Hypertrophy

In this chapter, we address the basic notions of cardiac chambers hypertrophy. Hypertrophy of the left ventricle causes a significant increase in the height and depth of the QRS complex. The thickening of the wall prolongs the activation of the ventricle and as a result, the duration of the QRS complex. ST segment changes can also be present because repolarisation starts in the sub-endocardium instead of the subepicardium, or because permanent ischemia is present due to the increased left ventricular mass and reduced coronary blood flow. Typically the ST and T wave vectors have an opposite direction to that of the QRS complex. Electrocardiographic changes of right ventricular hypertrophy are seen only with severe right ventricular hypertrophy. The right electrical forces dominate the left electrical forces. Anterior forces will predominate with a tall R wave in V1 and a small S wave. In some cases the forces are posteriorly directed without changes in V1 but with a deep S wave in the left precordial leads. As with left ventricular hypertrophy, repolarisation is significantly modified with the vector of the QRS complex having an opposite direction to the vector of the ST segment (ST segment depression, T wave inversion in the right precordial leads). Left atrial enlargement prolongs the terminal portion of the P wave with an increased duration and a "double hump" or m-shaped morphology. Right atrial enlargement prolongs the initial portion of the P wave with a superimposition of its activation on the activation of the left atrium. As a consequence, the amplitude of the P wave increases in a triangular form without increasing its duration. Depolarisation of the atrium is best seen in leads II and V1. Enlargement of both atria is present when the criteria for both right and left atrial enlargement are fulfilled on the same ECG.

Keywords: Atrial hypertrophy, ventricular hypertrophy, QRS amplitude, P wave prolongation, P wave amplitude, bi-atrial hypertrophy, bi-ventricular hypertrophy, QRS axis, P wave axis.