From time to time we evaluate children who are referred for an irregular heartbeat. This term typically refers to a heart rhythm that does not seem quite regular. An irregular heart beat is a little different from palpitations. The term palpitations refers to a sensation that the heart is not beating normally. Children with palpitations may feel their heart beating rapidly, pausing, or skipping beats. An irregular heartbeat, on the other hand, is usually something that a doctor hears when listening to the heart. Many children suspected of having irregular heartbeats may feel perfectly fine.
In many cases an irregular heartbeat is abnormal. The most common cause of an irregular heartbeat in children is isolated premature beats. Both premature atrial contractions and premature ventricular contractions are relatively common in children. Fortunately, in many instances these can be completely benign.
On occasion, a child referred for an irregular heartbeat may actually turn out to be completely normal. One cause of a suspected irregular heartbeat which is perfectly normal is sinus arrhythmia. In fact, I really don't like the term "sinus arrhythmia", because the term arrhythmia tends to imply an abnormal heart rhythm. Sinus arrhythmia, however, is perfectly normal. In fact, I like to tell parents that it's a sign of a normal, healthy heart!
Sinus arrhythmia refers to the normal variation in the heart rhythm that occurs with breathing. With inspiration, or breathing in, the chest cavity expands and the lungs take in air. Inspiration happens because a negative pressure is created in the chest. This negative pressure also affects the heart - with inspiration a slightly greater amount of blood returns to the heart. Because of this, heart volume increases slightly. The walls of the heart, especially in a healthy child, are sensitive to this slight stretch. The heart responds by beating slightly faster. With expiration, or breathing out, the opposite happens. As the heart volume slightly shrinks, the heart rate momentarily slows down.
Because of these changes in chest pressure, it can be normal to hear the heart rhythm periodically speed up and slow down in a completely healthy child who is breathing quietly. In some instances these changes might seem quite pronounced! It can be understandable that these normal changes can be confused on occasion with an abnormal heart rhythm or premature beats. Fortunately a simple ECG or rhythm strip can help clarify things in these questionable cases. So in conclusion, an irregular heartbeat certainly can be completely normal in some instances. Sinus arrhythmia is a good example of this.