[Observations on the sequence of endocardial activation in the left ventricle of the normal subject]

To obtain information on normal left ventricular activation, endocardial recordings with an electrode catheter were made a seven left ventricular sites in ten patients undergoing diagnostic heart catheterization. All the patients had: 1) sinus rhythm; 2) normal duration and shape of the QRS complex of left chest leads; 3) normal left ventriculography, i.e. normal volume and contractility of the left ventricle. The earliest left ventricular endocardial activation was recorded at septal and/or posterior level, i.e. at the septum (6 to 16 msec, average 9.7 msec, after the onset of intracardiac QRS complex) in seven patients; at the posterior wall (0 to 4 msec, average 2.6 msec, after the onset of intracardiac QRS complex) in three patients (in one of these, the earliest activation occurred at the posterior wall and apex simulaneously). If the earliest activation occurred at the left interventricular septum, the next excited point was found on the posterior wall or at the apex, and vice versa. The latest part to be activated was on the lateral free wall in seven patients; on the posterior wall in two patients; at the apex in the last one.