This ECG is taken from an 82-year-old man who called 911 because of chest pain. He has an unspecified “cardiac” history, but we do not know the specifics.
This ECG shows an underlying rhythm of normal sinus rhythm at a rate of 80 / min. There are two premature ventricular contractions (PVCs). The sinus rhythm actually continues uninterrupted, causing a “compensatory pause”. If you march out the P waves, you may even see hints of the hidden P waves in the ST segments of the PVCs. The P waves that occur in the ST segments of the PVCs land in the refractory period of the ventricles, and so are unable to continue into the ventricles and cause a QRS.
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