American Journal of Critical Care. 2007;16: 187-188
A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses ECG interpretation for clinical practice. To send an eLetter to the Editors or 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 to the Editors regarding this feature.
P Wave Alterations
By
Michele M. Pelter, RN, PhD and
Mary G. Carey, RN, PhD.
From
Renown Health and Orvis School of Nursing, University of Nevada, Reno, Nev (MMP), and the School of Nursing at the State University of New York at Buffalo (MGC).
Scenario: This ECG (V1 and lead II) was obtained from a 68-year-old woman following cardiac surgery for mitral valve repair. The patient has a history of hypertension as well as mitral valve disease, which had been followed for 10 years. At the time of the electrocardiogram the patient was recovering in the intensive care unit, intubated, sedated, and hemodynamically stable.
Interpretation: Sinus rhythm at 88/min, accelerated junctional escape rhythm at 68/min, P waves suggestive of left atrial enlargement, and ST elevation in lead II suggestive of early repolarization pattern.
Rationale
Following the second beat the R-to-R interval lengthens slightly from .76 seconds to .92 seconds and a small portion of the P wave is buried in the QRS complex. In situations in which sinus node automaticity is decreased, a lower pacemaker site compensates by generating a beat. Because the width of the QRS complex in this example is normal, this beat originated above the ventricular Purkinje system. Two more escape beats occur (8th and 9th beat) with a hint of the P wave buried in the initial part of the 9th QRS. This rhythm is characteristic of a junctional escape rhythm. Because the rate of the junctional rhythm is faster than would be expected (40 to 60/min) this is termed an accelerated junctional rhythm. The ST segment in lead II is elevated with a "fish-hook" pattern at the J-point (ie, the end of the QRS and start of the ST segment), which is characteristic of an early repolarization pattern. This form of ST segment elevation is considered nonischemic, but ischemia should be ruled out by evaluation of biomarker test(s) and assessment of a prior 12-lead ECG. Finally, in this example there are characteristics suggestive of left atrial enlargement (LAE) including (1) indentation of the P wave in lead II, giving the appearance of an "M" (in this example a slight indentation is visible in the sinus P waves); (2) P wave duration of > 0.11 seconds; and (3) small initial upstroke of the P wave in lead V1 with a negative deflection in the terminal portion > 0.04 seconds duration.
Nursing Actions
Accelerated junctional rhythm is not uncommon following cardiac surgery, especially valvular surgery, and typically no treatment is indicated. A potential cause is digitalis toxicity, hence it should be determined whether digitalis toxicity is a factor in this patient. The presence of LAE is common in patients with long-standing hypertension or those with valvular heart disease, both likely factors in this patient. Because atrial enlargement is permanent, evaluation of a 12-lead ECG prior to surgery may show these same characteristics. Although the ECG may show characteristics of LAE in some patients, it should be noted that the ECG is not the gold standard and an echocardiogram should be used for definitive diagnosis.
