[The surface ECG in the diagnosis of cardiac arrhythmias: the value of the right precordial leads].

The surface electrocardiogram (ECG) is a simple noninvasive method to assess the electrical activity of the heart and provides important information to identify patients with cardiac arrhythmias and increased arrhythmic risk. This brief review highlights cardiac conditions in which the right precordial leads recorded on the surface ECG during sinus rhythm or tachycardia are of important diagnostic and prognostic value. Epsilon waves seen in the right precordial ST segments are the electrocardiographic hallmark of arrhythmogenic right ventricular cardiomyopathy. The diagnosis of Brugada syndrome and risk stratification of affected patients are based on a coved-type >or=2 mm ST-segment elevation in the right precordial leads. This typical ECG pattern may be present persistently, intermittently or only after administration of sodium-channel blockers. The early repolarization syndrome, most commonly seen in healthy young individuals, is characterized by a ST-segment elevation of 1 to 4 mm in the mid-precordial leads with a notched and elevated J point in lead V4. The precordial ECG T-wave repolarization pattern may be helpful in identifying the genotype in patients with suspected long QT syndrome. In patients with overt preexcitation, the surface leads V1 and V2 play a key role in localizing the site of bypass-tract insertion. Finally, the right precordial lead V1 is often crucial in the diagnosis of narrow and broad QRS-complex tachycardias.