American Journal of Critical Care. 2005;14: 161-162
A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses ECG interpretation for clinical practice. We welcome letters to the Editors regarding this feature.
Nonrespiratory Sinus Arrhythmia
By
Stephanie S. DeBoor, RN, CCRN, MS,
Michele M. Pelter, RN, PhD and
Mary G. Adams, RN, PhD.
From
Washoe Health System and the University of Nevada Orvis School of Nursing, Reno, NV (SSD, MMP), and the School of Nursing at the State University of New York at Buffalo (MGA).
Scenario: This continuous lead II rhythm strip was obtained in a 25-year-old woman admitted to the intensive care unit for intracerebral hemorrhage. The patient presented to the emergency department with a headache after a skateboarding accident. The patient stated that she "bumped" her head during the accident. The bedside monitor alarmed for bradycardia/pause. Upon assessment, the patient was alert, oriented, and hemodynamically stable.
Interpretation: Sinus bradycardia at 55 beats per minute, nonrespiratory sinus arrhythmia. There are also intermittent U waves throughout this rhythm strip (see end of second beat).
Rationale
During the entire rhythm strip, the heart rate never exceeds 60 beats per minute, hence the diagnosis of sinus bradycardia. There are 2 types of sinus arrhythmia: respiratory and nonrespiratory. In the respiratory form, sinus arrhythmia typically varies with respirations, and the heart rate (RR interval) increases with inspiration and decreases with expiration. In this example, the irregularity of the rhythm is not associated with respirations as verified by the nurse (RR interval is random); therefore, the diagnosis of nonrespiratory sinus arrhythmia is appropriate. The first 2 beats of the bottom strip are sinus beats; however, the P waves are different (biphasic) from the preceding P waves, indicating that the impulse was generated from outside the sinus node. Because the PR interval is unchanged, these beats are not junctional. In addition, because the QRS duration is within normal limits, the impulse traveled down the normal pathway to the ventricles. It is likely that the sinus impulse was generated in the atrium, but at a focus other than the sinus node. Electrocardiographic abnormalities and arrhythmias are not uncommon in patients with brain injury and are most likely the cause of this arrhythmia. The mechanism of these abnormalities may include vasospasm, hypoxia, electrolyte imbalance, and sudden increase in intracranial pressure.
Nursing Actions
Sinus arrhythmias are usually asymptomatic and treatment is often unnecessary. However, long pauses can cause dizziness or syncope so that continuous ECG monitoring should be maintained. In addition, given this patient’s head injury, the nonrespiratory arrhythmia may be secondary to increased intracranial pressure, thus she should be monitored closely for acute and possibly subtle neurological changes indicating an increase in intracranial pressure.
