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Ann Thorac Surg 1996;62:456-461
© 1996 The Society of Thoracic Surgeons
Division of Cardiac Surgery, Department of Surgery, Deborah Heart and Lung Center, Browns Mills, New Jersey; and Division of Cardiovascular Surgery, Department of Surgery, and Division of Cardiology, Department of Pediatrics, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
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Abstract |
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Methods.All patients presenting in infancy with single-ventricle physiology were managed by early hemi-Fontan operation in anticipation of a subsequent completion Fontan operation. Between May 1989 and August 1995, 400 patients less than 2 years of age underwent hemi-Fontan operations. Mean age at operation was 8.5 months (range, 2 months to 24 months). The hemi-Fontan operation included association of superior vena(e) cava(e) with the branch pulmonary arteries, augmentation of the central pulmonary arteries, occlusion of the inflow of the superior vena cava into the right atrium, and elimination of other sources of pulmonary blood flow.
Results.Operative mortality (<30 days) was 31 of 400 patients (7.8%). For the last 200 patients, operative mortality was 8 of 200 (4.0%). Younger age at operation was not an independent risk factor for operative mortality. Urgent operation in the presence of a hemodynamic burden requiring concomitant procedures was associated with increased mortality.
Conclusions.The hemi-Fontan operation can be accomplished with low operative mortality in young patients, achieving early reduction of the volume work of the single-ventricle heart.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Contemporary management of patients with hearts with a functional single ventricle involves eventual performance of some modification of the Fontan operation. The goals of the Fontan operation include reduction to normal of the volume work of the single ventricle, and achievement of normal or near-normal systemic arterial oxygen saturation. Before the Fontan operation is accomplished, the unoperated or palliated state is characterized by a single ventricular pump that simultaneously ejects blood into both the pulmonary and systemic circulations, and thus of necessity does volume work in excess of normal. The adaptive response to this abnormal volume load includes increases in both cavity volume and myocardial muscle mass. As is true in relation to volume overload of the systemic ventricle in the normal or four-chambered heart, the duration of the hemodynamic burden and the magnitude of the adaptive changes in the properties of the myocardium itself both have an impact on the outcome of a surgical procedure that removes the volume load [1]. Thus in the case of single-ventricle hearts, older age and increased ventricular mass have both been identified as risk factors for mortality in association with the Fontan operation [2]. Above and beyond the objective of minimizing operative mortality, preservation of ventricular function to optimize functional capacity and longevity of survival after the Fontan operation must be the goals of any protocol for the management of patients with single-ventricle hearts.
Although reduction of the volume work of the single ventricle is a principal objective of the Fontan operation, it must be recognized that after removal of a chronic volume load, regression of myocardial mass proceeds slowly relative to diminution in cavity size [3]. The persistence of increased muscle mass in the setting of acutely diminished ventricular volume results in increased ventricular wall thickness and decreased cavity dimensions [4]. This abrupt change in the mass-to-volume relationship of the ventricle may result in significant alterations in both systolic and diastolic function of the ventricle. The recognition that a strikingly high wall thickness-to-cavity volume ratio is a frequent echocardiographic finding in patients exhibiting a low cardiac output state early after Fontan operation [5], and a frequent pathologic finding in postmortem specimens of nonsurvivors, has led to an appreciation of the impact of acute alterations in ventricular geometry on the outcome of Fontan operations.
We hypothesized that dividing the Fontan operation into two procedures could accomplish earlier reduction of the volume work of the single ventricle, and might minimize the impact of changes in ventricular geometry on outcome and survival. Thus the hemi-Fontan operation [6, 7] was conceived as a first step in a two-stage process of achieving total caval pulmonary connection. Obligating superior vena caval return to pass through the lungs before returning to the functional single ventricle, the hemi-Fontan operation is physiologically similar to the bidirectional Glenn anastomosis [8]. Because it is performed as an intermediate step before an anticipated completion Fontan procedure, it differs technically from the bidirectional Glenn anastomosis in ways that simplify the eventual completion Fontan operation or total caval pulmonary connection [9]. In addition, other sources of pulmonary blood flow including systemic-to-pulmonary shunts and antegrade flow to the pulmonary arteries are eliminated. This study was undertaken to review our initial experience with the hemi-Fontan operation as part of a strategy of early reduction of the volume work of the single ventricle and a two-staged approach to the Fontan operation.
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) including hypoplastic left heart syndrome (266 patients, 66.5%), tricuspid atresia (29 patients, 7.3%), single left ventricle (25 patients, 6.3%), complex double-outlet right ventricle (19 patients, 4.8%), atrial isomerism-heterotaxia syndrome (19 patients, 4.8%), pulmonary atresia with intact ventricular septum (10 patients, 2.5%), and other (32 patients, 8.0%). All patients were then further classified as to the morphology of the single or dominant ventricle: right ventricular or left ventricular dominance. In each instance, the hemi-Fontan operation was classified as either elective or urgent. Urgent procedures were those undertaken during an unscheduled hospital admission necessitated by deteriorating clinical status, eg, severe hypoxemia or ventricular failure. Age at operation ranged from 2 months to 24 months (Fig 2), with a mean age of 8.5 months, and with 227 patients (57%) having had operation at 5, 6, or 7 months of age. Follow-up (with respect to early and late deaths) was complete to October 1995. Thus follow-up ranged from 1 to 76 months, with a mean follow-up of 33 months.
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The hemi-Fontan procedure was performed as previously described by us [6]. An incision was made in the most superior portion of the right atrium and carried superiorly onto the medial aspect of the right superior vena cava. The confluence of the right and left branch pulmonary arteries was opened anteriorly from a point just medial to the upper lobe branch on each side. In the absence of naturally occurring or surgically created pulmonary atresia, the main pulmonary artery was transected and oversewn proximally at the level of the pulmonary valve. The right superior vena cava was anastomosed in side-to-side fashion to the right pulmonary artery. If a left superior vena cava was also present, it too was opened along its medial aspect, occluded at its cardiac end, and anastomosed in side-to-side fashion to the ipsilateral branch pulmonary artery. A single patch of cryopreserved pulmonary artery homograft was used to augment the branch pulmonary arteries anteriorly, to create a roof over the anastomoses of the vena(e) cava(e) to the ipsilateral branch pulmonary arteries, and to occlude the inflow of the right superior vena cava into the right atrium (the junction of the right superior vena cava with the right atrium having been enlarged to equal or exceed the caliber of the inferior vena cava). Resumption of bypass and removal of the cross clamp were followed by rewarming to 37°C and termination of bypass.
Sixty-one concomitant procedures were performed in 59 patients, including atrial septectomy (17 patients), relief of aortic arch obstruction (13 patients), proximal main pulmonary artery-to-ascending aortic anastomosis (6 patients), repair or revision of previous repair of anomalous pulmonary venous connection (6 patients), atrioventricular valvuloplasty (6 patients), and other procedures (13 patients).
Statistical Analysis
Early mortality was defined as death within 30 days of hemi-Fontan procedure including death after hospital discharge. Univariate analysis of the relationships of individual preoperative variables to early death after hemi-Fontan operation was performed with Fisher's exact test. This is inclusive of age as a dichotomous variable. The influence of age as a continuous variable was evaluated by Wilcoxon rank sum test. Age at operation and dichotomous variables including ventricular dominance, hypoplastic left heart syndrome (versus other diagnosis), concomitant procedures, and urgent operation were entered in a stepwise logistic regression to identify independent risk factors for mortality. A p value less than 0.05 was considered significant. Kaplan-Meier estimates were computed to show the actuarial survival rate.
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) was significantly lower in the second half of the series (patients 201 to 400, eight early deaths, mortality 4%; p < 0.01) and there was one early death in the last 100 consecutive patients.
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0.001), and urgent operation (p 0.0001) were predictors of early mortality. Hypoplastic left heart syndrome (versus other diagnosis) and ventricular dominance were not significantly related to early mortality. In the multivariate logistic regression analysis, only concomitant procedures and urgent operation were significantly related to early mortality. Age at operation was not an independent predictor of early mortality. The relationship of the age at operation to mortality was further investigated as follows: patients who had undergone urgent operation (n = 14) were deleted from the analysis, leaving 386 patients who underwent elective hemi-Fontan operations. Those who underwent hemi-Fontan operation at age less than 6 months (85 patients; mortality, 8.2%) were compared with those who underwent hemi-Fontan operation at age 6 months or greater (301 patients; mortality, 5.7%). Mortality was not significantly different (p = 0.44). Similarly, those who underwent hemi-Fontan operation at age less than 5 months (27 patients; mortality, 11.1%) were compared with those who underwent hemi-Fontan operation at age 5 months or greater (359 patients; mortality, 5.9%). Mortality was not significantly different (p = 0.23). Also of note is the lower mean age of patients in the second half of the series: patients 201 to 400 had a mean age of 7.5 months versus patients 1 to 200, who had a mean age of 9.5 months. This is noteworthy in relation to the significantly lower mortality rate in the second half of the series, despite equal prevalence of concomitant procedures and urgent operations in the first and second halves of the series. Although elective hemi-Fontan operation at age less than 5 months was not associated with increased mortality compared with that of patients aged 5 months or older, it was the case that urgent operation with one or more concomitant procedures at age less than 5 months was associated with a prohibitively high mortality (5 of 6 patients, mortality-83%). By way of contrast, 4 patients with no prior palliative procedures underwent hemi-Fontan operation electively at age less than 3 months with no early or late mortality.
Survivors of the hemi-Fontan operation were subjected to hemodynamic evaluation by cardiac catheterization 6 to 18 months after hemi-Fontan operation. Only 8 patients were thought to have hemodynamics unsuitable for eventual completion of the Fontan operation. Of these, 4 were listed for heart transplantation, with 3 patients undergoing four heart transplant operations with 2 long-term survivors. One patient died after tricuspid valvuloplasty 20 months after hemi-Fontan operation. One patient with elevated pulmonary vascular resistance died in an automobile accident. Two patients with chronic pulmonary insufficiency remain stable though dependent on mechanical ventilation 2 and 3 years after hemi-Fontan operation.
Analysis of actuarial survival rate, shown in the Kaplan-Meier plot (Fig 4), considers all early and late postoperative deaths inclusive of early and late mortality associated with subsequent completion Fontan procedures.
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Comment |
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That early reduction of volume overload reduces mortality associated with the unoperated or palliated condition is difficult to prove short of a randomized study, which would be difficult to justify on ethical grounds. Franklin and associates [10] reviewed the survival without definitive repair in 191 patients presenting with double-inlet ventricle before 1 year of age. Although the true natural history without intervention could not be determined because of study design, actuarial survival was 57% at 1 year and 43% at 5 years. Certainly experience with hypoplastic left heart syndrome at this institution and elsewhere has led to the recognition of a significant time-related risk of mortality associated with the palliated state [11, 12]. Interposition of the hemi-Fontan operation at about 6 months of age has resulted in an increased percentage of survivors of initial Norwood stage I palliation ultimately reaching physiologic repair by Fontan operation [6].
The altered relationship of ventricular mass-to-volume after an operation that reduces volume work of the systemic ventricle has been described in biventricular hearts after closure of ventricular septal defects [13] and in hearts with functional single ventricles after the Fontan operation [4], and more recently after bidirectional caval pulmonary anastomosis [14] and hemi-Fontan operation [15]. The negative impact of ventricular hypertrophy on survival after Fontan operation has long been recognized, but only more recently has it been understood in relation to the diastolic dysfunction that accompanies abrupt removal of the excessive volume load associated with palliated single-ventricle circulation [16]. Two separate phenomena favor the performance of the hemi-Fontan operation as an interim procedure to reduce the volume work of the ventricle before Fontan operation. One is the observation that although the volume work of the ventricle is reduced from the sum of pulmonary and systemic blood flow to systemic blood flow only after hemi-Fontan operation, just as it is after Fontan operation, the low output state associated with contracted ventricular cavity volume is only rarely observed and considerably less lethal after hemi-Fontan operation than it is after a primary Fontan operation [17]. This is partially explained by the fact that after hemi-Fontan operation only superior vena caval flow traverses the pulmonary vascular bed, impeding ventricular filling to a lesser extent than does the Fontan operation, wherein the complete cardiac output must passively traverse the pulmonary vasculature without the impelling force of a ventricular pump. The second phenomenon is the empiric observation described by Rychik and colleagues [15] that although ventricular geometry is acutely altered after both hemi-Fontan operation and Fontan operation, the degree of change in wall thickness, cavity volume, and wall thickness-to-cavity diameter ratio is of significantly lesser magnitude after the hemi-Fontan operation.
Whether the duration of exposure of the single ventricle to excessive volume work ultimately affects ventricular function late after the Fontan operation is not known. However, the observation of structural myocyte changes in experimental models of ventricular volume overload related to chronic mitral regurgitation [18], together with changes in cardiac collagen and elastin observed in experimental models of volume overload related to arteriovenous shunts [19], suggests that myocardial development is likely to be altered in infants with heart malformations characterized by a functional single ventricle. Concerning the reversibility of changes in morphology and function in relation to the duration of volume overload, observations by Cordell and associates [13] concerning the effects of corrective operation on left heart volume and mass in children with ventricular septal defect are consistent with the hypothesis that normalization of myocardial mass and ventricular function is more likely after removal of the volume load in infancy than in later years.
A potential advantage of a two-staged approach to the Fontan operation is the technical simplification of the eventual completion Fontan procedure. Conversion from hemi-Fontan to total caval pulmonary connection requires only the excision of the patch occluding inflow from the superior vena cava to the right atrium together with construction of a lateral atrial tunnel. Alternatively, interposition of an extracardiac tube graft from the inferior vena cava to the homograft roof over the anastomosis of the right superior vena cava to the pulmonary arteries completes an "extracardiac" Fontan operation. In the latter case, fenestration may be achieved simply by creating a hole in the portion of the homograft patch that occludes the junction of the right atrium with the right superior vena cava [20]. Another advantage of a two-staged approach to the Fontan operation may be the elimination of some risk factors by the hemi-Fontan operation. When the outcome of two-staged Fontan operation in 148 patients (a subset of the present series of 400 patients) was analyzed in relation to preoperative hemodynamic and angiographic characteristics by Apostolopoulou and associates (personal communication), multiple regression analysis identified only elevated ventricular end-diastolic pressure and significant atrioventricular valve regurgitation (before hemi-Fontan operation) as risk factors for mortality before or after completion Fontan operation. Some traditional risk factors, including pulmonary artery distortion, appeared to have been "neutralized" by interposition of the hemi-Fontan operation before the Fontan operation.
Our institutional experience with patients undergoing Fontan operations for heart malformations with single-ventricle physiology has been characterized by steadily declining rates of operative mortality associated with the Fontan operation. Norwood and Jacobs' 1993 report [21] of the Fontan procedure in two stages revealed a decrement in hospital mortality for the Fontan operation from 16% to 8%. Additional technical modifications were associated with a further reduction of the mortality to 4.5% among 112 successive patients who underwent completion Fontan operation [9]. Most recently, 46 patients have undergone completion Fontan operation between July 1994 and October 1995 with one hospital death (2.4%) and one late death (2.4%). Although reduction in the mortality associated with the Fontan operation for functional single ventricles is certainly multifactorial, the use of a two-staged approach and early referral for elective hemi-Fontan procedure (at 5 to 8 months of age) emerge as important elements of a strategy that has been associated with a marked improvement in outcome. Additional long-term follow-up, including hemodynamic assessment and estimation of exercise capacity, will be necessary to further assess the hypothesis that early reduction of the volume work of the single ventricle is an important ingredient of a management strategy based on the Fontan operation.
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Address reprint requests to Dr Jacobs, Department of Surgery, Deborah Heart and Lung Center, 200 Trenton Rd, Browns Mills, NJ 08015.
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