Respiratory sinus arrhythmia

ECG: This tracing shows an irregular sinus atrial activity with successive accelerations and slowings; the remainder of the electrocardiogram is within normal ranges; probable physiological sinus arrhythmia in an adolescent patient;

Comments: Childhood or adolescent respiratory sinus arrhythmia is one of the most common “arrhythmias” in clinical practice. It corresponds to fluctuations in periodicity of sinus node related to reflex variations in vagal tone. These rate variations following the respiratory cycles and occurring in asymptomatic patients can be considered as physiological. The incidence of sinus arrhythmia decreases with age probably in conjunction with the decrease in carotid baroreceptor sensitivity.

On the electrocardiogram, the phasic respiratory sinus arrhythmia results in a sinus-controlled rhythm whose rate is clearly irregular. We observe:

•  Identical P waves with no change in morphology;
•  An irregularity of the P waves with deviations of more than 160 ms between the PP intervals;
• Variations in PP interval duration which are periodic and follow the respiratory cycles; an acceleration of the sinus rhythm is observed at the end of expiration (resumption of vagal tone) while a slowing of the sinus rhythm occurs at the end of inspiration and at the onset of  expiration (decrease in vagal tone); these variations disappear during apneas and decrease during exercise with the increase in heart rate;
• The PR interval and the remainder of the electrocardiogram are generally normal;

Take-home message: Childhood or adolescent respiratory arrhythmia results in the presence of an irregular sinus rhythm (acceleration at the onset of inspiration and slowing at the onset of expiration) with no pathological features.