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Article Review
A contemporary comparison of the effect of shunt type in hypoplastic left heart syndrome on the hemodynamics and outcome at stage 2 reconstruction.
Jean A. Ballweg, MD, Troy E. Dominguez, MD, Chitra Ravishankar, MD, Jacqueline Kreutzer, MD, Bradley S. Marino, MD, Geoffrey L. Bird, MD, Peter J. Gruber, MD, PhD, Gil Wernovsky, MD, J. William Gaynor, MD, Susan C. Nicolson, MD, Thomas L. Spray, MD, and Sarah Tabbutt, MD, PhD
J Thorac Cardiovasc Surg 2007;134:297-303
Reviewer:
Denise Joffe, MD
Seattle Children’s Hospital
Background:
The RV to PA shunt is one of several innovative strategies instituted in an attempt to improve the survival of patients having staged procedures for hypoplastic left heart syndrome (HLHS). Theoretical benefits of the RV to PA shunt (RV-PA) over the modified Blalock-Taussig shunt (BTs) include an easier post operative course after stage 1 because of more balanced pulmonary to systemic blood flow, and better long-term myocardial preservation as a result of higher diastolic pressures and myocardial perfusion. This study compared the hemodynamic outcome, perioperative course and survival at stage 2 (and beyond) in patients having either the RV to PA shunt or BTs.
Design:
The study was conducted at the Children’s Hospital of Philadelphia from January 2002 to May 2005. It is a cross-sectional case series comparing patients having RV-PA shunts versus BTs in patients requiring surgery for HLHS or a variant.
All patients having stage 1 surgery for HLHS were included in the study. Overall survival data was compared. In addition, a myriad of data from those who survived stage 1 were compared.
Sources of data included chart reviews with emphasis on the hospital medical record including cardiac and ICU databases, assessments from the referring cardiologist, pre stage 2 and 3 echocardiography reports and catheterization data from the pre stage 2 procedure.
The following information was compared: pre stage 2 catheterization and echocardiographic data, age and degree of illness at stage 2, the caliber and architecture of the pulmonary arteries, and the morbidity and mortality at stage 2. Additional surgical procedures or catheterizations, length of stay, and a very inclusive data base of pertinent physiologic and functional variables were also compared.
Patients with aortic atresia were more likely to have had an RV to PA shunt, whereas a BTs was more often performed in patients with a single left ventricle. Presumably this was done because myocardial perfusion may be more precarious in patients with aortic atresia and they would benefit from the increased myocardial perfusion pressure provided by the RV-PA shunt.
At the discretion of the surgeon, either a bidirectional Glenn shunt or a Hemi-Fontan procedure was performed for stage 2 reconstruction.
Results:
A total of 176 patients underwent stage 1 surgery for HLHS or variants. One hundred and fourteen patients had a BTs placement and 62 patients had an RV-PA shunt. Surgical mortality for the stage 1 procedure was similar between groups; BTs 20/114 (17.5%), RV-PA 10/62 (16%). Of the 146 stage 1 survivors, 124 have undergone stage 2 procedures (BTs 78 and RV-PA conduit 46). There were no differences between groups in the number of interstage deaths.
Significantly more patients in the RV-PA shunt group received home oxygen (29/46 versus 5/81 p=.04), in addition their hemoglobin levels at the time of stage 2 precatheterization were significantly higher (15.8 g/dL vs BTs 14.8 g/dL, p=.01). Patients in the RV-PA group were significantly younger at stage 2 surgery (153 days versus 187 days for the BTs group). Interestingly, despite the younger age in the RV-PA group, there was no difference in weight between groups. There was a significantly greater incidence of surgical or transcatheter shunt interventions in the RV-PA group (surgical RV-PA 13/62, BTs 12/114, p=.06), transcatheter (RV-PA 9/62, BTs 6/114, p=.04).
Echocardiographic data demonstrated significantly worse qualitative moderate-severe ventricular dysfunction in the RV-PA group (31% versus BTs 12%, p=.03). There was no difference in the incidence of moderate-severe tricuspid regurgitation.
Angiographic data pre stage 2 demonstrated significantly higher aortic saturations in the BTs group (77% versus 73%, p<.01), significantly higher diastolic blood pressures in the RV-PA group (48 versus 40, p<.01), and significantly higher coronary perfusion pressure in the RV-PA group (39 versus 31, p<.01). The Qp/Qs was significantly higher in the BTs group compared to the RV-PA group (1.7+/-0.86 versus 1.3+/- 0.69, p=.025). There were no differences in mixed venous oxygen saturations, common atrial pressures or pulmonary artery pressures.
There were significant differences in the pulmonary artery architecture and size between groups. Patients in the RV-PA group had significantly larger left pulmonary arteries (LPA) than right pulmonary arteries (RPA); (LPA 7.04+/-1.8 mm versus RPA 5.99+/-2 mm), and their larger LPA’s were significantly larger than the LPA’s of patients with BTs. There was significantly more moderate or severe RPA stenosis in the RV-PA group (46% versus BTs 23%, p<.01). There was more frequent long segment PA hypoplasia or distortion at the shunt insertion site in the RV-PA group 58% versus BTs 36%).
There was no significant difference in morbidity or mortality after stage 2 between groups.
A total of 58 patients have undergone stage 3 reconstruction, (40 BTs, 18 RV-PA conduit.) Ventricular function, and atrioventricular and neoaortic valve regurgitation tended to be worse in patients with RV-PA conduits but did not reach statistical significance.
One third of the patients in both groups require ancillary services for speech and motor delays or other deficits.
Comment:
The major limitations of Ballweg et al’s study includes its retrospective non-randomized, uncontrolled design, small sample sizes and limited follow-up.
The non-randomized uncontrolled design may limit the significance of findings. Some examples, include, the decision to use RV-PA shunts versus BTs in patients with aortic atresia versus other variants of single ventricle. In addition, shunt size for either procedure was not indicated. This information is very relevant as it may significantly affect saturations and myocardial function. As far as the sample size is concerned, although the institution probably has one of the largest series of these patients, the smaller number of patients in the stage 2 cohort make statistical analysis difficult. Finally, a limited follow-up time can significantly impact the results. This is especially important in the assessment of the effect of shunt type on ventricular function and the long-term effect of shunt type on pulmonary artery abnormalities.
However, despite these limitations some important observations about shunt type in these patients can be made. When RV-PA shunts are used the negative effect of the ventriculotomy on ventricular function may be more critical then benefits from improved coronary perfusion.
Also, placement of the RV-PA shunt may negatively impact the architecture of the pulmonary vascular tree. These abnormalities were thought to contribute to a decrease in pulmonary blood flow but did not result in any short term debilitating effects on the pulmonary vasculature.
Conclusion:
Some of the data from this study concurred with other published reports looking at the difference in outcome with shunt type. Unfortunately, these studies all suffer from the same shortcomings in study design.
Most studies demonstrate that patients with RV-PA shunts present for stage 2 surgery earlier and with lower saturations compared to patients with BTs. The obligatory pulmonary insufficiency in these patients results in less pulmonary blood flow. Also, in contrast to patients with BTs, patients with RV-PA conduits have no diastolic pulmonary blood flow, and they have less forward flow as a result of segments of pulmonary stenosis at the shunt insertion site. All of these factors result in lower saturations in patients with RV-PA shunts.
Some surgeons routinely augment the main PA while inserting the shunt in order to avoid stenosis. The result of these surgical modifications may help address some of these shunt related effects on the PA’s.
RV-PA shunts seem to affect the growth and development of the pulmonary vasculature because of the decrease in pulmonary blood flow. Studies by Malec and Pizarro postulated that the pulsatility provided by the RV-PA shunt was beneficial for PA growth. However, most other studies demonstrate decreased PA growth in these patients. The long term implications of this decrease in PA development are unknown, although in the short-term it provides favorable hemodynamics for subsequent stages of surgical palliation.
Shunt thrombosis or obstruction is problematic in the RV-PA shunt group. This study demonstrated significantly more problems that required surgical or catheter based interventions to address shunt related issues than in the BTs group.
Studies consistently show that coronary perfusion is greater in patients with RV-PA shunts. However, improved coronary perfusion does not necessarily translate into improved ventricular function. The negative effect of the ventriculotomy may be more important than a higher perfusion pressure. “Coronary steal” was postulated to be the critical factor in the demise of many of these patients but that is difficult to demonstrate. Perhaps coronary perfusion is adequate in most cases regardless of shunt selection, or that residual “fixed” anatomical abnormalities as a result of the primary disease or the surgical procedure negates the effect of better coronary perfusion pressure provided by the RV-PA conduit.
The RV-PA conduit did not provide a salutatory effect on ventricular function on the basis of its ability to unload the ventricle. Perhaps the increased volume load from pulmonary insufficiency offsets the decrease in volume load as a result of a decrease in Qp/Qs. To confound the factor even more, the degree of pulmonary insufficiency seems to decrease with time and so the volume load on the ventricle is probably quite variable over time.
Although this study did not demonstrate any advantage of one shunt type over the other with respect to ICU care or mortality, some studies suggest an easier, less labile postoperative course and improved mortality with the use of RV-PA shunts. Sano’s improved survival data is impressive, although the mortality in their historical controls using BTs was significantly more than most other centers.
These results support the concern expressed in many centers about the need to examine the results of randomized controlled studies comparing the two shunt strategies since many surgeons have already adopted the RV-PA conduit in lieu of the BTs.
References:
1. Sano S, Ishino K, Kawada M, Arai S, Kasahara S, Asai T, et al. Right
ventricle-pulmonary artery shunt in first-stage palliation of hypoplastic
left heart syndrome. J Thorac Cardiovasc Surg. 2003;126:504-10.
2. Pizarro C, Malec E, Maher KO, Januszewska K, Gidding SS, Murdison
KA, et al. Right ventricle to pulmonary artery conduit improves
outcome after stage I Norwood for hypoplastic left heart syndrome.
Circulation. 2003;108(suppl II):II155-60.
3. Pizarro C, Norwood WI. Right ventricle to pulmonary artery conduit
has a favorable impact on postoperative physiology after stage I
Norwood: preliminary results. Eur J Cardiothorac Surg. 2003;23:
991-5.
4. Malec E, Januszewska K, Kolcz J, Mroczek T. Right ventricle to
pulmonary artery shunt versus modified Blalock Taussig shunt in the
Norwood procedure for hypoplastic left heart syndrome influence on
early and late haemodynamic status. Eur J Cardiothorac Surg. 2003;
23:728-34.
5. Sano S, Ishino K, Kado H, Shiokawa Y, Sakamoto K, Yokota M, et al.
Outcome of right ventricle to pulmonary artery shunt in first stage
palliation of hypoplastic left heart syndrome: a multi-institutional
study. Ann Thorac Surg. 2004;78:1951-8.
6. Bradley SM, Simsic JM, Mcquinn TC, Haviv DM, Shirali GS, Atz
AM. Hemodynamic status after the Norwood procedure: a comparison
of right ventricle to pulmonary artery connection versus modified
Blalock Taussig shunt. Ann Thorac Surg. 2004;78:933-41.
7. Bartram U, Grunenfelder J, Van Praagh R. Causes of death after modified Norwood procedure: A study of 122 postmortem cases. Ann Thorac Surg. 1997;64:1795-1802
8. Mair R, Tulzer G, Sames E, Lechner E, Steiner J, Hofer A, et al. Right ventricular to pulmonary artery conduit instead of modified BlalockTaussig shunt improves postoperative hemodynamics in newborns after the Norwood operation. J Thorac Cardiovasc Surg. 2003;126:1378-84.
9. Maher KO, Pizarro C, Gidding SS, Januszewska K, Malec E, Norwood
WI, et al. Hemodynamic profile after the Norwood procedure with right
ventricle to pulmonary artery conduit. Circulation. 2003;108:782-4.
10. Donnelly JP, Raffel DM, Shulkin BL, et al. Resting coronary flow and coronary flow reserve in human infants after repair or palliation of congenital heart defects as measured by positron emission tomography. J Thorac Cardiovasc Surg. 1998;115:103-110
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