[Electrical features of hypertrophied left heart]

Chronological and spatial characteristics of the main resultant vectors of the left atrial and ventricular depolarization in normal conditions and in presence of hypertrophy, due to a sustained overload, are described. The coexistence of interatrial, intraatrial, and intraventricular conduction disorders can modify the orientation of these vectors. The main electrocardiographic sign of left atrial hypertrophy is a P wave duration > 0.10 sec in adults. In case of left ventricle hypertrophy, the time of onset of the intrinsicoid deflection (TOID) is prolonged in the near left unipolar leads, and the S wave voltage is increased in opposite regions, i.e. in the right precordial or transitional leads. It is necessary to bear in mind other useful electrocardiographic signs. Hence, absence of the right basal vector (IIId) manifestation in a clockwise rotating heart is probably due to an increase in the basal electromotive forces of the left ventricle (vector IIIi) due to hypertrophy or ipsilateral ventricular conduction disorders. For a correct evaluation of these signs, it is mandatory to perform a rational analysis of the traings, not just a stereotyped electrical exploration. Besides it is very important to determine the Q-Tc interval in the left unipolar leads to establish whether, in these leads, the inverted T wave is of secondary type (normal Q-Tc) or of primary type (prolonged Q-Tc) due to a coexisting subepicardial or transmural ischemia. From these considerations, the usefulness of the thoracic circle and high abdominal unipolar leads is inferred.