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©2013 UpToDate ® Print Email Electrocardiogram in hypothermia The ECG reveals marked sinus bradycardia (about 40 beats/min) with a prolonged PR interval (PR interval = 0.23 sec). The slow heart rate in this patient is due to hypothermia (90°F, 32.2°C), which also produces prominent convex deflections at the J point (junction of QRS and ST segments) that are best seen in the precordial leads. The J waves or Osborn waves (arrows) are characteristic of severe hypothermia and resolve with rewarming; how they occur is not fully understood (Wang D, Yan GX, Antzelevitch C. The J Wave syndromes and their role in sudden cardiac death. Card Electrophysiol Clin 2011; 3:47). Courtesy of Ary Goldberger, MD.