Donor shortage has significantly limited the use of cardiac transplantation for treating advanced heart failure. Of the 500,000 patients with end-stage heart failure in the United States, 150,000 would potentially be candidates for cardiac transplantation. However, with only 2,000 transplants performed annually in the United States, its therapeutic impact on this disease is minimal.1,2 The landmark Randomized Evaluation of Mechanical Assistance in Treatment of Chronic Heart Failure trial3 initiated a new era in the treatment of heart failure. The HeartMate XVE device provided excellent hemodynamic support and significantly prolonged survival as it increased 2 year survival from 8% in patients receiving medical treatment to 24%. The pulsatile devices, although were significantly restricted by the large-sized pumps, limited the durability, requiring frequent device exchange and increased morbidity, predominantly driveline (DL)/pocket infections and strokes.4
Tremendous progress was made with the rotary-pump continuous-flow (CF) left ventricular assist devices (LVADs), which increased the 2 year survival to 60%.5–7 In addition, the newer-generation devices are more durable, quieter, and smaller and thus permitting more females and children to be appropriate candidates for implantation. Left ventricular (LV) assist devices reached another milestone in 2008 when the US Food and Drug Administration approved their use as a bridge to transplantation (BTT). Left ventricular assist device therapy has now evolved into the standard of treatment for patients with advanced heart failure, refractory to medical treatment, as a BTT or destination therapy (DT), and in some instances, as a bridge to recovery. However, despite these advances, CF LVADs are still associated with significant morbidity. Gastrointestinal bleeding (GIB), right heart failure, DL infections, and strokes remain a common occurrence after LVAD implantation. Many have also raised concerns regarding the loss of pulsatility and its negative effects on vasculature, end-organ function, and hemodynamic compromise with return to pulsatility after cardiac transplantation.8–11 The objective of this study was to review our institution’s 7 year experience with implanting CF LVADs as a BTT and DT and to analyze the lessons we have learned from our experiences, with an aim to improve clinical outcomes, patient selection, and postoperative management. To the best of our knowledge, this study constitutes the largest, single institutional review to evaluate overall outcomes in patients implanted with CF LVADs.
Our health system’s institutional review board approved this retrospective study. We reviewed our institutions’ LVAD dataset and analyzed patients who underwent CF LVAD implantation as a BTT or DT from March 2006 to July 2013. One hundred forty-nine patients were identified and formed the cohort of this study. They received either HeartMate II LVADs (n = 136; Thoratec Corp., Pleasanton, CA) or HeartWare ventricular assist devices (HVADs) (n = 13; HeartWare Inc., Framingham, MA).
Revolutions per minute (rpm) speed were clinically adjusted to optimize flow, peripheral perfusion, organ function, and LV decompression. Our goal was to maintain a flow index (cardiac index [CI]) greater than 2.2 L/min/m2 and a pulsatility index greater than 3.5. Patients underwent periodic echocardiograms to evaluate the degree of LV decompression, aortic ejection, residual mitral regurgitation, position of the interventricular septum, right ventricular (RV) function, and severity of tricuspid regurgitation.
All patients were postoperatively anticoagulated on aspirin 81 mg daily as well as warfarin with a target international normalized ratio (INR) of 2–2.5. Heart failure medications typically included a beta blocker, angiotensin-converting-enzyme (ACE) inhibitor, and diuretics, as well as sildenafil if they had significant residual pulmonary hypertension (HTN). Patients returned to clinic within a week of discharge, then at 2 weeks, and finally on a monthly basis if their postoperative course was uneventful. Routine blood draws were performed weekly and included coagulation profiles, complete blood count, biochemical profile, and lactate dehydrogenase.
Patient demographics and preoperative characteristics included age, sex, race, body surface area (BSA), body mass index, previous sternotomy, preoperative liver function tests, and associated comorbidities, including HTN, diabetes mellitus, chronic renal insufficiency (CRI), dialysis, chronic obstructive pulmonary disease, and peripheral vascular disease (PVD). Chronic renal insufficiency was defined as glomerular filtration rate (GFR) less than 60 ml/min/m2. Hemodynamic and echocardiographic data included pre-LVAD central venous pressure (CVP), pulmonary artery pressure, pulmonary capillary wedge pressure (PCWP), LV ejection fraction, cardiac output, and CI. Operative characteristics included the type of device (HeartMate II or HVAD), implantation for BTT or DT, cardiopulmonary bypass times, and cross clamp (XCl) times. Complications were evaluated in a univariate manner as a potential risk factor for 30 day readmission. Complications included reoperation for bleeding, DL infections, pneumonia, RV failure, respiratory failure, tracheostomy, acute renal failure (ARF), ischemic stroke, hemorrhagic stroke, GIB, severe aortic insufficiency, and pump thrombosis. We defined patients with ARF as those who experienced acute renal injury stage II and greater based on the Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease criteria: GFR decrease greater than 50% or doubling of the creatinine level. Chronic renal insufficiency was defined as GFR less than 60 ml/min/m2. Right ventricular failure was defined as: 1) need for inotropic support for more than 2 weeks, or 2) need for right ventricular assist device (RVAD) support. Respiratory failure was defined as inability to wean from the ventilator for at least 1 week. Gastrointestinal bleeding was defined as overt clinically evident lower or upper GIB that occurs with or without an obvious etiology after upper endoscopy, colonoscopy, or radiologic evaluation.
Patient demographics, operative characteristics, postoperative complications, and hemodynamic data were compared between the BTT and DT groups in a univariate analysis. Continuous variables were reported as mean, standard deviation, minimum, and maximum and were compared using two-sided two-sample t-tests. Alternatively, Wilcoxon rank sum tests were used if normality could not be assumed. Categorical variables were reported as count and percent and were compared using χ2 tests. Alternatively, Fisher’s exact tests were used if expected cell counts were not sufficiently large. Survival at 30 days, 180 days, 360 days, and 2 years was reported for all patients and compared between BTT and DT patients using a log-rank test. A univariate analysis of patient demographics, comorbidities, preoperative hemodynamic measurements, and operative characteristics was performed to identify significant predictors of survival. Using a conservative cutoff (p < 0.2), these variables were placed in a multivariate Cox regression model. Tests were considered significant at p value less than 0.05. All analyses were performed using SAS 9.2 (SAS Institute Inc, San Diego, CA).
Demographic and Operative Characteristics of LVAD Recipients
Mean age of our patient cohort was 53.7 years (range, 17–81), 74% were males and 26% females. The indication for LVAD implantation was BTT in 54.3% (81 of 149) and DT in 45.7%. Patients who received LVAD therapy as a BTT were significantly younger (50.4 vs. 57.6, p < 0.001). More females were implanted for DT rather than BTT (29% vs. 23%, p = 0.463). Additional demographics and comorbidities are summarized in Table 1. Bridge-to-transplantation patients were more likely to have nonischemic dilated cardiomyopathy as the etiology of their heart failure, were more likely to be on mechanical circulatory support (MCS) and inotropic support at the time of LVAD implantation, were less likely to have CRI, and less likely to have undergone previous cardiac surgery. Types of pre-LVAD MCS included intra-arterial balloon pumps (19 of 24, 79.1%), CentriMag devices (Thoratec Corporation, Pleasanton, CA) (4 of 24, 16.7%), and Abiomed support (Abiomed, Danvers, MA) (1 of 24, 4.2%). Hemodynamic data are presented in Table 1.
Survival and Competing Outcomes Analysis
Survival for our LVAD recipients at 30 days, 6 months, 12 months, and 2 years was 93%, 89%, 84%, and 81%, respectively (Figure 1). When comparing BTT to DT, patients survival rates were analogous (p = 0.32). Survival for BTT patients at 30 days, 6 months, 12 months, and 2 years was 95%, 90%, 87%, and 83%, respectively, whereas for the DT group, survival was 97%, 88%, 81%, and 79%, respectively (Figure 2). Table 2 shows the outcomes separately for BTT and DT patients. Of the 81 patients within the BTT group, 40.7% (33 of 81) received a heart transplant. Survival at 2 years for patients who received a heart transplant was 91% (31 of 33) which is superior although not significantly compared with our DT cohort (79%, p = 0.101). A competing outcomes analysis for all BTT patients is demonstrated in Figure 3. Duration of LVAD support was significantly longer in the BTT compared with the DT group (495 vs. 361 days, p = 0.041). Overall, the mean duration of support was 435 days (Table 3).
Causes of Death
Since our first CF LVADs implantation, 32 patients have died. Causes of death included septic shock (9 of 32, 28.1%; range, 5–145 days postoperatively; median, 41 days), stroke (6 of 8, 75% hemorrhagic stroke and 2 of 8, 25% embolic stroke) (8 of 32, 25%; range, 2–522 days postoperatively; median, 26 days), RV failure (5 of 32, 15.6%; range, 2–75 days postoperatively; median, 6 days), multiorgan failure (5 of 32, 15.6%; range, 4–110 days postoperatively; median, 36 days), refractory arrhythmia (2 of 32, 6.2% at 64 and 128 days postimplant), bowel perforation (1 of 32, 3.1% on postoperative day 11), disconnection from power source (1 of 32, 3.1%, at 14 months after implantation), and pump thrombosis (1 of 32, 3.1% at 18 months after implantation). Of the five patients who died from RV failure, four patients required an RVAD and all died within 30 days of LVAD implantation and one patient was on milrinone without RVAD support who died 10 weeks after LVAD implantation. Two deaths were caused by arrhythmias and more specifically from refractory ventricular tachycardia at 64 and 128 days post-LVAD implant. One of these patients did have an International Classification of Diseases (ICD) that failed to terminate the arrhythmia and the other was discharged without an ICD. Both patients did have signs of RV failure and worsened renal function but were not on milrinone infusion.
Postoperative complications are demonstrated in Table 3. Gastrointestinal bleeding was the most common complication (24%), followed by RV failure (18%), stroke (12%), ventilator-dependent respiratory failure (10%), and reoperation for bleeding (10%). Our DL infection rate was 9%. Adverse events were similar when comparing BTT and DT patients (p = not significant (NS)). Device exchange was performed in 4% of our patients (6 of 149), five for pump thrombosis and one for recurrent infections. Our overall pump thrombosis rate was 5.3% (8 of 149), with six (75%) occurring between 2010 and 2012. During the last year of our study period, we did not have any patients with pump thrombosis. The other two incidences occurred between 2006 and 2007. The higher rate of pump thrombosis between 2010 and 2012 is most likely related to less aggressive anticoagulation which is based on earlier reports supporting the lower anticoagulation strategies with HeartMate II. Since 2012, all our patients are postoperatively anticoagulated on aspirin 81 mg daily as well as warfarin with a target INR of 2–2.5.
Length of Intensive Care Unit and Overall Stay, 30 Day Readmissions
The mean length of intensive care unit (ICU) stay was 10.9 days, and the overall duration of hospital stay was 21.7 days. The readmission rate within 30 days of index hospitalization was 25% (Table 3). Cardiac-related causes were the most common etiology of 30 day readmission (47.2%) (recurrent heart failure, chest pain, and arrhythmia) followed by GIB (25%), infections (13.9%) (urinary tract infection (UTI), pneumonia, cellulitis, and DL infections), and stroke (5.6%). There were no differences in duration of hospital and ICU and readmission patterns between the BTT and DT groups (p = NS).
Predictors of Survival
On univariate analysis (Table 4), creatinine, aspartate transaminase (AST), alanine aminotransferase, hemorrhagic stroke, PVD, respiratory failure, tracheostomy, duration of ICU stay, and RV failure were significant predictors of survival. Using a conservative cutoff (p = 0.2), preoperative patient variables and postoperative complications were placed in a multivariate model. Pre-LVAD AST, the occurrence of hemorrhagic stroke, and the need for tracheostomy remained significant predictors of survival in multivariate analysis (Table 5).
Continuous-flow LVADs are now the universally accepted therapy for treating end-stage heart failure for BTT and DT. Our results during the past 6 years certainly supported this. Perioperative mortality in our study was 7%, and survival at 2 years was 81%. Our analysis also highlights the durability and reliability of the newer-generation devices. However, despite these improvements, long-term LVAD support is associated with serious and disabling complications. Certain adverse events, such as RV failure, strokes, GIB, and DL infections, continue to occur at a relatively frequent rate. Fortunately, except for hemorrhagic stroke, none of the other LVAD-related complications were independent predictors of short-term and long-term mortality. Other significant predictors of survival included pre-LVAD liver function tests and the need for postoperative tracheostomy. Liver dysfunction due to end-stage heart failure is related to poor end-organ perfusion leading to ischemic parenchymal changes with hepatocellular necrosis. It is also caused by passive hepatic venous congestion developed in the setting of right heart dysfunction. Poor end-organ perfusion, RV failure, and all sequelae of liver failure are expected to increase post-LVAD mortality. The need for a tracheostomy, as an indicator of critical illness and prolonged ICU care, is an expected predictor of outcomes, not only in LVAD patients but also in all surgical patients. Patients requiring tracheostomy have a significantly higher prevalence of chronic respiratory disease, current smoking status, higher New York Heart Association (NYHA) class, along with a significantly lower preoperative forced expiratory volume (FEV1) which would all higher post-LVAD survival rates. Early readmissions also remain a significant problem (25%), and this issue needs to be addressed, especially considering that 30 day readmissions will no longer be reimbursed by most providers.
The smaller CF devices have made LVAD therapy a viable option for females with a lower BSA, who previously would not have been candidates for long-term MCS due to anatomic body constraints.12 Females have generally been underrepresented in most multicenter randomized controlled trials for MCS, especially in the pulsatile device era.3,4,13 Fortunately, an increasing number of females are now being enrolled in LVAD therapy. In our study, although males constituted the majority of our patient population (109 vs. 38), we have seen in recent years an increase in the number of females receiving LVADs. Despite this, several reports suggest that females exhibit higher mortality and complication rates after LVAD implantation.5,14–18 It appears that females are referred for MCS when they are usually sicker and have worse clinical features.19 Less social support, poor economic status, higher self-refusal rates, and more religious and pessimistic attitudes are potential explanations for why females present for LVAD evaluation at a later stage of their disease.12 The unexpected finding in our study was that both males and females demonstrated similar postoperative survival and incidence of adverse events. Our findings are encouraging and suggest that medical and social awareness needs to be increased in order to encourage female patients to be referred earlier for surgical treatment of advanced heart failure.
Right ventricular failure remains an important complication of LVAD therapy and a significant contributor to postoperative morbidity and mortality. The etiology of RV failure with CF pumps is often multifactorial. The LVAD causes a leftward shift of the interventricular septum as it decompresses the LV. As the septum becomes disabled, contractility of the RV is reduced. At the same time, the RV output needs to equilibrate with the sudden increase in LV output by the LVAD. Finally, lung physiology and its response to acute injury of surgery and shock also play an important role in post-LVAD RV failure, as it increases pulmonary vascular resistance.20–22
In our study, RV failure occurred in 12% (18 of 149) of LVAD recipients, which is similar to the previously published data.5–8 Survival in our RV failure cohort was worse at both 30 days (96% vs. 83%, p = 0.047) and at 2 years (84% vs. 57%, p = 0.033). Patients who developed post-LVAD RV failure usually have pre-existing hemodynamic compromise and end-organ dysfunction, which predispose them to significant morbidity and mortality. Moreover, severe RV failure results in compromised flow to the LVAD and subsequent decreased pump output and peripheral perfusion. These findings reiterate the need for better selection of patients at risk for developing severe RV failure. Although several studies have identified risk factors associated with the need for RVAD support after LVAD implantation, such as abnormal renal function, abnormal liver function, high white blood cell count, increased CVP, increased CVP/PCWP ratio, and decreased RV stroke work index, the underlying mechanisms that lead to RV failure are complex and multifactorial, which makes it often difficult to predict which patient will develop severe RV failure.23–27
Stroke is a devastating adverse event and is one of the leading causes of death after LVAD implantation. The incidences of neurologic complications after LVAD have been reported as high as 25%.5,28,29 The underlying pathophysiology is not well defined although several authors have suggested that changes in microvascular structure that are associated with LVAD therapy, in conjunction with coagulation abnormalities, leads to neurologic events.30,31 The effect of unrecognized underlying HTN has also not been determined. Kato et al.,32 demonstrated, in their retrospective analysis of 307 who underwent HeartMate XVE and HeartMate II implantation, that previous history of stroke and postoperative infection were independent risk factors associated with post-LVAD cerebrovascular accidents. Our overall stroke rate was 12% (18 of 149), which is analogous to that reported in the literature.5–8 Hemorrhagic strokes were more common than ischemic strokes (8% vs. 5%). Certainly, newer-generation devices have lowered the rates of pump thrombosis and subsequent embolic strokes, and it is anticipated that newer LVAD technology will further reduce neurologic complications. In the meantime, reduction in the incidence of stroke can be achieved through strict blood pressure control with maintenance of mean arterial pressure in the 70–80 mm Hg range, close INR monitoring, and early postoperative evaluation for device thrombus formation.
Gastrointestinal bleeding remains one of our most common post-LVAD complications (24%, 35 of 149) and was the second cause of early readmissions after heart failure. Acquired von Willebrand syndrome has been described as a mediator of GIB in patients receiving CF LVAD.33 It has also been suggested that the continuous pulse wave associated with LVAD therapy may cause distention of submucosal venous plexuses, which subsequently leads to arteriovenous malformations and angiodysplasia in the gastrointestinal tract.34,35 These proposed pathophysiologic mechanisms may help identify important future management strategies to potentially reduce this complication. Currently, aside from close INR monitoring, we have no other interventions to prevent GIB in LVAD patients.
Although DL-related infections in CF devices have significantly been reduced when compared with pulsatile flow devices, this complication still remains a significant problem in the CF era with a reported incidence of 20%.36 Our DL infection rate was only 9% (13 of 149), and we have not had a DL infection since November 2011. This may be due to our recently introduced antibiotic and DL dressing protocol. Preoperative antibiotics are given the night before surgery: vancomycin 1,500 mg intravenous (IV) × 1 (or 1,000 mg × 1 if the patient weighs <60 kg), cefipime 2 g IV × 1, rifampin 600 mg IV × 1, and fluconazole 400 mg IV × 1. If allergic to penicillin or cephalosporins, cefipime is substituted with aztreonam 2 g IV × 1. Postoperatively, antibiotics are given as follows: vancomycin 15 mg/kg IV every 12 hours × four doses, cefipime 2 g IV every 12 hours × four doses (changed to aztreonam 600 mg IV every 24 hours × two doses if allergic), rifampin 600 mg IV every 24 hours × two doses, and fluconazole 400 mg IV every 24 hours × two doses. An Acticoat 3 with silver (releases silver during a 3-day period) dressing is applied to the DL in the operating room. The dressing is changed for the first time on postoperative day 3 and every 3 days thereafter, including after the patient is discharged. When the dressing is removed, before another dressing is applied, the DL area is washed with chlorhexidine and sterile water. A new Acticoat 3 and a tegaderm are then applied. We believe this regimen should be considered by other institutions, as we have had overwhelming success in preventing DL and pocket infections.
In the current era of extensive healthcare reform, there has been an increased awareness of cost due to hospital readmissions.37,38 Unfortunately, 30-day LVAD readmissions remain relatively high. The rate of 30-day readmission in our LVAD cohort was 25% and is comparable to that published in recent reports.39,40 Recurrent heart failure was responsible for the majority of readmissions, accounting for approximately one of three of all readmissions within 30 days. This may be due to inadequate diuresis during the index hospitalization or after patients are discharged. It may be possible to decrease the frequency of recurrent heart failure and need for rehospitalization with more aggressive diuresis and drainage of pleural effusions during the index hospitalization. Additionally, having patients return to clinic within the first week after discharge so that their overall volume status can be assessed and optimized may aid in preventing volume overload and decreasing readmission for recurrent heart failure. Some additional broad preventive measures to reduce 30-day LVAD readmissions may include more thorough discharge planning which permits a smoother transition of the new LVAD patient to their home or rehabilitation environment, solidifying patient’s accessibility to medical and ancillary LVAD providers in the outpatient setting and accurate tracking of readmissions by all LVAD centers.
We recognize our study’s limitations. First, the statistical power was limited. Second, our study was not a prospective, randomized trial and is subject to limitations inherent to any retrospective study. Third, our study was a single institution study, and selection bias may have been present. Finally, we did not collect data on patient quality of life and functional status, which are critical therapeutic goals of LVAD support.
In conclusion, our data demonstrate excellent survival with low mortality for both BTT and DT patients on long-term LVAD support. However, for LVAD therapy to become the gold standard for long-term treatment of end-stage heart failure and a plausible alternative to heart transplantation, we need to continue to improve the incidence of frequent postoperative complications, such as GIB, RV failure, strokes, and DL infections. It is possible that we are also moving toward implanting devices in earlier stages of heart failure. Implanting LVADs in less sick patients can only become compelling if the incidence of LVAD-related complications decreases significantly.
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Keywords:Copyright © 2015 by the American Society for Artificial Internal Organs
left ventricular assist device; outcomes; single institutional; heart failure