart. Specifically, this type of arrhythmia happens where there is a pause after a premature ventricular contraction (extra heartbeat). This causes the next P-to-P interval to shorten.

Currently, there are no medications for sinus arrhythmia. It doesn't affect life expectancy and usually does not require additional testing.

Published December 2020.