Response to Letters Regarding Article, “Comparison of the Profiles of Postoperative Systemic Hemodynamics and Oxygen Transport in Neonates After the Hybrid or the Norwood Procedure: A Pilot Study”
We appreciate the contribution of Dr Schranz and colleagues to the development of the hybrid procedure for single ventricle palliation and their insightful comments regarding our recent article.1 The hybrid procedure with bilateral pulmonary banding and arterial duct stenting was designed as a minimally invasive alternative to a Norwood procedure. By avoiding cardiopulmonary bypass and the consequent ischemia-reperfusion injury and systemic inflammatory response, we hypothesized that we would find minimally altered systemic hemodynamic and oxygen transport status as compared with the well-documented hemodynamic derangements associated with the Norwood procedure.2
We evaluated the hybrid strategy through analysis of dispassionate and objective data and, to our knowledge, our study represents the only published hemodynamic assessment of this strategy. As noted in our article, the patterns of hemodynamic alterations after hybrid procedures were more complex than might have been anticipated.
Although the data are precise, Dr Schranz and colleagues appear to be concerned that these data may not accurately represent all hybrid procedures. Our intuition (without data) would suggest that this may be so and, consequently, we will endeavor to obtain another dataset in the future to determine whether the early position of this cohort on our learning curve was an important modulator of our hemodynamic measurements. In terms of timing and techniques, our protocol is slightly more similar to the Columbus group than the Giessen group.3,4 There are no data available, however, to substantiate how these differences may influence postoperative hemodynamics and, in comparison to the large impact imposed by cardiopulmonary bypass and circulatory arrest, we would suggest that these differences in hybrid protocols are relatively small.
Like Dr Schranz et al, we also found it interesting that the hybrid procedure group had greater variation in Qp:Qs than did the Norwood procedure group, and we suspect that this is related to the aggressive pharmacological control of systemic vascular resistance, inherent resistance in a relatively long arteriopulmonary shunt, and tight ventilatory control of pulmonary vascular resistance in the Norwood group. In contrast, the Qp:Qs varied more widely in the hybrid procedure group and was quite frequently higher than that in the Norwood procedure patients. We suspect that the absence of cardiopulmonary bypass and cardioplegic arrest allows fluctuations in Qp:Qs to be better tolerated in the early postoperative hybrid patient than in the early postoperative Norwood patient. In a hybrid procedure patient who is brought to the operating room without myocardial dysfunction, these fluctuations in Qp:Qs are likely unimportant. In contrast, the important message here is for the clinician to be aware of this potential problem in patients with preoperatively diminished myocardial reserve.
With regard to the points raised by Dr Phillips, we recognize the contributions of the Columbus group to the development of the hybrid approach for first-stage single ventricle palliation and agree that caution must be exercised when extrapolating the clinical investigational results into clinical practice.1 Dr Phillips is concerned that the addition of a reverse BT shunt to the hybrid stage I procedures5 could add “differential perfusion, unnecessary volume load. and diastolic steal.” The reverse BT shunt provides a secondary source of antegrade flow into the aortic arch for patients in whom the sole source of aortic arch flow is retrograde flow through the aortic isthmus. In these patients, there is potential for obstruction at the level of the isthmus during ductal stent placement, during remodeling of the ductal tissue after cessation of prostaglandin therapy, or due to development of fibrosis through the jailed portion of the aortic isthmus. Because retrograde flow is critical to infants with aortic atresia, obstruction of retrograde flow by any of these mechanisms can be lethal.6 Some groups have cited the potential for this complication in certain anatomic substrates as an appropriate reason to recommend a Norwood reconstruction rather than a hybrid procedure. The reverse BT shunt may be a method to circumvent this issue, and we use it routinely in patients with critically reduced antegrade aortic flow. Further evaluation will be required to determine if this prophylactic procedure has a favorable risk/benefit ratio, and we currently place this shunt under an ethics review board–approved protocol.
The contention that the reverse BT shunt causes “differential perfusion” is unsubstantiated. The shunt provides access between the systemic cardiac output and the aortic arch (as does the aortic isthmus). There is no reason why this should cause differential perfusion; in fact, it may enhance perfusion of the cerebral and coronary circulations in patients in whom the aortic isthmus is stenotic. The contention that the shunt causes a volume load is also unclear. The shunt does not increase (or decrease) pulmonary blood flow. As noted above, the shunt provides a bridge between 2 portions of the systemic circulation. Similarly, it seems unlikely that the shunt would cause diastolic steal, as is simply provides a second flow path for the systemic cardiac output to reach the aortic arch. In patient with aortic atresia and iatrogenic obstruction of the aortic isthmus, the shunt can be expected to augment rather than diminish coronary perfusion.
The hybrid procedure patients had significant variability in Qp:Qs that was greater than the variability observed in the Norwood procedure patients. This variability is depicted in Figure 2 of our article,1 in which Qp:Qs trajectories were plotted for individual patients. The variability of Qp:Qs measurements in individual patients was presumably due to alterations in the pulmonary and systemic vascular resistance, as the tightness of the bands does not change once the bands are placed. It seems doubtful that the bands are excessively loose, as they are placed as described by the Columbus group.
The Columbus group has contributed important work to the concept of the hybrid strategy for palliation of neonates with single-ventricle physiology. Among the achievements of this group is a high rate of early extubation after stage 1 and stage 2 procedures. We are moving toward earlier extubation in this group of patients under a controlled and stepwise process with frequent rigorous assessments of objective physiological data. As our study demonstrates, objective measurements and commonly held clinical beliefs are not always identical.
Li J, Zhang G, Benson L, Holtby H, Cai S, Humpl T, Van Arsdell GS, Redington AN, Caldarone CA. Comparison of the profiles of postoperative systemic hemodynamics and oxygen transport in neonates after the hybrid or the Norwood procedure: a pilot study. Circulation. 2007; 116 (suppl I): I-179–I-187.
Akintuerk H, Michel-Behnke I, Valeske K, Mueller M, Thul J, Bauer J, Hagel KJ, Kreuder J, Vogt P, Schranz D. Stenting of the arterial duct and banding of the pulmonary arteries: basis for combined Norwood stage I and II repair in hypoplastic left heart. Circulation. 2002; 105: 1099–1103.
Bacha EA, Daves S, Hardin J, Abdulla R-I, Anderson J, Kahana M, Koenig P, Mora BN, Gulecyuz M, Starr JP, Alboliras E, Sandhu S, Hijazi ZM. Single-ventricle palliation for high-risk neonates: the emergence of an alternative hybrid stage I strategy. J Thoracic Cardiovasc Surg. 2006; 131: 163–171.