DOI: 10.1148/rg.246045031
RadioGraphics 2004;24:1725-1746
© RSNA, 2004
Medical Devices of the Chest1
Tim B. Hunter, MD,
Mihra S. Taljanovic, MD,
Pei H. Tsau, MD,
William G. Berger, MD and
James R. Standen, MD
1 From the Department of Radiology (T.B.H., M.S.T., W.G.B., J.R.S.) and Department of Cardiovascular and Thoracic Surgery (P.H.T.), University of Arizona College of Medicine, 1501 N Campbell Ave, PO Box 245067, Tucson, AZ 85724-5067. Received March 10, 2004; revision requested April 22 and received June 10; accepted June 11. All authors have no financial relationships to disclose. Address correspondence to T.B.H. (e-mail: tbh@3towers.com).
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Abstract
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Chest devices are encountered on a daily basis by almost all radiologists. A multitude of extrathoracic materials, from intravenous catheters to oxygen tubing and electrocardiographic leads, frequently overlie the chest, neck, and abdomen. Chest tubes, central venous catheters, endotracheal tubes, and feeding tubes are very common. Cardiac surgery involves the use of many sophisticated devices and procedures, ranging from valve replacement to repair of complex congenital anomalies. Coronary artery bypass surgery is no longer considered unusual, and in many large medical centers, ventricular assist devices and total artificial hearts are frequently encountered. Breast implants are visible at standard chest radiography, and many ancillary devices not intended for treatment of cardiac or thoracic diseases are visible on chest radiographs. New devices are constantly being introduced, but most of them are variations on a previous theme. Knowing the specific name of a device is not important. It is important to recognize the presence of a device and to have an understanding of its function, as well as to recognize the complications associated with its use.
© RSNA, 2004
Index Terms: Coronary vessels, stents and prostheses, 54.45 • Heart, pacemakers, 50.11, 50.45 • Heart, prostheses, 50.11, 50.45 • Thorax, radiography, 60.461
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Introduction
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Chest radiography represents a significant percent of the workload of a diagnostic radiology department in a modern general hospital. The proliferation of intensive care units and the advances in the treatment of the very ill have greatly increased the numbers of examinations performed at the patient’s bedside. Obtaining a daily chest radiograph is standard practice in most intensive care units, and any change in the patient’s condition, or an intervention, can lead to several more studies in a given day. A medical center that has an active cardiothoracic surgery service and a busy trauma center generates large numbers of daily chest radiographs, many of which display a confusing array of medical apparatus used to treat and monitor patients (Fig 1) (1–9). This article discusses the most common and important devices of the chest to help radiologists recognize their presence, have an understanding of their functions, and recognize the complications associated with their use.
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Figure 1. Typical postoperative cardiac surgery chest radiograph. First postoperative study for a 58-year-old radiologist (!) who underwent coronary artery bypass graft (CABG) surgery. The image is underexposed and shows a confusing array of apparatus, including overlying oxygen tubing, a pulmonary artery catheter, a nasogastric tube, an endotracheal tube, a mediastinal drain, median sternotomy wires, mediastinal clips, electrocardiographic (ECG) leads, and incipient left lower lobe atelectasis and pleural fluid.
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Extrathoracic Devices
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Most life-support devices are within the patient’s heart, blood vessels, lungs, or pleura. Tubing, clamps, syringes, and other apparatus often lie on or under the patient and are imaged with the chest during the radiographic examination (Fig 2). These objects are usually easy to recognize and of no great importance. Patients may also lie on trauma boards, foam mattresses, or other similar supports that may be visible on radiographs.
Ventilator support tubing is almost always visible somewhere on a chest image, as are attachments such as temperature and humidity sensors. ECG electrodes are now so ubiquitous that even healthy newborns rarely escape having them applied. A versatile device commonly used in cardiac patients being transported by helicopter or ambulance is the external pacemaker-defibrillator (Fig 3).
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Figure 3. Chest radiograph reveals an external pacemaker-defibrillator electrode plate overlying the left side of the chest. The rectangular Chinese character-like electrode (white arrows) goes on the patient’s back, and the round electrode (black arrows) goes on the patient’s front.
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Breast prostheses are usually recognizable on chest radiographs. Sometimes, breast reconstruction following mastectomy may require the gradual preparation of a pocket suitable for the prosthesis; in such cases, a tissue expander is used (Fig 4).
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Pleural Devices
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Thoracostomy (chest) tubes are commonly used for evacuating fluid or air from the pleural space. They vary from 10–40 F in size, depending on the viscosity of the material to be evacuated, and the preferences of the individual physician involved in the treatment of the case (5–9). The tube is usually placed anterosuperiorly to evacuate a pneumothorax and posteroinferiorly for fluid collections (Fig 5). The normally positioned tube lies on the surface of the expanded lung, between the visceral and parietal pleurae. Pigtail catheters may be used in place of standard thoracostomy tubes, and they are popular for empyema drainage and for installation of medication for treatment of an empyema (Fig 6).
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Figure 6. Frontal view of the chest shows a pigtail catheter that had been inserted under fluoroscopic guidance into a loculated right empyema for instillation of urokinase and fluid drainage.
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If the thoracostomy tube is not accomplishing its task of adequate fluid drainage or reexpansion of a collapsed lung secondary to a pneumothorax, the tube is probably malpositioned. To accurately assess the position of a tube, both frontal and lateral views of the chest or even chest computed tomographic scans may be needed. A chest tube may enter an interlobar fissure, and, with apposition of the visceral pleura of the two lobes, the end and side holes of the tube may become obstructed and the tube rendered ineffective. Malposition of chest tubes in lung parenchyma or subcutaneous soft tissues sometimes occurs. The proximal port of the chest tube may be in a superficial location outside the pleural cavity, or the tube may become kinked. The tube can also become occluded if its tip lies against the mediastinum.
In the era before antibiotics, a variety of pleural devices were used in the treatment of tuberculosis. These include "ping-pong" ball plombage and wax plombage (Figs 7, 8). Their appearance is quite dramatic, and they may occasionally be encountered in an older patient.
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Tracheal and Esophageal Devices
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Endotracheal intubation is a lifesaving procedure, but it can also be life threatening if the tube is incorrectly positioned. In an adult, the tip of the tube should be situated approximately 5 cm above the tracheal carina, so that excursions of 2 cm upward or downward (with neck extension or flexion) can be safely accommodated.
The carina may not be visible on every image, but the aortic "knob" usually is. The carina is just caudad to the aortic arch, so that if the tip of the endotracheal tube is just above the aortic arch, it is in good position, midway between the vocal cords and the carina (Fig 9). When advanced too far, the endotracheal tube usually enters the right main bronchus, causing various combinations of hyperinflation and atelectasis of the two lungs, depending on the positions of the end and side holes. Besides being placed into the right bronchus, endotracheal tubes can also be inadvertently placed in the esophagus or in the soft tissues of the neck. Sometimes, a double-lumen endotracheal tube is deliberately used for differential ventilation of the two lungs to accommodate differences in compliance between them (Fig 10).
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Figure 9. Chest radiograph shows that the tip of the endotracheal tube (black arrow) is slightly above the aortic arch and well above the carina, in good position. A right chest tube (white arrow), ECG leads (E), a gown snap (G), and oxygen tubing (O) are also visible.
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Nasogastric tubes and feeding tubes are frequently visualized passing through the mediastinum on their way to the stomach and intestines. Not infrequently, chest radiographs reveal medical devices in abnormal locations and unexpected foreign bodies (Figs 11, 12).
Esophageal balloons and esophageal stents used to treat benign and malignant esophageal disease may manifest themselves at chest radiography. Balloon dilatation and stent placement in the esophagus are safe, effective procedures for treating esophageal strictures and fistulas, and they provide reasonable palliative relief from malignant esophageal obstruction (Fig 13a) (10). Esophageal and gastric balloons are still occasionally used to treat bleeding varices. Probes to measure distal esophageal pH as part of a gastroesophageal reflux workup are sometimes seen and may be confused with a feeding tube if one is not careful or if a proper patient history is not provided. The ideal location for the pH probe is the distal portion of the esophagus, just above the gastroesophageal junction (Fig 13b).
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Figure 13a. (a) Frontal view of the chest shows an esophageal stent (black arrows) that was placed to ameliorate the effects of an esophageal malignancy. There are also two chest tubes (*), a peripherally inserted central catheter (white arrow), ECG leads (E), a gown snap (G), and a transjugular intrahepatic portosystemic shunt (T) in the liver. (b) Frontal chest radiograph of an infant shows a pH probe.
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Figure 13b. (a) Frontal view of the chest shows an esophageal stent (black arrows) that was placed to ameliorate the effects of an esophageal malignancy. There are also two chest tubes (*), a peripherally inserted central catheter (white arrow), ECG leads (E), a gown snap (G), and a transjugular intrahepatic portosystemic shunt (T) in the liver. (b) Frontal chest radiograph of an infant shows a pH probe.
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Tracheostomy tubes and other tracheal and bronchial apparatus are not infrequently visible on chest radiographs. Tracheoesophageal voice prostheses are not common but may occasionally be seen (Fig 14). Bronchial stents are occasionally seen in patients who have undergone lung transplantation and have developed a stricture at the anastomosis between the native tracheobronchial tree and the transplanted one. These stents may be metallic and easily recognized, or they may be composed of various plastic materials and be hard to recognize, especially if no history of stent placement or lung transplantation has been given (Fig 15). It is wise to look for these stents in all patients who have undergone lung transplantation.
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Vascular Devices
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Vascular catheters of various types are now routinely used for monitoring hemodynamic function; for performing hemodialysis; and for administering fluids, medications, and nutrition (Fig 16) (11–22). Some catheters are designed for short-term use in the postoperative or intensive care unit setting, whereas others are implanted for long-term use, such as those used in cancer patients (11,12). Venous devices are usually inserted, either percutaneously or surgically, via the subclavian, internal jugular, or femoral veins. Arterial devices usually are placed through the femoral artery, but sometimes the brachial or axillary route is employed (13–15).
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Figure 16. Portable chest radiograph shows a right subclavian single-lumen central venous catheter and a left subcutaneous port catheter, which enters via the left subclavian vein. Both catheter tips are in the superior vena cava.
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Central venous catheters (also known as central venous pressure [CVP] catheters, central catheters, and central lines) typically have one to three lumens and are constructed out of medical-grade silicone or polyurethane. The nomenclature for central catheters is confusing and inconsistent in daily use. For example, the terms Hickman, Broviac, Leonard, and Hohn are trademarks of C. R. Bard, Inc (Miami Lakes, Fla). Cordis sheath is a trademark of the Cordis Corporation (Covington, Ga). However, in many medical centers, these names are used generically to represent any central catheter, regardless of its actual construction, manufacturer, or particular use.
Swan-Ganz is a registered trademark of Baxter International (Deerfield, Ill). This name has come to represent any type of multilumen catheter used for measuring hemodynamic pressures and cardiac output (Figs 17, 18). A better term to use is pulmonary artery catheter. The Groshong (trademark of C. R. Bard) catheter is noted for its unusual closed, rounded tip (Fig 19). Near the tip in the side of the catheter is a three-position valve. The valve is designed to allow fluid to flow in and out through the valve, but it remains closed when it is not in use. This catheter does not require routine clamping or heparin solution to keep open. It does require periodic flushing with 0.9% normal saline.
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Figure 18. Frontal chest radiograph shows a Swan-Ganz catheter (white arrow) in the left pulmonary artery via the inferior vena cava. Note also the bilateral chest tubes (black arrows) and ECG leads (E).
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Figure 19a. (a) Frontal view of the chest shows a left subclavian Groshong catheter with its tip in the proximal most portion of the superior vena cava. (b) Close up view of the catheter tip.
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Figure 19b. (a) Frontal view of the chest shows a left subclavian Groshong catheter with its tip in the proximal most portion of the superior vena cava. (b) Close up view of the catheter tip.
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There are also a variety of implantable access devices (subcutaneous ports), most commonly represented by the Port-A-Cath (trademark of C. R. Bard). Such devices are designed for easy, long-term access to the vascular system or peritoneal cavity. Port access is accomplished by percutaneous needle insertion. The port itself typically sits in the infraclavicular fossa, over the upper abdomen, or over the lower ribs (Fig 16). The port is usually connected to a central venous catheter or to an arterial catheter and can be used for instillation of fluids, medications, chemotherapeutic agents, parenteral nutritional solutions, and blood products. It can also be used for withdrawal of blood samples. There are almost as many types of access ports as there are types of standard central venous catheters. Some of the commercial designs available include the Port-A-Cath, BardPort (C. R. Bard), SlimPort (C. R. Bard), Dialock (Biolink Corp, Middleboro, Mass), and LifeSite (Vasca, Inc, Tewksbury, Mass) devices.
A central venous catheter is ideally positioned in the superior vena cava for the monitoring of pressure or infusion of medication and nutrition. A catheter tip positioned in the right atrium increases the risk of perforation and cardiac arrhythmia (16,22). The same holds true for dialysis catheters. However, there is some controversy over the correct position for the tip of a central venous catheter. Some believe the usefulness and longevity of a catheter will be improved if its tip is positioned in the upper portion of the right atrium (12).
Flow-directed, balloon-tipped catheters (pulmonary artery, Swan-Ganz catheters) are now widely used for monitoring circulatory hemodynamics. Accurate measurement of pulmonary arterial wedge pressure in a supine patient requires the catheter tip to be in the lower lobe (zone 3 of West) so that left atrial pressure, not alveolar pressure, is measured (13,14,17,18). Over a period of time, pulmonary artery catheters may migrate toward the periphery of the pulmonary bed and become lodged in a small pulmonary artery. Such migration can cause vessel injury by prolonged occlusion or by overdistention of the vessel when the catheter balloon is inflated. Also, pulmonary infarction can result from this situation. The period of time during which the balloon remains inflated and wedged should be limited, particularly in patients with pulmonary hypertension. A central location of the catheter tip near the lung hilum helps prevent pulmonary artery perforation and is a good "parking" position for the catheter when it is not being used to measure pulmonary arterial wedge pressure.
The routine use of pulmonary artery catheters has been questioned by some authorities, but they are a common finding on intensive care unit portable chest radiographs. Even though these catheters are widely accepted and widely used, there are no definitive studies demonstrating their benefit (15,16).
Complications of catheter insertion vary with the catheters used and the sites employed (2,11–22). Catheter malposition usually involves the catheter passing into a tributary vessel rather than the one sought (Fig 20). The internal jugular vein, azygous arch, and internal mammary vein are frequent sites of catheter malpositioning. Catheters may take an unusual course or position because of a congenital anomaly. Arterial puncture may lead to an abnormal catheter position with pulsatile flow in the catheter.
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Figure 20. Frontal view of the chest shows a left jugular Swan-Ganz catheter (arrows), which passes through a persistent left superior vena cava into the coronary sinus, through the right atrium and right ventricle, and into the right pulmonary artery. Also seen are a subcutaneous port (P), an endotracheal tube (ET), an ECG lead (E), and a nasogastric tube (not labeled).
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Pneumothorax is a common complication of unsuccessful attempts at subclavian or low jugular catheter insertion. Nerve injury is usually a complication of improper puncture technique. Vessel lacerations and perforations can produce hematomas, hemothorax, and infusion of fluid into the mediastinum, thorax, or other inappropriate space. Looping of catheters may lead to knotting. Pinching of catheters and catheter shearing usually occur at the site of entry and suture fixation (21).
Although central venous catheters inserted into the subclavian vein or into the internal jugular vein represent the standard approach for establishing central venous access, a simpler, potentially less-injurious access to the central venous system is through the use of a peripherally inserted central catheter (PICC). PICC lines are smaller catheters that are peripherally inserted at or slightly proximal to the antecubital fossa, with the tip placed in the superior vena cava. They are often preferred over standard central lines in children.
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Cardiac Devices
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Treatment of heart disease has probably fostered more development of sophisticated medical interventions than all the interventions designed for all other organs combined. Coronary artery angioplasty, coronary artery stent placement, CABG surgery, the surgical correction of congenital cardiac defects, and even cardiac transplantation are no longer considered novel, experimental procedures. Cardiac pacemakers, valve prostheses, and artificial hearts are sophisticated biomedical engineering products that have drastically altered the course of many cardiac disorders. Because chest radiography is commonly employed in the assessment of patients with heart disease, recognition of cardiac devices and the problems associated with them is important for all individuals involved in the care of these patients.
Heart Valves
Heart valve prostheses have been used successfully since the 1960s, and there are two basic types: mechanical and biologic. The number, complexity, and use of prosthetic heart valves have increased dramatically to the point where most radiologists see them on a daily basis in their practices. Mechanical valves are composed of metals, polymers, and ceramics. A mechanical valve functions basically as an occluder, moving passively with changes in pressure and flow within the heart (Figs 21, 22). Most require life-long treatment with anticoagulants. Biologic valves contain tissue from human cadavers (homografts), porcine aortic cusps, or bovine pericardium (xenografts) (Figs 23–25). Biologic valves are less durable than mechanical valves, with some deterioration developing, frequently 5–10 years after placement, but they do not usually require anticoagulant treatment.
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Figure 21. Mechanical heart valve. Lateral view of the chest shows a Hemex tilting bileaflet mechanical mitral valve prosthesis. Median sternotomy wires and surgical clips are also evident.
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Figure 23. Biologic heart valve. Frontal view of the chest shows a Hancock porcine mitral valve prosthesis (arrow). A single-lead pacemaker, ECG leads, and median sternotomy wires are also seen.
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There are many types of prosthetic cardiac valves, and it is not possible to discuss them in any detail in this article. Some mechanical valves include the Starr-Edwards (Edwards Lifesciences, Irvine, Calif), Bjork-Shiley (Pfizer, New York, NY), Medronic Hall (Medronic, Minneapolis, Minn), St Jude Medical (St Jude Medical, Inc, St Paul, Minn), Sorin Bicarbon (Sorin Biomedica, Italy), and the Carbomedics (Sorin Biomedica). Some bioprosthetic (biologic) heart valves include the Carpentier-Edwards (Edwards Lifesciences), Tissue Med (Aor Tech International PLC, United Kingdom), and the Hancock (Medtronic, Minneapolis, Minn). It is not important and often impossible to know the specific name of a particular prosthetic heart valve, but it is important to recognize its presence (23–25). Because prosthetic heart valves are used in a large variety of congenital and acquired conditions in both adults and children, it is frequently difficult to ascertain which native valve has been replaced by a prosthesis. The heart in such cases may be markedly enlarged, displaced, or altered by cardiac surgery. The mitral and aortic valves are those most commonly replaced, whereas prosthetic tricuspid valves are seen less often. Prosthetic pulmonary valves are rare. There are also various shunts or conduits used as part of a complex cardiac surgical procedure to correct congenital heart disease. These shunts may contain a prosthetic heart valve (Fig 25).
Sometimes, an annuloplasty ring may be used instead of a prosthetic cardiac valve to treat valvular regurgitation (Fig 26). The annuloplasty rings narrow and reshape the heart valve for proper functioning (24).
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Figure 26. Lateral view of the chest in an elderly patient shows a mitral annuloplasty ring (black arrow) and a dual-lead cardiac pacemaker. Sternal wires, surgical clips, and ECG leads are also present. The sternal wires are used to close a sternal dehiscence. The patient has both horizontal sternal wires and vertical intercostal wires (white arrows).
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There are products designed to close nonphysiologic openings in the heart, such as a patent ductus arteriosus, atrial septal defect, or ventricular septal defect, without the need for open heart surgery (Figs 27–29) (25). The first of these products was the Rashkind "double umbrella" occlusion device (C. R. Bard) to close a patent ductus arteriosus. Other devices are the Bard Clamshell Septal Umbrella (C. R. Bard), the Amplatzer Septal Occluder (AGA Medical Corp, Golden Valley, Minn), and the Sideris device (AGA Medical) to close atrial septal defects, ventricular septal defects, and other intracardiac communications. In general, these devices consist of a basket (umbrella) or filter placed in the defect to occlude it. They are often self-adjusting and lie flat against the atrial or ventricular septum. This flat design helps create a natural profile.
Cardiac Pacemakers
Cardiac pacemakers are probably as common as prosthetic cardiac valves and are found in patients of all ages, although they are much more common in older adults being treated for abnormal cardiac rhythms caused by coronary artery disease (26–31). Cardiac pacemakers improve cardiac function, reduce the severity of clinical symptoms, and reduce mortality and morbidity.
A cardiac pacemaker is composed of two main elements: (a) a pulse generator and (b) lead wires with electrodes for contact with the endocardium or myocardium. Cardiac pacemakers were first used clinically in the 1960s, with stainless steel electrodes sewn directly onto the myocardium and attached to a fixed-rate pulse generator implanted in the subcutaneous tissues of the upper abdomen. Since then, there have been many advances, including small-caliber, fracture-resistant, transvenous leads and programmable multichamber atrioventricular pulse generators. The pacemaker generator (battery pack and control unit) is most commonly placed in the infraclavicular area.
There has been a steady improvement in pacemaker durability and utility. It is now possible for a patient traveling anywhere in the world to phone into his or her physician and have a scheduled periodic evaluation of pacemaker function over the phone. Pacemakers range from simple temporary epicardial electrodes to very complex pacemakers with multiple atrial and ventricular leads (Figs 30, 31). A single-lead intramyocardial pacer electrode may be appropriate in one patient, whereas a right atrial-biventricular synchronous pervenous device is indicated in another. Temporary, easily removable epicardial electrodes are now commonly placed at the time of cardiac surgery for immediate pacemaker access, should the need arise (Fig 32). The leads are simply pulled out through the incision when the patient is discharged from the hospital. Transvenous (pervenous) pacemaker leads are the most commonly used type today and are inserted through the subclavian or jugular vein with use of local anesthesia.
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Figure 30a. Frontal (a) and lateral (b) views of the chest show a single electrode epicardial "corkscrew" subxiphoid pacemaker (arrowhead in a, black arrow in b). There are also coils (white arrow) occluding a previous right Blalock-Taussig shunt. In addition, ECG leads and sternal wires are evident.
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Figure 30b. Frontal (a) and lateral (b) views of the chest show a single electrode epicardial "corkscrew" subxiphoid pacemaker (arrowhead in a, black arrow in b). There are also coils (white arrow) occluding a previous right Blalock-Taussig shunt. In addition, ECG leads and sternal wires are evident.
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Figure 31a. Frontal (a) and lateral (b) views show an atrioventricular sequential pacemaker with one electrode in the right atrial appendage (RA) and the other at the right ventricular apex (RV). Also shown are ECG leads (E) and the battery-control pack (B) for the pacemaker.
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Figure 31b. Frontal (a) and lateral (b) views show an atrioventricular sequential pacemaker with one electrode in the right atrial appendage (RA) and the other at the right ventricular apex (RV). Also shown are ECG leads (E) and the battery-control pack (B) for the pacemaker.
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Figure 32a. (a) Collimated frontal view of the chest shows typical epicardial pacing wires (arrows) coiled on the patient’s anterior chest wall after heart surgery. (b) Collimated lateral view of the chest shows the same epicardial pacing wires (arrows) as in a. Also shown but not labeled are sternal wires, surgical clips, and a central venous catheter.
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Figure 32b. (a) Collimated frontal view of the chest shows typical epicardial pacing wires (arrows) coiled on the patient’s anterior chest wall after heart surgery. (b) Collimated lateral view of the chest shows the same epicardial pacing wires (arrows) as in a. Also shown but not labeled are sternal wires, surgical clips, and a central venous catheter.
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Cardiac resynchronization therapy (CRT) or biventricular pacing is sometimes used to treat severe chronic congestive heart failure (Fig 33). Combined right and left ventricular pacing or left ventricular pacing alone may considerably improve heart function (27,28). CRT involves pre-excitation of the left ventricular wall by means of a lead placed in a tributary of the coronary sinus. There is often further benefit to the patient when CRT is combined with an implantable defibrillator, because there is a high risk of sudden death from ventricular tachycardia or ventricular fibrillation in all patients with heart failure. Current CRT usually involves atrial synchronized ventricular pacing to optimize atrioventricular timing with biventricular pacing to promote ventricular synchrony. CRT improves ejection fraction, left ventricular size, and mitral regurgitation.
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Figure 33. Frontal view of the chest shows a combination biventricular pacemaker and an automatic implantable cardioverter defibrillator with a battery pack (B) and right atrial (RA), right ventricular (RV), and coronary venous (CV) leads. Note also the left ventricular calcification from a past myocardial infarction. The coronary venous lead is positioned in a vein draining the posterior inferior wall of the left ventricle so that it can stimulate functional myocardial tissue rather than the nonfunctioning tissue represented by the ventricular wall calcification and probable myocardial aneurysm.
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There are several ways pacemakers can be placed for left ventricular or biventricular pacing. In some cases, left ventricular epicardial leads are used. The leads go directly to the surface of the left ventricle, and they are usually associated with typical pacing electrodes in the right atrial appendage and right ventricular apex. In other cases, the left ventricular pacing electrodes are introduced through the coronary sinus and wedged into a left ventricular cardiac vein (27,28). In these instances, the position of the pacing leads may seem unusual, and detailed knowledge of the coronary venous anatomy is necessary for the radiologist and cardiologist to appreciate the location of the leads.
Because there can be such a wide variation in the proper positioning of pacemaker leads, it is often difficult for the average radiologist to know if a pacemaker is properly positioned. Frequent consultation with the cardiologists and cardiac surgeons in one’s own medical center is important to gain familiarity with the pacemakers and therapeutic approaches used by the referring physicians. In this way, complications of pacemaker placement are more readily recognized and brought to the attention of the patient’s physicians.
Pacemaker lead fracture is now rarely seen because of improvements in the flexibility of the metal alloys used in electrode construction. Even when they are broken, the ends frequently do not separate, so the radiograph does not show the fracture. Electronic testing has largely replaced radiography to investigate cases of suspected lead malfunction. After being in place for several weeks, pacemaker leads become "epithelialized" and firmly attached to the myocardial wall. When a pacemaker is changed, the leads are simply cut for removal of the control pack, and they are left in place because they are adherent to the heart. New leads are then placed with the new pacemaker. If a patient has had his or her pacemaker changed a number of times, there is often a bewildering array of wires about the heart. In this circumstance, it can be impossible to trace the currently functioning pacemaker leads back to the pacemaker battery pack. On rare occasion, a central venous catheter may interfere with a pacemaker lead.
The safety of magnetic resonance (MR) imaging studies for patients with cardiac pacemakers is an important matter and is subject to much discussion (29–31). Many radiologists and cardiologists consider MR imaging to be contraindicated for patients with a cardiac pacemaker. This approach is the safest, but it may not always be in the best interest of a patient with a cardiac pacemaker who needs an MR imaging study. There are circumstances in which a patient with a pacemaker may undergo MR imaging, especially if a 0.5-T unit is used (29). It may also be safe to perform MR imaging with an extremity system for patients with cardiac pacemakers and implantable cardioverter defibrillator systems (30). It must be emphasized that MR imaging should be performed on patients with a pacemaker or similar device only after the patient has been cleared for the study by his or her physicians. Such a study should be performed in a medical center with experienced staff who are able to monitor the patient before, during, and after the MR imaging study as well as treat any problems that arise from the study. MR imaging is generally safe for patients who have artificial heart valves, who have undergone coronary artery surgery, or who have retained epicardial pacemaker leads after cardiac surgery (31).
The automatic implantable cardioverter defibrillator (AICD or ICD) is a common cardiac device designed for both patient monitoring and therapy in case of ventricular tachycardia or fibrillation (32,33). The early AICD designs consisted of two shocking electrodes, two sensing electrodes, and a generator implanted in the abdominal wall. The new designs are completely different, consisting of various combinations of sensing and shocking electrodes (Figs 32, 34). They are frequently combined with a pacemaker as a bundled system for the patient, treating both the patient’s established arrhythmia and also acting as a fail-safe system should ventricular fibrillation or ventricular tachycardia occur.
Coronary Artery Surgery and Stents
Since 1967, when the first aortocoronary saphenous vein bypass graft was performed, direct myocardial revascularization has gained wide acceptance. Revascularization techniques include CABG surgery, coronary artery angioplasty, and coronary artery stent placement. CABG surgery is probably the most common cardiac surgical procedure performed in adults. Until recently, CABG surgery was the primary surgical technique for treating coronary artery disease. Now it is competing with coronary artery angioplasty and stent placement as well as improved noninterventional medical treatments for coronary artery disease. CABG surgery has been refined over the years and varies from center to center, which is reflected in the variety of devices seen in the postoperative chest radiographs of these patients (Figs 1, 35–37).
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Figure 35a. (a, b) Frontal (a) and lateral (b) views show a sternal fixation pin or Kirschner wire. This sternal fixation was used for a patient who underwent lung transplantation in which a "clamshell" chest incision was made, resulting in a transverse sectioning of the sternum. In this case, the sternum is best stabilized by a vertical fixation wire or pin. Note also the surgical clips overlying the heart and the root of the aorta. (c) Collimated view of a cardiac surgery patient shows a Synthes Maxillofacial Sternal Fixation System (Synthes, Paoli, Pa) (arrows).
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Figure 35b. (a, b) Frontal (a) and lateral (b) views show a sternal fixation pin or Kirschner wire. This sternal fixation was used for a patient who underwent lung transplantation in which a "clamshell" chest incision was made, resulting in a transverse sectioning of the sternum. In this case, the sternum is best stabilized by a vertical fixation wire or pin. Note also the surgical clips overlying the heart and the root of the aorta. (c) Collimated view of a cardiac surgery patient shows a Synthes Maxillofacial Sternal Fixation System (Synthes, Paoli, Pa) (arrows).
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Figure 35c. (a, b) Frontal (a) and lateral (b) views show a sternal fixation pin or Kirschner wire. This sternal fixation was used for a patient who underwent lung transplantation in which a "clamshell" chest incision was made, resulting in a transverse sectioning of the sternum. In this case, the sternum is best stabilized by a vertical fixation wire or pin. Note also the surgical clips overlying the heart and the root of the aorta. (c) Collimated view of a cardiac surgery patient shows a Synthes Maxillofacial Sternal Fixation System (Synthes, Paoli, Pa) (arrows).
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Figure 36. Lateral view of the chest shows sternal wires (arrowhead), vascular clips of a saphenous vein bypass graft to the right coronary artery (curved arrow), and those of the left internal mammary graft to the left anterior descending coronary artery (straight arrow).
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Figure 37. Lateral view of the chest shows vascular clips of internal mammary artery bypass grafts (solid arrow) and marker rings on the ascending aorta around the ostia of two saphenous vein bypass grafts (open arrows).
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Median sternotomy is the usual surgical approach for CABG surgery, and sternal wires the common method of fixation of the two sternal segments (Figs 1, 36, 37). Vascular clips are used to occlude tributary branches of saphenous vein grafts and anterior intercostal branches of the internal mammary arteries. There may be a few clips or a great many, depending on the number and types of grafts used. Some surgeons place markers on the adventitia of the ascending aorta to indicate the proximal anastomoses of the bypass grafts. These markers, which facilitate subsequent graft angiography, vary considerably from center to center, and even from surgeon to surgeon.
In many cases, CABG surgery has been supplanted by coronary artery angioplasty and stent placement. At present, almost 90% of coronary interventions include stent placement (34,35). Coronary artery stent placement was introduced in 1964 by Dotter and Judkins and has been in regular clinical use since the end of the 1980s. The objectives of coronary artery stent placement are to improve on the results of coronary artery balloon angioplasty, to reduce the occurrence of coronary artery restenosis, and to treat an acute or threatened closure of a coronary artery.
Before 1997, only two coronary artery stents were approved for clinical use in the United States: the Gianturco-Roubin I (Cook, Bloomington, Ind) and the Palmaz-Schatz (Johnson and Johnson, Warren, NJ). By 2002, over 40 stent designs were used in clinical practice (Fig 38). Many more are under investigation, including drug-coated stents.
Based on their method of expansion, coronary artery stents are divided into three groups: balloon expandable (most frequently used), self-expandable, and thermally expandable. Most stents are composed of 316L stainless steel. Alternative stent designs have also incorporated nitinol, gold, tantalum, and other metals. They must maintain elasticity, radial strength, biocompatibility, and corrosion resistance. At present, the approved coronary artery stents range in size from 2.0 to 5.0 mm in diameter and 8.0 to 38.0 mm in length to accommodate the size of the target vessel. Stents of different designs have variable strut thickness. In addition to improvement in stent design and delivery technologies, further development includes covered stents, biodegradable stents, and drug-delivery stents. Stent selection is determined by a variety of factors, including operator familiarity with the stent, lesion morphology and location, and balloon delivery system characteristics. Complications associated with coronary artery stents are stent thrombosis and restenosis.
Circulatory Assist Devices
The high mortality from cardiogenic shock continues to spur efforts to develop mechanical support for the circulatory system (36–39). It is estimated that 100,000 patients in the United States could benefit from heart transplantation. However, only 2,000 donor hearts are available each year (38). Most devices currently available provide temporary assistance until the damaged heart can recover or until a donor heart becomes available for transplantation (36–39). Most mechanical support for patients with heart failure consists of devices that assist the heart without replacing it.
Mechanical cardiac assist devices can be divided into three groups: (a) temporary cardiac assist devices, (b) permanent cardiac assist devices, and (c) heart replacement devices. Examples of short-term cardiac assist devices are the intraaotic balloon pump and newer left ventricular assist devices (VADs), such as the TandemHeart (Cardiac Assist, Inc, Pittsburgh, Pa). The Biventricular System 5000 short-term VAD (ABIOMED, Danvers, Mass), for example, is approved by the U.S. Food and Drug Administration (FDA) for treating postcardiotomy shock and as a bridge to either heart transplantation or implantation of a long-term device. It consists of two disposable, dual-chamber, extracorporeal blood pumps connected by transcutaneous cannulas to a console. This pump fills passively and ejects actively.
The intraaortic counterpulsation balloon device (also known as IACB, IAB, IABP, IAC, and IACD) is used to support the circulation after cardiac surgery or an acute myocardial infarction until the heart recovers adequate function of its own. The device consists of an inflatable balloon approximately 25 cm long mounted on a catheter, which is introduced via a femoral artery. The tip of the catheter is placed just distal to the left subclavian artery in the descending thoracic aorta (Fig 39) (39). The balloon is inflated with gas (carbon dioxide) during ventricular diastole to augment diastolic coronary artery perfusion and to reduce left ventricular afterload. This technique improves cardiac function by both increasing the oxygenation and decreasing the work requirements of the myocardium.
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Figure 39. Frontal view of the chest shows an intraaortic counterpulsation balloon used in a patient with heart failure. The balloon (black arrows) is inflated. Usually, only the balloon tip (white arrow) is visible.
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The mainstays of mechanical support for patients with severe congestive heart failure are VADs (38). These devices are mechanical pumps used for temporary or permanent blood circulation support (Figs 40–42). They can be used for a single right or left ventricle or for both ventricles. The left VADs are used in patients with end-stage heart failure, as a bridge to transplantation, but they may also be used as a destination therapy. These devices have been in clinical use since 1984. The HeartMate (Thoratec Corp, Pleasanton, Calif) became the first left VAD that was FDA-approved as a bridge to transplantation and for treating reversible cardiogenic shock (Fig 41). The newer, vented-electric HeartMate device is powered by an internal electric motor. This device has been in use since 1991. The HeartMate blood pump is a flexible polyurethane diaphragm within a titanium shell. The woven Dacron inflow and outflow cannulas each contain a 25-mm caged porcine xenograft valve.
Another left VAD is the Novacor pump (Novacor Corp, Oakland, Calif), which is implanted in the subcutaneous tissue of the left upper abdomen with power lines and sensors exiting via the right lower quadrant to connect with a control console (Fig 42). The pump takes blood through a Dacron conduit from the apex of the left ventricle and pumps it via another Dacron conduit to the aorta. Both the HeartMate and Novacor devices have a demonstrated durability for periods more than 2 years. Other similar or developing VADs include the Jarvik 2000 left VAD (Jarvik Heart, Inc, New York, NY), the MicroMed DeBackey VAD (MicroMed Technology, Inc, Houston, Tex), the HeartMate II and HeartMate III, the Incor (Berlin Heart, Hamburg, Germany), and the Terumo (Terumo Medical Corp, Somerset, NJ). The risks associated with implantation of a VAD include postoperative hemorrhage, sepsis, thromboembolism, renal failure, technical failure, and neurologic sequelae. It is extremely important to note if any central venous catheter is near the tricuspid prosthetic valve of a VAD or total artificial heart. If a catheter becomes entangled in the valve, it can cause malfunction of the valve, which will in turn stop venous return to the heart, rapidly endangering the patient’s life.
The total artificial heart requires removal of the native heart. It serves as a bridge to cardiac transplantation, but occasionally it becomes the patient’s permanent circulatory support for the rest of his or her life. The Jarvik 7 was the first attempt at an implantable artificial heart, but the recipient patients were completely hospital bound and suffered major complications. Other artificial hearts include the CardioWest (SynCardia Systems, Inc, Tucson, Ariz) and the AbioCor implantable replacement heart (ABIOMED) (Fig 43). The AbioCor, for example, consists of two blood-pumping chambers; the right supplies blood to the lungs, and the left supplies the blood to the rest of the body. It is made of titanium and Angioflex (a proprietary polyether-based polyurethane plastic), and it is powered in part by an internal battery that can be recharged through the intact skin, obviating external power lines. Permanent implantable artificial hearts may be a reality in the not too distant future, but they still suffer the major hurdles of severe infections and thromboembolism, and their use remains very limited (38).
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Figure 43a. Cropped frontal view (a) and full lateral view (b) of the chest show a CardioWest total artificial heart. Note the four prosthetic valves and the two coil, reinforced polyurethane tubes carrying pulses of compressed air to the two artificial ventricles.
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Figure 43b. Cropped frontal view (a) and full lateral view (b) of the chest show a CardioWest total artificial heart. Note the four prosthetic valves and the two coil, reinforced polyurethane tubes carrying pulses of compressed air to the two artificial ventricles.
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Miscellaneous Devices
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From time to time, other medical devices not commonly found at chest radiography may be seen (Figs 44–48). These devices include embolization coils, remote telemetry ECG monitoring devices, pericardial drainage catheters, and left atrial catheters (40). An interesting new device is the insertable (implantable) loop recorder, which is used for prolonged monitoring of the cardiac rhythm. It is a small electronic device implanted in the left pectoral region, and it can provide more than a year of continuous monitoring that may be activated by the patient or automatically activated (Fig 44) (41). It has a variety of uses including monitoring of patients with unexplained syncopal episodes and assessment of patients with atrial fibrillation, ventricular arrhythmias, or conduction disturbances.
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Figure 44. Collimated frontal view of the chest shows an implantable loop recorder (arrow) in the left breast of a 25-year-old woman with a history of heart palpitations and surgical repair of a tetralogy of Fallot as a young child.
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Figure 45. Frontal view of the chest of a patient with hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease) shows numerous coils, which had been used in multiple coil embolizations to treat repeated bouts of significant hemoptysis.
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Figure 47a. Frontal (a) and lateral (b) views of the chest in a patient who had undergone vertebroplasty. The vertebroplasty material extruded from the vertebrae and entered the spinal venous system with ultimate embolization to the patient’s lungs. The patient suffered no known sequelae.
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Figure 47b. Frontal (a) and lateral (b) views of the chest in a patient who had undergone vertebroplasty. The vertebroplasty material extruded from the vertebrae and entered the spinal venous system with ultimate embolization to the patient’s lungs. The patient suffered no known sequelae.
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Figure 48. Portable chest radiograph of a patient undergoing extracorporeal membrane oxygenation shows pulmonary edema in the lungs and the tubing (**) going to the patient’s right carotid artery and right jugular vein. Also seen are an endotracheal tube (ET), a right internal jugular vein catheter (black arrow), a left internal jugular vein catheter (white arrows), a nasogastric tube (NG), and a feeding tube (F).
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Sometimes, unexpected neck, abdomen, and spinal apparatus may be visible at chest radiography (42). Such objects include tracheostomy tubes; voice prostheses; neck drainage catheters; cervical, thoracic, or lumbar spine fixation apparatus; temperature monitoring catheters in the hypopharynx or esophagus; vagus nerve stimulators; abscess and biliary drainage catheters in the abdomen; umbilical arterial and venous catheters; and transjugular intrahepatic portosystemic shunts (TIPS) in the liver (Fig 13a). Vertebroplasty is not uncommon, and in some medical centers extracorporeal membrane oxygenation apparatus may be seen in premature infants and other patients with severe heart and lung disease (Figs 47, 48). Most of these devices have nothing to do with the cardiovascular or pulmonary structures in the chest, but they happen to overlie the chest or be visible on chest images, because they lie contiguous to the thorax in the neck, spine, or upper abdomen. Recognizing and evaluating such apparatus is just as important as recognizing and evaluating apparatus primarily designed for the chest.
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Footnotes
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Abbreviations: CABG = coronary artery bypass graft,
CRT = cardiac resynchronization therapy,
ECG = electrocardiographic,
FDA = Food and Drug Administration,
VAD = ventricular assist device
Editor’s note: Material for this article was adapted from "Medical Devices of the Thorax" by James R. Standen, MD, originally published as chapter 4 in Radiologic Guide to Medical Devices and Foreign Bodies, edited by T. B. Hunter and D. G. Bragg, St Louis, MO, Mosby-Year Book, 1994. Permission for use of this material was granted by Tim B. Hunter, copyright holder.
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Abstract
Introduction
