By Ken Grauer, MD
Figure. 12-lead ECG and lead II rhythm strip obtained from an 84-year-old man with acute dyspnea.
Clinical Scenario: The 12-lead ECG and accompanying rhythm strip in the Figure were obtained from an 84-year-old man who presented to the Emergency Department with acute dyspnea from pneumonia and heart failure. What’s going on? Is RBBB (right bundle branch block) among the findings?
Interpretation: Attention to the simultaneously recorded lead II rhythm strip is essential for understanding the subtleties that are seen in this tracing. The first finding noted is that a bigeminal rhythm is present, characterized by the repetitive "short-long" pattern in the rhythm strip. Of interest is the fact that each of the relatively longer R-R intervals is preceded by a pointed upright P wave that confirms the underlying sinus rhythm. The beat labeled "X" is one of these sinus conducted impulses. Every other beat (the early occurring impulses) is preceded by an especially peaked T wave compared to the T wave that follows these beats. Each of these early occurring beats is a PAC (premature atrial contraction), with its premature P wave combining with the preceding T wave to produce this peaking. The rhythm is therefore atrial bigeminy. The most interesting feature of the rhythm is the subtle variation in QRS morphology among the early occurring complexes. This is the result of varying degrees of aberrant conduction among the PACs. A look at the simultaneously occurring QRS complex in V1 (above beat "Y) and V6 (above beat "Z), in conjunction with the deeper and wider S wave in many of the lead II PACs is consistent with a pattern of RBBB/LAHB (left anterior hemiblock) aberration. Analysis of the sinus conducted beats on this 12-lead ECG is consistent with prior anterolateral infarction (note the QR pattern in leads aVL, and V2 through V4), but without acute ST-T wave changes.
Dr. Grauer, Professor, Assistant Director, Family Practice Residency Program, University of Florida, is Associate Editor of Internal Medicine Alert.