By Ken Grauer, MD
Figure. 12-lead ECG and lead II rhythm strip obtained from
a 62-year-old woman shortly before her cardiac arrest.
Clinical Scenario. The ECG in the Figure was obtained from a 62-year-old woman who was admitted for chest pain. She was doing poorly from a clinical standpoint at the time this tracing was obtained, and suffered a cardiac arrest shortly thereafter. How would you interpret her precode ECG that is shown in the Figure?
Interpretation. This is a complex tracing. Dots in the lead II rhythm strip suggest that after some initial irregularity, 2:1 AV conduction becomes established. We suspect that the rhythm is 2° AV block, mostly Type I (Wenckebach) with atrial tachycardia at a rate of 140/min. It is difficult to be certain if beats No. 2 and 4 represent junctional escape or Wenckebach conduction with a long preceding PR interval—but the presence of normal QRS width and the suggestion of acute inferior infarction (subtle but real ST segment elevation in leads II, IIII, and aVF) are most consistent with a Mobitz I etiology for the 2:1 AV block. Marked ST segment depression exists in virtually all other leads on the tracing. This suggests extensive, evolving acute infarction that also may involve the posterior wall or signal anterolateral ischemic changes. The combination of acute infero-postero wall infarction with extensive reciprocal ST segment depression in conjunction with atrial tachycardia and 2:1 AV block explain why the patient soon suffered a cardiac arrest. v
Dr. Grauer, Professor and Associate Director, Family Practice Residency Program, Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, is on the Editorial Board of Emergency Medicine Alert.