DOI: 10.1148/rg.23si035508
(Radiographics. 2003;23:S35-S48.)
© RSNA, 2003
PERIOPERATIVE CROSS-SECTIONAL IMAGING |
Multi–Detector Row CT of the Left Atrium and Pulmonary Veins before Radio-frequency Catheter Ablation for Atrial Fibrillation1
Joan M. Lacomis, MD,
William Wigginton, BS, RTR(CT),
Carl Fuhrman, MD,
David Schwartzman, MD,
Derek R. Armfield, MD and
Karen M. Pealer, BA, CCRC
1 From the Division of Thoracic Imaging of the Department of Radiology and the Atrial Arrhythmia Center, University of Pittsburgh, Rm 4660 CHP-MT, 200 Lothrop St, Pittsburgh, PA 15213. Presented as an education exhibit at the 2002 RSNA scientific assembly. Received February 12, 2003; revision requested April 28 and received May 19; accepted May 29. Supported in part by a grant from General Electric Medical Systems. Address correspondence to J.M.L. (e-mail: lacomisjm@msx.upmc.edu).
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Abstract
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Radio-frequency catheter ablation (RFCA) of the distal pulmonary veins and posterior left atrium is increasingly being used to treat recurrent or refractory atrial fibrillation that resists pharmacologic therapy or cardioversion. Successful RFCA of atrial fibrillation requires resolution of abnormal rhythms while minimizing complications and can be achieved with precise, preprocedural, three-dimensional (3D) anatomic delineation of the target, the atriopulmonary venous junction. Three-dimensional multi–detector row computed tomography (CT) of the pulmonary veins and left atrium provides the necessary anatomic information for successful RFCA, including (a) the number, location, and angulation of pulmonary veins and their ostial branches unobscured by adjacent cardiac and vascular anatomy, and (b) left atrial volume. The 3D multi–detector row CT scanning and postprocessing techniques used for pre-RFCA planning are straightforward. Radiologists must not only understand these techniques but must also be familiar with atrial fibrillation and the technical considerations and complications associated with RFCA of this condition. In addition, radiologists must be familiar with anatomic variants of the left atrium and distal pulmonary veins and understand the importance of these variants to the referring cardiac interventional electrophysiologist.
© RSNA, 2003
Index Terms: Atrial fibrillation, 522.1299 • Heart, CT, 522.1211, 522.12117 • Pulmonary veins, CT, 565.1211 • Radiofrequency (RF) ablation, 522.1299
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:
- Discuss the prevalence, significance, and complications of chronic atrial fibrillation in adults.
- Delineate the relationship between the pulmonary veins and atrial fibrillation.
- Describe the use of RFCA in the treatment of atrial fibrillation and of 3D multi– detector row CT in pretreatment evaluation.
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Introduction
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Atrial fibrillation is a common disorder associated with significant morbidity, mortality, and economic costs. Radio-frequency catheter ablation (RFCA) of the distal pulmonary veins and posterior left atrium is increasingly being used by cardiac interventional electrophysiologists to treat patients with atrial fibrillation. The success of RFCA is highly dependent on a preprocedural understanding of the complex three-dimensional (3D) anatomy of the distal pulmonary veins and posterior left atrium. Neither fluoroscopy nor echocardiography can adequately depict this anatomy.
Earlier reports have shown that 3D gadolinium-enhanced magnetic resonance (MR) angiography can successfully demonstrate left atrial and distal pulmonary venous anatomy (1–4); however, many atrial fibrillation patients have pacemakers or defibrillators and cannot undergo MR angiography. Initially, we developed a 3D multi–detector row computed tomographic (CT) technique to image the left atrium and pulmonary veins in patients with atrial fibrillation who were to undergo RFCA and who had pacemakers or defibrillators (5). Subsequently, over an approximately 3-year period, we evaluated the pulmonary venous and left atrial anatomy in 50 patients without atrial fibrillation and in over 100 patients with atrial fibrillation prior to their undergoing RFCA. In the vast majority of cases, we used 3D multi–detector row CT, reserving MR angiography for those patients with contraindications to intravenously administered iodinated contrast material. Over the last 3 years at our institution, a high-volume atrial arrhythmia referral center, 3D multi–detector row CT has become not only routine, but an essential part of pre-RFCA evaluation of patients with atrial fibrillation and has replaced 3D MR angiography as our pre-RFCA imaging procedure of choice in this context.
In this article, we review atrial fibrillation and its association with the pulmonary veins; briefly describe RFCA in atrial fibrillation patients, including possible complications and the need for pre-RFCA imaging; review left atrial and distal pulmonary venous embryologic development; present anatomic definitions pertinent to pre-RFCA atrial fibrillation patients; describe the 3D multi–detector row CT scanning and postprocessing techniques used to evaluate these patients; and discuss and illustrate some common anatomic variants of the left atrium and pulmonary veins.
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Atrial Fibrillation
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Atrial fibrillation is the most common of the sustained cardiac arrhythmias, and its prevalence increases with age (6,7). In adults, its prevalence nearly doubles every 10 years, affecting up to 5% of people over 65 years old, with an overall domestic prevalence of 2.5 million (6). Atrial fibrillation occurs when multiple ectopic electrical foci "fire" independently, sending the atrioventricular node as many as 300 discharges per minute. The irregular ventricular response depends on the refractoriness of the atrioventricular node, resulting in heart rates ranging from 30 to 300 beats per minute (8).
Atrial fibrillation can be acute or chronic and is often associated with underlying cardiac or noncardiac disease. If atrial fibrillation occurs without underlying cardiac disease or hypertension, it is termed lone atrial fibrillation (6). Acute or new onset atrial fibrillation can be associated with pulmonary embolism or hyperthyroidism (8). Chronic atrial fibrillation can be either persistent or paroxysmal. Persistent atrial fibrillation occurs when an episode of this phenomenon lasts more than 1 week (6).
The two major complications associated with atrial fibrillation are hemodynamic compromise and formation of thrombi within the fibrillating atrium or atrial appendage (6). Hemodynamic compromise in atrial fibrillation is secondary to loss of the atrial contribution of ventricular filling (the atrial "kick") and to heart rates that are either too fast or too slow to maintain cardiac output. Chronic poorly controlled tachycardia can lead to ventricular dysfunction (6). Thrombi that form within the atrium or atrial appendage can embolize systemically. As a major risk factor for embolic stroke (7), atrial fibrillation is associated with significant morbidity, mortality, and economic costs.
Both pharmacologic therapy and cardioversion have demonstrated only limited success in the treatment of atrial fibrillation, with patients often failing therapy or developing recurrent atrial fibrillation after treatment (9).
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Pulmonary Veins and Atrial Fibrillation
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Although commonly known triggers for the initiation of atrial fibrillation include cardiothoracic surgery, alterations in autonomic tone, changes in atrial wall tension (eg, in chronic mitral stenosis), and ectopic electrical foci arising in the atria, it has been recognized more recently that the muscular sleeves of the distal pulmonary veins are also a frequent source of ectopic foci (6,10). The left superior pulmonary vein alone accounts for one-half of all ectopic beats leading to atrial fibrillation (10). The myocardium of the left atrium extends a variable distance into the distal pulmonary veins, with the myocardial sleeves of the superior and left pulmonary veins being longer than those of the inferior and right pulmonary veins (Fig 1) (11,12). Newer approaches to the treatment of atrial fibrillation focus on interrupting the con-duction pathways that lead to atrial fibrillation by electrically isolating the sources of ectopic beats either surgically (with a modified maze procedure) or nonsurgically (with RFCA of the distal pulmonary veins and posterior left atrium) (9, 12–14).
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Figure 1. Left atrium and myocardial sleeves of the distal pulmonary veins. Schematic illustrates how the myocardium (white outline) of the left atrium (LA) extends into the distal pulmonary veins. Note that the sleeves of the left-sided veins are longer than those of the right-sided veins and that the left superior pulmonary vein (LSPV) has the longest myocardial sleeve. LIPV = left inferior pulmonary vein, RIPV = right inferior pulmonary vein, RSPV = right superior pulmonary vein.
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RFCA for Atrial Fibrillation
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Initially, RFCA of ectopic foci of electrical activity within the distal pulmonary veins was shown to be often curative for patients with refractory or recurrent atrial fibrillation despite undergoing pharmacologic therapy or cardioversion (9,14). However, RFCA for treatment of atrial fibrillation is an evolving therapy. With newer techniques, the target for ablation is shifting from site-specific arrhythmogenic sites in the distal pulmonary veins to the pulmonary vein ostia to the pulmonary vein inflow vestibules of the posterior left atrium (Fig 2) (15). Regardless of which techniques are used, RFCA remains a long and technically challenging procedure.
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Figure 2. RFCA targets. Gated multi-detector row CT scans (endocardial view) obtained in a patient with paroxysmal atrial fibrillation in normal sinus rhythm during the study show the left side of the left atrium. One or more of the distal pulmonary veins (a) was the original target for RFCA. As the procedure has evolved, newer targets include the pulmonary vein ostia (b) and (as in this patient) the pulmonary vein inflow vestibule (c). LAA = orifice of the left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein.
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Figure 2. RFCA targets. Gated multi-detector row CT scans (endocardial view) obtained in a patient with paroxysmal atrial fibrillation in normal sinus rhythm during the study show the left side of the left atrium. One or more of the distal pulmonary veins (a) was the original target for RFCA. As the procedure has evolved, newer targets include the pulmonary vein ostia (b) and (as in this patient) the pulmonary vein inflow vestibule (c). LAA = orifice of the left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein.
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Figure 2. RFCA targets. Gated multi-detector row CT scans (endocardial view) obtained in a patient with paroxysmal atrial fibrillation in normal sinus rhythm during the study show the left side of the left atrium. One or more of the distal pulmonary veins (a) was the original target for RFCA. As the procedure has evolved, newer targets include the pulmonary vein ostia (b) and (as in this patient) the pulmonary vein inflow vestibule (c). LAA = orifice of the left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein.
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Under fluoroscopic guidance, with femoral vein access, a catheter with an ablation electrode at its tip and an intracardiac echocardiography catheter are guided retrograde up the inferior vena cava into the right atrium, then via a transseptal puncture into the left atrium to gain access to the distal pulmonary veins (Fig 3a). The pulmonary veins must be found and selectively cannulated before they can be electrically mapped to decide which pulmonary vein, pulmonary venous ostium, or pulmonary venous inflow vestibule to ablate. The ablation procedure itself, even in the most experienced hands, is tedious and time consuming, often lasting several hours. The tip of the ablation catheter covers only a few millimeters of tissue at a time and is guided either (a) to a specific ectopic focus within the distal pulmonary vein or (b) along the entire circumference of the pulmonary vein ostium, or pulmonary vein inflow vestibule, with thermal energy applied every few millimeters (Fig 3b).
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Figure 3a. RFCA technique. (a) Fluoroscopic image depicts the ablation electrode (arrowheads) and the intracardiac echocardiography catheter (arrow) within the left superior pulmonary vein ostium. (b) As thermal energy is applied, an electroanatomic virtual map (CARTO-Biosense/Webster, Diamond Bar, Calif) shows the aggregate of ablated regions. Each red sphere represents a few millimeters of ablated tissue.
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Figure 3b. RFCA technique. (a) Fluoroscopic image depicts the ablation electrode (arrowheads) and the intracardiac echocardiography catheter (arrow) within the left superior pulmonary vein ostium. (b) As thermal energy is applied, an electroanatomic virtual map (CARTO-Biosense/Webster, Diamond Bar, Calif) shows the aggregate of ablated regions. Each red sphere represents a few millimeters of ablated tissue.
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Complications of RFCA
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Some of the complications encountered during RFCA are similar to those associated with other cardiac catheterization procedures. In addition, endocardial charring, pulmonary vein dissection, and atrial or pulmonary vein perforation can occur (16). Because vagus nerve fibers are found within the walls of the pulmonary veins, significant bradyarrhythmias, including asystole, can occur as the thermal energy is applied (10–12).
After RFCA, mild complications such as small pleural or pericardial effusions, transient small atrial septal defects, and hemodynamically insignificant pulmonary vein stenoses can occur (10). More important are the potentially devastating complications, including stroke, hemopericardium, hemothorax, pulmonary vein thrombosis, and hemodynamically significant pulmonary vein stenosis (10,11,17–19). The latter can lead to venous infarction and has been associated not only with fibrosing mediastinitis but also with pulmonary veno-occlusive disease, including development of severe pulmonary arterial hypertension over time (19). Lengthy fluoroscopic procedures can pose a radiation risk to both the patient and the personnel in the electrophysiology suite during the procedure (20). There has been at least one reported case of radiation dermatitis in a patient with supraventricular tachyarrhythmia who had undergone RFCA (21).
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Need for Pre-RFCA Imaging
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In the past, much of the time spent performing RFCA for atrial fibrillation was used to try to fluoroscopically define the anatomy of the pulmonary vein ostia by injecting contrast material into the left atrium and attempting to reflux the contrast material retrograde into the distal pulmonary veins to identify them—all prior to the start of ablation. Fluoroscopy was traditionally used for RFCA in atrial fibrillation patients but proved incapable of providing accurate 3D anatomic information. Intracardiac echocardiography may be used during RFCA. However, intracardiac echocardiography has a small field of view, which is useful for guiding the ablation catheter around the inner circumference of the target but is inadequate for 3D visualization of the relationship between the distal pulmonary veins within the left atrium, which is often dilated.
As RFCA for atrial fibrillation evolves, we realize that a successful outcome involves not only stopping atrial fibrillation but also minimizing complications. Doing so increasingly requires a precise, preprocedural understanding of the complex 3D anatomy of the atriopulmonary venous junctions and posterior left atrium from both epicardial and endocardial perspectives, rather than relying on intraprocedural electrophysiologic mapping alone.
Information necessary for successful RFCA includes (a) the number, location, and angulation of pulmonary veins and their ostial branches unobscured by adjacent cardiac and vascular anatomy, and (b) left atrial volume. In addition, pre-RFCA exclusion of atrial or atrial appendage thrombi is mandatory because their presence is an absolute contraindication to the procedure. Currently, transesophageal echocardiography is con-sidered the standard of reference for exclusion of atrial or atrial appendage thrombi.
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Embryologic Development
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Familiarity with the embryologic development of the pulmonary veins and left atrium is helpful in understanding the complex anatomy of this region. In early embryologic development, the lungs are initially drained by a vascular plexus, which has many connections with the cardinal veins. Then, a common pulmonary vein develops in the sinoatrial region and connects with the vascular plexus, and the cardinal vein connections degenerate and disappear. If a vascular plexus–cardinal vein connection does not degenerate, drainage from that portion of the lung may continue to flow into the derivatives of the cardinal veins (ie, left brachiocephalic vein, right or left superior vena cava, azygous vein) rather than into the left atrium, resulting in either complete or partial anomalous pulmonary venous return (22).
Most of the adult left atrium is also derived from the primitive common pulmonary vein. Initially, the single common pulmonary vein opens into the primitive left atrium. Later, the atrium expands, and this vein is absorbed or incorporated into the wall of the left atrium, which explains why most of the left atrial wall is relatively smooth. The left atrial appendage is derived from the primitive atrium and has a rough, trabeculated surface. The proximal portions of the branches of the common pulmonary vein are absorbed, leaving four pulmonary veins with separate openings into the left atrium. Accessory pulmonary veins can develop and induce regression of a portion of the primitive pulmonary vein, resulting in additional openings into the left atrium and connections between the accessory pulmonary veins and the left atrium (22).
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Anatomic Definitions
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The pulmonary vein ostium is the atriopulmonary venous junction. On epicardial views, it is identified as the point of reflection of the parietal pericardium from the left atrium (Fig 4). The distal or central pulmonary veins are those portions of the pulmonary veins in proximity to the left atrium. Electrophysiologists divide the pulmonary veins into segments between branch points retrograde from the atriopulmonary venous junctions. For example, the V1 segment, which is often the ablation target, extends retrograde from the ostium to the "first" branch point, which anatomically is actually the last junction or confluence of branches (Fig 5). An ostial branch is a vein branch within 5 mm of the atriopulmonary venous junction; therefore, if there is an ostial branch, the V1 segment is less than 5 mm long (Fig 6). The vein wall interposed between branches of a single pulmonary vein is termed the intravenous saddle (5).
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Figure 4. Normal pulmonary vein ostium. Volume-rendered (VR) image (left posterior oblique epicardial view) from nongated multi-detector row CT shows the right inferior pulmonary vein ostium.
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Figure 5. Segments of the distal pulmonary veins. Slab reformatted image shows the V1 through V3 segments of an accessory right middle lobe pulmonary vein. The V1 segment is the most important segment to include on epicardial views.
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Figure 6. Normal ostial branches. VR image (posteroanterior epicardial view) from nongated multi-detector row CT shows ostial branches (arrows) of the left superior (LS), right inferior (RI), and right superior (RS) pulmonary veins. The V1 segment of each of these veins is less than 5 mm in length.
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The intervenous saddle is the region of atrial wall interposed between separate ipsilateral pulmonary veins (Fig 7). The pulmonary vein inflow vestibule includes the ipsilateral pulmonary vein ostia and the intervenous saddle atrial wall. The posterior left atrium includes the bilateral pulmonary vein inflow vestibules and the interposed posterior atrial wall. There is a variable amount of endocardial ridging of the posterior left atrium (5).
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Figure 7a. Intervenous saddle in a patient with normal pulmonary venous anatomy and accessory drainage of the right middle lobe. Bilateral VR images (endocardial view) from nongated multi-detector row CT show the intervenous saddles (solid white lines) between the right superior (RS) and right middle lobe (RM) pulmonary veins and the right superior and right inferior (RI) pulmonary veins (a), and between the left superior (LS) and left inferior (LI) pulmonary veins (b). The left inferior pulmonary vein intravenous saddle is also seen (dotted white line in b). Note the artifact from a pacer lead (arrows in a).
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Figure 7b. Intervenous saddle in a patient with normal pulmonary venous anatomy and accessory drainage of the right middle lobe. Bilateral VR images (endocardial view) from nongated multi-detector row CT show the intervenous saddles (solid white lines) between the right superior (RS) and right middle lobe (RM) pulmonary veins and the right superior and right inferior (RI) pulmonary veins (a), and between the left superior (LS) and left inferior (LI) pulmonary veins (b). The left inferior pulmonary vein intravenous saddle is also seen (dotted white line in b). Note the artifact from a pacer lead (arrows in a).
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Normal pulmonary venous anatomy is defined as the presence of any combination of pulmonary veins that is nonanomalous (Figs 8 –10), including conventional anatomy as well as conjoined or accessory pulmonary veins. Conventional pulmonary venous anatomy is defined as the presence of single right and left superior and inferior pulmo-nary veins that drain into the left atrium without any accessory veins (Fig 8). A common or conjoined vein occurs when superior and inferior veins combine proximal to the left atrium, resulting in only one atriopulmonary venous junction on the involved side (Fig 9), whereas supernumerary or accessory pulmonary veins are extra veins with independent atriopulmonary venous junctions separate from the superior and inferior pulmonary veins (Fig 10). Conjoined veins occur more frequently on the left side, which is also the side more frequently targeted for ablation (5). Conjoined veins typically have a broad, atriopulmonary venous junction. Accessory veins are named for the pulmonary lobe or segment that they drain, sometimes crossing pulmonary lobar fissures before emptying into the left atrium. Accessory drainage can be complex but occurs more frequently on the right side, with separate drainage of the right middle lobe or superior segment of the right lower lobe occurring most often (5). Accessory veins typically have a narrower atriopulmonary venous junction than do the superior and inferior pulmonary veins.
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Figure 8. Normal pulmonary venous anatomy. On a nongated multi-detector row CT scan (right posterior oblique epicardial view), single right and left superior and inferior pulmonary veins drain into the left atrium without accessory veins. LI = left inferior, LS = left superior, RI = right inferior, RS = right superior.
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Figure 9a. Common (conjoined) veins. (a) VR image (posteroanterior epicardial view) from nongated multi-detector row CT shows a right common vein (RCV). LI = left inferior pulmonary vein, LS = left superior pulmonary vein. (b) VR image (right posterior oblique epicardial view) from nongated multi-detector row CT performed in a different patient shows a left common vein (LCV). RI = right inferior pulmonary vein, RS = right superior pulmonary vein. Both right and left common veins are normal variants of the pulmonary venous anatomy, but the latter occurs much more frequently than the former.
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Figure 9b. Common (conjoined) veins. (a) VR image (posteroanterior epicardial view) from nongated multi-detector row CT shows a right common vein (RCV). LI = left inferior pulmonary vein, LS = left superior pulmonary vein. (b) VR image (right posterior oblique epicardial view) from nongated multi-detector row CT performed in a different patient shows a left common vein (LCV). RI = right inferior pulmonary vein, RS = right superior pulmonary vein. Both right and left common veins are normal variants of the pulmonary venous anatomy, but the latter occurs much more frequently than the former.
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Figure 10a. Supernumerary (accessory) pulmonary veins. VR images (epicardial view) from gated (a, c) and nongated (b) multi-detector row CT performed in three different patients show an accessory right middle lobe pulmonary vein (RM in a), a superior segment right lower lobe (ssRLL) pulmonary vein (b), and a lingula pulmonary vein (c). Accessory veins contribute to the complexity of normal pulmonary venous anatomy and may drain a pulmonary lobe or lobe segment.
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Figure 10b. Supernumerary (accessory) pulmonary veins. VR images (epicardial view) from gated (a, c) and nongated (b) multi-detector row CT performed in three different patients show an accessory right middle lobe pulmonary vein (RM in a), a superior segment right lower lobe (ssRLL) pulmonary vein (b), and a lingula pulmonary vein (c). Accessory veins contribute to the complexity of normal pulmonary venous anatomy and may drain a pulmonary lobe or lobe segment.
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Figure 10c. Supernumerary (accessory) pulmonary veins. VR images (epicardial view) from gated (a, c) and nongated (b) multi-detector row CT performed in three different patients show an accessory right middle lobe pulmonary vein (RM in a), a superior segment right lower lobe (ssRLL) pulmonary vein (b), and a lingula pulmonary vein (c). Accessory veins contribute to the complexity of normal pulmonary venous anatomy and may drain a pulmonary lobe or lobe segment.
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Anomalous pulmonary venous anatomy occurs when pulmonary veins drain into a structure other than the left atrium (Fig 11) (4,13,21,23). If no pulmonary veins drain into the left atrium, there is total anomalous pulmonary venous return. Partial anomalous pulmonary venous return occurs when at least one of the pulmonary veins drains into the left atrium.
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Figure 11. Anomalous pulmonary venous anatomy. Chest CT was performed to evaluate for pulmonary embolism in a patient without atrial fibrillation but with partial anomalous pulmonary venous drainage of the left upper lobe into the left brachiocephalic vein. This CT scan shows a vessel (arrow) to the left of the aortic arch that courses toward the mediastinum.
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Multi–Detector Row CT
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CT is performed with multi–detector row scanners and basic CT angiographic techniques (5,24). The majority of our patients have undergone CT with GE LightSpeed Plus quad-detector scanners (General Electric, Milwaukee, Wis). Drug therapy should be adjusted for maximal rate control in patients with persistent atrial fibrillation prior to their undergoing CT. If the patient has paroxysmal atrial fibrillation with normal sinus rhythm or has atrial fibrillation with a stable, ventricular response and a heart rate of less than 93 beats per minute (or whatever rate the gating mode on the scanner will accept), gated CT should be performed because this provides the best endocardial reformatted images. Nongated CT should be performed in patients who do not meet these criteria.
Examination and reformatted image quality depend on optimal contrast material enhancement of the left atrium and distal pulmonary veins. In most cases, an initial test bolus of 20 mL of nonionic contrast material is injected intravenously via a 20-gauge catheter with a power injector at a rate of 4 mL/sec and timed for the left atrium. However, if the heart rate is alternating between bradycardia and tachycardia, thus causing large variations in cardiac output, use of bolus tracking should be considered because the optimal timing of the contrast material may change significantly between the test injection and the scanning injection. A scanning bolus of 125 mL of nonionic contrast material is injected at a rate of 4 mL/sec with the calculated timed delay (or with bolus tracking performed for the left atrium), and images are obtained from the top of the aortic arch through the heart during a single breathhold. For gated examinations, the following parameters are used: 0.5 cardiac segment, 70% R-R interval, 1.25-mm collimation, and high-speed mode (6:1 pitch). For nongated examinations, images are obtained at a collimation of 2.5 mm. All images are reconstructed to 1.25 mm and a 25-cm field of view with lung and soft-tissue algorithms and transferred to a workstation for postprocessing.
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Postprocessing
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Before any postprocessing takes place, a skilled radiologist must review all lung and soft-tissue source images to help identify any anatomic variants or potentially significant incidental findings. Often, the lung windows are the most helpful in determining which pulmonary lobe or segment an accessory vessel is draining. Anteroposterior diameters of the pulmonary vein ostia are obtained from the initial source images. The left atrium and left atrial appendage should be scrutinized for thrombi.
Postprocessing can be performed on a stand-alone workstation such as the Advantage Workstation with 4.0-version software (General Electric). Both epicardial (extraatrial) and endocardial (intraatrial) VR views of the left atrium and distal pulmonary veins are obtained, along with surface-rendered views of the left atrium (5).
Epicardial VR
The epicardial VR views must include the left atrium (with or without its appendage) and the distal third of the pulmonary veins and exclude the rest of the heart, pulmonary arteries, aorta, and superior and inferior vena cavae to display the external anatomy of the imaging volume unobscured by adjacent anatomy. Either a "paintbrush" or "cutting" technique may be used to accomplish this. The paintbrush technique is preferred because, although it requires moving through the source image set and applying "paint" to each section individually, it requires less work than "cutting away" all the overlapping anatomy without sacrificing the anatomy in question. Accessory vessels must be identified prior to VR because if they are not "painted" they will not show up on the 3D rendering (Fig 12).
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Figure 12a. Potential pitfall of the paintbrush technique. (a, b) Posteroanterior epicardial VR image (b) shows a truncated ssRLL pulmonary vein because the vein was incompletely included in the "painting" of the axial multi-detector row CT source image (a). Arrow indicates vein. (c, d) Lateral reformatted image (c) with the ssRLL vein correctly "painted" (arrowheads) results in the posteroanterior epicardial VR image seen in d, which shows the vein draining into the top of the left atrium. These four images illustrate the need for careful review of the source images prior to VR.
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Figure 12b. Potential pitfall of the paintbrush technique. (a, b) Posteroanterior epicardial VR image (b) shows a truncated ssRLL pulmonary vein because the vein was incompletely included in the "painting" of the axial multi-detector row CT source image (a). Arrow indicates vein. (c, d) Lateral reformatted image (c) with the ssRLL vein correctly "painted" (arrowheads) results in the posteroanterior epicardial VR image seen in d, which shows the vein draining into the top of the left atrium. These four images illustrate the need for careful review of the source images prior to VR.
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Figure 12c. Potential pitfall of the paintbrush technique. (a, b) Posteroanterior epicardial VR image (b) shows a truncated ssRLL pulmonary vein because the vein was incompletely included in the "painting" of the axial multi-detector row CT source image (a). Arrow indicates vein. (c, d) Lateral reformatted image (c) with the ssRLL vein correctly "painted" (arrowheads) results in the posteroanterior epicardial VR image seen in d, which shows the vein draining into the top of the left atrium. These four images illustrate the need for careful review of the source images prior to VR.
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Figure 12d. Potential pitfall of the paintbrush technique. (a, b) Posteroanterior epicardial VR image (b) shows a truncated ssRLL pulmonary vein because the vein was incompletely included in the "painting" of the axial multi-detector row CT source image (a). Arrow indicates vein. (c, d) Lateral reformatted image (c) with the ssRLL vein correctly "painted" (arrowheads) results in the posteroanterior epicardial VR image seen in d, which shows the vein draining into the top of the left atrium. These four images illustrate the need for careful review of the source images prior to VR.
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A minimum of eight standardized epicardial VR views are obtained for the electrophysiologist to refer to during RFCA: a posteroanterior view with a 30°–45° cranial tilt; two anteroposterior views, one with a 45° cranial tilt and one with a 45° caudal tilt; bilateral lateral and bilateral posterior oblique views (four views in all), each with a 30°–45° cranial tilt; and an inferior view (Fig 13).
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Figure 13a. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13b. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13c. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13d. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13e. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13f. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13g. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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Figure 13h. Standard epicardial views: posteroanterior view, 30°-45° cranial tilt (a), anteroposterior view, 45° cranial tilt (b), anteroposterior view, 45° caudal tilt (c), 45° right posterior oblique view, 30°-45° cranial tilt (d), 45° left posterior oblique view, 30°-45° cranial tilt (e), right lateral view, 30°-45° cranial tilt (f), left lateral view, 30°-45° cranial tilt (g), and inferior view (h). Multiple extraatrial projections, either filmed or displayed as a cine loop, are needed to display the left atrium and pulmonary veins in three dimensions without overlap. Together, these projections provide an accurate 3D model to help the electrophysiologist gain an understanding of the complexity of the relevant anatomy and anatomic relationships prior to RFCA.
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No routine measurements need be made on the epicardial VR views. These views clearly de-pict atrial shape and size, the number and angula-tion of pulmonary veins, and the location of ostial branches (Fig 14).
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Figure 14a. Usefulness of epicardial views. (a) VR image from CT performed in a patient with a nondilated left atrium (left atrial volume = 52 mL) demonstrates normal pulmonary venous anatomy, with right superior and right inferior ostial branches (arrows). (b) VR image (epicardial view) from multi-detector row CT performed in a patient with a dilated left atrium (left atrial volume = 181 mL) depicts a left common vein (LCV).
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Abstract
LEARNING OBJECTIVES FOR TEST...
