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Patient
67-year-old man with no prior history; ECG performed for an insurance checkup;
Trace
Atrial activity originated initially from the sinus node with a normal duration of the PR interval and QRS complex; there are two premature ventricular beats corresponding to extrasystoles; the QRS complexes are narrow and identical to the sinus beats, indicating that these are not premature ventricular complexes; a careful analysis (lead III) of the T wave preceding the premature beat shows a slight change in the T wave pattern pointing to the diagnosis of premature atrial complexes;
Exergue
An early premature atrial complex can be completely or partially hidden in the T wave of the preceding QRS-complex. Careful analysis of all leads is sometimes necessary, as changes in the amplitude of the T wave may be modest. They may be manifested by a simple notching or irregularity of the T wave. When they are not visualized, it can lead to erroneous diagnosis of sinus node dysfunction (when the premature atrial complex is blocked) or premature ventricular contraction (when the atrial extrasystole is followed by aberrant ventricular conduction).
A premature atrial complex may occur, as on this tracing, during ventricular repolarization (on the T wave following the preceding QRS complex). The surface electrocardiogram registers on the skin, all of the potentials generated by the heart.