Echocardiography of the Superior Vena Cava

Transcription

1 Clin. Cardiol. 28, (2005) Echocardiography of the Superior Vena Cava RAMI N. KHOUZAM, M.D., DANIEL MINDERMAN, R.D.C.S., IVAN A. D CRUZ, M.D., FRCP Division of Cardiology, University of Tennessee Health Science Center and Memphis VA Medical Center, Memphis, Tennessee, USA Summary The anatomy and applied echocardiographic anatomy of the superior vena cava (SVC) are briefly described. Right supraclavicular interrogation of the SVC has been in use for many years, but supraclavicular two-dimensional (2-D) imaging of the SVC has been virtually ignored. We have recently shown that supraclavicular 2-D imaging can provide excellent views of the SVC and its main tributaries. Transthoracic echocardiography (TEE) is suitable for imaging of the lower (juxtaatrial) SVC. Persistence of a left SVC is an uncommon variant, diagnosed echocardiographically by coronary sinus dilatation and passage of contrast into it from a left arm vein. Extensive SVC compression by mediastinal masses is well known, but recently intravascular SVC obstruction has been increasingly reported as a complication of radiofrequency ablation for ectopic atrial tachycardia, for thrombosis of the SVC or its main tributaries following indwelling catheters, or following insertion of pacemaker leads. Doppler interrogation or TEE imaging of the SVC have been used in recent years to elucidate such pathology. Key words: two-dimensional echocardiography, Doppler echocardiography, superior vena cava, thrombosis Introduction Address for reprints: Ivan D Cruz, M.D. Cardiology Section VA Medical Center 1030 Jefferson Ave. Memphis, TN 38104, USA khouzamrami@yahoo.com Received: December 3, 2004 Accepted with revision: March 8, 2005 The two-dimensional (2-D) echocardiographic features of the inferior vena cava (IVC) were described over 20 years ago, but much less is known about superior vena cava (SVC) ultrasound imaging. Yet 2-D and Doppler echocardiography of the SVC can provide clinically useful information, most of which has come to light only in recent years. In this brief article, we survey such advances in SVC echocardiography. Applied Anatomy The SVC is a straight tube, about 7 cm long, that is formed by the confluence of the right and left innominate veins and ends by entering the right atrium at its superior pole. The right innominate vein, which is formed by the joining of the right subclavian and right internal jugular veins, is in line with the SVC and much shorter than the left innominate vein. The latter is twice as long as the right innominate vein because it courses obliquely across the superior mediastinum anterior to the aortic arch. 1 No major tributary vein drains into the SVC except the azygos vein, which enters it posteriorly at mid SVC level. The azygos vein cannot be visualized in standard transthoracic echocardiographic (TTE) views, but may be identified by transesophageal echocardiography (TEE). The SVC runs vertically down from the level of the first costal cartilage to about the level of the third costal cartilage, approximately posterior to the right sternal border. Echocardiography of the Superior Vena Cava Until now, the suprasternal or supraclavicular windows have been used for recording Doppler flow signals from the SVC, 2 but have virtually not been used for 2-D imaging of the SVC and its tributaries. We have briefly described 2-D imaging of the SVC in normal subjects and in patients with congestive heart failure. 1 Right supraclavicular scanning, with the transducer placed in the fossa between the sternal and clavicular heads of the sternomastoid muscle and with the patient lying supine, reveals not only the top 4 cm of the SVC but also the right innominate vein, its formation by the right subclavian and internal jugular veins, and often the left innominate vein. There are usually no venous valves in the SVC or right innominate vein, but small rapidly moving valves are consistently present in the right subclavian and the internal jugular veins just proximal to their junction with each other. 1 Very little was found about the SVC caliber in the echocardiographic literature. It was measured in one study by Gindea et al. 3 as 10 ± 3 mm in five nor-

2 R. N. Khouzam et al.: Echocardiography of the SVC 363 FIG.1 Two-dimensional imaging of the normal superior vena cava (SVC) from the right supraclavicular window. RSV = right subclavian vein, IJV = internal jugular vein, LSV = left subclavian vein. mal adults when imaged in the supraclavicular view. The SVC can be visualized sometimes through the subcostal approach as a straight narrow tube opening into the right atrium at its upper pole. Imaging of the SVC from these two opposite windows (supraclavicular and subcostal) provides complementary information. The proximal (lower) part of the SVC is better defined in the subcostal view; the distal (upper) half of the SVC is more clearly seen in the right supraclavicular or suprasternal view. Imaging of the normal SVC from the right supraclavicular approach is shown in Figures 1, 2, and 3, demonstrating various aspects of its anatomy. Doppler interrogation of the SVC can be done either by regular transducer or by the blind Pedof transducer. The latter is of smaller size and easier to handle for supraclavicular scanning in some patients, with the echocardiographer relying on the auditory as well as visual Doppler signal rather than on the 2-D image. The normal SVC flow pattern is seen in Figure 3; SVC dilatation in congestive heart failure is represented in Figure 4. Satisfactory visualization of the upper SVC was obtained by Shala et al. from the right supraclavicular window in 80% of patients. 1 A correlation existed between SVC and IVC mean calibers. Dilatation of the SVC was found to correlate positively with that of the IVC. Concordance between SVC caliber and mean right atrial (RA) pressure existed when rightsided cardiac catheterization was performed within 24 h of obtaining echo data. Thus, 2-D echocardiographic visualization of SVC dilatation might be useful clinically when IVC dilatation is uncertain or when the IVC cannot be imaged because of obesity, recent epigastric incision, or bandages. 1 In a Doppler study by Byrd and Linden, the SVC flow velocity was measured from the right supraclavicular fossa. 4 The sample volume (size 2 mm) was placed in the SVC of supine patients at a depth of 4 to 7 cm (5.0 ± 0.7 cm) to obtain an optimal Doppler flow signal. The forward flow through the SVC is biphasic in healthy subjects. The first phase occurs during ventricular systole and the second phase during early diastole. Expiratory SVC diastolic flow velocities (Dfe) was 23 ± 3 cm/s in normal subjects, and a ratio of systolic to diastolic flow velocity (Sfe/Dfe) was < 1.1 in normal subjects as well as in patients with constrictive pericarditis, but was very high in pa- FIG. 2 Right supraclavicular view of the superior vena cava (SVC) to show its anatomy and relationship to adjacent structures. Ao Ar = aortic arch, RPA = right pulmonary artery, LA = left atrium, IJV = internal jugular vein, LIV = left innominate vein, RIV = right innominate vein. FIG. 3 Normal supraclavicular two-dimensional recording of the superior vena cava (SVC) in the two upper panels. The left upper panel also shows the right subclavian vein (RSV), right internal jugular vein (RIJV), right innominate vein (RIV), and left innominate vein (LIV). Doppler interrogation of the SVC, in the lower panel, shows systolic and diastolic phases of flow toward the heart and retrograde flow after the P wave (ReA).

3 364 Clin. Cardiol. Vol. 28, August 2005 (A) FIG. 4 (A) Right suprasternal view showing dilatation of the superior vena cava (SVC) in a patient with congestive heart failure. The right subclavian vein (RSV) and right internal jugular vein (RIJV) are also mildly dilated. (B) Subcostal view in the same patient shows mild dilatation of the inferior vena cava (IVC). RA = right atrium. Calibration is depicted on the right margin of each image. (B) tients with cardiac tamponade. Brief backward flow occurs during atrial contraction. However, in most patients with chronic obstructive pulmonary disease (COPD), the diastolic forward flow wave during expiration and the atrial reversal wave during inspiration disappear, and only the systolic flow wave could be examined, reflecting respiratory variation of the SVC forward-flow velocities. 4 Imaging of the SVC by TEE is obtained by clockwise (rightward) rotation of the probe from the aortic root position, which moves the vertical plane to the right, displaying the SVC in long axis. In this plane, the left atrium and the right pulmonary artery are seen posterior to the SVC, which can be followed to the point where it opens into the right atrium. Left Superior Vena Cava Persistence of left superior vena cava (LSVC) is uncommon; it has been reported to occur in approximately 0.3% of the general population in a single, large report (> 4,000) of unselected autopsies. Its prevalence is, in fact, much higher in patients with congenital cardiac abnormalities than in the general population, ranging from 2.8 to 4.3%. 5 The left SVC drains into a dilated coronary sinus. The combination of persistent LSVC and absent right superior vena cava (RSVC) with no other congenital cardiovascular abnormalities has been reported very rarely. A case of persistent LSVC and absent RSVC observed during pacemaker implantation was confirmed by transthoracic contrast echocardiography. 6 Examples of the usual form of LSVC, as well as the unusual form of LSVC with absence of RSVC, have been observed and illustrated by D Cruz and Shala. 7 The clue for diagnosing LSVC is the presence of a dilated coronary sinus, which can be seen in the posterior atrioventricular groove in the parasternal long-axis view. The LSVC can be seen anterior to the left pulmonary artery in the parasternal short-axis view, whereas its drainage into the coronary sinus is better seen from the high left parasternal sagittal view. Color flow and pulsed Doppler imaging from the suprasternal longaxis view will show a systemic venous flow directed away from the transducer. In rare cases of coronary sinus obstruction, the LSVC will drain the coronary sinus to the left innominate vein and the flow will be directed superiorly. 8 Opacification of LSVC and the dilated coronary sinus with agitated saline injected into the left arm vein will confirm the diagnosis of LSVC. Partial anomalous pulmonary venous connection (PA- PVC) involving the LSVC can be diagnosed by identifying venous flow direction. Color-flow and pulsed-doppler imaging from the suprasternal view will show a systemic venous flow directed away from the transducer. In rare cases of coronary sinus obstruction, the LSVC will drain the coronary sinus to the left innominate vein and the flow will be directed superiorly. Contrast echocardiography with contrast agents, by opacification of the vertical vein, can differentiate PAPVC from a persistent LSVC. 8 Superior Vena Cava Obstruction Following Ablation for Therapy of Atrial Arrhythmias The delivery of multiple radiofrequency (RF) ablation lesions, often necessary for cure of inappropriate sinus tachycardia (IST), can cause considerable atrial swelling and resultant narrowing of the SVC-RA junction. Smaller venous structures, such as the coronary sinus and the pulmonary veins, would also be expected to be vulnerable to this complication. Intracardiac echocardiography (ICE) imaging, used to measure the orifice-size of the SVC-RA junction pre and post ablation may be helpful in preventing excessive tissue swelling leading to venous occlusion during catheter ablation procedures. 9 Central Venous Catheters, Thrombosis, and Superior Vena Cave Syndrome Thrombosis of the SVC is an important clinical problem that requires prompt diagnosis. Confirmation of suspected

4 R. N. Khouzam et al.: Echocardiography of the SVC 365 SVC syndrome requires the use of an imaging study to document the obstruction and presence of collateral venous channels. 10 In a study by Hammerli and Meyer, flow in the SVC could be recorded by using color-flow Doppler examinations in the setting of central venous catheters. 11 The SVC flow in the subjects before catheter placement was characterized by two distinct peaks, respiratory variability, and maximal velocities between 0.5 and 1.5 m/s; these were unchanged by the catheters. Patients with thrombus or obstruction had turbulent flow, loss of a distinct biphasic profile, and increased velocity downstream to the thrombus and decreased velocity upstream. It appears that Doppler study is a worthwhile adjunct to 2-D echocardiography in the evaluation of catheter-related thrombus, and that an altered SVC flow profile with increased velocity suggests thrombus formation with obstruction. 11 Similarly, thrombosis of upper extremity veins and the SVC can occur in patients with indwelling central venous catheters, 12 as shown in Figure 5. Contrary to earlier reports, pulmonary embolism (PE) can result from these thrombi, especially when they are attached to catheters (sleeve thrombi) rather than to the venous wall (mural thrombi). Removal of catheters may be required when sepsis occurs or to reduce risk of sepsis when lines have been left in for several days. Transesophageal echocardiography may have a role in showing thrombus dislodgment and embolization during removal of venous catheters complicated by SVC thrombi. 12 Direct visualization of thrombus dislodgment may aid in early diagnosis of PE because signs and symptoms of PE are often missed or mistaken for underlying cardiopulmonary disease. Transesophageal echocardiography may also play a role in implementing appropriate treatment in patients with PE who show right ventricular strain. 12 Thrombosis of the innominate vein and SVC is also a serious complication in patients with pacemakers, inducing pulmonary embolism or SVC syndrome. Venography is the definitive method for its diagnosis; however, in a study on 53 patients with pacemakers, sensitivity and specificity for detecting severe innominate vein stenosis due to thrombosis using combined color-flow and pulse Doppler were 94 and 100%, respectively. 10 Superior vena caval syndrome may be caused by extravascular compression or intravascular obstruction. Knowing the mechanism of SVC syndrome allows the physician to choose appropriate treatment. The valuable role of TEE in demonstrating the mechanism of SVC syndrome has been reported by Ayala et al. 13 A randomized trial by Mugge et al. concluded that TEE was superior to TTE for diagnosing right heart and SVC lesions such as thrombi, vegetations, and tumors. 14 and that TEE was the only reliable noninvasive method for imaging the SVC to evaluate these lesions. 15 Superior Vena Cava in Old Myocardial Infarction FIG. 5 Transesophageal view of the superior vena cava (SVC) in a patient with an infected thrombus (arrow) in the lower end of the SVC, complicating an indwelling catheter. The latter had been removed shortly before this echocardiogram. RA = right atrium. The two frames shown are in slightly different imaging planes. The clinical significance of flow velocity of the SVC in old myocardial infarction (MI) with severe left ventricular dysfunction was evaluated by Iuchi et al. using pulsed Doppler echocardiography. Tricuspid flow velocity revealed impaired diastolic filling of the right ventricle, which might be one of the causes of the abnormal response of SVC flow velocity during normal spontaneous respiration in patients with old MI. 16 Acknowledgment The authors are indebted to the Veterans Affairs Hospital, Memphis, Tenn., for imaging data, and to the Medical Media department for the illustrations. References 1. Shala MB, D Cruz IA, Johns C, Kaiser J, Clark R: Echocardiography of the inferior vena cava, superior vena cava, and coronary sinus in right heart failure. Echocardiography 1998;15: Reynolds T, Appleton CP: Doppler flow velocity patterns of the superior vena cava, inferior vena cava, hepatic vein, coronary sinus, and atrial septal defect: A guide for the echocardiographer. J Am Soc Echocardiogr 1991;4: Gindea AJ, Slater J, Kronzon I: Doppler echocardiography flow velocity measurements in the superior vena cava during the Valsalva maneuver in normal subjects. Am J Cardiol 1990;65: Byrd BF III, Linden RW: Superior vena cava Doppler flow velocity patterns in pericardial disease. Am J Cardiol 1990;65: Biffi M, Boriani G, Frabetti L, Bronzetti G, Branzi A: Left superior vena cava persistence in patients undergoing pacemaker or cardioverter defibrillator implantation. Chest 2001;120:

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