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American Journal of Critical Care. 2007;16: 405-406
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ECG PUZZLER
A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses electrocardiogram (ECG) interpretation for clinical practice. To send an eLetter or to contribute to an online discussion about this article, visit www.ajcconline.org and click "Respond to This Article" on either the full-text or .pdf view of the article. We welcome letters regarding this feature.

ECG Puzzler Slow Escape Rhythms

By Michele M. Pelter, RN, PhD and Mary G. Carey, RN, PhD. Michele M. Pelter is the Director of Nursing Research and Outcomes at Renown Health and a research liaison at the Orvis School of Nursing, University of Nevada, Reno. Mary G. Carey is an assistant professor in the School of Nursing at the State University of New York at Buffalo.

Scenario: This ECG (lead V2) was obtained from a 90-year-old woman presenting to the emergency department with complaints of "dizziness." The patient’s only history includes weekly dialysis for renal insufficiency; otherwise she had been healthy and living independently. The patient’s vital signs are normal: blood pressure 135/43 mm Hg, respirations 18/min, and O2 saturation 100% via pulse oximetry.


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Interpretation

Third-degree atrioventricular (AV) block with junctional escape rhythm

Rationale

Although the second, third, and sixth QRS complexes appear to have a P wave associated with them, careful evaluation of the entire strip indicates several problems: (1) the atrial rate is faster than the ventricular rate (atrial = 82/min, ventricular = 33/min), (2) there are more P waves than QRS complexes, and (3) none of the P waves are associated with any QRS complex.

Together these criteria indicate complete AV dissociation, meaning the atria and ventricles are functioning independently. The terms complete heart block or CHB, complete AV dissociation, and third-degree AV block are the same terms and can be used to describe this rhythm. Because the width of the QRS complex is normal (<0.12), this "escape" beat is most likely generated from the AV node, hence the term junctional escape. An escape beat originating from below this site (ie, His’ bundle) would result in a wide QRS complex.

Etiology of third-degree AV block includes acute myocardial infarction, drug toxicity, and age-related degeneration of the electrical system; each is possible in this patient. For example, because the ST segment is elevated 3 mm, evaluation of a 12-lead ECG and cardiac troponins for ischemia and/or infarction are indicated. Because this patient’s renal insufficiency is managed with dialysis, both drug and electrolyte toxicity are a possibility. And, finally, given that this patient is 90 years old, the possibility that this rhythm is due to age-related degeneration of the electrical system also must be considered.

Nursing Actions

Although this patient’s vital signs are currently stable, immediate nursing action includes application of multifunction pads for transcutaneous pacing to ensure an adequate cardiac output in case her heart rate slows or progresses to ventricular standstill. As mentioned, because drug toxicity or electrolyte imbalance can be a cause of third-degree heart block, the patient’s current medications and blood work should be evaluated. According to Advanced Cardiac Life Support, management is guided by the patient’s symptoms. Therefore, clinicians should be prepared with (1) cardiac drugs including atropine, (2) transcutaneous pacing, (3) transvenous pacing, and (4) permanent pacing.

ACKNOWLEDGMENTS

Our thanks to Kimberly E. Stephens, RN, BSN, MPH, Renown Regional Medical Center, for providing the ECG used in this example.





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