Nonrespiratory or Nonphasic Sinus Arrhythmia

The second kind of sinus arrhythmia is the nonrespiratory or nonphasic type. This type of sinus arrhythmia is not associated with the respiratory cycles or any other physiologic events. It occurs spontaneously and has no definite pattern, with the P-P interval varying at random throughout the strip. There is no gradual increase and decrease in the rate.

In contrast to respiratory sinus arrhythmia, nonrespiratory sinus arrhythmia occurs in the elderly and in patients with serious ischemic heart disease or structural abnormalities. Because of its association with pathologic states, this type of sinus arrhythmia should be considered a true arrhythmia and should not be considered a variant of normal. This does not mean that it requires treatment, emergent or otherwise, but it does mean that you need to approach those patients with care and a suspicious clinical eye. In other words, if they tell you they are having any symptoms, believe them!

Additional Information

Changes in the Main Pacemaker Site

Recent information from electrophysiology studies has shown that, in some patients, there can be a transient change in the location of the main pacemaker during respiration within the SA node itself. Remember, the SA node is a large, horseshoe-shaped structure. The main pacemaking site can transiently change in these patients because of vagal stimulation from an area in the upper pole to an area in the lower pole. This could account for the small changes seen in the morphology of the P waves and the PR intervals seen in some sinus arrhythmia patients.

Because of its association with pathologic heart disease, consider this type of sinus arrhythmia a true arrhythmia and not a variant of normal.