American Journal of Critical Care. 2006;15: 231-232
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.
ST-Segment Changes in Right Ventricular Paced Rhythms
By
Michele M. Pelter, RN, PhD and
Mary G. Carey, RN, PhD.
From
Washoe Health System and Orvis School of Nursing, University of Nevada, Reno, NV (MMP), and the School of Nursing at State University of New York at Buffalo (MGC).
Scenario: The top strip was obtained in an 83-year-old woman admitted to the coronary care unit with intermittent chest pain just before going to the cardiac catheterization laboratory for percutaneous coronary intervention (PCI). The patient has a history of coronary artery disease and a permanent pacemaker. The bottom strip was taken upon return to the coronary care unit after a stent was placed in the right coronary artery. The patient was complaining of chest pain, which started during the PCI procedure and never resolved.
Interpretation: (Top Strip) Atrioventricular pacing at 69 beats per minute (bpm) with 1 premature ventricular complex. (Bottom Strip) An intrinsic atrial rhythm is present with ventricular pacing at 72 bpm. The QRS morphology is different, with new ST-segment elevation suggestive of acute inferior myocardial infarction (MI).
Rationale
In patients with right ventricular paced rhythms (VPR), the endocardial electrode generating the impulse is positioned in the right ventricle, hence activation of the ventricles spreads from right to left. This activation sequence creates a QRS morphology similar to left bundle branch block; a wide QRS complex and secondary ST T-wave changes that are discordant (opposite) to the QRS complex. The top strip shows a typical right VPR pattern. Note that the ST segment is slightly above the isoelectric PR segment, which is considered a normal finding. In fact, it is not unusual to see several millimeters of discordant ST deviation, making diagnosis of acute MI difficult. The bottom strip shows considerable change in the QRS pattern. Although the QRS is still predominately negative, the ST segment is elevated, as much as 5 mm in lead III. Although some debate exists about specific criteria for diagnosing acute MI in right VPR, ST-segment elevation of 5 mm or more in leads with discordant QRS polarity has a relatively high sensitivity and specificity.
Nursing Actions
Given the patient’s signs and symptoms, recent stent placement, and ECG changes, the nurse must consider acute MI as a possibility and notify the physician. The nurse should ensure that the QRS changes are not due to inaccurate lead placement and should initiate ST-segment monitoring. A resting 12-lead ECG should be obtained and compared with a prior 12-lead ECG. Continue monitoring the patient carefully for lethal arrhythmias, and prepare her for possible recatheterization.
