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Ann Thorac Surg 2001;71:54-59
© 2001 The Society of Thoracic Surgeons
a Division of Thoracic Surgery, Department of Surgery, Duke University Medical Center, Durham, North Carolina, USA
Address reprint requests to Dr Forbess, Department of Cardiovascular Surgery, Children’s Hospital, 300 Longwood Ave, Boston, MA 02115
e-mail: forbess{at}cardio.tch.harvard.edu
Presented at the Poster Session of the Thirty-sixth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 31–Feb 2, 2000.
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Abstract |
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Methods. We reviewed 185 consecutive pulmonary position implants performed between September 1985 and January 1999. We examined three age groups: patients less than 1 year of age (n = 53), patients 1 to 10 years of age (n = 46), and patients more than 10 years of age (n = 86).
Results. Five-year Kaplan-Meier homograft survival was 25%, 61%, and 81% for the groups, respectively (p < 0.02). Smaller homograft size, younger patient age, and truncus arteriosus were risk factors for homograft failure in univariate analysis (p < 0.05). Smaller homograft size was the only predictor for homograft failure in multivariate analysis (p < 0.001). Twenty of 99 implants in patients less than 10 years old underwent transcatheter intervention. The 3-year Kaplan-Meier implant survival of this group (79%) was not different from those who did not undergo intervention (77%, p = 0.84). Survival of aortic and pulmonary homografts in patients less than 10 years of age was not different (p = 0.35). Ross procedure implants appear to have optimal survival (94%) at 5 years. Non-Ross implants in patients more than 10 years of age have 76% 5-year Kaplan-Meier survival, which is not different from Ross patients (p = 0.33).
Conclusions. Small homografts have limited durability. Aortic homografts perform as well as pulmonary homografts in young patients. Once patients receive an "adult-size" homograft, at approximately 10 years of age, risk for implant failure approximates that of patients undergoing the Ross procedure. Transcatheter interventions, when indicated, may prolong homograft life.
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Introduction |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Several series have recently reviewed institutional experiences with cryopreserved homografts in the pulmonary position [1–5]. These reports have included relatively low numbers of infants and neonates, where the durability of any nongrowing conduit will be limited [6–8]. The published durability of pulmonary position homografts in these reports may not accurately reflect their longevity in these very young, rapidly growing patients. In addition, some institutional experiences contain relatively greater numbers of patients undergoing the Ross procedure [2]. Patients undergoing the Ross procedure are typically fully grown adults with normal pulmonary arteries, and the homograft is placed in the orthotopic position. All of these factors likely favor increased conduit durabilty in these patients versus those with congenital anomalies of the right ventricular outflow tract.
In an attempt to address these limitations, we have undertaken a retrospective evaluation of the durability of cryopreserved pulmonary position homografts at our institution. The analysis of this consecutive series of implants, spanning approximately 15 years of an entire institutional experience, seeks to identify factors associated with homograft failure.
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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On the basis of hypothesized homograft durability differences, the age of the patient receiving the implant was used to stratify the implant population. Group 1 included patients less than 1 year old, group 2 included patients 1 to 10 years of age, and group 3 was comprised of patients more than 10 years old. Table 1 depicts these three patient age groups with the respective anatomic diagnoses of the implant recipients. Table 1 also shows the number of primary implants and conduit changes by age group and anatomic diagnosis.
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Homograft failure was defined as reoperation for homograft replacement or patient death. Homograft obstruction was the universal indication for replacement. No homografts were replaced for isolated homograft regurgitation. Performance of transcatheter interventions on implants was noted. Late follow-up was obtained between March 1 and June 30, 1999, and is 96% complete.
Statistical analysis was performed using the Statistica software package (Statsoft, Tulsa, OK). Dichotomous variables were compared using the 
2 method or Fischer’s exact test where appropriate. Potential differences between more than two groups were assessed using one-way analysis of variance and the Student-Newman-Keuls test. Homograft survival was determined using the Kaplan-Meier method. Comparisons of these survival data were performed using the log-rank test. Univariate analysis of factors associated with homograft failure was performed using a Cox proportional hazards model. Significant variables were then entered into the multivariate model using stepwise logistical regression. For all tests, a p value of less than 0.05 was considered significant.
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Results |
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Figure 1 depicts the homograft size distributions for the three patient groups. The differences between these populations were significant (p < 0.05). Figure 2A depicts the overall relationship between homograft diameter and recipient patient age. There is a linear increase in homograft diameter up to 10 years of age, at which point the homograft diameter reaches a plateau. Figure 2B shows the similar relationship between homograft diameter and patient weight. Again, there is a relatively rapid increase in homograft diameter up to a body weight of approximately 25 kg. There is a much slower increase in conduit diameter in patients weighing more than this.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Having established that these three patient groups have different homograft survival, one is compelled to explain this difference. A commonly held opinion is that younger patients have decreased homograft durability because they are receiving smaller implants during a period of rapid growth and accumulation of body mass. These data seem to corroborate this proposition. The univariate analysis identified patient age less than 1 year, and lower patient weight as significant risk factors for earlier homograft failure. The statistical strength of smaller homograft size was quite powerful in the multivariate analysis (p < 0.001), and no additional variables achieved significance when entered into the multivariate model.
In addition to patient growth versus homograft size, the pulmonary arterial anatomy and pulmonary vascular resistance could play a significant role in longevity of a pulmonary position homograft. One could speculate that small or distorted pulmonary arteries, or an elevated pulmonary vascular resistance for any reason, could adversely affect the lifespan of a pulmonary position homograft [14]. These concerns bring the issue of anatomic diagnosis to the fore, as it is recognized that certain congenital heart defects, such as truncus arteriosus and tetralogy of Fallot with pulmonary atresia, are much more likely to have pulmonary arterial abnormalities than, for instance, a patient undergoing a Ross procedure for aortic valve dysfunction in the setting of a congenital bicommissural valve. Despite these considerations, in this study, patients identified with diminutive or distorted pulmonary arteries, or elevated pulmonary-to-systemic arterial pressure ratio could not be identified as "at risk" for earlier homograft failure. The presence of truncus arteriosus as a diagnosis was, however, a risk factor for early homograft failure in univariate analysis. The majority of these patients were infants receiving primary implants and children less than 10 years of age undergoing conduit changes. This likely explains the univariate significance of this diagnosis, as truncus arteriosus did not emerge from the multivariate analysis as a statistically significant risk factor for homograft failure.
If the status of the pulmonary arteries has a significant impact on homograft longevity, one would expect patients undergoing the Ross procedure, whose pulmonary artery anatomy and pulmonary vascular resistance are generally normal, to have improved pulmonary position homograft survival. This premise has been borne out in the literature [2, 15, 16]. In the present series, only 2 patients undergoing the Ross procedure have had to undergo pulmonary position homograft replacement. The Kaplan-Meier survival curve for the Ross cohort demonstrates excellent estimated survival but, as shown in Figure 6, there was no statistical difference between this group of implants and the non-Ross implants in group 3. We speculate that this is due to the relatively short follow-up period for many of these implants. We further speculate that continued follow-up of this institutional series of Ross procedure patients will demonstrate pulmonary position homograft survival comparable to that seen in the literature [2, 15, 16]. If so, future comparison between the Ross and non-Ross implants in group 3 could more confidently answer the question whether, in a group of similarly aged patients receiving homografts of similar diameter, the Ross procedure pulmonary implants have increased longevity.
The impact of transcatheter interventions on either the homograft itself or the central pulmonary arteries just distal to the conduit was also evaluated. In all implants in patients less than 10 years of age, we found that the survival of homografts undergoing interventions was not different from those who did not undergo interventions (see Fig 7). Homografts undergoing transcatheter interventions survived a median additional 2.3 years after initial intervention. If one assumes that the majority of these conduits would have been replaced at the time of the first transcatheter procedure in the preinterventional era, it is likely that appropriately indicated transcatheter interventions do prolong homograft survival. This can be particularly beneficial in the growing patient. Adding life to a patient’s homograft in this setting allows the surgeon to place larger conduit in an older, larger patient at the time of conduit change. As we have demonstrated, this will significantly increase the durability of that subsequent pulmonary position homograft.
Previous researchers have found that aortic homografts placed in the pulmonary position have reduced durability compared to homografts of pulmonary origin [1, 2, 5–9]. This earlier failure has typically been attributed to accelerated calcific degeneration in the aortic homograft [1, 13]. Figure 5A shows that the present series appears to confirm that finding. An examination of all homografts in patients less than 10 years of age (Fig 5B) reveals that there is no significant difference in survival between aortic and pulmonary homografts in patients in this age range. We speculate that in this younger age range the patients simply outgrow their conduit before any underlying difference between aortic and pulmonary homograft durability can become apparent. This finding may have clinical implications with regard to size and availability of cryopreserved homografts. Smaller homografts, as in the size ranges used in infants, are available in limited numbers. Some institutions have advocated the use of alternative conduits, or the downsizing of larger homografts, to address this problem [17]. It is our opinion that the use of aortic homografts in the pulmonary position should be encouraged to effectively expand the availability of infant-sized conduits. We even speculate that the aortic conduit, as it has been "designed" for a higher pressure circulation, may offer superior hemodynamic performance in the neonate or infant with relatively higher right ventricular pressure and pulmonary vascular resistance.
In conclusion, the cryopreserved homograft has proven to be a versatile valved conduit for the reconstruction of the right ventricular outflow tract or replacement of the pulmonary valve in patients with a wide range of ages and anatomic diagnoses. Small conduits placed in very young patients have predictably limited durability. Aortic homografts appear to function as well as pulmonary homografts in these individuals. Transcatheter interventions likely prolong the lifespan of homografts in patients less than 10 years of age. We believe that this may offer significant benefit to patients in the immediate preadolescent period. If after a transcatheter intervention the patient can continue to grow, he or she might then be able to receive an adult-sized homograft, which would be expected to last considerably longer than a smaller-sized conduit. Patients undergoing the Ross procedure who are older than 10 years appear to have optimal conduit survival. Continued follow-up of the Ross procedure patients in this group is required to determine this conclusively.
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