American Journal of Critical Care. 2003;12: 77-78
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.
Heart Blocks
By
Mary G. Adams-Hamoda, RN, PhD and
Michele M. Pelter, RN, PhD.
From the Department of Physiological Nursing, University of California, San Francisco, Calif.
Scenario: A 73-year-old woman presents to the emergency department complaining of dizziness. Her past medical history includes coronary artery disease with controlled hypertension. She is currently under the care of a cardiologist.
Interpretation: Second-degree atrioventricular (AV) block type II.
Rationale
In second-degree AV block type II (Mobitz II), the PR interval of the conducted P wave will be constant for each QRS complex. Because second-degree AV block occurs in the Purkinje system, an escape rhythm may not develop. Consequently, this may progress to a third-degree heart block or ventricular standstill, making this rhythm dangerous. Causes may include acute anterior myocardial infarction, cardiomyopathy, rheumatic heart disease, coronary artery disease, digitalis, ß-blockers, and calcium channel blockers. The ventricular rate will depend on the number of impulses conducted through the AV node and will be less than the atrial rate. In this case, the block is continuous with a 3 to 1 conduction of P waves to the QRS complexes, resulting in a ventricular rate of fewer than 40 beats per minute. Notice the large T waves in leads V3 and V4; they are caused by nonconducted P waves hidden in the T wave.
Nursing Actions
Obtain vital signs and notify the physician immediately. Be ready for a code situation. Apply multifunction pads to the patient to prepare for transcutaneous pacing at the bedside, because a permanent pacemaker may be necessary. Since there are no signs of an acute myocardial infarction in this 12-lead ECG, consider any pharmacologic agents that may be causing this dangerous AV block.
