This is taken in the postero-anterior (p A) direction at maximum inspiration with the heart close to the X-ray film to minimize magnification with respect to the thorax. A lateral may give additional information if the PA is abnormal. The cardiac structures and great vessels that can be seen on these X-rays are indicated.
Heart size can be reliably assessed only from the PA chest film; the maximum transverse diameter of the heart is compared with the maximum transverse diameter of the chest measured from the inside of the ribs.
The cardiothoracic ratio (CTR) is usually less than 50%, except in neonates, infants, athletes and patients with skeletal abnormalities such as scoliosis and funnel chest in general. A transverse cardiac diameter of more than 15.5 ern is abnormal. Pericardial effusion or cardiac dilatation causes an increase in the ratio. A pericardial effusion produces a globular, sharp-edged shadow. This enlargement may occur quite suddenly and, unlike heart failure, there is no associated change in the pulmonary vasculature. The echocardiogram is more specific than the chest X-ray for the diagnosis of pericardial effusion, particularly because at least 250 ml of fluid must accumulate before X-ray changes are apparent. Certain patterns of specific chamber enlargement may be seen on the chest X-ray:
LEFT ATRIAL DILATATION results in prominence of the left atrial appendage on the left heart border, a double atrial shadow to the right of the sternum, and splaying of the carina because a large left atrium elevates the left main bronchus . On a lateral chest X-ray an enlarged left atrium bulges backwards, displacing the left main stem branches.
LEFT VENTRICULAR ENLARGEMENT results in an increase in the CTR and a smooth elongation and increased convexity of the left heart border. A left ventricular aneurysm may produce a distinct bulge or distortion of the left heart border.
RIGHT ATRIAL ENLARGEMENT results in the right border of the heart projecting into the right lower lung field.
RIGHT VENTRICULAR ENLARGEMENT, due to congenital heart disease, results in an increase of the CTR and an upward displacement of the apex of the heart because the enlarging right ventricle pushes the left ventricle leftwards, upwards and eventually backwards. Differentiation of left from right ventricular enlargement may be difficult from the shape of the left heart border alone, but the lateral view shows enlargement anteriorly for the right ventricle and posteriorly for the left ventricle.
ASCENDING AORTIC DILATATION OR ENLARGEMENT is seen as a prominence of the aortic shadow to the right of the mediastinum between the right atrium and superior vena cava.
DISSECTION OF THE ASCENDING AORTA is seen as a widening of the mediastinum, although this is often difficult to assess on an AP chest X-ray. A left-sided pleural effusion may be evident if the aneurysm is leaking or there may be blood around the apex of the lung (‘capping’). ENLARGEMENT OF THE PULMONARY ARTERY in pulmonary hypertension, pulmonary artery stenosis and left-to-right shunts produces a prominent bulge on the left-hand border of the mediastinum below the aortic knuckle.
Calcification in the cardiovascular system occurs because of tissue degeneration. Calcification is visible on a lateral or a penetrated PA film, but is best studied by fluoroscopy or CT scanning. Various types of calcification can occur:
PERICARDIAL CALCIFICATION may be seen as plaquelike opacities over the surface of the heart, but particularly concentrated in the atrioventricular groove. Such calcification often results from tuberculous pericarditis and may be associated with pericardial constriction.
VALVULAR CALCIFICATION may result from longstanding rheumatic or bicuspid aortic valve disease.
The aortic and mitral valves are most commonly affected. On the lateral film, a calcified aortic valve is seen on or above a line joining the carina to the sternophrenic angle. Mitral valvular calcification is seen below and behind this line.
MYOCARDIAL CALCIFICATION may occur after myocardial infarction, especially in association with a left ventricular aneurysm.
CALCIFICATION OF THE AORTA is a common, normal finding in patients over the age of 40 years and appears as a curvilinear opacity around the circumference of the aortic knuckle. Calcification in the ascending aorta usually denotes syphilitic aortitis, whereas in the descending aorta it is due to atheroma or, in the younger patient, to non-specific aortitis. CORONARY ARTERIAL CALCIFICATION, especially of the proximal left coronary artery, is associated with coronary atheroma but does not necessarily correspond to the site of maximal stenosis.
Pulmonary plethora results from left-to-right shunts, e.g. atrial or ventricular septal defects. It is seen as a general increase in the vascularity of the lung fields and as an increase in the size of hilar vessels, e.g. in the right lower lobe artery, which normally should not exceed 16 mm in diameter. Pulmonary oligaemia is a paucity of vascular markings and a reduction in the width of the arteries. It occurs in situations where there is reduced pulmonary blood flow, such as pulmonary embolism, severe pulmonary stenosis and Fallot’s tetralogy. Pulmonary arterial hypertension may result from pulmonary embolism, chronic lung disease or chronic left heart disease such as shunts due to a ventricular septal defect or mitral valve stenosis. In addition to X-ray features of these conditions, the pulmonary arteries are prominent close to the hili but are very reduced in size (pruned) in the peripheral lung fields. This pattern is usually symmetrical.
limbs (I, II, III, AVR, AVL and AVF). The other six leads record potentials between points on the chest surface and an average of the three limbs: RA, LA and LL. These are designated YI-Y6 and aim to select activity from the right ventricle (YI-Y2), interventricular septum (YrY.) and left ventricle (YS-Y6). Note that leads AVR and YI are oriented towards the cavity of the heart, leads II, III and AVF face the inferior surface and leads I, AVL and Y6 face the lateral wall of the left ventricle.
The ECG potentials are picked up by electrodes attached to the patient. Disposable, self-adhesive electrodes are more convenient and hygienic than the nickel plates and cup electrodes which are still used with some older machines. The electrodes are connected to the ECG recorder by a multicolour or coded cable.
Although some single-channel ECG machines still exist, most are simultaneous three-channel recorders with output either as a continuous strip or with automatic channel switching. Many modern ECG machines present the ECG (all 12 standard leads and a rhythm strip) in a convenient page-sized format. Many ECG machines also analyse the recordings and print the analysis on the record. Usually the machine interpretation is correct, but many arrhythmias still defy automatic analysis.