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Second-Degree AV Block (Mobitz I, Wenckebach). The PR interval gradually increases until a P wave is not followed by a QRS and a beat is “dropped.” The process then recurs. P waves occur at regular intervals, though they may be hidden by T waves. (ECG contributor: James Paul Brewer, MD.)


The authors acknowledge the excellent contributions of James V. Ritchie, MD, and Michael L. Juliano, MD, to prior editions of this chapter.

ECG Findings

  • New ST-segment elevation at the J point in at least two anatomically contiguous leads.

    • Men ≥ 40 years of age: 2 mm (0.2 mV) in V2-V3 and 1 mm (0.1 mV) in all other leads

    • Men < 40 years of age: 2.5 mm (0.25 mV) in V2-V3 and 1 mm (0.1 mV) in all other leads

    • Women: 1.5 mm (0.15 mV) in V2-V3 and 1 mm (0.1 mV) in all other leads


  1. The recommended therapy is emergent percutaneous coronary intervention (PCI). If PCI cannot be performed within 90 minutes, then thrombolysis is recommended (unless there are absolute contraindications to thrombolysis).

  2. Reciprocal changes increase the specificity of ST-segment elevations for ST-segment elevation myocardial infarction (STEMI). Reciprocal changes are ST depressions in leads found at a 180-degrees vector opposite to the leads with ST elevations.

  3. The development of pathologic Q waves suggests progression from myocardial injury to infarction.


ST-Segment Elevation Myocardial Infarction (STEMI). (ECG contributors: Clifford L. Freeman, MD, and Nicole S. McCoin, MD.)


Pathologic ST-segment elevation (upward arrows) is seen in the inferior leads (II, III, aVF) with reciprocal ST-segment depression seen here in lead aVL (downward arrow).

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