Imaging of Implantable Devices

Published on 21/06/2015 by admin

Last modified 21/06/2015

Print this page

This article have been viewed 10141 times

27 Imaging of Implantable Devices

Bryan Baranowski, Elizabeth Vickers Saarel, Mina K. Chung

Thoracic imaging (and occasionally abdominal imaging) plays an important role in the implantation, maintenance, and removal of pacing and defibrillation systems. Many available contemporary modalities, including radiography, fluoroscopy, venography, echocardiography, computed tomography (CT), and magnetic resonance imaging (MRI), are frequently used in the diagnosis and treatment of patients with pacemaker and implantable cardioverter-defibrillator (ICD) devices. The most common modalities used before, during, and after device implantation are radiography, fluoroscopy, and venography, critical tools for physicians who perform pacemaker and ICD surgery. In addition, echocardiography has widespread applications, ranging from confirmation of the acute procedural complication of cardiac rupture with cardiac tamponade to optimization of pacing in cardiac resynchronization therapy (CRT). CT imaging is primarily used in preoperative and postoperative settings to assess complex cardiac anatomy, especially in patients with corrected and uncorrected congenital heart conditions. In contrast, MRI may be used for preoperative assessment of cardiovascular anatomy but is more often employed for diagnosis of pathologic conditions outside the thoracic cavity. Its potential for electromagnetic interference with implanted pacemaker and ICD devices is discussed here.

Radiography

Radiographs provide essential information about the location, type, and integrity of the pulse generators and leads of both pacing and defibrillation systems. X-ray films also provide basic details of patient anatomy. Interpretation of a chest radiograph should be focused and systematic, with examination of the bony structures, cardiac silhouette, lung fields, trachea, and aorta as well as the presence and location of all preexisting hardware, prosthetic valves, and valve rings or calcification (Fig. 27-1). Abdominal radiographs should be obtained when abdominal device implantation is anticipated.

Figure 27-1 Overlay of diagram on posteroanterior chest radiograph.

Typical location for formation of subclavian veins, brachiocephalic veins, superior vena cava, and right atrium along with their associated osseous landmarks; Lt, left; Rt, right.

(From Castle LW, Cook S: Pacemaker radiography. In Ellenbogen KA, Kay GN, Wilkoff BL, editors: Clinical cardiac pacing. Philadelphia, 1995, Saunders, p 538.)

Preprocedural Chest Radiography

Preprocedural posteroanterior (PA) and lateral chest radiographs provide essential information about patient anatomy and help identify the location, type, and integrity of implanted lead and device hardware in patients with preexisting pacing and defibrillation systems.

Identification of Patient Anatomy

Chest wall deformities, such as scoliosis and kyphosis, can occasionally make the implantation of endovascular leads difficult because of distortion of venous and cardiac anatomy. Identification of massive cardiomegaly may influence the choice of lead length. Anomalies such as a right-sided aortic knob suggest the presence of congenital abnormalities, discussed later.

Identification of Pacing and Defibrillation Systems

It is important to identify the type and location of preexisting pacing or defibrillation systems, particularly in the significant and growing numbers of patients presenting for generator exchange, lead addition, lead extraction, or device upgrade. With expanding indications and longevity of patients, a patient can have multiple functional and abandoned leads or even separate pacemaker and ICD devices. The type and position of the generators as well as the type, position, and integrity of all leads should be examined. A thorough examination requires a PA as well as a lateral chest radiograph and, in the patient with an abdominally located device, an abdominal film.

Pacemaker/ICD Pulse Generators and Implantable Loop Recorders

For transvenous systems, the pulse generator is typically located in the subcutaneous, prepectoral region caudal to the clavicle, overlying the pectoralis major muscle. In some patients, the device is located in a subpectoral or submammary position (Fig. 27-2). In pediatric patients and patients with older, larger ICD pulse generators or epicardial ICD lead systems, devices may be located in the abdomen, typically in the left upper quadrant and occasionally in the right upper quadrant or epigastrium (Fig. 27-3). Although most pulse generators are implanted in the subcutaneous region in adult patients, many have been implanted below the rectus abdominis muscle in children and younger women. The pulse generator is also generally implanted abdominally in patients in whom a femoral vein approach is required (Fig. 27-4).

Figure 27-2 Transvenous pacemaker system in subpectoral position.

Posteroanterior and lateral chest radiographs in child with congenital complete heart block and dual-chamber pacemaker.

Figure 27-3 Abdominal pacemaker and implantable cardioverter-defibrillator (ICD) systems.

A, Posteroanterior and lateral chest radiographs of an abdominal pacemaker system with epicardial leads in a child with congenital heart disease. B, Abdominal ICD system with epicardial leads. C to E, Abdominal ICD system with transvenous leads. F, Abdominal ICD lead system with an epicardial and a transvenous lead.

Figure 27-4 Implantable cardioverter-defibrillator with defibrillation leads, including azygos coil lead.

The leads are inserted using a right femoral vein approach. A, Posteroanterior chest radiograph shows the coils of the dual-coil defibrillation-pace/sense lead are positioned in the right atrium and right ventricle. The second lead is placed in the azygos vein. B, Lateral chest radiograph demonstrates the posterior positioning of the azygos coil. C, Abdominal radiograph displays the leads tunneled from the right femoral vein access site to the ICD device pocket in located in the left upper quadrant.

The generator manufacturer and type can be identified from radiography. Most pacemaker and ICD pulse generators have a radiopaque code or logo identifying the manufacturer and model of the device (Figs. 27-5 and 27-6). If the manufacturer can be determined, the proper programmer can be selected. Most current manufacturer programmers can “auto-identify” the specific devices of that manufacturer. Manufacturer technical support divisions may be able to aid in identification of lead systems and devices and can often access device data, such as leads implanted, pacing or shocking configurations, and implant thresholds. Some patients may have both pacing and ICD systems, as well as leads or devices that originate from different manufacturers. Figure 27-7 shows the appearance of implantable loop recorders.

Figure 27-5 Pacing pulse generators and radiographic appearance.

A, Dual-chamber pacemakers. B, Cardiac resynchronization therapy pacemakers (CRT-P) indicated for biventricular pacing.

(Courtesy Medtronic, Minneapolis; St. Jude Medical, St. Paul, Minn; Guidant, Boston Scientific, Natick, Mass; Biotronik, Berlin; and ELA/Sorin, Milan.)

Figure 27-6 Implantable cardioverter-defibrillator (ICD) pulse generators and radiographic appearance.

A, Single-chamber and dual-chamber ICD pulse generators. B, Cardiac resynchronization therapy ICDs (CRT-D) indicated for biventricular pacing. Arrows denote manufacturer’s identification symbol.

(Courtesy Guidant, Boston Scientific, Natick, Mass; St. Jude Medical, St. Paul, Minn; Medtronic, Minneapolis; Biotronik, Berlin; and ELA/Sorin, Milan.)

Figure 27-7 Implantable loop recorders.

The Medtronic Reveal XT and St. Jude Medical SJM Confirm implantable loop recorders and corresponding radiographic appearance.

(Courtesy Medtronic, Minneapolis, and St. Jude Medical, St. Paul, Minn.)

The pacemaker or ICD connector block should be carefully examined radiographically. The connector pins should be advanced beyond the distal pin set-screw blocks (Fig. 27-8). It is usually difficult to determine radiographically whether set screws are in contact with the electrodes. Clues to the polarity of pacing pulse generators include the number and type of connector pins. Determining the type of connector pins (International Standard 1 [IS-1], 3.2-mm Voluntary Standard [VS]-1, 5- or 6-mm, or the new IS-4 connectors) before device replacement avoids an intraoperative discovery that a compatible device is not readily available for the exchange. Radiographically, detection of connector pins that appear longer than the conventional IS-1 pins should prompt checking of lead connector type.

Figure 27-8 Examination of device for lead connector pin insertion into header.

Pins can be visualized extending past the distal connector blocks (arrows).

Migration of the pulse generator may be seen radiographically in older patients with loosened prepectoral fascia, patients who have lost significant amounts of weight, or with pulse generators implanted within larger areas of subcutaneous prepectoral fatty tissue.¹

In patients who have symptoms associated with the current generator location, revision of the pocket or anchoring of the generator may be considered. The migration of the pulse generator may influence the sterile draping area before device replacements.

Pacing and Defibrillation Leads

When planning lead revision and/or extraction, one should assess the types, location, and integrity of all leads radiographically. Higher radiographic penetration may be required to more clearly demonstrate lead components. Dislodgment can be identified and is aided by comparison with old films. Leads generally do not have manufacturer-specific, characteristic radiopaque identifiers, but radiography may provide clues to the lead type (active or passive fixation; unipolar or bipolar) and integrity.²

Venous Anatomy for Localization of Lead Positions

Most pacemaker and ICD leads are inserted transvenously. The subclavian, axillary, and cephalic veins are most often used for lead insertion, with the internal or external jugular or femoral veins used rarely. The cephalic vein courses lateral to the biceps, continuing in a groove between the deltoid and pectoralis major muscles, then empties into the axillary vein (Fig. 27-9). The axillary vein drains the basilic and brachial veins, coursing medially over the lateral margin of the first rib to become the subclavian vein under the clavicle. This marks the usual site for insertion of pacemaker or defibrillator leads (see Fig. 27-1). A change in the directionality of the lead can sometimes indicate the location of the venous insertion site or suture tie-down sleeve. A more lateral insertion site suggests a cephalic or lateral axillary insertion site. Medial insertions into the subclavian vein should be inspected for evidence of lead crush injuries. Lateral axillary insertion sites should be examined for excessive angulation.

Figure 27-9 Right upper-extremity axillary/subclavian venography showing typical venous anatomy.

A, Venogram shows axillary vein. B, Digital subtraction image demonstrates axillary vein with entry of cephalic vein and coursing under the clavicle, where the axillary vein transitions to the subclavian vein. C, Bilateral upper-extremity venography shows patency of both subclavian veins and the superior vena cava.

After entering the venous system, leads typically pass through the brachiocephalic veins, which are formed by the joining of the internal jugular and subclavian veins behind the head of the clavicle, to the superior vena cava (SVC), and then to the right atrium or right ventricle. In a small percentage of patients, a persistent left SVC is present and drains into the coronary sinus (see later).³

On preparation for a procedure requiring insertion of a new lead, peripheral subclavian and SVC venography can be helpful in anticipating the need for lead extraction or preparation of a new site for venous access because of venous occlusion or severe stenoses (Fig. 27-10). Chronic venous occlusion is often marked by the presence of venous collaterals.

Figure 27-10 Peripheral venography demonstrating occlusion of subclavian vein.

A, Left panel shows patency of left subclavian/brachiocephalic vein to superior vena cava. Right panel is peripheral right venogram demonstrating location of an occlusion (arrow) of the right subclavian vein with collateralization. B, Peripheral right venography showing occlusion of the right subclavian vein. C, Peripheral left venography in the same patient as in B, demonstrating occlusion of the left subclavian vein with extensive collateralization.

The coronary sinus (CS), which enters the inferior septal region of the right atrium, just anterior and superior to the opening of the inferior vena cava, receives most of the venous drainage of the heart (see Coronary Sinus Lead Positions). The main CS traverses the atrioventricular (AV) groove between the left atrium and left ventricle. Tributaries include the middle cardiac vein; posterior ventricular branch; posterolateral, lateral, and anterolateral marginal branches; and great cardiac vein, which is the extension of the CS beyond the takeoff of the left atrial oblique vein of Marshall. When the vein of Marshall is not present, the valve of Vieussens is used to define the interface of the CS and great cardiac vein. The posterior, posterolateral, and lateral branches of the CS are typical targets for left ventricular or biventricular pacing in CRT devices (see Chapter 22).

Chest radiography can be essential in determining whether absence of clinical response to CRT is caused by inadequate lead position (e.g., lead placement in anterior branch) or lead dislodgment.

The azygos vein, which enters the posterior wall of the SVC, is sometimes the target vessel for ICD coil-lead implantation in patients with high defibrillation threshold (DFT), as the vessel travels posteriorly behind the heart, providing an additional favorable “shock vector” option ⁴ (Fig. 27-11; see also Fig. 27-4).

Figure 27-11 Azygos vein occlusive venography.

A balloon catheter was inserted near the origin of the azygos vein, to delineate its course before addition of a defibrillation coil, which was advanced to a position just above the diaphragm, behind the left ventricle. The atrial lead is in the upper left corner of the image, and the anterior or right ventricular defibrillation coil is in the lower portion.

(Courtesy Kalyanam Shivkumar, MD, PhD.)

Pacemaker Leads

Besides identification of the venous and cardiac insertion sites of pacing leads, chest radiographs can help determine polarity and fixation types. A unipolar lead has a single electrode at the tip of the lead; a bipolar lead has two electrodes separated by a space. Active-fixation leads have screws that extend from the tip of the lead (Fig. 27-12, A). Passive-fixation leads have various types of tines that are radiolucent (cannot be visualized radiographically) (Fig. 27-12, B). Active-fixation leads may be fixed in the extended position or may have an extendable/retractable screw. Different manufacturers denote extension of the latter with various markers (Fig. 27-13).

Figure 27-12 Radiographic appearance of transvenous leads.

A, Active-fixation, bipolar lead. B, Passive-fixation ICD lead.

Figure 27-13 Active-fixation screw positions.

A, Medtronic 5076 bipolar pacing lead with extended and retracted screw positions. The fluoroscopy image shows the screw is extended with appearance of a space between the two distal radiopaque rings (arrow). B, St. Jude 1688T bipolar pacing lead with radiographs of extended and retracted screw positions. In the extended position, two helical turns of the screw are visible. C, Medtronic 6947 ICD lead with extended and retracted screw positions. The fluoroscopy image shows the screw is extended with disappearance of the space between the two distal radiopaque rings. D, St. Jude 1580 ICD lead with radiographs of extended and retracted screw positions, showing two helical turns of the screw in the extended position. E, Biotronik ICD lead with screw extended. F, Boston Scientific 0186 ICD lead in extended and retracted screw positions. G, Biotronik Setrox lead in extended and retracted screw positions.

(Courtesy Medtronic, Minneapolis; St. Jude Medical, St. Paul, Minn; and Biotronik, Berlin.)

Atrial Lead Positions

In patients who have not undergone cardiac surgery, most atrial leads are fixed to the right atrial (RA) appendage and will exhibit a J shape with an anteriorly directed curve on the lateral view.⁵ Patients who have undergone cardiac surgery may not have suitable RA appendage remnants for fixation. Lead placement is generally guided by optimization of electrical characteristics, such as sensing and pacing thresholds and lead fixation stability. Leads may be implanted laterally, septally, caudally, or cranially in the right atrium, generally requiring active-fixation leads. Although most pacing systems use one atrial lead, pacing for atrial arrhythmia suppression may incorporate alternative-site or dual-site pacing.^6,⁷ Placements targeting Bachmann’s bundle or the RA septum typically display lead tips directed near the high septum of the right atrium.^8,⁹ The CS or septum near the CS may also be targeted; leads placed in the CS generally exhibit a large, open posterior curve. Higher posterior crossings on lateral films may suggest passage of the lead through a patent foramen ovale or atrial septal defect to the left atrium or ventricle.¹⁰

Ventricular Lead Positions

Ventricular pacing leads have traditionally been targeted to the right ventricular apex (RVA). The lead should display some slack, particularly as it traverses and is lifted by the tricuspid valve. The RVA is generally located to the left of the spine on the PA view with a slight inferior direction. On the lateral view, the lead is usually directed anteriorly (Fig. 27-14), unless the septal aspect of the apex is targeted. A more posterior course suggests positioning in the CS or middle cardiac vein. A large posterior curve suggests possible passage through a patent foramen ovale or atrial or ventricular septal defect to the left ventricle (Fig. 27-15).

Figure 27-14 Ventricular pacing lead position in right ventricular apex and atrial lead in right atrial appendage.

Posteroanterior (A) and lateral (B) radiographs demonstrate the anterior course of the right atrial appendage lead and the apical anterior course of the right ventricular apex lead.

Figure 27-15 Abnormal lead placement into left ventricle.

A and B, Posteroanterior (PA) and left lateral views show a dual-chamber pacing system. The ventricular wire has an unusually high curve on the PA view; on the lateral view, it can be seen to extend in a posterocranial direction, only then to curve back on itself with the tip of the lead in the wall of the left ventricle (arrow). This is an example of improper ventricular lead placement, with the wire traversing the foramen ovale and extending through the body of the left atrium, through the mitral valve, and into the left ventricle. C and D, PA (C) and lateral (D) views demonstrating a single-chamber ICD system with the defibrillation lead crossing an atrial septal defect (ASD) to the left ventricle. The lead courses posteriorly through the ASD, through the mitral valve to the left ventricle.PA (E) and lateral (F) views during a BiV device implant demonstrating a single-coil ICD lead crossing an ASD to the left ventricle. G and H, Ventricular lead placement into the coronary sinus. Anteroposterior (G) and lateral (H) views demonstrating inferior, posterior course of the ventricular lead placed into the middle cardiac vein of the coronary sinus via a left sided superior vena cava.

(A and B from Trohman RG, Wilkoff B, Byrne T, Cook S: Successful percutaneous extraction of a chronic left ventricular pacing lead. Pacing Clin Electrophysiol 14:1448, 1991.)

Although the RVA has been the traditional site for ventricular pacing lead placement, awareness of the potential for left ventricular (LV) dyssynchrony from RVA pacing has led to more frequent use of right ventricular outflow tract (RVOT) or septal pacing ¹¹ (Fig. 27-16). A position away from the RVA may also be sought when there are high pacing thresholds at the apex or if an ICD lead is present at the apex, to avoid device-device interactions (Fig. 27-17). His bundle pacing has been proposed as an alternative to RVA pacing in the absence of infra-Hisian conduction system disease¹² (Fig. 27-18). An extra set of bipolar sensing electrodes at the level of the right atrium on a ventricular lead body identifies a VDD single-lead pacing system, which is designed to sense in the atrium and allow atrial-synchronous ventricular pacing (Fig. 27-19).

Figure 27-16 Ventricular pacing lead position in right ventricular outflow tract.

Posteroanterior (A) and lateral (B) chest radiographs with a left-sided single-chamber pacemaker. The lead tip is in the anterior RVOT, and the abdominal transvenous ICD lead tip is placed in the right ventricular apex.

(Courtesy Walid Saliba, MD.)

Figure 27-17 Posteroanterior (A) and lateral (B) chest radiographs of dual-chamber pacing system on the left, with ventricular pacing lead placed higher on the right ventricular wall, and a dual-chamber ICD system implanted on the right, with the ventricular ICD lead at the apex. The ventricular pacing lead is implanted higher and away from the high-voltage ICD lead.

Figure 27-18 His bundle pacing.

Posteroanterior (A) and lateral (B) views of a pacemaker system with right atrial, right ventricular apical, and lead placed at the His bundle (arrows).

Figure 27-19 Posteroanterior (A) and lateral (B) views of the single-lead VDD pacing system with a bipolar atrial sensing electrode (arrow) and bipolar ventricular pace/sense electrodes. The system was subsequently upgraded with the addition of a new atrial bipolar lead, as shown on PA (C) and lateral (D) views, because of inadequate atrial sensing.

Coronary Sinus Lead Positions

The branches of the CS are common targets for leads placed for LV or biventricular pacing for CRT.¹³ Placement of the CS lead involves localization and cannulation of the CS, CS venography, and placement of the lead in the target branch. Coronary sinus ostium (CS os) cannulation is accomplished using an angiographic approach or electrophysiologic approach. Angiographic technique involves the use of a variety of guiding sheaths and diagnostic catheters (described in Chapter 22) with boluses of contrast agent for locating the CS os. The EP technique involves the use of guiding sheaths with mapping catheters to help determine the presence of CS recordings on intracardiac electrograms.

Typically, in patients with congestive heart failure, CS anatomy is extremely variable because of cardiac dilation as well as to rotation and alteration from prior cardiac procedures, making localization of the ostium difficult. In addition, patients with atrial fibrillation may have a greatly enlarged right atrium, for which larger-curve guiding sheaths or catheters may be helpful in CS os cannulation. A quick fluoroscopic visualization may show the extent of cardiomegaly or cardiac rotation, or anatomic markers, such as right coronary artery calcifications or the radiolucent fat pad in the AV groove. In the anteroposterior (AP) view, the CS os can be on either side of the spine and variable vertically, relative to the floor of the tricuspid valve. A thorough understanding of the RA anatomy with judicious use of contrast material helps the implanting physician assess the position of the catheter tip relative to the CS os.

After gaining access to the CS, the outer guide sheath is advanced into the proximal portion of the CS at least 3 to 4 cm over a guidewire or a softer inner catheter to prevent mural dissection. Balloon occlusion with contrast venography can then identify potential target tributaries, strictures, and collateral vessels in selection of an optimal target vessel (Fig. 27-20). Balloon inflation must be performed with caution to avoid overinflation and dissection of the vein. After visualization of the distal vessels, the balloon is deflated to promote proximal runoff, allowing visualization of tributaries proximal to the balloon tip. Continued acquisition of images for a few extra seconds after contrast injection allows flow to tributaries through collaterals, which might highlight the posterior and posterolateral LV veins that could otherwise go unnoticed. Two radiographic planes are helpful for assessing the CS tributaries and ostia for optimal target vessel determination. The most common positions used are left anterior oblique (LAO) 25 to 45 degrees, AP, and right anterior oblique (RAO) 15 to 30 degrees.

Figure 27-20 A, Coronary sinus balloon (CS) venography demonstrating branch anatomy in the left anterior oblique view; ACV, anterior cardiac vein; AL, anterolateral marginal vein; L, lateral marginal vein; MCV, middle cardiac vein; PL, posterolateral marginal vein; PV, posterior ventricular branch. B, CS venography demonstrating dissection of the CS from sheath insertion. Extravasation of contrast is limited within the epicardium. C, Contrast visualized layering in the pericardial space, indicating perforation.

Coronary sinus anatomy is variable, and no consensus exists regarding the nomenclature of CS branch anatomy; as discussed earlier, however, common terminology is used, as depicted in Figure 27-20. From the CS ostium, the first branch is the middle cardiac vein (MCV), near which a posterior ventricular branch may enter. The distal CS becomes the great cardiac vein (GCV) after the takeoff of the vein of Marshall/valve of Vieussens. The GCV terminates at the takeoff of the anterior cardiac vein (ACV), which courses down the anterior interventricular groove. Between the MCV and ACV, posterior, posterolateral, lateral, anterolateral, and anteroseptal branches may be present. Using clock face positions as viewed in LAO projection, the CS os generally is located at 7 o’clock, the MCV at about 6 o’clock, the posterolateral veins at 5 o’clock to 2 o’clock, and GCV/ACV at 12 o’clock. If present, a persistent left SVC drains into the CS directly.¹⁴ Figure 27-21 illustrates typical lead tip positions.