- Chest X-ray: most common imaging test to evaluate the heart and great vessels; usually the initial test before using more expensive diagnostic tools:
- Shadows that form the cardiac silhouette allow for assessment of the size and shape of the heart and major vessels.
- Lung parenchymal findings also give information regarding pulmonary pathologies secondary to cardiac abnormalities (e.g., pulmonary edema).
- Also used in the evaluation of the mediastinum
- Positioning for specific views:
- Posteroanterior (PA):
- Board is against the anterior chest.
- X-ray beams posterior → anterior direction through patient
- Anteroposterior (AP):
- Board is against the back.
- X-ray beams anterior → posterior direction through the patient
- Lateral (from side):
- Patient is upright.
- Board is against the left or right side.
- Lateral decubitus (from side while laying down):
- Patient is supine.
- Board is against the side.
- Usually left side down on table
- Posteroanterior (PA):
- Penetration: degree to which radiation has passed through body, resulting in darker or lighter image
- Good penetration:
- Ribs are only faintly visible behind the heart.
- Vascular markings are nonprominent but clear.
- Underpenetration: film appears whiter and features are less apparent.
- Overpenetration: film appears darker and features are less apparent.
- Good penetration:
The following structures must be identified and checked for abnormalities in size or shape:
- PA projection:
- Trachea: should be on the midline
- Superior vena cava (SVC)
- Ascending and descending aorta (aortic arch)
- Pulmonary hilum (right and left)
- Pulmonary artery
- Right atrium (right heart border)
- Left ventricle (left heart border)
- To easily identify the structures on the left border in a cephalocaudal order, remember:
- 1st bump: aorta
- 2nd bump: pulmonary artery
- 3rd (the largest) bump: left ventricle
- Lateral projection:
- Retrosternal space
- Right ventricle
- Right hemidiaphragm
- Aortic arch
- Pulmonary hilum
- Left ventricle
- Left hemidiaphragm
- Posterior cardiac space
- On a plain chest film, heart size is quickly assessed calculating the cardiothoracic index (CI): the percentage of the chest diameter occupied by the heart.
- A normal CI is < 50%.
- However, this is reliable only on a PA projection taken upright.
- An enlarged heart can be due to:
- Pericardial effusion (water-bottle heart): pericardial effusions must be ≥ 250 mL to be detectable on a chest X-ray.
- Valvular disease
- Congenital heart disease
|Rotation||The shadow of the heart appears bigger in the projection because of the rotation of the subject to either side.|
|Suboptimal inspiration||The diaphragm moves upward and compresses the heart.|
|Portable supine film||Cardiac silhouette undergoes magnification because the cassette is placed in contact with the posterior aspect of the patient and the X-ray beam penetrates from the anterior aspect.|
|Pectus excavatum||The heart is compressed between the sternum and the spine.|
- In the PA and AP projections, the great vessels can be identified at either side of the mediastinal shadow.
- Right mediastinal margin (cephalocaudal):
- Right pulmonary artery coinciding with the right pulmonary hilum
- Left mediastinal margin (cephalocaudal):
- Left pulmonary artery coinciding with the left pulmonary hilum
- Right mediastinal margin (cephalocaudal):
- In a lateral projection, only the shadow of the aorta can be distinguished.
- Ultrasound principles are used in echocardiography to produce anatomical images of the heart and great vessels.
- Common indications:
- Evaluation of ventricular function
- Congenital heart disease
- Valvular heart disease
- Pericardial effusion
- Cardiac masses
- Proximal aortic disease
- Echocardiography is likewise an essential tool in assessing the dynamic function of the heart in stress tests (exercise or dobutamine stress echocardiography).
Evaluation of the heart and great vessels
- Transthoracic echocardiography (TTE):
- More common; noninvasive
- Uses a handheld transducer positioned on the chest to scan the heart
- Provides the clinician with the ability to quickly assess the heart, especially in life-threatening situations
- Allows for the rapid distinction between cardiac (e.g., pericardial effusion) and extracardiac (e.g., pulmonary embolus) causes of illness
- Transesophageal echocardiography (TEE):
- Improved image quality (especially posterior cardiac structures) because of the proximity of the esophagus to the heart
- Because of TEE’s invasive nature, TTE often precedes TEE.
- Commonly used in:
- Evaluation for a cardiac source of embolus
- Valvular assessment in cases of endocarditis
- Determination of left atrial appendage (LAA) thrombi in patients with atrial fibrillation
- 2-Dimensional: by undergoing complex processes (e.g., filtering, signal amplification), the signal received forms a cardiac image displayed on the monitor.
- M = motion
- Movement of the structures is graphically imaged over time by directing a linear beam of ultrasound at a single structure.
- Provides information regarding blood flow (hemodynamics)
- Especially helpful in valvular and cardiac function assessment, as well as in evaluating intracardiac shunts
- Interpretation includes:
- Reason for the test
- Quality of image
- Rate and rhythm
- Chamber sizes
- Right ventricular function
- Left ventricular systolic function:
- Ejection fraction = (stroke volume [end diastolic volume – end systolic volume]/end diastolic volume) × 100
- Wall motion
- Left ventricular diastolic function
- Mass or thrombus
- Atrial or ventricular septal defect
- Other findings can include aneurysms, pleural effusion, and incidental findings.
- Cardiac scan:
- Also called heart scan or myocardial perfusion imaging
- Detects variation in blood flow and myocardial extraction of radiotracers
- Isotopes: technetium-99m, thallium-201
- Radiopharmaceutical (radioisotope + organic molecule): sestamibi, teboroxime
- In normal coronary arteries, significant arterial dilatation is seen in response to exercise/stress.
- Stenotic areas do not show dilatation; thus, ischemia and ECG changes occur.
- In this test, stress is either:
- Exercise-induced by running on a treadmill
- Pharmacologically induced by injecting adenosine or dobutamine for those who cannot run
- Imaging is obtained both during stress and at rest.
- Radiopharmaceuticals are injected when 85% of the maximum predicted heart rate (MPHR) is reached.
- Myocardial ischemia or MI evaluation
- Wall-motion abnormalities: done by ECG-gated SPECT scan
- Calculate left ventricular ejection fraction
- Normal cardiac scan obtained in 3 different planes:
- The top row of each set is performed under cardiac stress
- Bottom row of each set is performed at rest
- Normal flow to all aspects of the heart both at rest and during stress
- Thoracic CT is very useful for studying the anatomy of the heart, great vessels, and mediastinum.
- The use of IV contrast allows for adequate visualization of the heart chambers and the venous and arterial anatomy.
- Even though a CT scan is usually displayed as slices, the image data can be manipulated to obtain a 3-dimensional reconstruction of the anatomy.
- Cardiac CT, though, is associated with high dose of ionizing radiation, and use of contrast material carries a risk for renal failure.
- Coronary CTA (CCTA):
- For evaluation of the coronary arteries in cases of indeterminate stress tests
- Characterizes coronary or cardiac anomalies, including location and patency of bypass grafts
- Triple rule-out in emergency situations of atypical chest pain:
- Atherosclerotic disease
- Pulmonary embolism
- Aortic dissection
- Coronary artery calcium (CAC) scoring:
- Noninvasive test that detects and quantifies CAC.
- Generally recommended in asymptomatic adults ≥ 40 years of age with intermediate atherosclerotic cardiovascular disease risk
- Requires a relatively low radiation dose (comparable to that for a screening mammography)
- The amount of calcified plaque present in the epicardial coronary arteries, reported as the total calcium score (Agatston score):
- No identifiable disease: 0 Agatston units
- Mild disease: 1–99 Agatston units
- Moderate disease: 100–399 Agatston units
- Severe disease: ≥ 400 Agatston units
- Scoring provides guidance on further management (e.g., recommending aspirin and lipid-lowering agents).
- Contrast-enhanced CT can provide information on the thickness and composition of the vessel wall.
- Most common initial imaging for aortic dissection evaluation
- Allows for:
- Documentation of size and shape of aneurysms
- Visualization of the true and false lumen in aortic dissection
- Characterization of calcification and stenoses
- Visualization of the anatomy of congenital anomalies
- Evaluation of vasculitis
- Also useful to detect postoperative complications:
- Endoleak after aneurysm repair
CT pulmonary angiography (CTPA):
- Also called chest CT angiography with contrast
- Most frequently used imaging to evaluate the pulmonary arteries
- High sensitivity and specificity for pulmonary embolism
- A thoracic MRI is for studying the heart and great vessels; it has greater definition of anatomy than CT.
- The function of MRI is based on the utilization of magnetic fields and radiofrequencies to generate 3-dimensional, high-fidelity images.
- Use is restricted to large medical centers because of its great cost and required operational expertise.
- MRI is often reserved for evaluation of complex thoracic pathology initially assessed with more accessible imaging methods (e.g., CT).
- Contraindications: patients with metallic or electrical implants, devices, or foreign bodies that are not MRI-compatible.
- Cardiac MRI (CMR):
- Single-plane 2-dimensional (2D) or multiple-plane 2D or 3-dimensional (3D) images can be obtained.
- Can provide images of the heart going through a cardiac cycle
- Usual indications:
- Congenital heart disease
- Valvular dysfunction
- Suspected intracardiac masses
- Myocardial disease, including cardiomyopathy, ischemic heart disease, myocarditis
- Pericardial disease (e.g., noncalcified constrictive pericarditis, pericardial tumor invasion)
- Aortic abnormality (e.g., aneurysm, aortic dissection)
- Contrast-enhanced angiography
- Can be used to identify anomalous coronary arteries as well as other blood vessels (aorta) and to monitor coronary artery aneurysms
Cardiac Catheterization and Angiography
- Among the most commonly performed cardiovascular imaging tests
- A catheter is introduced into a peripheral vessel such as the femoral or axillary vein or artery (catheterization) and is positioned in the region of interest:
- Performed under fluoroscopic guidance
- Contrast material is injected to confirm the location of the catheter and to highlight the cardiac structures for diagnostic evaluation (angiography).
- Images are digitally recorded and stored and can be videotaped.
- While complications are rare, the following can occur:
- Allergic reaction (to contrast agent)
- Renal failure (due to contrast agent)
Evaluation of the heart and great vessels
- Cardiac catheterization:
- Defines the cardiac and coronary artery anatomy, cardiac function, and pulmonary arterial hemodynamics
- Also used for endomyocardial biopsy and intravascular ultrasonography
- For coronary artery disease therapy (percutaneous coronary intervention (PCI))
- For valvuloplasty and valve replacement
- Left heart catheterization:
- Coronary angiography to assess coronary arteries (gold standard)
- Assessment includes the ventricular outflow tracts, left ventricular motion, ejection fraction, mitral valve, and aortic valve function.
- Aortic angiography evaluates the aortic structure and function (e.g., aortic dissection).
- Right heart catheterization:
- Checks right atrial and ventricular pressure
- Assesses pulmonary artery pressure and pulmonary artery occlusion pressure
- Pulmonary angiography can evaluate for pulmonary embolism (though this has been largely replaced by CTPA).
Congestive heart failure
- Congestive heart failure (CHF) refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs.
- Multiple causes, including ischemia/coronary artery disease, hypertension, valvular heart disease, and cardiomyopathy.
- Heart failure with reduced ejection fraction (HFrEF) or systolic failure: left ventricle unable to contract normally
- Heart failure with preserved ejection fraction (HFpEF) or diastolic failure (or diastolic dysfunction): left ventricle unable to normally relax to fill the ventricle with blood
- Initial test used in evaluating patients with symptoms of CHF (e.g., shortness of breath, orthopnea)
- Gives information regarding any chamber enlargement or associated pulmonary congestion
- Can confirm the diagnosis
- Results include EF, associated structural and hemodynamic abnormalities which depend on the type and etiology of the heart failure (HF).
- Disorder in which the heart muscle is structurally and functionally impaired and is not due to coronary artery, valvular, or congenital heart disease or hypertension.
- Dilated CM: dilated ventricle(s) associated with impaired contraction
- Hypertrophic CM: hypertrophy of the left (and, occasionally, the right) ventricle (seen as increased wall thickness)
- Restrictive CM: ventricles not dilated or hypertrophied but have impaired ventricular filling
- Arrhythmogenic right ventricular CM:
- Genetic heart muscle disease
- Ventricular arrhythmias with fibrofatty tissue in the myocardium of the right ventricle
- Tests (findings depend on the CM type):
- Echocardiography: 1 of the initial tests for suspected cardiomyopathy, giving information on cardiac structure and function
- Cardiac MRI provides assessment of:
- Ventricular volumes and systolic function (ejection fraction)
- Myocardial mass and wall thickness
- Wall motion (in cine sequences)
- A potentially fatal condition resulting from the mechanical obstruction of the pulmonary artery or its branches
- Can be due to any material (such as thrombus, air, or fat) from anywhere in the body.
- 1st-choice diagnostic imaging method, especially in emergent settings
- Highly sensitive in detecting pulmonary emboli (seen as filling defects)
- Alternative diagnoses can be ruled out.
- A condition in which the inner coat (tunica intima) of the aortic wall develops a fissure allowing blood to enter the media layer to form a secondary lumen.
- Most common initial test
- Findings include:
- Intimal flap with a false lumen (which is often larger than the true lumen)
- Possible thrombus
- Enlarged aorta
- An alternative is MRA.
- For those with suspected ascending aortic involvement or for hemodynamically unstable patients
- Requires skilled operators and patient sedation
- Aortography: when initial tests are inconclusive.
Coronary artery disease
- The most common type of heart disease, occurring when the coronary arteries narrow, usually due to the buildup of plaque (atherosclerosis)
- As narrowing worsens, less blood can flow through the arteries, resulting in ischemia and cell death → MI
- Multiple methods used:
- Stress echocardiography: can be used with exercise or pharmacologic stress test
- Cardiac scan (stress):
- Myocardial ischemia: areas of photopenia (i.e., decreased uptake) under stress that improves at rest
- MI: persistent photopenia (i.e., decreased uptake) despite rest state
- CAC scoring: screening for patients with moderate or intermediate risk
- CTA: screening for those with indeterminate stress tests and/or ECGs
- Cardiac catheterization and coronary angiography:
- Both for diagnostic and therapeutic management of acute coronary syndrome (ST-segment elevation MI)
- For evaluation of patients with chronic debilitating angina despite maximal medical therapy
- When noninvasive testing suggests severe ischemic disease
- Inflammatory disease of the interior cardiac lining that can be due to either infectious or noninfectious causes; primarily and most notably affects the valves
- All patients with suspected infective endocarditis should undergo echocardiography.
- Findings can include:
- New dehiscence of a prosthetic valve
- 1st diagnostic test
- If images are inadequate, or complications are suspected (abscess, valvular abnormality needing cardiac surgery), TEE is performed.
- Pericardial effusion:
- Accumulation of fluid in the pericardial cavity of the heart
- Since the pericardium does not expand, after enough fluid accumulates under pressure, the cardiac filling becomes restricted → cardiac tamponade
- Inflammation of the pericardium
- Can be idiopathic or caused by a variety of conditions, including infection, previous MI, or systemic diseases
- Chest X-ray: initial test done showing enlargement of the heart (in effusion)
- Often normal in pericarditis
- In pericardial effusion, pericardial fluid is seen as an echolucent space between the epicardium and the pericardium.
- CMR and cardiac CT: help in quantification of pericardial fluid
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