A 63-year-old woman with Turner syndrome and coronary artery disease was admitted for elective coronary artery bypass grafting. Intraoperative transesophageal echocardiogram (TEE) showed normal left and right ventricular systolic function, mild left ventricle hypertrophy, mild left and severe right atrial dilations, mild tricuspid and aortic insufficiency, mild dilation of the ascending aorta, and a severely enlarged azygos vein (Fig. 1; Supplemental Digital Content 1, Supplemental Video 1, http://links.lww.com/AA/B281). Dilated hepatic veins were noted, draining via a common vein into the right atrium (RA), and the inferior vena cava (IVC) was not visible. A dual-stage venous cannula was used with the tip of the cannula placed in the RA and, using real-time TEE, care was taken to not insert the cannula into the hepatic vein. Additional images were obtained by postoperative transthoracic echocardiogram (Supplemental Digital Content 2, Video 2, http://links.lww.com/AA/B282). The patient was weaned from cardiopulmonary bypass with minimal inotropic support and transferred to the intensive care unit sedated for an uneventful postoperative course. Written consent was obtained from the patient for the authors to publish this report.
Interrupted IVC with azygos continuation (also known as absence of the hepatic segment of the IVC with azygos continuation) is an uncommon vascular anomaly characterized by absence of the IVC between the renal veins and the hepatic veins and a connection of the caudal IVC to the azygos vein (Fig. 2), which then enters the thorax through the aortic hiatus and joins the superior vena cava (SVC) above its junction with the RA.1 The azygos vein normally connects the IVC and the SVC. Interruption of the IVC with azygos continuation results in a dilated azygos vein system, as seen in our patient on TEE, because of the increased amount of blood from the lower body, which now flows through the azygos. The observed dilated hepatic veins, as well as the inability to observe the IVC on TEE or transthoracic echocardiogram, are consistent with this explanation. The incidence of interrupted IVC was reported to be 0.6% to 2.9% among patients with congenital heart disease undergoing cardiac catheterization.1 Although usually an asymptomatic anomaly, it does carry an increased risk of thrombosis because of venous stasis1 and can complicate cardiopulmonary bypass venous cannulation. It may require a larger size venous cannula placed in the RA (as opposed to placement in the RA with the tip of the cannula sitting in the IVC) to provide adequate venous return2 or could cause malpositioning of the IVC cannula3 because its tip would be placed into a hepatic vein with ineffective heart draining. This condition would also be very important to recognize before femoral venous cannulation in minimally invasive or other cardiac surgical procedures. Intraoperative identification of this anomaly would also be of interest during esophagectomy, liver transplant, renal procedures, right heart catheterization, or IVC filter placement.4
A major clue to the diagnosis was the dilated hepatic vein. A normal (nondilated) azygos vein can typically be visualized during routine TEE examinations and is easiest to detect traveling alongside the mid-descending thoracic aorta while examining the aorta in short-axis view. Because the enlarged azygos lies parallel to the descending thoracic aorta, it may be mistaken on TEE for aortic pathology (dissection, aneurysm, or contained rupture) or adenopathy5 or possibly even dismissed for a mirror image artifact. Color flow Doppler revealed the vascular nature of the structure and no communication between the aorta and the azygos vein. This was further investigated in the longitudinal plane with pulsed-wave Doppler (Fig. 3), which showed an opposite direction of blood flow in the 2 vessels: a high-velocity arterial pattern in the descending thoracic aorta and a low-velocity venous pattern in the adjacent vessel (Supplemental Digital Content 1, Video 1, http://links.lww.com/AA/B281). This confirmed that the somewhat circular structure flanking the aorta posteriorly on the transverse image (Fig. 1) was indeed a different vessel.5 Mirror image artifact is commonly encountered when imaging the descending aorta and would show duplication of both 2D and color. The differences in color flow, size, shape, and pulsed-wave Doppler patterns clearly distinguished the venous structure from a mirror image artifact. Another major clue was the then observed lack of connection between the hepatic veins and a distal large venous vessel: the retro- and infrahepatic IVC. Because the imaging quality was satisfactory overall, we did not attempt to infuse a bolus of agitated saline to the lower extremity. In the case of an interrupted IVC, a lower extremity infusion would be expected to show the appearance of bubbles entering the RA from the SVC. Given that the total flow into the RA is not increased with an interrupted IVC, because there is no shunt, the observed severe RA dilation could possibly have been because of altered fluid dynamics.
Echocardiography is befitting to diagnose interrupted IVC with azygos dilation. Abnormalities of the IVC and azygos vein were reported in previous Echo Rounds. Kuroda et al.3 discussed an abnormal connection of the IVC to the RA identified by TEE. Kuzumi et al.6 presented an abnormal connection of the azygos vein to the SVC also by TEE. Mihmanli et al.4 were able to detect an interrupted IVC with azygos continuation by abdominal ultrasound. They confirmed their diagnosis by echo that demonstrated agenesis of the IVC and a dilated azygos vein, which was draining into the SVC. As in our patient, the hepatic veins also drained directly into the RA in their patient.
In addition to enabling vigilance to the presence of an IVC abnormality, real-time TEE imaging can guide venous cannula placement particularly by preventing unintentional cannulation of a hepatic vein, a more likely scenario in our case, given that the hepatic veins were enlarged.7 At our institution, the use of TEE is a standard of care during cardiac procedures.
Clinician’s Key Teaching Points
By Kent H. Rehfeldt, MD, Nikolaos J. Skubas, MD, and Martin J. London, MD
- Interrupted inferior vena cava (IVC) is a rare condition characterized by absence of the IVC between the renal and the hepatic veins. IVC continuity is established via the azygos vein, which typically receives blood from the lung, esophagus, diaphragm, and pericardium and flows parallel to the thoracic spine before draining into the superior vena cava (SVC). Rather than emptying into the IVC, the hepatic veins form a confluence, which then drains directly into the right atrium (RA).
- Echocardiographic features consistent with interrupted IVC with azygos vein continuation include the inability to visualize the intrahepatic portion of the IVC by transesophageal echocardiogram (TEE) (usually at a multiplane angle of 60° near the RA in the transgastric view) and the presence of a dilated azygos vein, which can be imaged just anterior to the descending thoracic aorta in a descending thoracic aorta long-axis or short-axis view. Because the IVC ultimately drains into the SVC by way of the azygos vein, an agitated saline injection performed via a lower extremity vein that demonstrates the appearance of contrast bubbles entering the RA from the SVC confirms the diagnosis of interrupted IVC.
- In this case of an adult undergoing coronary artery surgery, the TEE findings were consistent with interrupted IVC with azygos continuation. The dilated azygos vein was distinguished from the aorta by the clear difference in size and shape between the 2 vessels. Color Doppler imaging displayed qualitatively different flow patterns between the 2 structures and pulsed-wave Doppler obtained in a descending aorta long-axis view detected a biphasic arterial flow pattern in the aorta, whereas a venous flow pattern in the opposite direction was identified in the azygos vein. On the basis of these TEE findings, the tip of the 2-stage venous cannula was inserted only into the RA instead of advancing further toward the RA-IVC junction as usual.
- Recognition of interrupted IVC with azygos vein continuation is important because it may impact venous cannulation strategies for cardiopulmonary bypass. For example, in other cases where peripheral cannulation for cardiopulmonary bypass might be desired, a femoral venous cannula would not be able to be advanced to the RA. If interrupted IVC is diagnosed, TEE should be used to guide direct RA cannulation, so that the tip of a dual-stage venous cannula is not inadvertently inserted into a hepatic vein confluence that could result in poor venous drainage. Examination of the IVC and knowledge of this unusual variant may be important for surgical and other procedures involving the upper portion of the IVC.
Name: Enrique J. Pantin, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Enrique J. Pantin approved the final manuscript.
Name: Rotem Naftalovich, MD, MBA.
Contribution: This author helped analyze the data and write the manuscript.
Attestation: Rotem Naftalovich approved the final manuscript.
Name: John Denny, MD.
Contribution: This author helped conduct the study and write the manuscript.
Attestation: John Denny approved the final manuscript.
This manuscript was handled by: Martin London, MD.
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