Unexpected Death After Reconstructive Surgery for Hypoplastic Left Heart Syndrome

Transcription

1 Unexpected Death After Reconstructive Surgery for Hypoplastic Left Heart Syndrome William T. Mahle, MD, Thomas L. Spray, MD, J. William Gaynor, MD, and Bernard J. Clark III, MD Divisions of Cardiology and Cardiothoracic Surgery, The Cardiac Center at the Children s Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania Background. Although operative mortality for reconstructive surgery for hypoplastic left heart syndrome continues to improve, nonoperative mortality, especially in the first year of life, remains relatively high. A number of patients who are thought to be clinically well at hospital discharge die unexpectedly. The goal of the present study was to determine the incidence of and risk factors for unexpected death in patients with hypoplastic left heart syndrome. Methods. Retrospectively, we determined the incidence of unexpected death among 536 patients with hypoplastic left heart syndrome who were discharged to home after stage I surgical procedure. To identify potential risk factors, a nested case-control analysis was undertaken. Results. Unexpected death occurred in 22 of 536 patients (4.1%) discharged to home after stage I surgical procedure. The median age at unexpected death was 79 days (range, 25 to 227 days). Seizures preceded cardiac arrest in 2 patients, and ventricular arrhythmias were documented in 3 additional patients during attempted resuscitation. Autopsy studies were performed in 12 patients and identified residual lesions that may have contributed to death in 2 patients. In multivariate analysis documented perioperative arrhythmia and earlier year of stage I surgical procedure were associated with an increased risk for unexpected death (p 0.03 and p 0.04, respectively). There were 4 additional patients who had unexpected death after subsequent cavopulmonary operation at a median age of 1.6 years (range, 0.9 to 3.8 years). Conclusions. Unexpected death occurred in more than 4% of patients with hypoplastic left heart syndrome who were discharged to home after stage I surgical procedure and was most common in the first several months of life. Factors that may contribute to unexpected death include residual lesions, arrhythmias, and neurologic events, although in the majority of cases the cause remains largely unknown. (Ann Thorac Surg 2001;71:61 5) 2001 by The Society of Thoracic Surgeons Accepted for publication July 17, Address reprint requests to Dr Mahle, The Children s Hospital of Philadelphia, 34th & Civic Center Blvd, Philadelphia, PA 19104; mahle@ .chop.edu. The outlook for patients with hypoplastic left heart syndrome (HLHS) has improved dramatically since the introduction of reconstructive surgical procedure in the late 1970s. In recent years several centers have reported hospital survival for stage I surgical procedure of greater than 70% [1 3]. The mortality for subsequent staging operations, such as the hemi-fontan and Fontan procedures, has also decreased significantly in the last decade [4, 5]. Although considerable attention has been paid to the operative mortality, much less is known about the nonoperative mortality in this patient population. Nearly every series on reconstructive surgical procedure for HLHS published to date has reported a nonoperative mortality of greater than 5% among initial hospital survivors [1 3, 6]. A variety of factors have been implicated in these deaths including residual lesions, such as aortic arch obstruction; infectious complications; and ventricular dysfunction. In addition, a significant number of patients, many of whom appear clinically well, die unexpectedly, most commonly in the first months of life. There are many potential risk factors for unexpected death in patients with HLHS, including abnormal coronary flow patterns [7], diminished coronary reserve [8], and a high incidence of neurologic complications after stage I surgical procedure [9]. However, most published series examining reconstructive surgical procedure for HLHS have been limited by relatively small patient populations and lack of long-term follow-up. As such, it has been difficult to determine the significance of unexpected death in the HLHS population. We recently reviewed our 15-year institutional experience with more than 800 patients who have undergone reconstructive surgical procedure for HLHS [10]. Using this database, we sought to determine the incidence of and identify potential risk factors for unexpected death among patients discharged to home after stage I surgical procedure. Material and Methods Patient Population We reviewed the surgical database at our institution to identify all patients who underwent stage I surgical procedure for HLHS between January 1, 1984, and Janu by The Society of Thoracic Surgeons /01/$20.00 Published by Elsevier Science Inc PII S (00)

2 62 MAHLE ET AL Ann Thorac Surg UNEXPECTED DEATH IN HLHS 2001;71:61 5 ary 1, Hypoplastic left heart syndrome was defined as aortic atresia or stenosis, arch hypoplasia, and diminutive left ventricle. Patients with variants of HLHS such as unbalanced atrioventricular canal or double-outlet right ventricle with mitral atresia and arch hypoplasia were also included. Those subjects who underwent stage I reconstruction for lesions with single left ventricle were not included. Patient follow-up was performed between January 1, 1999, and May 1, Patient status was determined by direct patient contact or by communication with the referring cardiologist. The present study was limited to those patients who underwent stage I surgical procedure and survived to hospital discharge. Medical records and autopsy reports were reviewed to determine the circumstances of death for patients who died after hospital discharge. For the purposes of this study, unexpected death was defined as cardiovascular collapse from which the subject did not regain consciousness. Risk Factors To identify potential risk factors for unexpected death, a nested-case-control study was performed. The control group comprised 66 additional randomly selected patients with HLHS (3:1 ratio of controls to cases) who underwent stage I reconstruction and survived to hospital discharge. Patients who had unexpected death after subsequent cavopulmonary surgical procedure were not included in this analysis. Potential risk factors for unexpected death were identified from the medical records. Variables investigated included prenatal diagnosis, degree of preoperative acidosis, anatomic subtype of HLHS, type of aortopulmonary shunt, age at stage I, length of stay after stage I, the occurrence of perioperative seizures or arrhythmias, and the need for supplemental nasogastric feedings at discharge. The latter variable was included because feeding difficulties may be a marker for neurodevelopmental impairment and may put the patient at risk for an aspiration event. Ventricular systolic function was determined by two-dimensional echocardiography in a qualitative fashion (normal or depressed). Atrioventricular valve insufficiency was determined by color Doppler echocardiography, according to accepted classifications. Statistical Analysis Data are expressed as mean standard deviation or median and range, where appropriate. Survival was estimated by the Kaplan-Meier method, defined as the elapsed time from the date of birth to date of death or last known follow-up. Comparison between the two groups was performed with Fischer s exact test or 2 test for categorical variables and Wilcoxon rank-sum test for continuous variables. Multivariate analysis was performed using logistic regression. Analysis was performed with STATA 6.0 (Stata Corporation, College Station, TX). Significance was determined at p value of less than All p values are two-sided and confidence intervals are 95%. Results Patient Characteristics Between January 1, 1984, and January 1, 1999, 840 patients underwent stage I reconstruction for HLHS at our institution. The median age at stage I surgical procedure was 6 days (range, 0 to 216 days). There were 536 patients who survived to hospital discharge. The median interval from stage I surgical procedure to discharge was 14 days (range, 6 to 270 days). Complete follow-up, as of January 1, 1999, was available for 478 (89.2%) of the initial hospital survivors. Of the 58 patients who were lost to follow-up, 41 (71%) were known to be alive as of 6 months of age and 29 (50%) were known to be alive as of 1 year of age. Of the 536 patients who survived to stage I hospital discharge, 22 (4.1%) had unexpected death. The median age at death was 79 days (range, 25 to 227 days). The median interval from hospital discharge to unexpected death was 40 days (range, 1 to 208 days). There were 6 patients discharged to home who had unexpected death within 30 days of stage I surgical procedure. The hazard function for unexpected death is shown in Figure 1. In addition to the 22 unexpected deaths among the 536 initial survivors, there were 63 additional nonoperative deaths, the majority of which occurred in-hospital [10]. Unexpected death, therefore, accounted for just over one quarter of the nonoperative mortality in this series. Autopsy and Clinical Data Autopsy reports including evaluation of the heart and great vessels were available for 12 of 22 patients (54.5%) who had unexpected death. In 2 patients the autopsy demonstrated a residual cardiac lesion that may have accounted for the death. One patient had narrowing of the Blalock-Taussig shunt. A second patient had coarctation of the distal portion of the reconstructed arch to a diameter of 3 mm. Review of this patient s echocardiogram obtained before hospital discharge suggested that the distal arch reconstruction was of adequate caliber; however, complete Doppler interrogation was not performed. Both of the patients with residual lesions identified at autopsy had been evaluated by cardiologist less than 4 weeks before death and were thought to be doing well clinically. In the remaining 10 autopsy investigations, there were no residual cardiac lesions that could be linked to an unexpected death event. Microscopic analysis of the myocardium was available for 10 patients. Three had normal right ventricular histology. Necrosis was detected in 2, ischemia in 3, fibrosis in 4, and calcification in 3 subjects. Microscopic analysis of the left ventricular myocardium revealed endocardial fibroelastosis in 3 patients. There were 5 additional patients in whom the clinical history suggested other factors, which may have contributed to unexpected death. Three patients had documented ventricular arrhythmia at the time of attempted resuscitation. Two of these patients were brought to the emergency department by fire-rescue in ventricular fibrillation and could not be resuscitated. One 6-monthold patient had ventricular tachycardia and subsequent cardiovascular collapse 10 hours after routine hemody-

3 Ann Thorac Surg MAHLE ET AL 2001;71:61 5 UNEXPECTED DEATH IN HLHS 63 multivariate analysis (Table 3) documented perioperative arrhythmias and earlier year of surgical procedure were associated with an increased risk for unexpected death (p 0.03 and p 0.04, respectively). Fig 1. Hazard function for unexpected death (time 0 date of birth) in the first year of life; age in months is shown on the x-axis. namic catheterization. There were 2 additional patients who manifested tonic-clonic movements, which preceded the unexpected death, suggesting that a generalized seizure may have been the inciting event. The unexpected death events occurred at home in 20 patients. One patient died in the primary physician s office. One patient died in-hospital after a cardiac catheterization. The patient characteristics from the initial hospital admission of the 22 subjects with unexpected death and 66 control patients are shown in Tables 1 and 2. Two patients who later had unexpected death were noted to have junctional ectopic tachycardia in the postoperative period. One patient had sustained supraventricular tachycardia before stage I surgical procedure. None of these patients received antiarrhythmic pharmacotherapy other than digoxin at the time of discharge. None of the 22 patients had significant ventricular arrhythmias during the hospital stay. Risk Factor Analysis In univariate analysis none of the patient-related or procedure-related factors was significantly associated with unexpected death (Tables 1 and 2). However, in Table 1. Preoperative Data for Patients With Subsequent Unexpected Death and Control Subjects Variable Unexpected Death (n 22) Control Subjects (n 66) p Value Anatomic subtype 0.57 AA/MA 12 (55%) 26 (39%) AA/MS 3 (14%) 15 (23%) AS/MS 5 (23%) 15 (23%) Other variants 2 (9%) 10 (15%) Preoperative Prenatal diagnosis 3 (13.6%) 15 (22.7%) 0.54 Highest recorded base 7.2 (0 20) a 5.3 (0 32) a 0.84 deficit (mmol/dl) Age at admission (d) 2 (0 69) a 2 (0 84) a 0.94 Unexpected Death After Cavopulmonary Operation Of the 422 patients with HLHS who had subsequent cavopulmonary operation, 4 patients (0.9%) not included in the above analysis had unexpected death after hospital discharge. Two had unexpected death after the hemi-fontan and 2 after the Fontan procedure. Median age at unexpected death for these 4 patients was 1.6 years (range, 0.9 to 3.8 years). Three patients died suddenly at home, one died suddenly while awaiting laboratory studies in the physician s office. None were known to have had prior arrhythmias. One patient had been diagnosed with protein-losing enteropathy. In this series there were 204 patients followed to 5 years of age and 65 patients followed beyond 10 years of age. Comment The greatest risk for mortality for patients with HLHS who undergo staged reconstruction is at the time of the stage I procedure, with most of the deaths occurring within the first 48 postoperative hours [1, 10]. Those patients who are discharged to home after stage I surgical procedure, however, are still at significant risk for mortality within the first year of life. Several single institution and multi-institution studies have reported considerable early attrition among the hospital survivors of stage I surgical procedure for HLHS. Bove and Lloyd [2] reported a 1-month survival of 80% and a 1-year survival of 67% for 158 consecutive patients. During this time operative mortality for the hemi-fontan was less than 3%. Table 2. Procedure-Related Data at Stage I Surgical Procedure for Patients With Subsequent Unexpected Death and Control Subjects Variable Unexpected Death (n 22) Control Subjects (n 66) p Value Age at stage I (d) 6 (1 75) a 6 (1 90) a 0.86 Aortopulmonary shunt 0.64 Central 9 (41%) 19 (29%) Modified Blalock-Taussig 13 (59%) 47 (71%) Interval stage I to 12 (7 56) a 14 (6 104) a 0.31 discharge (d) Perioperative seizure 5 (23%) 8 (12%) 0.29 Perioperative arrhythmia 3 (14%) 3 (5%) 0.16 Depressed ventricular 3 (14%) 4 (6%) 0.36 shortening AV valve insufficiency ( 2 ) 0 6 (9%) 0.33 Feeding difficulties b 2 (9%) 7 (11%) 0.84 Discharge medications Digoxin 22 (100%) 63 (95%) 0.57 Furosemide 22 (100%) 62 (94%) 0.57 a Data are shown as median (range). AA aortic atresia; AS aortic stenosis; MA mitral atresia; MS mitral stenosis. a Data are shown as median (range). feedings at discharge. AV atrioventricular. b Patients receiving nasogastric

4 64 MAHLE ET AL Ann Thorac Surg UNEXPECTED DEATH IN HLHS 2001;71:61 5 Table 3. Multivariate Analysis of Risk Factors for Unexpected Death Risk Factor Odds Ratio (95% CI) p Value Prenatal diagnosis 0.41 ( ) 0.32 Aortic atresia 0.71 ( ) 0.57 Age at admission 0.94 ( ) 0.37 Age at stage I 1.06 ( ) 0.38 Aortopulmonary shunt 2.00 ( ) 0.34 Interval stage I to discharge 1.02 ( ) 0.35 Perioperative seizure 1.07 ( ) 0.94 Perioperative arrhythmia 9.32 ( ) 0.03 Depressed ventricular 4.28 ( ) 0.15 shortening Later year of surgical 0.81 ( ) 0.04 procedure Feeding difficulties 0.86 ( ) 0.86 CI confidence interval. Ishino and colleagues [3] reported 6 late deaths among 82 patients discharged to home after stage I surgical procedure. Although the cause of these interstage deaths is not specified in all of these reports, unexpected death is one of the likely mechanisms [11]. In our analysis of 536 hospital survivors of stage I surgical procedure, unexpected death was relatively common, occurring in more than 4% of patients. This represents a significant cause of mortality in this patient population, and is higher than most other forms of repaired or palliated congenital heart lesions [12, 13]. In lesions such as aortic stenosis, transposition of the great arteries, or tetralogy of Fallot the risk of sudden death appears to either increase with time or stay the same [12, 13]. In HLHS conversely, the risk of unexpected death is greatest within the first several months of life and decreases significantly thereafter. There was an association between earlier year of stage I surgical procedure and an increased risk for unexpected death. This would agree with our report of a significant decrease in hospital mortality for stage I surgical procedure between 1984 and 1999 from 45% to less than 20% [10]. Why the incidence of unexpected death may be less in more recent years remains a matter of speculation. One could hypothesize that many of these unexpected deaths may be related to residual lesions after stage I surgical procedure. The current study includes some of the earliest experience with staged reconstruction for HLHS, during which time many technical modifications were undertaken. There were 2 patients from the earlier surgical experience who had identifiable residual lesions on autopsy. Other factors that may also be associated with a lower risk of unexpected deaths in more recent years include a trend toward shorter periods of circulatory arrest and advances in perfusion techniques. The relationship of arrhythmias to unexpected death in patients with HLHS is poorly understood. In other congenital heart lesions, such as tetralogy of Fallot, ventricular arrhythmia is thought to be one mechanism of sudden death [13]. In this series there was an association between perioperative arrhythmias and unexpected death. Interestingly, 2 patients had junctional ectopic tachycardia, which is generally considered a transient postoperative phenomenon [14]. Further studies will be needed to show a causal relationship between perioperative arrhythmias and unexpected death in this population. It must be recognized that retrospective analysis may underestimate the incidence of arrhythmias. Published data regarding the incidence of arrhythmias in patients with HLHS are limited. Cohen and associates [15] performed ambulatory electrocardiography on 149 patients with single ventricle, 57% of whom had HLHS, at a mean of years after Fontan operation and found atrial flutter in 4.1% and supraventricular tachycardia in 5.0%. The incidence of atrial arrhythmias was no different between the patients with HLHS and those with other forms of single ventricle. The incidence of ventricular tachycardia at late follow-up was 2.7% (MI Cohen, personal communication). Whether the incidence of atrial and ventricular arrhythmias is different in those patients with HLHS less than 1 year of age is not known. One factor that does distinguish patients with HLHS from other forms of single ventricle, and which may account for the increased risk of unexpected death, is myocardial perfusion. In a study of coronary flow reserve using positron emission tomography, Donnelly and colleagues [8] found that infants who had undergone stage I reconstruction had less perfusion and oxygen delivery to the systemic ventricle than infants with other forms of congenital heart disease. The pattern of coronary blood flow also appears to be abnormal in some patients with HLHS. In patients with aortic atresia who have undergone stage I reconstruction, Fogel and colleagues [7] demonstrated that coronary blood flow occurs primarily in systole. This abnormal pattern of coronary blood flow may limit endocardial perfusion. The lack of coronary blood flow during diastole presumably results from runoff into the pulmonary artery through the aortopulmonary shunt. Theoretically patients with aortic atresia, in whom coronary blood flow depends entirely on retrograde perfusion, might be at greater risk for unexpected death than those patients with aortic stenosis. Although previous studies have suggested an association between anatomic subtype and the risk for late death after stage I [16], our study found no association between unexpected death and the presence of aortic atresia. Interestingly, the data from Fogel and coworkers [7] suggest that once patients have undergone a volume-unloading operation, such as the hemi-fontan, coronary blood flow shifts primarily to diastole. If abnormal coronary blood flow is a factor in sudden death, then this might explain the significantly decreased risk of unexpected death after hemi-fontan or Fontan surgical procedure. Adverse neurologic events may also contribute to unexpected death in this population. In our series several patients were noted to have tonic-clonic movements that preceded the arrest. It is known that patients with HLHS are at risk for adverse neurologic sequelae after stage I surgical procedure and that the incidence of perioperative

5 Ann Thorac Surg MAHLE ET AL 2001;71:61 5 UNEXPECTED DEATH IN HLHS 65 seizures in this population can exceed 15% [9]. In this retrospective analysis postoperative seizures were noted in 5 of 22 patients (22.7%) who later had unexpected death. Although it is uncommon for generalized seizures to lead to a cardiac arrest in infants, patients with HLHS, who have shunt-dependent pulmonary blood flow, may be particularly vulnerable to changes in systemic and pulmonary vascular resistances. Alternatively, it is possible that the seizure activity noted in several patients may have been secondary to hemodynamic instability and acidosis. Late unexpected death events in our patient population were very uncommon. There were 2 patients who had sudden death after successful Fontan surgical procedure. In this series there were 204 patients followed to at least 5 years of age and 65 patients followed to at least 10 years of age. No unexpected death events occurred after 4 years of age in our study cohort. Several other large series examining long-term outcome after the Fontan procedure have suggested a small but significant risk of late sudden death thought to be related primarily to atrial arrhythmias. Mair and colleagues [17] reported 3 late sudden death events among 155 patients who had undergone the Fontan procedure. Gelatt and associates [18], however, reported 1 late unexpected death among 236 patients discharged to home after the Fontan procedure. Most reports of long-term follow-up after Fontan have focused on patients who have undergone an atriopulmonary anastomosis. It appears that the risk of unexpected death may be less in patients with a lateral tunnel-type Fontan procedure [18]. In our series more than 95% of patients who underwent Fontan surgical procedure had a lateral tunnel-type Fontan procedure [10]. Limitations The retrospective study design and the lack of autopsy studies for half of the patients may have limited our ability to identify a mechanism of death. In addition, complete follow-up data were not available for approximately 10% of the patients. Lastly, it is important to recognize that several of the unexpected deaths in this series might also be classified as operative deaths because they occurred within 30 days of stage I surgical procedure. These deaths are included in the present study to draw attention to the risk of mortality immediately after hospital discharge and to highlight the difficulty in identifying patients who might be at risk for unexpected death. Conclusion Unexpected death occurs in more than 4% of patients discharged to home after stage I surgical procedure for HLHS. The majority of these events occur within the first 3 months of life. Factors that may contribute to sudden death include residual lesions, arrhythmias, and neurologic events, although in the majority of cases the cause is unknown. Multivariate analysis demonstrated that perioperative arrhythmias and earlier year of stage I surgical procedure were risk factors for unexpected death. Continued investigations into the mechanisms of unexpected death after stage I surgical procedure and potential preventive strategies are warranted. References 1. Kern JH, Hayes CJ, Michler RE, Gersony WM, Quaegebeur JM. Survival and risk factor analysis for the Norwood procedure for hypoplastic left heart syndrome. Am J Cardiol 1997;80: Bove EL, Lloyd TR. Staged reconstruction for hypoplastic left heart syndrome. Ann Surg 1996;3: Ishino K, Stumper O, De Giovanni JJV, et al. The modified Norwood procedure for hypoplastic left heart syndrome: early to intermediate results of 120 patients with particular reference to aortic arch repair. 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