Figure 34-9 Enhanced detection of atrial electrical activity using an esophageal electrocardiogram (EsECG). The EsECG demonstrates arrhythmia progression from normal sinus rhythm (NSR), with one premature contraction (PAC), to atrial flutter (A flutter) and atrial fibrillation (A fibrillation). Lack of information about atrial activity from lead V₅ made definitive diagnosis impossible. (Adapted from Thys DM, Kaplan JA: The ECG in Anesthesia and Critical Care. New York, Churchill Livingstone, 1987.)