The examiner should stand on the right side of the patient, with the bed at a level comfortable for the examiner. Palpation for the PMI is most easily performed with the patient in a sitting position. Only the examiner's fingertips should be applied to the patient's chest in the fifth intercostal space, midclavicular line, because they are the most sensitive for assessing localized motion. The PMI should be noted. This technique is demonstrated in Figure 14-27. If the apical impulse is not felt, the examiner should move his or her fingertips in the area of the cardiac apex. The PMI is usually within 10 cm of the midsternal line and is no larger than 2 to 3 cm in diameter. A PMI that is laterally displaced or is felt in two interspaces during the same phase of respiration is suggestive of cardiomegaly.
Figure 14-27 Technique for assessing point of maximum impulse.
*Low-frequency cutaneous vibrations associated with loud heart murmurs.
The PMI is felt in approximately 70% of normal individuals while they are sitting. If it cannot be felt in the sitting position, the patient should be reevaluated while supine and in the left lateral decubitus position. The position of the PMI in the left lateral decubitus position must be assessed with the understanding that the normal cardiac impulse is now shifted slightly to the left. If the patient is in the left lateral decubitus position and the PMI is not laterally displaced, the examiner can suspect that cardiomegaly is not present.
In a patient without conditions predisposing to left ventricular hypertrophy, a palpable apical impulse felt in the left lateral decubitus position that is greater than 3 cm is said to be a specific (91%) and sensitive (92%) indicator of left ventricular enlargement. An apical diameter greater than 3 cm is predictive (86%) of an increased LVEDV. In patients with an apical diameter of less than 3 cm and a normal LVEDV, the negative predictive value is 95%.
The PMI usually corresponds to the left ventricular apex, but in patients with an enlarged right ventricle, the heart is rotated clockwise, as viewed from below, and the PMI may actually be produced by the right ventricle. This rotation turns the left ventricle posteriorly and makes it difficult to palpate. The apical impulse by the right ventricle is diffuse, whereas that of the left ventricle tends to be more localized.
In patients with chronic obstructive lung disease, the overinflation of the lungs displaces the PMI downward and to the right. The PMI in such patients is felt in the epigastric area, at the lower end of the sternum. In patients with chronic obstructive lung disease, a PMI in the normal location is suggestive of cardiomegaly.