To understand clearly the effects upon the position of the heart of disease of contiguous organs, we must bear in mind their mutual relations. Situated in the mediastinum between the lungs on either side, it is subject to the elastic traction of these organs, which counterbalance each other, but if from any cause the elastic tension of one lung is suppressed, as in pneumothorax or in pleural effusions, then the other lung may also collapse to a slight degree, and pull over the mediastinum and with it the heart. The pericardium is firmly fixed below to the diaphragm, chiefly to the central tendon, to a slight extent also to the muscular substance, but the union with the diaphragm is so intimate that there can be but little movement of the attached portion. The mobility of the heart is measured by that of the mediastinum and pericardium, and through these alone the displacing forces act. The limits of dislocation are determined by the attachments of the central tendon, of the inferior cava, and the great vessels at the root. Within the pericardium the heart has a certain degree of mobility, but this is confined, as regards pressure or traction effects, to rotation upon its axes.
Of the malpositions due to changes in contiguous organs, the following may be considered:
Changes in the Chest-wall.—The gradual incurvation of the ribs and costal cartilages in some cases of rickets may alter the position of the heart.
Curvature of the spine, particularly cases which narrow to a great extent the upper outlet of the thorax, may produce very considerable displacement of heart and great vessels. There may be areas of extensive pulsation on either side of the sternum, and the condition may simulate aneurism of the aorta, as in a case reported by Bramwell.5
5 Lancet, 1878, i.
In certain affections of the lungs the position of the heart is much altered. In emphysema, when extensive, the apex is directed more to the right, and the organ is somewhat lower than normal, on account of the depressed condition of the diaphragm. The heart may also occupy a more transverse position. The area of cardiac dulness may be greatly reduced by the distended left lung, and there is usually forcible epigastric pulsation, due to the lower position of the organ and the hypertrophy of the right ventricle which almost always accompanies emphysema.
The most marked displacement is produced by fibroid induration of the lung, with contraction—cirrhosis. As the process of condensation goes on, the chest-wall is gradually flattened, and the mediastinum, with the heart, drawn toward the affected side. When the left lung is involved, the heart may be completely to the left of the median line, and is usually drawn upward as well. There may in such cases be a very wide area of impulse, as the heart occupies the position of the left lung in front. In cirrhosis of the right lung the organ is drawn toward the right side, and the area of visible impulse may be in the third and fourth interspaces to the right of the sternum. In the process of slow traction the heart revolves upon itself and the left chambers come uppermost. In many cases of chronic phthisis, when the anterior margin of the left lung is involved, the retraction from induration may leave a large portion of the heart exposed and increase the area of visible pulsation; sometimes, when there is much contraction of the upper lobe, the organ is drawn up and to the left, and the apex-beat may be in the fourth interspace.
The pressure of a pneumonic lung may depress the diaphragm and draw down the heart.
Abnormal conditions of the pleuræ are frequent causes of cardiac displacements. In pneumothorax there is collapse of the lung on the affected side, and the elastic traction of the sound lung draws over the mediastinum and heart. It is not that the heart is pushed over, as so often stated, but the tension of the other lung, being unopposed, pulls the mediastinum toward the sound side. Later, when, as usually happens, effusion takes place, the pressure assists in the displacement. In pleuritic effusion dislocation of the heart to one side is almost constant if the amount of fluid is at all considerable. Here pressure plays the most important part, and the heart is gradually pushed over by the effusion; but the elastic tension of the lung on the sound side is also concerned in the result. In right-sided effusion the whole organ may be to the left of the median line, and from the depression of the diaphragm it is usually lower in the chest, so that the apex-beat may be in the sixth, rarely the seventh, interspace in the axillary line. When the exudation is on the left side, the dislocation is more marked, and there may be a cardiac impulse at the right nipple or even beyond it. A common error is to regard the pulsation as due to the apex, but it is invariably caused by some portion of the right chambers, usually the ventricle. Even in the most extensive effusion the apex is probably never pushed beyond the right border of the sternum, and the relative position of apex and base is not changed. This I have carefully noted in several autopsies.6
6 Fig. 76 of Sibson's article on "Displacements of the Heart" in Reynolds's System of Medicine gives an incorrect idea of the position of the organ in these cases, as the apex is represented as beating beneath the right nipple.