American Journal of Critical Care. 2004;13: 355-356
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.
Wide QRS Duration
By
Michele M. Pelter, RN, PhD and
Mary G. Adams, RN, PhD.
From
Washoe Health System, Reno, NV (MMP), and the School of Nursing at the State University of New York at Buffalo (MGA).
Scenario: This 12-lead ECG waveform was obtained in a patient transferred to the intensive care unit from the general medicine floor because of acute shortness of breath. The patient has a history of chronic obstructive pulmonary disease, hypertension, coronary artery disease, and prior myocardial infarction (MI).
Interpretation: Normal sinus rhythm with first-degree atrioventricular block and left bundle branch block (BBB) with notching of the S wave in leads V3-V5, suggesting prior anterior MI.
Rationale
The QRS complex duration is wide (>0.12 seconds or 3 small boxes) in every lead. Causes of a widened QRS complex include right or left BBB, pacemaker, hyperkalemia, ventricular preexcitation as is seen in Wolf-Parkinson-White pattern, and a ventricular rhythm. Because there is a P wave associated with every QRS complex, a ventricular rhythm can be ruled out. A Wolf-Parkinson-White pattern can also be ruled out because there is a P-R segment and no slurring of the initial part of the QRS complex. The patient’s history and current lab results also help eliminate other possible causes (ie, no history of pacemaker and potassium level of 3.5mEq/L). Hence, the cause of the wide QRS complexes in this example is left BBB. Lead V1 is a key lead used to distinguish between right and left BBB. With left BBB, the electrical impulse cannot travel along the left bundle branch; it must first travel to the right ventricle, then to the intraventricular septum, and finally to the left ventricle. The result is a wide QRS pattern. Of note, abnormal depolarization results in abnormal repolarization, and therefore ST deviation can be expected. The notching of the S wave in leads V3 and V4 of greater than 0.50 seconds indicates that this patient has had a prior anterior MI.
Nursing Actions
Obtain a previous 12-lead ECG to determine if the left BBB and anterior infarction were present before the acute changes that prompted the patient’s transfer to the intensive care unit. This may help rule out a cardiac cause for the acute shortness of breath. ST-segment monitoring for myocardial ischemia is not recommended in patients with left BBB because the associated ST-segment changes result in numerous false positive alarms. However, continue to monitor the patient for arrhythmias.
