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Ann Thorac Surg 2003;76:1993-1998
© 2003 The Society of Thoracic Surgeons
a Departments of Cardiovascular Surgery and Anesthesia, University Hospital, Linköping, Sweden
e Institution for Medical Informatics, University Hospital, Linköping, Sweden
b University Hospital, Lund, Sweden
c University Hospital, Gothenburg, Sweden
d University Hospital, Uppsala, Sweden
Accepted for publication June 5, 2003.
* Address reprint requests to Dr Granfeldt, Departments of Cardiovascular Surgery and Anesthesia, University Hospital, S-58185 Linköping, Sweden.
e-mail: hans.granfeldt{at}lio.se
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Abstract |
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METHODS: All Swedish patients on the waiting list for heart transplantation, treated with LVAD since 1993 were retrospectively collected into a database and analyzed in regards to risk factors for mortality and morbidity.
RESULTS: Fifty-nine patients (46 men) with a median age of 49 years (range, 14 to 69 years), Higgins score median of 9 (range, 3 to 15), EuroScore median of 10 (range, 5 to 17) were investigated. Dominating diagnoses were dilated cardiomyopathy in 61% (n = 36) and ischemic cardiomyopathy in 18.6% (n = 11). The patients were supported with LVAD for a median time of 99.5 days (range, 1 to 873 days). Forty-five (76%) patients received transplants, and 3 (5.1%) patients were weaned from the device. Eleven patients (18.6%) died during LVAD treatment. Risk factor analysis for mortality before heart transplantation showed significance for a high total amount of autologous blood transfusions (p < 0.001), days on mechanical ventilation postoperatively (p < 0.001), prolonged postoperative intensive care unit stay (p = 0.007), and high central venous pressure 24 hours postoperatively and at the final measurement (p = 0.03 and 0.01, respectively). Mortality with LVAD treatment was 18.6% (n = 11). High C-reactive protein (p = 0.001), low mean arterial pressure (p = 0.03), and high cardiac index (p = 0.03) preoperatively were risk factors for development of right ventricular failure during LVAD treatment.
CONCLUSIONS: The Swedish experience with LVAD as a bridge to heart transplantation was retrospectively collected into a database. This included data from transplant and nontransplant centers. Figures of mortality and morbidity in the database were comparable to international experience. Specific risk factors were difficult to define retrospectively as a result of different protocols for follow-up among participating centers.
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Introduction |
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This review of the Swedish LVAD bridge-to-transplant experience is a part of the development of a clinical decision support system called Assist Me [4].
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Material and methods |
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The demographics of the patient group are shown in Table 1. The different LVADs used are shown in Table 2. All patient records were reviewed, and a total of 304 variables were categorized into preoperative, intraoperative, and postoperative groups. Mortality was defined as death before HTx. Several complications were recorded as morbidity. This includes the entire postoperative period until the HTx. The variables were postoperative device-related infection, signs of right ventricular (RV) failure, cerebral thromboembolic complications, or any technical malfunction of the device or its components. The definition of an infectious complication was a clinically deep driveline infection, verified pocket infection, or septicemia with positive blood cultures. Right ventricular failure is a clinical diagnosis made with the combination of elevated right heart filling pressures and the need for long-term inotropic medication, verified with echocardiographic findings.
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Hemodynamic measurements were recorded on five different occasions with thermodilution technique using a Swan-Ganz catheter: (1) baseline, when the Swan-Ganz catheter was inserted, or the preoperative invasive catheterization (base); (2) preoperatively, directly before surgery, when patients were anesthetized, with mechanical ventilation and mostly on inotropic medication (preop); (3) postoperatively, in the operating room after LVAD implantation, when patients were circulatory and respiratory stable (postop); (4) 24 hours after surgery (24 hours); and (5) end point, before the Swan-Ganz catheter was removed (end point).
Laboratory blood samples were measured at three times: baseline, 24 hours postoperatively, and just before transplantation (end point). Laboratory variables and blood gas analyses were obtained from the intensive care unit (ICU) charts.
All continuous variables had normal distribution. Statistical analysis was performed with analysis of variance (parametric tests) and discriminant analysis using SPSS software (v 10.1.0; SPSS Inc, Chicago, IL). Descriptive data are expressed as median and range. In the variance analyses mean ± standard deviation are used. For the nonparametric data a 
2 test was used. A p value of less than 0.05 was considered statistically significant. A variable with more than 33% of the values missing was not used in the statistical analyses.
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Results |
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Preoperative results
Higgins score [5], median of 9 (range, 3 to 15) and EuroScore [6] median of 10 (range, 5 to 17) indicate the severity of the disease. Nine (15.2%) of the patients had a mechanical assist device before the LVAD implant. Two patients were supported with the Hemopump, 4 patients with an intraaortic balloon pump counterpulsation, 2 patients with extracorporeal membrane oxygenation, and 1 patient with a biventricular assist device.
Intraoperative results
Intraoperatively the patients had a median cardiopulmonary bypass time of 116 minutes (range, 39 to 261 minutes), with a median aortic cross-clamp time of 44 minutes (range, 0 to 131 minutes). Median amount of bleeding was 1,625 mL (range, 400 to 10,700 mL). Eighteen (30.5%) of the patients had additional surgery; 3 patients underwent coronary artery bypass grafting; 9 patients had aortic valve replacements; 2 patients atrial septal defect repairs; 1 patient had mitral valvuloplasty; 1 patient had a pericardial patch sutured over a preexisting mechanical aortic prosthesis; and 2 had explantation of pacemakers.
Postoperative results
Mortality occurred in 11 patients (18.6%) before transplantation. Four patients were treated with an RV assist device because of RV failure. The patients were mechanically ventilated for a median of 3.5 days (range, 0.5 to 79 days). The treatment with inotropic drugs continued for a median of 4 days (range, 1 to 25 days). The ICU stay was a median of 12 days (range, 1 to 79 days). The patients received a median total amount of 17 U of transfused autologous blood (range, 0 to 127 U), a median of 17.5 U (range, 0 to 145 U) of fresh-frozen plasma, and a median of 3 U (range, 0 to 27 U) of platelets. Reoperation was performed in 33 (55.9%) of the patients; 20 (33.9%) were acute and the majority of these were because of bleeding. Four (6.8%) patients were weaned off the device as a result of recovery. One of them received HTx after 13 days as a result of deteriorating heart failure. No mortality was recorded among these patients in the follow-up.
In 5 patients (8.5%), the LVAD had to be replaced because of mechanical failure: two pneumatic HeartMate (IP) pumps (one driveline breakage and one pump membrane rupture), three vented electrical HeartMate (VE) pumps (one driveline breakage [trauma], one mechanical pump arrest, and one inflow valve incompetence). In total, 5 patients had inflow valve incompetence and valve endocarditis. The inflow valve insufficiency was detected with echocardiography of the left ventricle. Only 1 patient had to change the device because of deteriorating heart failure. The infected patients had vented electrical pumps. The patients were treated with long-term intravenous antibiotics.
The diagnosis was made by means of blood cultures, in which coagulase-negative staphylococci were cultured in the majority of cases. Nine of 59 patients (15.2%) had an infection around the driveline exit site or LVAD pocket. A total of 26 patients (44%) had some kind of infection in the postoperative course (septicemia, pneumonia, device-related). Significant values for any infection postoperatively are shown in Table 3. Intraoperative significant variables were cardiopulmonary bypass and aortic cross-clamp time.
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Posttransplantation follow-up of all patients in January 2003 showed 11 late deaths (24%), after a median of 100 days (range, 0 to 1,092 days).
Seventeen of 38 (45%) of the vented electrical HeartMate pump patients were discharged to home while on pump treatment. The patient treated for 873 days was treated as an ambulatory patient for 441 days before HTx.
Risk factors for mortality
Eleven patients (18.6%) died during LVAD treatment. Significant factors for mortality before transplantation are shown in Table 5. The preoperative Higgins score was not statistically significant in this series. Intraoperatively, excessive bleeding was significant. A large number of units of blood as well as fresh-frozen plasma transfusions were highly significant in the postoperative period. The calculated statistics for the postoperative course concerning hemodynamics and laboratory tests are also depicted in Table 5. The remaining high central venous pressure during the ICU period in nonsurvivors may reflect an overloaded RV and developing or existing RV failure. Prolonged stay in the ICU with mechanical ventilation and intravenous inotropic support indicates the severity of the postoperative period and was statistically significant for mortality. Blood gases are difficult to interpret and thus to draw any conclusions from. Increased levels of serum creatinine and bilirubin showed strong significance in the end measurement point for mortality.
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Comment |
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The mortality and morbidity figures in our series are comparable with other investigations [9, 10]. The RV function in the initial postoperative phase is crucial for the outcome [11]. Right ventricular failure is a common reason for mortality during LVAD treatment [12]. The combination of echocardiographic and invasive hemodynamic measurements provides often-helpful information for the diagnosis [11]. In some published cases of RV failure in combination with LVAD implantation, the use of an RV assist device is the definition [12, 13]. Several patients implanted with an LVAD have a postimplantation transient RV failure that in most cases can be managed with inotropic treatment, prostacyclin, or nitric oxide treatment [2]. The use of an RV assist device, as defined, might be a reason why some RV failures are not recorded in the early stage. Many centers use nitric oxide routinely after LVAD implantation to improve RV function [14, 15]. It is described that the use of RV assist devices has decreased with the introduction of nitric oxide and phosphodiesterase inhibitors [7, 13]. Right ventricular failure is associated with perioperative bleeding and the need for blood transfusions [7, 11], connecting these variables as risk factors for mortality and morbidity. A high cardiac index before surgery as a risk factor for the development of RV failure is difficult to explain. One explanation could be the influence of inotropic support and the care in the ICU preoperatively; those temporarily disguise the fatigue of the RV.
The amount of intraoperative bleeding and the need for autologous blood transfusions are significant risk factors for mortality using LVAD [11]. A large amount of bleeding intraoperatively and postoperatively was the major cause of emergency reoperation and reflects the complexity of the patients undergoing extensive surgery, including disturbed coagulation, activated cascade systems with the use of cardiopulmonary bypass, and the effects of the surfaces in the pump. Postoperative bleeding necessitating reoperation was more common in the early experience of our centers. The learning curve and the increased experience with LVAD implantation probably reduced this with time.
Infectious complications are the long-term limit with today's LVAD systems [16]. As long as there is a percutaneous driveline, ascending infections might arise, and with time there is a risk of valvular endocarditis. Classification of LVAD infection differs among published data [17].
Clinically, there seems to be a complication-free time gap from the third to the sixth month after implantation of the LVAD. In our series, after 6 months most of the serious infections started with ascending driveline infections, pump endocarditis, and inflow valve incompetence. The majority of LVAD patients will have positive cultures on the driveline exit site with time. Fewer patients have more serious infection deep along the driveline or pump pocket. The infection rate in our series was low compared with that of others but corresponds well to the incidence of deep infection [11]. One would expect that a high serum C-reactive protein preoperatively was a risk factor for infection. This series suggests otherwise. The significant high serum C-reactive protein at the end measurement point supports more the clinical picture for risk patients. Interestingly we found that different hospitals have different risks for the development of device infections, probably as a result of different driveline fixating techniques among the hospitals.
The diagnosis of LVAD endocarditis is difficult, and scintigraphic methods have been suggested [17]. Pump endocarditis with valve incompetence in our patients was diagnosed by the combination of signs of recurrent bacteremia despite adequate antibiotic treatment, positive blood cultures for significant pathologic strains, signs of pump dysfunction, and echocardiographic findings [18]. Vilchez and coworkers [19] suggest these patients to have priority for orthoptic HTx because of difficulties in eradicating the bacteria and the high mortality associated with this condition. Prolonged stay in the ICU probably demonstrates that the colonization of bacteria that occurs in the ICU environment is a risk factor for development of infections. Morbidity and mortality is considerable in this group [20]; however, some authors describe no impact of the posttransplantation outcome [21]. None of our patients with valve endocarditis died before HTx.
The definition of thromboembolic events varies in the literature [22]. The 10% rate of transient neurologic events in this series corresponds well to others [2, 11]. The anticoagulation regimen for these patients follows the generally accepted methods. Warfarin was given to Jarvik and Novacor patients, and all the HeartMate patients received antiplatelet therapy and with any other indication, warfarin was used. This regimen with the HeartMate patients is questioned by Pasque and Rogers [22], owing to the rate of thromboembolic events recorded and the problem with the definition of these events. They assume an underestimation of the real number of events. A more aggressive anticoagulation strategy is perhaps wise, but the risk of bleeding complications and patient compliance has to be considered.
Preoperative risk factors for death before HTx were difficult to determine in our study. One explanation is the small number of patients and variables excluded as a result of missing values. Preoperative variables from hemodynamic measurements and blood gases are difficult to interpret as they are discrete coindicators of multiorgan hypoperfusion. A large amount of autologous blood transfusions is known to cause morbidity with respiratory dysfunction and RV failure [11, 13]. The strong significance of serum creatinine and bilirubin at the end point measurement probably mirrors the development of irreversible multiorgan failure, independent of cause, which is responsible for the mortality of these patients.
Using risk stratification systems have become more important as a result of the focus on quality medical care and overall current economic situation. More patients are demanding information about the prognosis and risk for morbidity and mortality. New technology is often associated with increasing costs, and this is one reason for the development of risk stratification systems. Existing risk score systems like Higgins (both preoperative and ICU admission) [5, 23] and EuroScore [6] are based on cardiac surgery. The scores for our LVAD recipients are high, but do not predict mortality or morbidity before HTx. One reason could be that scoring systems are based on a different procedure. The prognosis for those patients who undergo any kind of cardiac surgery, without implanting an LVAD, would have been considered as poor. Oz and colleagues [3] have described a screening scale more adjusted for LVAD recipients and allows stratification of high-risk, medium-risk, and low-risk patients. The outcome of this scale in a larger series is not known, but gives to hand a reasonable amount of variables for preoperative evaluation of potential LVAD recipients.
The first 12 patients from one center were analyzed regarding costs. There were five pneumatic HeartMate pumps and seven vented electrical HeartMate pumps. The cost per day with the LVADs were calculated as SKr 9,418 (US $1,046) and with medical treatment SKr 11,857 per day (US $1,317). Moskowitz and associates [24] discuss costs for long-term LVAD implantation on a yearly basis. The reimbursement system in Sweden is different from the US system in regards to the health care that is provided from the government through taxes.
Retrospective multicenter analyses have several disadvantages. Different centers are using different variables and definitions with the same expression. This produces much missing data that interfere with the statistical analysis. It is difficult to draw any wider conclusions from these figures because of the limited number of patients as well as missing values in this retrospective analysis.
Some of our 304 values could not be found because of the use of different routines of different centers. With the limit of less than 33% of missing values in the input data, the variables were reduced to 110 to minimize this.
The experience with using the LVAD as a bridge to HTx was retrospectively collected from all Swedish transplanting and nontransplanting cardiac surgery facilities. The incidence of mortality and morbidity in this study was comparable with larger centers, even though the number of patients was small in each Swedish center. No specific preoperative risk factors were found. Reasons could be the small number of patients or the large amount of variables investigated, which makes the retrospective interpretation difficult as a result of different definitions of the same variables among the facilities. We are now in the process of implementing a prospective, customized clinical decision support system in an attempt to organize and treat data in a systemic and user-friendly manner.
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