Author: Charles Allison, MB ChB
Preauthor: Bryan Callaghan
Background
It is important for a physician to quickly and accurately determine if chest pain can be dismissed or if it is potentially life threatening. However, the innumerable causes of chest pain can often present a diagnostic challenge. The range of potentially affected organ systems, including heart, lungs, esophagus, muscle, bone, nerves and skin, make a ?global? approach of imaging impossible; no single modality will reliably investigate each of these possibilities. Indeed, for many of the possible underlying etiologies imaging will not be not helpful. The patient?s description of chest pain and physical examination will narrow down the possible causes and help to determine what would be the safest and best use of the hospital?s imaging technology. Decisions on imaging fall to the ordering physicians, but the choices may differ from those of radiologists, or indeed insurers; for example, insurers have recently felt that there has been an overuse of nuclear medicine cardiac studies throughout the country. As such, it would be mutually beneficial to develop appropriate criteria for selection of studies based on clinical indictors.
Which Study?
Choice of imaging clearly hinges on the suspected diagnosis. Pathologies that require may prompt identification and treatment to avoid morbidity and mortality, such as cardiac pain, are pursued more thoroughly on lower suspicion.
Plain radiograph
Rapid, inexpensive with low radiation exposure, the standard chest x-ray can often provide clues if not the diagnosis. For example, a widened mediastinum may suggest the possibility of an aortic dissection, or cardiomegaly may indicate chronic hypertension, putting the patient at higher risk for coronary artery disease as cause of the pain.
Indications
Pleuritic chest pain
Cough
Shortness of breath
Rule out diagnoses with appropriate clinical evidence
Pneumonia
Pulmonary edema
Lung cancer
Rib fracture
Echocardiogram
The standard 2-D echocardiogram is rapid, inexpensive, non-invasive and portable. It provides information on both the structure and function of the heart and allows estimation of the ejection fraction, calculation of valve areas and Doppler measurements of low. Wall motion abnormalities can identify areas of infarct. It is somewhat operator dependent, though this is less true than previously due to operator training to standardize measurement techniques or improve visualization with contrast cavity opacification.
Stress echocardiogram, or 3-D echocardiograms, allow comparison of the structure and function of the heart both at rest and during a pharmacological stressor (typically dobutamine administration). This technique is highly sensitive and specific for detecting areas of ischemia and determining if revascularization is warranted, known as assessing myocardial viability. It requires specialist operator training, more time and resources and as such is more significantly more expensive (about twice that of ECG treadmill stress testing)
Indications
Chest pain
Orthopnea / Paroxysmal nocturnal dyspnea
Cardiac murmurs
Assessing myocardial viability
Rule out diagnoses with appropriate clinical evidence
Cardiomyopathy ? dilated / hypertrophic
Valvular heart disease
Thrombi ? intracardiac / pulmonary artery emboli
Vegetations / endocarditis
Barium Swallow
The barium swallow is performed when the whole esophagus needs to be evaluated and includes an evaluation of the cervical, thoracic and abdominal esophagus together with the gastro-esophageal (GE) junction. If the patient is able to swallow easily, both a double contrast (air and barium) as well as a single contrast study is performed. The double contrast study enables optimal visualization of the mucosa, while the single contrast evaluates the peristaltic function as well as an overall appearance of the mucosa. The radiologist usually decides whether the patient will be able to tolerate the double contrast study. The stomach is not evaluated in a barium swallow.
Indications
Chest Pain,
Chronic Cough
Dysphagia
Heartburn,
Reflux Symptoms
Odynophagia
Foreign Body
Rule out diagnoses with appropriate clinical evidence
Aspiration
Achalasia and cardiospasm
Carcinoma
Diverticulum of esophagus, acquired
Dysmotility
Esophageal reflux
Feeding difficulties and mismanagement
Stricture and stenosis of esophagus
Dysphagia
Foreign Body
Nuclear Imaging
Nuclear imaging for chest pain may include ventilation/perfusion scanning (V/Q scan) and myocardial perfusion scans. V/Q scans may be used to class probability as high/intermediate or low for pulmonary embolism in patients with appropriate symptoms. It is most sensitive when the patient has no concurrent pulmonary pathology and thus a normal chest x-ray.
Single Positron Emission Computed Tomography (SPECT) utilizes the radioisotope technetium 99m sestamibi to map myocardial perfusion. This is typically done both at rest and immediately after stress (exercise or pharmacological) to build a three dimensional image of healthy myocardium, ischemia and infarct. This can be used to estimate which cardiac vessels are affected and to predict cardiovascular risk. At rest, myocardial perfusion is impaired only when coronary stenosis exceeds 90%. During stress, perfusion is impaired with stenosis above 50%. Pharmacological agents may be vasodilators (adenosine / dipyridamole), which rely on stenosed vessels not dilating to allow increased flow, or inotropes (dobutamine), which produce true myocardial ischemia. Dobutamine is favored only when the patient is unable to tolerate the vasodilators (e.g. patients with asthma or COPD in whom adenosine may provoke bronchospasm). Such nuclear tests can also detect increased pulmonary uptake of the isotope during stress, which correlates to left ventricular dysfunction, and transient ischemic dilatation of the left ventricle after exercise, which correlates to a higher cardiovascular risk.
Position Emission Tomography (PET) has a limited role in cardiac imaging due to its limited availability and high expense (about 14 times that of an echocardiogram). Unlike other imaging modalities, it allows direct and dynamic quantitative measurement of myocardial metabolic activity. As such is has been used to measure regional myocardial perfusion and can be viewed as the gold standard for assessment of myocardial viability
Indications
Shortness of breath
Exertional chest pain
Assessment of myocardial viability
Assessment of cardiovascular risk
Rule out diagnoses with appropriate clinical evidence
Pulmonary embolus
Myocardial ischemia
Myocardial infarct
Computed tomography
CT is highly sensitive for thoracic pathology. It is rapid, acquiring images in a few seconds, provides high resolution anatomical detail, and the cost is approximately three times that of an echocardiogram. Pulmonary infiltrates, effusions, parenchymal and pleural disease can all be readily diagnosed, though in many non-complicated cases a plain radiograph would be sufficient. Intravenous contrast with an iodine based dye is preferred and enhanced diagnostic yield, particularly of mediastinal disease and malignancy / lymphadenopathy. Contrast is nephrotoxic however and may lead to hypersensitivity reactions.
CT Angiography is employed as a first line investigation for diagnosis of pulmonary embolus by timing the scan to when a bolus of intravenous contrast has reached to pulmonary arteries. CT angiography may also refer to using computed tomography to evaluate the coronary vasculature. This technique relies on detecting calcification in coronary atherosclerotic plaques and formulating a total coronary artery calcium score. This score correlates well to cardiovascular risk. However in cannot be used to delineate coronary stenosis as not all plaques are calcified.
Indications
Weight loss
Hemoptysis
Early detection of asymptomatic coronary artery disease
Risk stratification in known coronary artery disease
Rule out diagnoses with appropriate clinical evidence
Pneumonia
Bronchiectasis
Pulmonary embolus
Lung cancer
Lymphoma
Trauma
Coronary atherosclerosis
Aortic dissection
Pleural / pericardial effusion (including cardiac tamponade)
Magnetic Resonance Imaging
MRI is not usually used for thoracic imaging as lung pathologies are typically poorly visualized compared to CT.
Cardiac MRI, however, is an emerging field that allows measurement of cardiac function, anatomy and flow. It is superior to ultrasound in terms of higher resolution and better visualization of the left ventricular apex and hypertrophic states. Gadolinium contrast is safe and accumulates in scar tissue and is highly sensitive for prior infarct. Cardiac MRI is also highly sensitive in detecting perfusion abnormalities, even in angiographically normal yet symptomatic individuals. Coronary anatomy cannot currently be accurately mapped, though composition and size of atheromatous plaques can be assessed which may eventually lead to predictions of likelihood of rupture (and hence of MI). It is safe in pregnancy (though avoided in the first trimester) but relatively expensive and requires patient co-operation in remaining motionless for approximately 20 minutes in a confined space. Furthermore, implanted pacemaker or defibrillator devices and other magnetic hardware such as cerebral aneurysm clips are contraindicated.
Indications
Determination of questionable prior infarcts
Assessment of myocardial viability
Assessment of cardiovascular risk
Rule out diagnoses with appropriate clinical evidence
Myocardial infarction
Cardiomyopathy
Pericarditis
Aortic dissection
Coarctation of aorta
Aortic stenosis
Anomalous coronary vessels
Coronary Angiography
An arterial catheter is advanced retrograde from a peripheral access site (typically femoral) and is used to infect iodine-based contrast into the coronary arteries under fluoroscopy. An interventional cardiologist typically performs the procedure. If necessary, interventions such as balloon dilatation or stenting of stenosis can be performed. It is the gold standard for evaluation of coronary anatomy, but the technique also lends itself to collecting other data ? pressure in left and right cardiac chambers and hence calculations of valvular gradients. However the use of resources and personnel leads to a high cost ? around 20 times that of an ultrasound scan. The dye load may also precipitate renal failure, particularly since patients are often diabetic +/- hypertensive with pre-existing microvascular renal disease.
Indications
Chest pain of likely cardiac origin
Murmurs / symptomatic valvular disease
ST elevation myocardial infarction
Diagnosis of coronary artery disease
Pre-op evaluation before valve or bypass surgery
Retrieval of lost guidewires
Rule out diagnoses with appropriate clinical evidence
Coronary artery disease
Valvular heart disease
Congestive heart failure
Cardiac tamponade
Pulmonary hypertension
Anomalous coronary vessels
References:
Economic and biological costs of cardiac imaging ? E Picano
Cardiovasc Ultrasound 2005; 3:13
Nuclear Cardiology ? First of Two Parts ? BL Zaret, FJ Wackers
NEJM 1993; 329:775-783
Nuclear Cardiology ? Second of Two Parts ? BL Zaret, FJ Wackers
NEJM 1993; 329:855-863
Recent developments in non-invasive cardiology ? SK Prasad, RG Assomull, DJ Pennell
BMJ 2004; 329:1386-1389
EMPIRE study ? Underwood et al.
Eur Heart J 1999; 20:157-166