American Journal of Critical Care. 2003;12: 477-478
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.
Ventricular Escape Rhythms
By
Mary G. Adams, RN, PhD and
Michele M. Pelter, RN, PhD.
From the School of Nursing at the State University of New York at Buffalo (MGA) and the Department of Physiological Nursing, University of California, San Francisco, Calif (MMP).
Scenario: This is the resting 12-lead ECG waveform of a 75-year-old white man presenting to an acute care clinic with complaints of shortness of breath, intermittent chest pain, and dizziness.
Interpretation: Third degree atrioventricular (AV) block with accelerated idioventricular rhythm (AIVR).
Rationale
Evaluation of the V1 rhythm strip at the bottom of the 12-lead ECG waveform is necessary for diagnosing this cardiac rhythm. In this example, there is no relationship between the P waves and the QRS complexes indicating that there is complete failure of the atrial impulses to conduct to the ventricles. The atria and ventricles are acting independently—each firing at an intrinsic rate with no relationship to one another. Third-degree (complete) heart block is caused by a conduction block most commonly in bundle branch-Purkinje system (61%) at the level of the AV node (21%) or the His bundle (15%). An escape rhythm above the His bundle typically produces a faster heart rate (40–60 beats per minute [bpm]) and narrow QRS complex compared with an escape rhythm that occurs at or below the His bundle, which produces a slower heart rate (20–40 bpm) and wide QRS complex. In this case, the ventricular rate is about 48 bpm, but the QRS complex is wide. Thus, the block is probably below the AV node yet faster than expected, referred to as an AIVR.
Nursing Actions
Given the patient’s age, gender, symptoms, and newly developed AV block, acute myocardial infarction should be suspected. With a left bundle branch block pattern, it is difficult to interpret if the ST/T wave changes are due to ischemia. Other causes of third-degree AV block include drug toxicities (digitalis, beta blockers, and calcium channel blockers), metabolic disturbances, and cardiomyopathies. Generally, patients with complete heart block are hemodynamically unstable. Thus, the priority is transferring the patient to an acute care facility with revascularization capabilities. Nursing responsibilities include (1) diligent cardiac monitoring, (2) administering oxygen, (3) establishing intravenous access, and (4) preparing for temporary transcutaneous pacing if necessary.
