9. Diagnostic imaging of cardiac diseases. Methods, indications. Cardiomyopathies. Diseases of the pericardium.

Echocardiography

Echocardiography refers to the use of ultrasonography to evaluate the heart. With the help of duplex ultrasonography, one can estimate the ejection fraction, the pressure gradient across valves, the speed of blood through valves, and the pressure of the pulmonary vasculature.

There are two types:

• Transthoracic echocardiography (TTE)
  • The ultrasound probe is placed on the chest wall
  • Least invasive
  • Easiest to do
  • Usually the first choice
  • What one usually means when they just say "echocardiography"
• Transoesophageal echocardiography (TEE)
  • A special ultrasound probe is placed in the oesophagus
  • Gives more information on the ascending aorta and the atria than TTE
  • More invasive, requires sedation

Indications

Echocardiography is the basic imaging modality of the heart, used in most heart disorders, including valvular disorders, wall motion disorders, pericarditis, and pericardial effusion.

Transoesophageal echocardiography is most commonly indicated for infective endocarditis and to rule out left atrial appendage thrombus in case of atrial fibrillation.

Cardiac CT

Cardiac CT is a frequently performed modality for the evaluation of coronary artery disease. Commonly used techniques include coronary CT angiography and calcium scoring.

A beta blocker and nitrate are usually given beforehand. The beta blocker reduces the heart rate to the ideal 60 bpm, while the nitrate dilates the coronary arteries, improving visualisation.

Cardiac CT can be “coupled” to an ECG so that it only takes pictures during the same part of the cardiac cycle. This reduces noise made from movement of the heart.

Coronary CT angiography

Coronary CT angiography is a non-invasive alternative to invasive coronary angiography, used for the diagnosis of coronary artery disease in those at low or intermediate pretest probability. Those with high pretest probability proceed directly to invasive coronary angiography, as this allows for percutaneous coronary intervention of any stenoses in the same setting. Coronary CT angiography is ECG-coupled.

A so-called "triple-rule-out CT angiography" is an extended form of coronary CT angiography which can rule out pulmonary embolism, acute aortic syndrome, and acute coronary syndrome in one procedure.

Calcium scoring

Calcium scoring refers to using non-contrast CT to evaluate the amount of calcium in the coronary artery walls, giving a coronary artery calcium (CAC) score. Calcium scoring can be performed during the non-contrast phase of coronary CT angiography or as a separate examination. The score is called Agatston score.

Calcium scoring is used in those with intermediate pretest probability for coronary artery disease. It gives a score which represents the severity of the patient's coronary artery disease:

Agatston score	Coronary artery disease severity
0	No coronary artery disease
1-10	Minimal
11-100	Mild
101-300	Moderate
>300	Severe

Cardiac MRI

Cardiac MRI (sometimes called CMR) is an infrequently used modality in the evaluation of heart disease. It's mostly used for the evaluation of myocardium, either in case of myocarditis or evaluation of complications of acute myocardial infarction. It can measure ejection fraction and volume of the myocardium, among other parametres.

Cardiac MRI can be “coupled” to an ECG so that it only takes pictures during the same part of the cardiac cycle. This reduces noise made from movement of the heart.

When used to evaluate the complications of acute myocardial infarction, infarcted or scarred myocardium will show “delayed” or “late” enhancement with gadolinium contrast.

Chest x-ray

Chest radiography, often called chest x-ray, is a commonly performed radiological procedure. Some indications include:

• Symptoms
  • Dyspnoea
  • Chronic cough
• Suspicion of
  • Pneumonia
  • Pleural effusion
  • Heart failure
  • Lung cancer

Findings

See also imaging of pneumonia.

• Enlarged cardiac shadow (cardiomegaly)
  • Defined as a cardio-thoracic ratio > 50%
    • Meaning that the width of the heart is more than 50% the width of the chest wall on a standing PA x-ray
  • Causes
    • Pericardial effusion
    • Heart failure
    • Hypertrophic cardiomyopathy
    • Dilated cardiomyopathy
• White-out of a hemithorax
  • Complete opacification of one hemithorax
  • Differential diagnosis
    • Total pneumonectomy
    • Extended pleural effusion or hydropneumothorax
    • Large mass obstructing airways, causing atelectasis of the whole lung
• Flattening of diaphragm
  • Due to increased pressure/hyperinflation of lungs
    • Tension pneumothorax
    • COPD/emphysema

Pulmonary oedema

Pulmonary oedema refers to accumulation of fluid in the alveoli. It may be very severe and life threatening, but in most cases it's not.

Etiology

We distinguish cardiogenic and non-cardiogenic causes of pulmonary oedema:

• Cardiogenic causes
  • Acute decompensated heart failure (wet type)
  • Acute aortic stenosis
  • Acute mitral regurgitation
• Non-cardiogenic causes
  • Acute respiratory distress syndrome
  • High altitude
  • Vaping products
  • Opioid overdose

Diagnosis and evaluation

Imaging is important to evaluate pulmonary oedema. On a chest radiograph, one can see the following findings:

• Kerley B lines
  • Increased prominence of interlobular septa at the periphery of the lungs
  • They are perpendicular to the pleural surface
  • Usually seen at the lung bases
• Peribronchial cuffing
  • Increased density around the walls of the bronchi
  • Due to fluid around the bronchi
• Butterfly opacities
  • Bilateral increased density around the lung hila
• Stag's antler sign or apicobasal caliper discrepancy
  • Apical vessels are more expanded than basal vessels
  • Due to redistribution of blood flow to the upper lung
• Pleural effusion

Pulmonary hypertension

Pulmonary hypertension (PH) is defined as elevated blood pressure beyond 20 mmHg MAP in the pulmonary artery (physiological MAP is 10-20). It most commonly occurs as a consequence of heart disease or lung disease. Pulmonary arterial hypertension (PAH) is one form of pulmonary hypertension which is not secondary to heart or lung disease.

Pulmonary hypertension is relatively common, the prevalence being approximately 1%, mostly due to the high prevalence of COPD and heart disease. PH itself can lead to right-sided heart failure.

Etiology and types

We distinguish multiple different types according to the etiology and pathomechanism:

Group	Name	Frequency	Common causes	Pathomechanism
Group 1	Pulmonary arterial hypertension	Rare	Idiopathic Drugs Connective tissue disorder Persistent pulmonary hypertension of the newborn Eisenmenger syndrome	Elevated pulmonary vascular resistance
Group 2	Pulmonary hypertension secondary to left-sided heart disease	Very common (70% of PH)	Heart failure Valvular disease
Group 3	Pulmonary hypertension secondary to lung disease or hypoxaemia	Common	COPD Interstitial lung disease	Chronic hypoxia causes pulmonary vasoconstriction and remodelling of the pulmonary vascular bed
Group 4	Pulmonary hypertension secondary to pulmonary artery obstruction	Rare	Chronic pulmonary embolism	Pulmonary embolism increase pulmonary vascular resistance
Group 5	Pulmonary hypertension secondary to unknown or multifactorial causes	Rare	Chronic kidney disease Sarcoidosis Haematological disorder

Diagnosis and evaluation

Neither chest radiography or CT are required in the evaluation, except for evaluation of underlying disorders. On x-ray, the central vessels may be more prominent than normal. On CT, one can see that the pulmonary artery is larger than the ascending aorta, and that there is a so-called centroperipheral caliber discrepancy  or “pruning” of the peripheral vessels, which means that the central pulmonary vessels are larger than normal while the peripheral vessels aren't.

Echocardiography is the main modality for the evaluation, as it can estimate the pulmonary artery pressure. Typical findings include tricuspid regurgitation, pulmonary regurgitation, dilated right atrium and ventricle, and right ventricular hypertrophy. However, right heart catheterisation is obligatory for the final diagnosis, as it can directly measure the pressure.

Dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a form of cardiomyopathy characterised by dilation of all four heart chambers, in the absence of ischaemic heart disease, hypertension, valvular disease, and congenital heart disease. The ejection fraction is <45% and the left ventricular end-diastolic volume is >117% of predicted based on body surface area.

DCM is the most common cardiomyopathy, affecting 1/250. The prognosis is poor with a 5-year survival rate of 50%.

Diagnosis and evaluation

X-ray shows cardiomegaly, and possibly signs of pulmonary oedema or congestion. Echocardiography shows dilation of all four chambers, decreased EF, and secondary mitral and tricuspid regurgitation.

MRI is the gold standard for evaluation, as it can measure the volumes of the chambers in addition to showing the dilatation. It’s also helpful in the evaluation of myocarditis, a common cause.

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a form of cardiomyopathy characterised by left ventricular hypertrophy in the absence of a provoking disease like hypertension or aortic stenosis. The hypertrophy is often asymmetric.

Hypertrophic obstructive cardiomyopathy (HOCM) is a subtype of HCM characterised by obstruction of the left ventricular outflow tract due to excessive hypertrophy of the ventricular septum.

Diagnosis and evaluation

ECG shows signs of left ventricular hypertrophy and strain. Echocardiography shows left ventricular hypertrophy, a septum which is thicker than the posterior wall, normal LV chamber size. SAM may also be visualised.

MRI is the gold standard for the evaluation. 1st degree relatives should be screened for the condition.

Pericardial effusion

Pericardial effusion refers to accumulation of pathological amounts of fluid in the pericardial cavity. In physiological cases there is 15-50 mL of fluid in the cavity. It may cause cardiac tamponade, which is an emergency. If the fluid is blood it's called haemopericardium.

Cardiac tamponade is a condition where a pericardial effusion compresses the heart, leading to life-threatening acute heart failure. This occurs if the pericardial effusion develops rapidly or is large, causing the pressure in the pericardial space to exceed the pressure in the heart chambers. It’s an emergency which should be treated empirically even before a proper diagnosis is made.

Etiology

• Pericarditis
• Tuberculosis
• Following heart surgery
• Thoracic injury
• Metastasis
• Cardiac wall rupture (trauma, MI)

Diagnosis and evaluation

A chest x-ray may not always show a pericardial effusion. The cardiac shadow may be enlarged. If the effusion is large enough, the heart may appear water bottle-shaped, called "water bottle sign". Echocardiography is the investigation best suited to evaluate pericardial effusion, as it will directly visualise the anechoic fluid around the heart. The effusion is mild when < 10 mm on echo, severe when > 20 mm, and moderate in between.

If cardiac tamponade is suspected based on the clinical features, one should not waste time with time-consuming investigations. A quick echocardiography to confirm pericardial fluid, together with typical clinical features, is usually sufficient to start treatment.

Should one make these investigations (for example if the diagnosis isn't immediately clear), they might show the following:

• ECG – low voltage, electrical alternans
  • Electrical alternans refers to alternating amplitude (height) of the QRS complex with each heartbeat
• Echocardiography – large effusion, collapse of chambers, swinging of the heart

Anomalous pulmonary venous return

Anomalous pulmonary venous return refers to a form of rare cyanotic congenital heart disease characterised by som or all of the pulmonary venous return entering the systemic circulation through embryological connections.

In case of total anomalous pulmonary venous return (TAPVR), the entire pulmonary venous return enters the systemic circulation, while in case of partial anomalous pulmonary venous return (PAPVR), only some of the pulmonary venous return enters the systemic circulation.In case of TAPVR, chest x-ray may show the snowman sign, as the heart makes a snowman-shape.

In case of PAPVR, chest x-ray may show Scimitar syndrome, as the anomalous draining vein makes a scimitar-shape.

Transposition of the great arteries

Transposition of the great arteries or the great vessels is a cyanotic congenital heart disease characterised by the aorta arising from the right ventricle (rather than the left) and the pulmonary trunk arising from the left ventricle (rather than the right). This essentially creates two parallell circuits which are not connected. This is incompatible with life unless there is some intracardiac shunt, like patent ductus arteriosus or ventriculoseptal defect.Echocardiography will reveal the diagnosis. Chest radiography will show the "egg on a string" sign.

Ebstein anomaly

Ebstein anomaly is a rare form of cyanotic congenital heart disease characterised by a downwards displacement of the septal and posterior leaflets of the tricuspid valve into the right ventricle. This displaces the "border" between the right atrium and right ventricle inferiorly, making the right atrium larger and right ventricle smaller, a process called atrialisation.

Diagnosis and evaluation

Echocardiography confirms the diagnosis. Chest radiography shows a box-shaped heart.

Tetralogy of Fallot

Tetralogy of Fallot (ToF) is a cyanotic congenital heart disease caused by anterior displacement of the aorticopulmonary septum, causing unequal division of the truncus arteriosus. This causes four separate malformations, hence the name “tetralogy”:

• Pulmonary infundibular stenosis (narrow right ventricular outflow tract)
• Ventricular septal defect
• An overriding aorta
  • The aorta originates right over the VSD, so blood from the right ventricle enters the aorta during systole
• Right ventricular hypertrophy

Diagnosis and evaluation

Echocardiography confirms the diagnosis. Chest x-ray would show a boot-shaped heart.

Left atrial enlargement

Left atrial enlargement (LAE) is a consequence of increased left atrial pressure or volume over a longer period of time. This may be due to left-to-right shunt, hypertension, mitral regurgitation, or mitral stenosis.

Diagnosis and evaluation

Echocardiography is the best modality for measuring the size of the left atrium. ECG may show:

• Wide P wave > 0.11 s
• "P mitrale" - a notched or bifid P wave
• P wave axis < 30 degrees

Chest radiography may show superior displacement of the left main bronchus, best visible on the lateral radiograph as the "walking man sign".