American Journal of Critical Care. 2006;15: 321-322
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.
Differentiating ST-Segment Strain Pattern From Acute Ischemia
By
Mary G. Carey, RN, PhD,
Susan J. Ponivas, RN, BSN and
Michele M. Pelter, RN, PhD.
From the School of Nursing at the State University of New York at Buffalo (MGC, SJP) and Washoe Health System and Orvis School of Nursing, University of Nevada, Reno, Nev (MMP).
Scenario: Currently under the care of a cardiologist for cardiomyopathy with a low ejection fraction, a 58-year-old man comes to his outpatient cardiology clinic with complaints of recurrent chest discomfort and shortness of breath. Other complaints include a cold "shivering" feeling and nocturnal dyspnea.
Interpretation: Normal sinus rhythm at 85 beats per minute, diffuse ST-segment depression and T-wave inversion, consider acute ischemia, left ventricular hypertrophy (LVH) with strain pattern.
Rationale
The ST-segment depression and T-wave inversion present in the inferior (II, III, aVF) and the anterolateral (V3 through V6) leads suggest non-ST elevation myocardial infarction (NSTEMI) or unstable angina. The type of ischemia in these conditions typically results from a partially occluded or intermittently occluded coronary artery. Of note, because of the location of the exploring electrode of aVR (right arm), this lead has an endocardial "view" of the heart; therefore, with subendocardial ischemia, aVR typically shows ST elevation. The diagnostic criteria (Sokolow-Lyon) of LVH are met because the amplitude of the S wave in lead V1 plus the amplitude of the R wave in V5 is greater than 35 mm. With LVH, the ST segment and T wave are directed opposite the QRS complex, resulting in a "strain" pattern, often in all leads. However, given that the typical ST-T wave changes of LVH are absent in leads I and aVL and the patient’s complaints of unstable angina, NSTEMI must first be ruled out.
Nursing Actions
Because of the ST-segment changes and presenting symptoms, this patient should be considered at high risk for NSTEMI. Assuming no contraindications are present, adjunctive therapies should be started immediately, including heparin, aspirin, glycoprotein IIb/IIIa receptor inhibitors, nitroglycerin, and ß-blockers until acute ischemia is ruled out. Coronary catheterization and possible revascularization are likely treatment options. Because this patient is at risk for arrhythmias and ongoing myocardial ischemia, maintain continuous bedside ECG monitoring with ST-segment analysis.
