From pictures to practice paradigms |
Noncoronary Applications of Cardiac Multidetector Row Computed Tomography
Laurens F. Tops, MD*,*,
Subramaniam C. Krishnàn, MD ,
Joanne D. Schuijf, MSc*,
Martin J. Schalij, MD, PhD*,
Jeroen J. Bax, MD, PhD, FACC*,1
* Department of Cardiology, Leiden University Medical Center, Leiden, the Netherlands
Division of Cardiology, University of California, Irvine, California.
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Abstract
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Multidetector row computed tomography (MDCT) has a high diagnostic accuracy to evaluate coronary artery stenoses. Additionally, the 4-dimensional aspect of cardiac MDCT allows a comprehensive evaluation of cardiac structure and function. Left ventricular volumes and systolic function can be accurately assessed with MDCT, and imaging of myocardial infarction is a promising application of cardiac MDCT. In addition, MDCT may provide anatomical visualization of heart valves. Also, evaluation of anatomy of the pulmonary veins and cardiac venous system render MDCT a valuable tool for the cardiologist performing electrophysiological procedures. In this article, the role of MDCT in the noninvasive evaluation of cardiac structure and function is discussed. An overview of the wide range of noncoronary applications of cardiac MDCT is provided, focusing on the assessment of left ventricular function, valvular heart disease, and cardiac venous anatomy.
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Abbreviations and Acronyms
| | 2D = 2-dimensional | | 3D = 3-dimensional | | CAD = coronary artery disease | | CRT = cardiac resynchronization therapy | | CT = computed tomography | | LPCB = left pericardiophrenic bundle | | LV = left ventricle/ventricular | | LVEF = left ventricular ejection fraction | | MDCT = multidetector row computed tomography | | MRI = magnetic resonance imaging | | SPECT = single-photon emission computed tomography |
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Multidetector row computed tomography (MDCT) is an emerging technique for noninvasive coronary angiography (1). In direct comparison to invasive angiography, a high level of diagnostic accuracy for the detection of significant coronary artery stenoses has been shown (2). Accordingly, MDCT is finding increasing use as an alternative imaging modality in the diagnostic testing of patients with suspected coronary artery disease (CAD) (3). Because MDCT not only acquires a 3-dimensional (3D) volumetric dataset of the entire heart but additionally can be reconstructed at any desired time instant during the cardiac cycle, it can also provide functional information. Consequently, cardiac MDCT allows for a comprehensive evaluation of cardiac structure and function and may be used for a broad range of applications (1). In this article, the role of MDCT in the noninvasive evaluation of cardiac morphology and function is discussed. An overview of the wide range of noncoronary applications of cardiac MDCT is provided, focusing on the assessment of left ventricular (LV) function, valvular heart disease, and cardiac venous anatomy.
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Cardiac Function Assessment With MDCT
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LV volumes and ejection fraction.
For global function analysis with MDCT, thick slices (2 mm) are typically reconstructed in the short-axis orientation throughout the cardiac cycle (every 5% or 10% of the RR interval) to identify end-diastolic and -systolic phases. Subsequently, LV end-diastolic and -systolic volumes are derived to calculate left ventricular ejection fraction (LVEF), either using the Simpson method or volume threshold method. For the Simpson method, endocardial borders are traced manually or with automated software to obtain LV volumes. The threshold volume, on the other hand, uses the high contrast between the LV cavity and myocardium to derive LV volumes automatically after manual definition of the mitral valve plane and LV axis. Examples of both methods are provided in Figure 1. The accuracy of LV volume and ejection fraction measurements with MDCT has been investigated extensively. Comparisons with various other imaging modalities, including 2-dimensional (2D) echocardiography (4), gated single-photon emission computed tomography (SPECT) (5), and magnetic resonance imaging (MRI) (6) have consistently demonstrated high accuracy of MDCT for the assessment of LV volumes and LVEF.
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Figure 1 Analysis of LVEF With MDCT
(A) Analysis based on the volumetric threshold method is illustrated. From left to right, end-diastolic images are displayed in short-axis, 4-chamber, and 2-chamber views. The left ventricular end-diastolic volume is semi-automatically derived. (B) An example of left ventricular ejection fraction (LVEF) assessment based on the Simpson method is provided. Endocardial contours are drawn on reconstructed short-axis slices to calculate volumes and subsequently LVEF. MDCT = multidetector row computed tomography.
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With the introduction of newer MDCT technology, such as dual-source computed tomography (CT), additional improvements in accuracy for the assessment of LV function can be expected because of enhanced temporal resolution (7). It is noteworthy that "ECG pulsing," the reduction of radiation exposure in systole that is often applied to reduce radiation doses in cardiac CT, does not prevent accurate assessment of LV function. Although systolic images may have slightly reduced image quality and higher noise, the endocardial borders are still visualized with sufficient accuracy.
Regional wall motion.
By displaying images in cine-loop format, regional wall motion can be evaluated in addition to LVEF. In general, the 17-segment model as proposed by Cerqueira et al. (8) is applied for this purpose and segments are scored as normokinetic, hypokinetic, akinetic, or dyskinetic (the latter 2 often being combined for practical purposes). In a recent study, excellent agreement of 64-slice MDCT and 2D echocardiography was shown, with 96% of segments scored identically on both techniques, resulting in a kappa value of 0.82 (9). However, it is important to realize that the agreement was particularly high for segments displaying normal wall motion (99%), whereas slightly lower agreement was observed for segments showing moderate (hypokinesia, 70%) and severe (akinesia or dyskinesia, 78%) contractile dysfunction (9). An example of MDCT images of a patient with regional contractile dysfunction is provided in Figure 2.
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Figure 2 Analysis of Regional Wall Motion With 64-Slice MDCT
(A) Short-axis reconstruction in end diastole. (B) Short-axis reconstruction in end systole. Akinesia and thinning of the myocardium is observed in the lateral wall (black arrows). In addition, hypoattenuation (dark endocardial rim) corresponding to previous myocardial infarction is present in this region. Quantification of left ventricular volumes reveals severely reduced left ventricular systolic function (LVEF 28%). Abbreviations as in Figure 1.
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Myocardial infarction and perfusion.
An emerging application of MDCT is the evaluation of myocardial perfusion. This concept, dating back to animal studies in the late 1970s (10), is based on the kinetics of the iodinated contrast agent used for noninvasive coronary angiography. Similar to MRI, MDCT data are acquired during administration of a bolus of contrast agent. As a result, hypoperfused myocardial regions are identified as areas displaying hypoattenuation (Fig. 2). Subsequent measurements of attenuation in Hounsfield units allow differentiation between areas of infarction and remote myocardium (11). In comparison to the techniques traditionally used to visualize myocardial infarction (gated SPECT and MRI), a good accuracy to detect myocardial infarction has been observed for MDCT (12–14). However, in general, the area of infarction seems to be slightly overestimated by MDCT (11,14).
Importantly, MDCT allows assessment of both chronic and acute myocardial infarcts (15). In an animal model of chronic myocardial infarction, Lardo et al. (16) showed that delayed enhancement MDCT imaging could accurately identify the morphological characteristics of the infarct, including infarct size and transmurality. Furthermore, the accuracy of MDCT for the assessment of acute myocardial infarction has been shown in humans (17,18). A close relationship between enhancement patterns (both early hypoenhancement and late hyperenhancement) on MDCT and recovery of myocardial function at 3-month follow-up has been shown, suggesting that MDCT may indeed provide valuable information for further management after myocardial infarction (18).
Ideally, not only evaluation of scar tissue but also assessment of myocardial ischemia would be possible. Indeed, one of the major limitations of MDCT coronary angiography is the inability to evaluate the functional significance of detected coronary artery lesions (19). Diagnosis and management, however, would be substantially improved if this information could be obtained in addition to the anatomical data. Recently, the feasibility of adenosine stress myocardial perfusion imaging with MDCT has been shown in a canine model (20). Accordingly, MDCT may have the potential to provide information on stress-induced perfusion defects in addition to coronary anatomy. However, it is important to realize that adenosine-induced tachycardia may hamper simultaneous interpretation of the coronary arteries.
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Assessment of Valvular Anatomy With MDCT
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Because of the excellent spatial and temporal resolution and the ability to reconstruct the dataset at any time point during the cardiac cycle, MDCT is a valuable technique for the assessment of valvular disease. However, the recent Appropriateness Criteria for Cardiac Computed Tomography and Cardiac Magnetic Resonance Imaging (1), from the American College of Cardiology, graded the characterization of native (and prosthetic) cardiac valves and assessment of valvular function as an uncertain indication for cardiac MDCT. Nonetheless, MDCT permits assessment of different aspects of heart valves, including valvular and annular calcifications, the number of leaflets, valvular anatomy and geometry, and valve area (21–32). Aortic and mitral valves can usually be well visualized with MDCT, whereas visualization of tricuspid and pulmonary valves is not reliable. This is likely because the left-sided heart valves are thicker, and because contrast enhancement in the right atrium and ventricle is not as homogeneous as in the left-sided chambers. If right-sided heart valves are to be visualized, the contrast injection protocol must be adjusted to ensure enhancement in the right cardiac chambers during image acquisition. This usually requires a longer injection of contrast as compared with CT coronary angiography studies.
The assessment of valve areas in MDCT is based on direct planimetry because the quantification of pressure gradients and transvalvular flow is not possible with MDCT (33). Correlative studies on MDCT and echocardiography for the assessment of aortic and mitral valve stenosis and regurgitation are summarized in Table 1.
Aortic valve.
Various aspects of the aortic valve can be assessed with MDCT (34). Calcification can be quantified in nonenhanced datasets (35). However, for the accurate assessment of valve morphology and quantification of the orifice area, contrast-enhanced scans are necessary (33,36,37). In 57 patients referred for MDCT coronary angiography, Abbara et al. (33) performed planimetry of the aortic valve at 5 different time points during the cardiac cycle (0 to 200 ms after the R-wave). It was noted that image quality for analysis of the aortic valve area was optimal at 50 ms after the R-wave (midsystole). Finally, MDCT may be of value for the assessment of aortic stenosis or aortic regurgitation. Numerous studies have shown close correlation between MDCT and echocardiography for the assessment of aortic valve opening area and regurgitant orifice area (Table 1).
Mitral valve.
It has been shown that contrast-enhanced MDCT allows visualization of mitral valve annulus, leaflets, papillary muscles, and even tendinous cords (Fig. 3). Typically, a long-axis plane reconstructed perpendicular to the mitral valve yields optimal image quality for assessment of mitral valve morphology. Furthermore, the optimal systolic and diastolic reconstructions for functional assessment are at 5% and 65% of the RR interval, respectively (38). Importantly, it has been shown that there is an excellent agreement between MDCT, echocardiography, and surgery (by means of direct visualization) for the assessment of thickening of the mitral valve leaflets and the assessment of mitral valve and annular calcifications (39). Several studies have investigated mitral valve stenosis and regurgitation with MDCT (Table 1).
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Figure 3 Assessment of Mitral Valve Anatomy With MDCT
This reconstructed long-axis view clearly shows how the anatomy of the mitral valve and the subvalvular apparatus can be assessed. In the diastolic phase, the mitral valve leaflet (open arrow), the tendinous cords (solid arrow), and the papillary muscles (PM) are well visualized. Ao = aorta; LV = left ventricle; MDCT = multidetector row computed tomography.
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Management of valvular heart disease.
An MDCT scan may be of clinical value in the surgical and percutaneous treatment of valvular heart disease. It has been shown that MDCT has a high diagnostic accuracy to rule out CAD in patients with aortic stenosis before surgical aortic valve replacement (40). In addition, LV function and valvular anatomy (including the aspect of the mitral and aortic valve [bicuspid/tricuspid], the diameter of the valve, and the extent of calcifications of the valve and annulus) can be accurately assessed with MDCT. An example of a bicuspid aortic valve assessed with MDCT is shown in Figure 4. Preoperative knowledge of these aspects may influence the surgical strategy or type of valvular prosthesis.
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Figure 4 Assessment of the Aortic Valve With MDCT
In this patient, a bicuspid aortic valve is demonstrated with contrast-enhanced multidetector row computed tomography (MDCT) (left panel). The extent and location of calcifications (white arrows) can be well visualized with MDCT and correlate well with the findings during cardiac surgery (right panel).
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Recently, the feasibility of percutaneous mitral annuloplasty in patients with severe mitral regurgitation has been reported (41). The rationale of this technique is to remodel the mitral annulus by placing a device in the coronary sinus, adjacent to the mitral annulus. In this context, MDCT can provide useful information by depicting the relationship between the coronary sinus, mitral annulus, and coronary arteries (42). An example of a 3D volume-rendered reconstruction depicting this relation is shown in Figure 5. Importantly, it has been noted that in the majority of the patients, the coronary sinus is located cranial to the mitral valve annulus (43). Furthermore, in 68% of the patients, the circumflex artery coursed between the coronary sinus and the mitral annulus, with an increased risk of occlusion of the circumflex artery when performing percutaneous mitral annuloplasty (43).
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Figure 5 Coronary Venous Anatomy and Relation Between Coronary Sinus and Mitral Annulus
With the use of 3D volume rendered reconstructions, the anatomy of the coronary venous system and the relation between the coronary sinus (CS) and the mitral valve annulus can be assessed. In this patient, the CS courses along the posterior wall of the left atrium (LA), rather than along the mitral valve annulus. In patients with a large distance between the CS and the mitral annulus (indicated by the white arrow), a percutaneous mitral annuloplasty may not be feasible. GCV = great cardiac vein; LMV = left marginal vein; PIV = posterior interventricular vein; PVLV = posterior vein of the left ventricle.
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Assessment of Left Atrium and Pulmonary Vein Anatomy
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The role of MDCT in catheter ablation procedures for atrial fibrillation has rapidly expanded in the past few years. Radiofrequency catheter ablation has become an important and increasingly used therapy for patients with drug-refractory atrial fibrillation (44). The aim of these procedures is to electrically isolate the pulmonary veins because these are the dominant foci initiating atrial fibrillation (45). The venoatrial junctions, the antrum, anatomical variations, and other left atrial landmarks, such as the ridge between the left superior pulmonary vein and the left atrial appendage, are critical structures to identify during catheter ablation procedures.
With the use of standard orthogonal planes and 3D volume-rendered reconstructions, MDCT can depict the number, location, and size of the pulmonary veins (46). Thereby, MDCT can accurately visualize variations in pulmonary vein anatomy. Anatomical variations include single insertions (common ostium) of the pulmonary veins and additional pulmonary veins (Fig. 6). In a large cohort of 201 patients undergoing MDCT scanning, Marom et al. (47) noted a left-sided common ostium in 14% of patients, and an additional right-sided pulmonary vein in 28% of patients. In addition, wide variation in left atrial anatomy in patients with atrial fibrillation may exist. It has been shown that the anatomy and size of the left atrial appendage, roof, and septum varies considerably in patients with atrial fibrillation (48). All of these variations in left atrial and pulmonary vein anatomy have important implications for catheter ablation procedures. Therefore, a detailed "road map" of the left atrium and pulmonary veins is needed, both before and during the actual ablation procedure. In addition, detailed knowledge on surrounding structures such as the esophagus and the coronary arteries is of critical importance for avoiding complications such as atrioesophageal fistula (49) and coronary artery injury (50). Because MDCT can provide highly detailed information on left atrial and pulmonary vein anatomy and the surrounding structures, it can provide the necessary anatomical reference for ablation procedures.
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Figure 6 Pulmonary Vein Anatomy Assessment With MDCT
Three-dimensional volume-rendered reconstructions of 64-slice MDCT scans to illustrate pulmonary vein anatomy. (A) Normal pulmonary vein anatomy is shown. Four pulmonary veins with separate insertions in the left atrium (LA) are present. (B to D) Variations in pulmonary vein anatomy. (B) A common ostium of the left-sided pulmonary veins is shown (arrows). (C) An additional right-sided pulmonary vein (arrow). (D) An aberrant insertion of the additional pulmonary vein is present (arrow). All of these anatomical variations in pulmonary vein anatomy may likely impact catheter ablation procedures. LIPV = left inferior pulmonary vein; LSPV = left superior pulmonary vein; MDCT = multidetector row computed tomography; RIPV = right inferior pulmonary vein; RSPV = right superior pulmonary vein.
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Image integration.
Ideally, the anatomical information derived from the MDCT scan is available on-line during the catheter ablation procedure. Recently, image integration systems have been introduced that allow the fusion of MDCT images and conventional electroanatomical maps (51). With dedicated algorithms, the left atrial cavity and pulmonary veins are extracted from the raw MDCT data (Fig. 7). The 3D volume-rendered reconstruction of the left atrium and pulmonary veins can then be aligned with the reconstructed electroanatomical map during the actual ablation procedure. This registration process is based on minimizing the distance between the MDCT image and the electroanatomical map (Fig. 7). Eventually, the catheter ablation can then be performed with the use of the real anatomy of the left atrium and pulmonary veins.
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Figure 7 Image Integration: Fusion of MDCT and Electroanatomical Mapping
The process of image integration consists of several steps. First, multidetector row computed tomography (MDCT) scanning is performed (left panel). With the use of dedicated algorithms based on setting intensity levels for Hounsfield units, the MDCT scan is segmented into different structures (middle panel). During the catheter ablation procedure, the segmented left atrium is aligned with the reconstructed electroanatomical map (registration). Finally, the actual ablation can be performed guided by the anatomy of the left atrium and pulmonary veins (right panel). Based on the real anatomy derived from the MDCT scan, the radiofrequency lesions (represented by the red dots, right panel) can be targeted around the pulmonary veins.
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Both pre-clinical (52) and clinical (53) validation studies have shown the feasibility of importing the MDCT scan into the electroanatomical mapping system, and the subsequent use of the MDCT scan during the actual catheter ablation procedure. The reported accuracy (or registration error) ranges between 1.9 ± 0.6 mm and 2.4 ± 0.4 mm (52–55). The accuracy of the image integration process may be limited by motion caused by respiration, changes in heart rhythm and heart rate, and different fluid status during scanning and during the ablation procedure. Furthermore, variation of pulmonary vein location throughout the cardiac cycle may decrease the accuracy (56). However, potential advantages of the integration of MDCT and the electroanatomical map include the possibility to monitor the exact catheter position in relation to the endocardial border, the pulmonary veins, and the surrounding structures. This may facilitate catheter ablation procedures and may help in avoiding potential complications such as pulmonary vein stenosis, radiation skin burns, and the like.
Importantly, it has been shown that the use of MDCT during the catheter ablation procedure may reduce procedure and fluoroscopy times, and even may improve the outcome of the ablation procedure. Kistler et al. (55) treated a total of 94 patients, using conventional mapping alone (n = 47) and with MDCT image integration (n = 47). It was noted that in the image integration group, fluoroscopy times were significantly shorter (49 ± 27 min vs. 62 ± 26 min, p < 0.05) and the number of patients with maintenance of sinus rhythm without antiarrhythmic medication was significantly higher (83% vs. 60%, p < 0.05). However, these data need to be confirmed in larger, randomized trials.
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Assessment of Coronary Venous Anatomy With MDCT
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Numerous clinical trials have shown that in appropriate patients, cardiac resynchronization therapy (CRT) provides substantial symptomatic benefit and reduces mortality (57–59). The implantation of a CRT device requires the insertion of an LV pacing lead, generally at the posterolateral wall of the LV. In more than 90% of patients, this can be accomplished via a transvenous approach. The main factor determining the success of a transvenous LV lead implantation is cardiac anatomy, particularly of the coronary venous system. However, there is large interindividual variation in the anatomy of the cardiac veins (60). Ideally, the anatomy of the cardiac venous system should therefore be assessed noninvasively before the implantation procedure. Several studies (43,61,62) have shown the feasibility of MDCT for the noninvasive assessment of cardiac venous anatomy (Fig. 5). In particular, in patients with abnormal venous anatomy, MDCT can provide valuable information on the course of the coronary sinus and its tributaries. Abnormal venous anatomy assessed with MDCT is shown in Figure 8. In addition to the anatomical data, MDCT can also provide quantitative data of the coronary venous structures, including dimensions of the ostium of the coronary sinus and the diameter of the target veins (61).
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Figure 8 Congenital Anomaly of the Coronary Venous System in a Patient Referred for CRT
This patient has a persistent left superior vena cava (LSVC) and a markedly enlarged coronary sinus and great cardiac vein (GCV). The upper panel shows a 3-dimensional volume-rendered reconstruction, illustrating the LSVC and coronary venous system. The lower panels show multiplanar reformatted images, where the target vein (posterolateral branch) for left ventricular lead implantation is identified (arrows). Left ventricular lead implantation for cardiac resynchronization therapy (CRT) is significantly more complicated in patients like these. A noninvasive pre-procedure evaluation with multidetector row computed tomography for elucidation of the "road map" can be very helpful.
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Importantly, with the use of MDCT, an association between anatomical variations and the history of a previous myocardial infarction has been shown (62). In patients with a history of infarction, a left marginal vein was significantly less often observed as compared with control patients and CAD patients (Fig. 9). None of the patients with a lateral infarction and only 22% of patients with anterior infarction had a left marginal vein (62). This pre-procedural identification of patients who lack the presence of posterolateral branches with a sufficient diameter to allow passage of a pacemaker lead has important implications for clinical practice. Accordingly, MDCT may be used to identify patients who do not have suitable target branches, and therefore could be referred directly for a minimally invasive surgery for epicardial LV lead placement.
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Figure 9 Variations in Coronary Venous Anatomy
With the use of 64-slice multidetector row computed tomography, the prevalence of the PIV, PVLV, and LMV was assessed in 28 normal control patients, 38 patients with coronary artery disease (CAD), and 34 patients with a history of myocardial infarction. The LMV was less frequently identified in patients with a history of myocardial infarction as compared with CAD patients and control patients (27% vs. 61% and 71%, respectively). This may hamper left ventricular lead positioning in case of CRT. *p < 0.01. **p < 0.0001. Abbreviations as in Figure 5. Adapted from Van de Veire et al. (62).
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Assessment of Cardiac Morphology: Specific Conditions
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Congenital heart disease.
The role of cardiac MDCT in the diagnosis and follow-up of congenital heart disease has increased over the past few years. Detailed anatomical information, even in complex situations, including congenital coronary artery anomalies, atrial and/or ventricular septal defects, aortic coarctation, and pulmonary anomalies, can be obtained by MDCT (63). An example of an anomalous pulmonary venous connection assessed with MDCT is shown in Figure 8. In addition, accurate visualization of cardiac anatomy by MDCT may facilitate interventional procedures, such as catheter ablation procedures for atrial arrhythmias after surgical correction of congenital heart disease (64). Although the use of radiation limits repeated MDCT scanning in the follow-up of congenital heart disease patients, MDCT is less hampered by metal artifacts compared with MRI, and MDCT may be particularly valuable for patients with implanted pacemakers or defibrillators.
Cardiac masses.
An MDCT scan may be of value in the evaluation of patients with suspected cardiac masses (tumor or thrombus), in particular in patients with technically limited images from echocardiography or MRI (1). Intracardiac thrombi, most frequently located in the left atrial appendage, may be depicted as contrast-filling defects, and can be detected with a high sensitivity (but rather low specificity) using MDCT (65).
Pericardial abnormalities.
Abnormal pericardial conditions, such as pericardial thickening and calcification, can be evaluated with MDCT. In particular, after cardiac surgery or when echocardiography is inconclusive, MDCT can provide detailed information on the presence or absence of pericardial effusion (66).
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Assessment of Surrounding Structures
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Phrenic nerves.
Phrenic nerve injury after catheter ablation for atrial fibrillation is a rare but serious complication (67). In addition, phrenic nerve stimulation and subsequent diaphragmatic stimulation has been commonly associated with LV lead placement for CRT (68). Both injury and stimulation of the phrenic nerves can be explained by the proximity of the phrenic nerves to the pulmonary and coronary veins (69). Most commonly, the phrenic nerves are identified with the use of high-output pacing maneuvers. However, noninvasive evaluation of phrenic nerve anatomy and the relationship with the pulmonary and coronary veins may help the cardiologist in planning ablation and LV lead implantation procedures.
Unfortunately, it is difficult to image thin, isolated nerve fibers with MDCT. Matsumoto et al. (70) visualized the blood vessels that accompany the phrenic nerve and used the course of these vessels as a marker of the phrenic nerve. Along with the pericardiophrenic artery and vein, the phrenic nerves form a neurovascular bundle (right pericardiophrenic bundle and left pericardiophrenic bundle). Using 3D volume-rendered reconstructions of contrast-enhanced MDCT scans, the anatomical course of the right pericardiophrenic bundle and left pericardiophrenic bundle can be assessed and relations between the left phrenic nerve and cardiac and vascular structures may be analyzed (Fig. 10). Noninvasive visualization of the phrenic nerves and their relation with the pulmonary and coronary veins with the use of MDCT may be of value in planning interventional procedures. An example of the visualization of the coronary veins and the phrenic nerves with the use of MDCT in a patient referred for CRT is shown in Figure 11. By depicting the exact course of the phrenic nerves, MDCT may help avoid injury or stimulation of the phrenic nerves during catheter ablation and LV lead implantation procedures.
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Figure 10 Assessment of the Pericardiophrenic Bundles With MDCT
Examples of the left (left panel) and right (right panel) pericardiophrenic bundles as shown with 64-slice multidetector row computed tomography (MDCT). The yellow arrows indicate the course of the neurovascular bundles.
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Figure 11 Use of MDCT in LV Lead Implantation
(A) A 3-dimensional volume-rendered reconstruction demonstrates the left pericardiophrenic bundle (LPCB), representing the left phrenic nerve. The course of the LPCB is indicated by white and yellow arrows. (B) The same view as in (A), after adjustment of the window level. The course of the LPCB is again represented by yellow arrows. In this reconstruction, the GCV and the lateral marginal branch (white arrow) are well visualized. Consequently, the relationship between the phrenic nerve and the cardiac veins can be well appreciated. (C) An occlusive venogram of the coronary sinus. The tortuous lateral marginal branch (white arrow) is clearly visualized. A good correlation with the noninvasive evaluation by MDCT (B) is seen. This vein was chosen as the target branch because it was not seen to intersect the course of the LPCB. (D) A unipolar lead placed in the target vein (white arrows). High-output pacing from the lead during the procedure did not reveal any diaphragmatic capture. Abbreviations as in Figures 3 and 5.
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Esophagus.
Visualization of the esophagus and its relation to the posterior wall of the left atrium may be of interest in patients referred for catheter ablation of atrial fibrillation. The development of atrioesophageal fistulas is a lethal complication of ablation procedures, likely caused by direct thermal injury of the esophagus (44,49). The relation between the esophagus and the left atrium is highly variable (71), and visualization of the esophagus before and during the catheter ablation procedures may be important. It has been shown that with the use of MDCT, the relationship, size, and thickness of the tissue layers between the left atrium and the esophagus can be determined (72). Importantly, the esophagus lies close to the ostia of the pulmonary veins in more than 90% of the patients, and the left atrial and esophageal walls are very thin (72). However, the early enthusiasm has considerably died down, and it is increasingly realized that static images of the esophagus and the left atrium are of limited to no value in patients undergoing left atrial ablation. This is in large part because the esophagus is a mobile structure. It has been frequently observed to move during the course of a single ablation procedure (73). Therefore, if imaging is performed to determine the atrioesophageal relationship, it has to be done in real time.
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Conclusions
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The imaging modality of MDCT has potential for use in diagnosis of a wide variety of cardiac diseases and in guiding a variety of invasive and surgical cardiac procedures. The main attraction of this technology is the ability to provide comprehensive information and likely decrease the need for additional testing. The 4-dimensional character of the technique allows an evaluation of cardiac morphology and function. Whereas assessment of LV systolic function is well validated, evaluation of myocardial infarction and myocardial perfusion with MDCT warrants further study.
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Acknowledgments
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The authors acknowledge the assistance of J. M. Van Werkhoven in preparing the figures.
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Footnotes
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1 Dr. Bax receives research grants from GE Healthcare, Bristol-Myers Squibb Medical Imaging, Boston Scientific, Medtronic, and St. Jude Medical. 
* Reprint requests and correspondence: Dr. Laurens F. Tops, Department of Cardiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, the Netherlands. (Email: l.f.tops{at}lumc.nl).
Manuscript received October 5, 2007;
revised manuscript received October 14, 2007,
accepted October 17, 2007.
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S. C. Krishnan, L. F. Tops, and J. J. Bax
Cardiac resynchronization therapy devices guided by imaging technology.
J. Am. Coll. Cardiol. Img.,
February 1, 2009;
2(2):
226 - 230.
[Full Text]
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Abstract
Cardiac Function Assessment With...