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Ann Thorac Surg 2003;75:1624-1626
© 2003 The Society of Thoracic Surgeons

Case report

Timing of transesophageal echocardiography in diagnosing patent foramen ovale in patients supported with left ventricular assist device

Kenneth K Liao, MDa,*, Leslie Miller, MDb, Cynthia Toher, MDb, Sophia Ormaza, RNa, Cynthia S Herrington, MDa, Hartmuth B Bittner, MDa, Soon J Park, MDa

a Divisions of Division of Cardiovascular and Thoracic Surgery, Minneapolis, Minnesota, USA
b Division of and Cardiology, University of Minnesota, Minneapolis, Minnesota, USA

Accepted for publication October 21, 2002.

Keywords 27

* Address reprint requests to Dr Liao, Division of Cardiovascular and Thoracic Surgery, University of Minnesota, Box 207, 420 Delaware St SE, Minneapolis, MN55455, USA (Email: liaox014{at}umn.edu).


   Abstract
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 Abstract
Introduction
 Comment
 References
 
Left ventricular assist devices unload the left ventricle and decrease left atrial pressure. This hemodynamic change may cause a right to left atrial shunt and hypoxemia in patients with patent foramen ovale. We prospectively studied the best time for performing diagnostic transesophageal echocardiography in left ventricular assist device patients. Intraoperative transesophageal echocardiography was performed in 14 patients before cardiopulmonary bypass was initiated and after left ventricular assist device was implanted. No patent foramen ovale was detected when transesophageal echocardiography was done before bypass, but a patent foramen ovale was found in 3 patients when transesophageal echocardiography was performed after left ventricular assist device was activated. Patent foramen ovale was confirmed by inspection in all three patients and surgically closed during the same procedure. There were no patent foramen ovale closure-related complications.


   Introduction
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 Abstract
 Introduction
Comment
 References
 
Left ventricular assist devices (LVADs) unload the left ventricle and decrease left atrial pressure (LAP). Although LVADs may lower right atrial pressure (RAP) to some extent, its main effect is to lower LAP [1]. This hemodynamic change may cause right to left atrial shunt if patent foramen ovale (PFO) exists after LVAD implantation. There have been a few scattered case reports of severe hypoxemia caused by right to left atrial shunt through the PFO after LVAD implantation [2, 3]. The diagnosis and treatment of PFO were often delayed because of the lack of understanding of the above mentioned hemodynamic change. Because the overall incidence of PFO in the general population is about 27% [4], we speculate that PFO in patients supported with LVAD might be underdiagnosed. In this article, we prospectively studied the best timing to establish the diagnosis.

Intraoperative transesophageal echocardiography (TEE) with bubble contrast study to detect PFO was performed in 16 consecutive patients receiving the HeartMate (Thoratec, Pleasanton, CA) VE LVAD between December 2000 and October 2001 at our institution. The surgical technique of LVAD implantation was similar to that described elsewhere [1], except that we routinely used bi-caval venous cannulation in preparation for possible PFO closure. In 14 patients, both pre–bypass and post LVAD TEE were performed. In the remaining 2 patients only post-LVAD TEE was performed and they were excluded from the study.

Our study protocol was as follows: (1) TEE was obtained before cardiopulmonary bypass and after LVAD activation. (2) Two-dimensional echocardiography was performed first with special attention paid to the atrial septum configuration and motion. (3) Then the bubble contrast study was performed. The contrast was created by injecting 10 mL of agitated Dextrose50 solution (Abbott Lab, Chicago, IL) into the right atrium. Appearance of microbubbles in the left atrium within three to four cardiac cycles was considered positive for PFO. (4) If PFO was detected, it was closed.

Intraoperative TEE in the 14 patients who were included in the study showed that the atrial septum was bulging toward the right atrium before cardiopulmonary bypass. However, after LVAD activation, the atrial septum was bulging toward the left atrium (Fig 1A, 1B). The bubble contrast study was negative for PFO when it was performed before bypass in these 14 patients, but it became positive in 3 of the same 14 patients when it was performed after LVAD activation (Fig 2A, 2B). All PFO detected by TEE were confirmed upon surgical exploration (sizes, 4 to 12 mm), and they were closed. The pre–bypass TEE missed all three surgically confirmed PFO. There were no complications related to PFO closure. None of these 14 patients experienced postoperative hypoxemia.


Figure 1
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  		Fig 1. Transesophageal echocardiography four-chamber view. (A) Atrial septum bulges toward the right atrium (RA) before left ventricular assist device insertion. (B) Atrial septum bulges toward the left atrium (LA) after left ventricular assist device activation. The arrow illustrates the direction of the atrial septum shift. (LV = left ventricle; RV = right ventricle.)

 

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  		Fig 2. Transesophageal echocardiography four-chamber view with bubble contrast study. (A) Before left ventricular assist device insertion, bubbles are seen only in the right atrium (RA). (B) After left ventricular assist device activation, bubbles are seen in both the right atrium and the left atrium (LA). Atrial septum is shifted toward the left atrium. (LV = left ventricle; RV = right ventricle.)

 

   Comment
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 Abstract
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 Comment
References
 
The diagnosis of PFO is a dynamic process. It is based on the detection of blood shunting at the atrial level. Most PFO is a probe patent or flap valve competent foramen ovale, allowing blood to flow only from the right to the left atrium [4]. Under normal physiologic conditions, LAP is higher than RAP and there is no right to left shunt. The PFO remains clinically benign. Only under abnormal physiologic conditions when RAP exceeds LAP, the PFO may cause hypoxemia or exacerbate a preexisting hypoxemic condition due to right to left shunt. In congestive heart failure the patient’s LAP is usually much higher than the RAP. PFO stays closed even tighter that routine provocative maneuvers may fail to detect it. This explains why the pre–bypass TEE missed all PFO in this group of patients. After LVAD implantation, LAP is decreased significantly. Right atrial pressure (RAP) may drop secondary to decreased pulmonary vascular resistance and right ventricular afterload, but it still remains much higher than LAP. Nakatani and colleagues [1] demonstrated that after LVAD implantation the patient’s mean LAP was 8 mm Hg, whereas the mean RAP was 17 mm Hg; it is this reversed atrial pressure gradient that causes blood to shunt from right to left atrium through the PFO. Such pressure gradient change before and after LVAD implantation was reflected by the atrial septum shift seen in the two-dimensional echocardiogram (Fig 1A, 1B). Based on our study the diagnosis of PFO in congestive heart failure patients can be made reliably by TEE only after LVAD implantation when the atrial pressure gradient allows blood to shunt from right to left atrium (Fig 2A, 2B). The diagnosis cannot be made by pre–bypass TEE.

The severity of PFO induced hypoxemia is unpredictable. It is determined by the amount of right to left shunt, which can be affected by multiple factors such as the size of PFO, the pressure gradient between left and right atrium, and sometimes the redistribution of shunt flow related to atrial anatomic distortion. In patients with LVAD, the atrial pressure gradient may vary because of different preload conditions (volume status), and the direction of shunt flow may change because of the different gravity effects of the device when the body is at different positions. These may explain the characteristics of intermittent hypoxemia caused by PFO in LVAD patients [2, 3]. It is difficult to estimate the size of PFO or the extent of shunt by TEE. The amount of contrast microbubbles crossing the atrial septum does not necessarily correlate with the size of defect or the magnitude of shunt [3]. Once the PFO is detected, it should be treated as a large defect and closed during initial LVAD implantation.

Twenty-one percent of patients in this study were found to have PFO. With the increased application of LVAD, it is important to identify PFO and repair it during initial LVAD implantation to avoid postoperative hypoxemic complications.

Our study has demonstrated that the diagnosis of PFO by TEE in patients receiving LVAD can be made reliably only when LVAD is activated. Currently we adopt the protocol in our center that bi-caval venous cannulation was used routinely in patients receiving LVAD. Intraoperative TEE contrast study was performed immediately after LVAD was activated. If TEE study is positive for PFO, the heart is placed on total cardiopulmonary bypass and the PFO is closed with the heart being fibrillated. This approach adds minimal extra surgical complexity.


   References
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 Abstract
 Introduction
 Comment
 References
 

  1. Nakatani S, Thomas JD, Savage RM, Vargo RL, Smedira NG, McCarthy PM. Prediction of right ventricular dysfunction after left ventricular assist device implantation Circulation 1996;94(Suppl II):II-216-II-222.
  2. Baldwin RT, Duncan M, Frazier OH, Wilansky. Patent foramen ovale: a cause of hypoxemia in patients on left ventricular support. Ann Thorac Surg 1991;52:865–7.
  3. Nguyen DQ, Das GS, Grubbs BC, Bolman RM, Park SJ. Transcatheter closure of patent foramen ovale for hypoxemia during left ventricular assist device support J Heart Lung Transplant 1999;18:1021-1026.[Medline]
  4. Hagen PT, Scholz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life. an autopsy study of 965 normal hearts. Mayo Clin Proc 1984;59:17-20.[Medline]



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This Article
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