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Cardiovascular Anesthesiology: Echo Rounds

A Chiari Network and Difficult Cannulation of the Coronary Sinus for Retrograde Perfusion

Teo, Elrond Y. MBBS*; Ittleman, Frank MD; Hamlin, Mark P. MD, MS*

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doi: 10.1213/ANE.0b013e3181e05329

In Brief

A 74-year-old woman with critical aortic stenosis and a history of a 3-vessel coronary artery bypass graft was admitted for an elective aortic valve replacement after experiencing shortness of breath on exertion. After induction of general anesthesia, a transesophageal echocardiography (TEE) probe was inserted to assess the intraoperative ventricular function and the competency of the new aortic valve. The TEE examination revealed normal biventricular function and an aortic valve area of 0.8 cm2 (using the continuity equation). In the 30° midesophageal view, a highly mobile, strand-like structure that flapped within the right atrium (RA) during all phases of the cardiac cycle was noticed (Fig. 1) (Video 1, see Supplemental Digital Content 1, https://links.lww.com/AA/A143; see Appendix for Video 1 caption). On further evaluation, this structure was made of multiple strands and extended from the eustachian valve toward the interatrial septum, attaching near the ostium of the coronary sinus (CS), consistent with a Chiari network (CN). This network was reproduced in multiple views (Fig. 2). Color-flow Doppler assessment of the midesophageal bicaval view (Nyquist limit scale decreased to 30 cm/s with the Valsalva maneuver) did not reveal the presence of a patent foramen ovale. Because of the patient's prior revascularization with an intact left internal mammary artery, the surgeon planned to administer retrograde cardioplegia through a cannula inserted into the CS. After identification of the CN, the surgeon was advised that placement of the cannula could be difficult. The patient gave consent for the publication of this case report.

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Figure 1:
The 4-chamber midesophageal view: the probe was rotated to the right to center on the right atrium. The 30° rotation of the multiplane imaging array was required in this case to perpendicularly intercept the fibers of the Chiari network (CN). The network is easily seen to attach to the thebesian valve (*) and looks insignificant. Right atrium (RA), right ventricle (RV), and tricuspid valve (TR) shown with the coronary sinus (CS) entering the view.
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Figure 2:
A modified midesophageal 4-chamber view of the coronary sinus obtained by advancing the probe and retroflexing it. The 2 images depict the Chiari network (CN) and its lasso-like variability during different phases of the cardiac cycle; diastole (a), systole (b). The thebesian valve (*), coronary sinus (CS), and right atrium (RA) are labeled.

As the surgeon attempted to place the CS cannula (DLP® PVC RCSP 94535 Cannula with Auto-Inflate Cuff; Medtronic, Minneapolis, MN), it was observed that the tip of the cannula was near, but not entering, the orifice of the CS. A modified midesophageal 4-chamber view (probe rotated to the right to better visualize the RA and CS) showed fibers of the CN entangling both the balloon (soft, auto-inflating balloon without pilot) and the tip of the cannula, thereby impeding its advancement into the CS (Video 2, see Supplemental Digital Content 2, https://links.lww.com/AA/A144; see Appendix for Video 2 caption). Because the placement of the cannula is frequently guided by palpation, that act itself obscured the view of its placement. The surgeon was shown the findings on the TEE screen and it was suggested that he withdraw the catheter, and then rotate the tip of the cannula to release it from the network of fibers. This maneuver was successful and the cannula was successfully released from the CN. The positioning of the cannula within the CS was confirmed with TEE as well as the classic findings of dark blood return and typical pulsatile CS waveform.

The CN is on a spectrum of congenital malformations arising from the failure of regression of the right valve of the fetal sinus venosus. The valves of the sinus venosus, derivatives, and function are summarized in Table 1. Total persistence of the right valve exists as cor triatriatum dexter. Incomplete regression can result in a variety of different appearances from a muscle bar, a fenestrated membrane, an elongated eustachian valve1 to a network of fibers within the RA. Some networks may be fenestrated versions of the eustachian or thebesian valves.2 The CN is diagnosed by the presence of fibers originating from the eustachian or thebesian valve with attachments to the interatrial septum or crista terminalis.3

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Table 1:
The Valves of the Sinus Venosus, Its Derivatives, and Function

The CN has a prevalence of 2% for all patients requiring a TEE examination.4 In an autopsy study of 213 hearts, 13.6% had a form of a CN and deaths were unrelated to its presence.2 Therefore, on its own, the CN seems clinically insignificant. However, its presence is associated with an increased incidence of a patent foramen ovale (83% with vs 28% without a CN, P < 0.001) and also atrial septal aneurysm (24% with vs 1.6% without a CN, P < 0.001). Other pathologies associated with this network are endocarditis, arrhythmia, and embolic phenomena.4 It has been reported that the network has hindered the placement of right heart catheters and pacemaker wires. Its association with complications and other pathologies warrant a detailed examination of the RA structures.

TEE assessments of the sinus venosus derivatives are best performed by attaining the midesophageal 4-chamber view. Rotating the probe to the right brings the RA into the center of the screen (Fig. 1) (Video 1, see Supplemental Digital Content 1, https://links.lww.com/AA/A143; see Appendix for Video 1 caption). Modifying the midesophageal 4-chamber view by advancing or retroflexing the probe allows the assessment of the CS. Rotating the multiplane array between 80° and 110° brings the bicaval view and allows the assessment of the interatrial septum, cavae, and thebesian and eustachian valves. From this position, rotating the probe slightly to the left toward the midesophageal 2-chamber view allows the assessment of the cannula and balloon as the CS courses through the atrioventricular groove.5

The traditional method of placing a CS cannula is usually successful with a CS injury rate of 0.65%.6 However, when the CN causes an obstruction (as encountered in this patient), TEE offers a valuable resource in assisting the surgeon. In minimally invasive cardiac surgery, a modified bicaval view obtained by rotating the probe to the left from the bicaval view (multiplane imaging array between 80° and 110°) allows the guidance of a percutaneously placed CS cannula through the internal jugular vein. When a modified 4-chamber view is used, the plane along which the surgeon will place the cannula and the CS is better aligned. This requires the surgeon to look at the TEE view screen and remove his or her hand from behind the heart to maintain contact for ultrasound transmission. From there the surgeon will be able to see that the CN fibers are impeding advancement. With this view, the surgeon can be advised to advance or withdraw the cannula and rotate it in and out of the TEE plane to negotiate the fibers of the CN.

This case exemplifies a seemingly insignificant CN obstructing the placement of a CS cannula. Use of TEE in the appropriate plane and communication between anesthesiologist and surgeon should result in atraumatic and precise placement of the cannula within the CS.

REFERENCES

1. Stechert MM, London MJ. Functional separation of the right atrium by an elongated eustachian valve. Anesth Analg 2009;108:443–5
2. Bhatnagar KP, Nettleton GS, Campbell FR, Wagner CE, Kuwabara N, Muresian H. Chiari anomalies in the human right atrium. Clin Anat 2006;19:510–6
3. Werner JA, Cheitlin MD, Gross BW, Speck SM, Ivey TD. Echocardiographic appearance of the Chiari network: differentiation from right-heart pathology. Circulation 1981;63:1104–9
4. Schneider B, Hofmann T, Justen MH, Meinertz T. Chiari's network: normal anatomic variant or risk factor for arterial embolic events? J Am Coll Cardiol 1995;26:203–10
5. Clements F, Wright SJ, de Bruijn N. Coronary sinus catheterization made easy for Port-Access minimally invasive cardiac surgery. J Cardiothorac Vasc Anesth 1998;12:96–101
6. Elwatidy A. Coronary sinus injuries following retrograde cardioplegia. Asian Cardiovasc Thorac Ann 2000;8:118–20
7. Felle P, Bannigan JG. Anatomy of the valve of the coronary sinus (thebesian valve). Clin Anat 1994;7:10–2

Video 1. A modified 4-chamber midesophageal view obtained by rotating the echo probe to the right. The 30° rotation of the multiplane imaging array was required in this case to perpendicularly intercept fibers of the Chiari network (CN). They are seen to extend from the thebesian valve (*) to the wall of the right atrium (RA). CS = coronary sinus; RV = right ventricle; TV = tricuspid valve.

Video 2. A modified 4-chamber view of the coronary sinus (CS) was obtained by advancing the probe and retroflexing it. The retrograde cannula (RC) is seen entangled on the fibers of the Chiari network (CN) and impeding its advancement into the CS. When the cannula is withdrawn slightly, the fibers appear snagged to its tip. The balloon is often not easily visualized because of thin wall and filling with saline/blood cardioplegia, which has similar acoustic properties to blood. RA = right atrium; RV = right ventricle; TV = tricuspid valve. *Thebesian valve.

Teaching Points By Martin M. Stechert, MD, Kent H. Rehfeldt, MD, and Martin J. London, MD
  • A Chiari network is a filamentous, net-like structure in the right atrium extending from the orifice of the inferior vena cava and coronary sinus to the upper wall of the right atrium or the intraatrial septum. Present in nearly 14% of autopsies, it results from incomplete regression of the embryologic sinus venosus and is associated with patent foramen ovale and atrial septal aneurysm. Differential diagnoses include eustachian and thebesian valves, right atrial tumors, thrombi, and vegetations.
  • A Chiari network is recognized by mobile, strand-like fibers arising near the eustachian valve or coronary sinus on transesophageal echocardiographic imaging. A smooth-walled echogenic mass is usually not consistent with a Chiari network and should raise the suspicion for clot or vegetation formation. Rotating the probe rightward from the midesophageal (ME) 4-chamber view (along with advancement or retroflexion) facilitates imaging of a Chiari network; the ME bicaval or modified bicaval (multiplane angle between 80° and 110°) is also useful for imaging the inferior vena cava–right atrial junction and the coronary sinus orifice area. Use of the ME 4-chamber and ME bicaval views is also suggested when examining the interatrial septum for a potential associated patent foramen ovale.
  • In this case, surgical placement of a retrograde cardioplegia catheter into the coronary sinus was hindered when it became entangled in the fibers of a Chiari network. Transesophageal echocardiographic visualization of this facilitated diagnosis, redirection of the catheter, and proper placement.
  • Embryologic remnants of the sinus venosus include Chiari network, crista terminalis, and eustachian and thebesian valves. Although their typical location in the right atrium and characteristic appearance facilitate correct identification, a Chiari network may display significant variability in appearance ranging from a thin strand to a prominent membrane. Echocardiographers should be able to distinguish a Chiari network from pathologic masses and recognize the potential for entrapment of medical devices in it.

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