Midclavicular Line

MIDCLAVICULAR LINE, a line drawn vertically downward from the midpoint of the clavicle along the anterior chest wall. In clinical practice, it is used mainly for determining the size of the left ventricle of the heart; normally, the left border of the relative cardiac dullness, or the cardiac apex impulse, usually lies somewhat medial to and does not extend beyond the left midclavicular line. The distance of this line from the vertical line drawn through the midpoint of the sternum varies in different individuals, depending mainly on the width of the chest. Consequently, the midclavicular line can be used only approximately for assessing the size of the left heart, with appropriate corrections in each individual case, and with special consideration of the configuration of the chest (for example, in a narrow chest, the heart, even with normal dimensions, may extend to the left beyond the midclavicular line).