American Journal of Critical Care. 2006;15: 103-104
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.
Resynchronization Therapy
By
Mary G. Carey, RN, PhD and
Michele M. Pelter, RN, PhD.
From the School of Nursing at State University of New York at Buffalo (MGC), and the Washoe Health System and Orvis School of Nursing, University of Nevada, Reno, NV (MMP).
Scenario: This is the beginning ECG strip (leads II and V1) from a 24-hour Holter study of a 72-year-old white man with congestive heart failure (CHF). The patient is asymptomatic and the Holter study is part of the patient’s routine cardiac care. What is your interpretation of his baseline rhythm?
Interpretation: One hundred percent biventricular (BiV) pacing at 77 beats per minute.
Rationale
Given the rapid evolution of electrical device therapy, there are multiple pacemaker options to consider. The rhythm is regular, and a pacemaker spike can be appreciated preceding every QRS complex. Many patients with CHF have asynchronized ventricular contraction. This asynchrony diminishes ventricular filling time and compromises the cardiac output, which eventually leads to an increase in signs and symptoms of heart failure. Thus, resynchronization therapy with BiV pacing is designed to improve ventricular coordination. Biventricular pacemakers use 3 leads implanted into the right atrium and ventricle and through the coronary sinus vein to sense and pace the left ventricle. After the atrium lead senses and contraction occurs, both ventricles are paced simultaneously, causing the walls of the left ventricle (septum and free wall) to contract synchronously, resulting in narrower QRS duration than would occur without BiV pacing, thus reducing ventricular asynchrony.
Nursing Actions
Approved BiV pacers currently result in a ventricular pacing spike. With BiV pacing, the nurse must monitor for 100% ventricular capture and be watchful for QRS widening, which may indicate a loss of capture in 1 ventricle, typically the left ventricle because of the distal access. Another consideration in BiV pacing is the PR interval. The programmed PR interval for pacing is shorter than the intrinsic PR interval, ensuring that BiV capture occurs consistently. Because of the improvement with bipolar pacing (bipolar electrodes generate a smaller pacing spike), it is not possible to see the atrial spike in this example; however, ECG monitoring confirms that the PR interval remains fixed.
