Clinical Outcomes and Quality of Life With an Ambulatory Counterpulsation Pump in Advanced Heart Failure Patients
WHAT IS NEW?
WHAT ARE THE CLINICAL IMPLICATIONS?
Introduction
See related article by Burkoff et al
The number of patients with advanced heart failure (HF) continues to increase and represents a large percentage of health care costs in the United States.1 For end-stage HF, heart transplantation is the gold standard; however, a shortage of donor hearts prevents many patients from receiving this therapy. Continuous-flow left ventricular assist devices (CF-LVAD) are used for short- and long-term therapy for advanced HF patients, including those awaiting heart transplantation.2 However, CF-LVAD often results in serious adverse events such as bleeding, stroke, and infection, limiting their application to a narrower HF population. Although Food and Drug Administration–approved for implantation, the use of CF-LVAD in the subset of patients who are not dependent on inotropes, yet refractory to optimal medical therapy, including cardiac resynchronization, is controversial.3,4 This unmet need creates a need for a less invasive cardiac support therapy that allows patients to return to activities of daily living, while having a low complication profile and low economic burden to the healthcare system.
We recently reported an FIH (first-in-human) experience with the NuPulseCV intravascular ventricular assist system (iVAS),5 which consists of a durable counterpulsation pump placed through the distal subclavian artery (Figure 1). We demonstrated that iVAS provides circulatory support, lowering left ventricular afterload sufficiently to allow ambulation, and management outside of the hospital. Our initial experience found iVAS to be a promising therapeutic tool for the above-described less sick patients, as the implant was minimally invasive, and the device was durable enough for long-term ambulatory support with few complications. Of note, there are no dischargable minimal invasive LVADs that can be placed without access to the heart. In this study, we report the results of a prospective single-arm multicenter feasibility trial (FT) of iVAS therapy in patients potentially eligible for transplantation.
Figure 1. Schema of intravascular ventricular assist system.
Methods
Patient Selection
The data that support the findings of this study are available from the corresponding author upon reasonable request. In this multicenter, nonrandomized, single-arm, Food and Drug Administration–approved FT following the FIH trial, transplant-eligible patients with advanced HF (as determined by each center) prospectively received iVAS implantation as bridge to transplant (listed United Network for Organ Sharing status 1B or 1A) or as bridge to decision between April 2016 and August 2018 at 6 large academic centers with experience in subclavian intraaortic balloon pump (IABP) implantation and management.
An aortic diameter >19.0 mm and a subclavian artery diameter >7.0 mm were required. Key exclusion criteria included aortic dissection, greater than mild aortic valve regurgitation, resting heart rate over 100 beats per minute, and uncontrollable atrial or ventricular arrhythmias (>5% of heartbeats). Other exclusion criteria are provided in Appendix A in the Data Supplement. Informed consent was obtained from all patients, and the study was approved by the Food and Drug Administration and each local Institutional Review Board.
End Points
The primary end point was to assess survival to transplant or stroke-free survival at 30 days. The same outcome was also assessed at 180 days to provide clinical perspective as it relates to other contemporary CF-LVAD trials. Secondary end points included procedural success rate, functional outcomes, the incidence of adverse events (defined in Appendix B in the Data Supplement), and changes in quality of life during iVAS support. All adverse events were adjudicated by an independent clinical events committee. Serious adverse events were defined as resulting in an adverse event associated with death, prolonged inpatient hospitalization, inpatient hospital admission, required intervention (medical or surgical), and persistent or significant disability or incapacity or as otherwise life-threatening. Although neurological dysfunction was not prespecified to be separated into disabling and nondisabling categories in the protocol, we elected to evaluate them this way to allow 30 days to determine whether a stroke was disabling or not. Disabling and nondisabling categories are typically used for defining stroke in this patient population and were determined by patient assessment and modified Rankin Scale score. An modified Rankin Scale score >3 is considered disabling.
Device Technology and Management
The iVAS is an ambulatory, nonobligatory, and external heart assist device (Figure 2). The intravascular element is a 50-mL displacement pump that is located in the descending aorta. The skin interface device (SID) is an implanted electromechanical and pneumatic conduit with a chimney (that protrudes 1–2 cm out of skin) that allows for shuttling of air between the pump and external driver and for capturing the ECG signals that are transmitted to the driver from 3 subcutaneous electrodes. An external and wearable drive unit provides compressed ambient air to inflate and deflate the pump. The iVAS pumps were operated at 1:1, 1:2, or 1:3 modes, and the amount of augmentation was adjusted as clinically appropriate. Anticoagulation with coumadin was targeted at an international normalized ratio between 1.5 and 2.0.
Figure 2. Six-minute walk distance, 2-minute step times, and Kansas City Cardiomyopathy Questionnaire (KCCQ) score before intravascular ventricular assist system (iVAS) implantation and on iVAS support. Variables were presented as mean and SDs, and those among 2 time points were compared by the paired t test. *P<0.05.
Variables Evaluated
Baseline characteristics before iVAS implant and clinical outcomes during iVAS support were collected. At baseline, 2 weeks, and 4 weeks after iVAS implantation, the 6-minute walk test and 2-minute step test were performed. The 2-minute step test was proposed as an effective tool regarding the functional capacity of patients with HF.6 The movements of the test mimic climbing stairs, the most exhaustive form of locomotion for patients with HF. Because of the rigorous nature and the reflection of daily activity, it may constitute a more realistic assessment. Additionally, the test may reveal discrete differences in exercise capacity that may not be noted with other testings. It also provides a safety feature as the patient may perform the test at the bedside making multiple lines, constant monitoring, exacerbation of symptoms more manageable as opposed to walking far from the bedside. At baseline and 4 weeks after iVAS implantation, quality of life was quantified with the Kansas City Cardiomyopathy Questionnaire.
Statistical Analyses
The last patient was enrolled in August 2018, and the database was locked in April 2019. Data are expressed as medians and interquartile ranges or mean and SD as appropriate. Continuous variables were compared using the repeated analyses of variance and post hoc paired t test for paired measurements or unpaired t test for unpaired measurements. All statistical analyses were performed using SPSS Statistics 22 (SPSS Inc, Chicago, IL), and a 2-tailed P<0.05 was considered significant.
Results
Baseline Characteristics
In total, 47 patients were enrolled and 2 did not undergo iVAS implantation due to inadequately sized subclavian arteries on visual examination. Forty-five patients received iVAS implantation at 6 large academic medical centers in the United States. Most of them (35/45) were performed at the pioneering institute. This included 14 patients whose data were previously reported in the FIH trial.5
The median age was 61 (55–66) years old, 82% were men, and 60% of patients were Interagency Registry for Mechanically Assisted Circulatory Support level 3 (Table 1). Thirty patients (67%) were listed as United Network for Organ Sharing status 1 or 2 (using listing criteria before November 2018). Thirty-six patients (80%) were treated with inotropes or IABP before iVAS therapy. Echocardiographic and hemodynamic data before iVAS therapy are shown in Table 2. Six (13%) patients had left ventricular ejection fraction >40% and were implanted due to transplant arteriopathy, intractable angina, diastolic dysfunction, or arrhythmogenic cardiomyopathy.
| N=45 | |
|---|---|
| Age, y | 61 (55–66) |
| Male | 37 (82%) |
| Ischemic cardiomyopathy | 22 (49%) |
| INTERMACS patient profile | |
| Level 2 | 7 (16%) |
| Level 3 | 27 (60%) |
| Level 4–5 | 7 (16%) |
| Others | 2 (4%) |
| Unknown | 2 (4%) |
| United Network for Organ Sharing listing | |
| Status 1a | 10 (22%) |
| Status 1b | 16 (36%) |
| Status 2 | 4 (9%) |
| Unlisted—bridge to decision | 15 (33%) |
| N=45 | |
|---|---|
| Echocardiography | |
| Left ventricular ejection fraction, % | 20.6 (15.5–39.0) |
| Left ventricular ejection fraction >40% | 5 (11%) |
| Left ventricular end-diastolic diameter, cm | 6.7 (5.6–7.3) |
| Hemodynamics | |
| Mean arterial pressure, mm Hg | 86 (75–96) |
| Central venous pressure, mm Hg | 9 (6–12) |
| Mean pulmonary artery pressure, mm Hg | 30 (20–39) |
| Pulmonary capillary wedge pressure, mm Hg | 20 (14–25) |
| Cardiac index, L/(min·m2) | 1.9 (1.7–2.3) |
| Preimplant hemodynamic support | |
| Unknown | 1 (2%) |
| None | 8 (18%) |
| Single inotropes | 21 (47%) |
| Dual inotropes | 3 (7%) |
| Multiple inotropes | 0 (0%) |
| Intraaortic balloon pump alone | 5 (11%) |
| Intraaortic balloon pump and inotropes | 7 (16%) |
Thirty-six patients (80%) received iVAS implantation via the left subclavian artery, whereas 9 (20%) were implanted via the right subclavian artery. Using the 30-day and 6-month cutoff, the median iVAS support duration was 30 (25–30) and 44 (25–87) days, respectively. Twenty-seven patients (64%) were supported for >30 days. Four patients (4%) received iVAS support for over 180 days. Thirty patients (67%) were transplanted after 34 (25–65) days of iVAS support.
Primary End Point—Evaluated at 30 Days
Forty patients (89%) successfully met the primary end point of the FT at 30 days (Table 3). Thirteen patients underwent heart transplantation, and 27 patients remained on iVAS without a stroke. Five patients did not meet the primary end point at 30 days: 1 patient died (following a stroke), 1 patient had a disabling stroke, and 3 patients required escalation of circulatory support. There were 2 disabling strokes within 30 days. One patient developed a new left ventricular thrombus, which embolized on day 29. The other patient developed left-sided numbness without an abnormality on neurological imaging. He received tissue plasminogen activator and subsequently developed an intracranial hemorrhage and died on day 1. There were no disabling strokes after 30 days. In 3 patients, the iVAS was explanted, and alternative mechanical circulatory support was used. One patient had an aneurysmal and tortuous aorta, which caused the pump to fold on itself and rupture. The pump was replaced and the replacement also ruptured. He was transitioned to a CF-LVAD on day 9. Two other patients developed obstruction to airflow in the driveline between the subclavian implant site and the SID. One was transitioned to a CF-LVAD on day 14, and the other was put on extracorporeal membrane oxygenation on day 24 and transplanted. There was only 1 death during 30 days of iVAS support.
| 30 Days | 6 Months | |
|---|---|---|
| Success | 40/45 (88.9%) | 36/45 (80.0%) |
| Failed | 5/45 | 9/45 |
| Death | 0 | 1 |
| Death+CVA (disabling) | 1 | 1 |
| Escalation of support | 3 | 4 |
| CVA (disabling) | 1 | 1 |
| Explantation | 0 | 2 |
| iVAS support duration | 30 (25–30) | 44 (25–87) |
| Transplantation | 13 | 30 |
| Ongoing | 27 | 4 |
| Successful bridge to LVAD | 0 | 2 |
Primary End Point—Evaluated at 180 Days
Stroke-free survival or transplant at 180 days was 80% (Table 3). In addition to the patients mentioned above, 4 additional patients without success included 1 sudden death at home in a patient implanted for intractable angina, 1 patient with atrial fibrillation who needed escalation to a CF-LVAD, and 2 patients with infections of the SID, where the team decided to explant the iVAS. Four additional patients on device beyond 30 days required escalation of support over baseline. Thirteen remained on inotropes and another 28 achieved withdrawal of inotropes.
Secondary End Points
Procedural Success
Two patients had screening imaging failures, and iVAS was not attempted after artery visualization in the operating room. Device implantation was performed in the other 45 patients successfully without perioperative complications. Three patients received a total of 4.5 units of packed red blood cells intraoperatively across the entire study.
Outcomes and Adverse Events Within the First 6 Months of iVAS Support
During 6 months of iVAS support, there were 2 deaths, including the hemorrhagic stroke on day 1 and the sudden death described above. Other serious adverse events are summarized in Table 4. Eight device failures occurred in 7 patients. There were 3 device exchanges for pump rupture: 2 on the same patient due to the aneurysmal aorta described above on days 2 and 7. He had a small nondisabling residual visual field cut. The other patient had a severely calcified aorta and developed a pump rupture on day 26 without any neurological dysfunction. The iVAS was replaced, and he underwent an uneventful transplant 3 weeks later. In all patients, the device functioned as intended and shut down when the leak was detected. Three device failures occurred due to driveline kinking, requiring adjustment of the driveline length. Two device failures occurred due to the failure of proper electrodes or SID implantation, requiring replacement of these components. There were 3 patients with SID-related infections. One patient developed erythema treated with antibiotics. Two patients developed infections for which the heart team decided to explant the iVAS. There were no infections related to other components of the iVAS, including the pump. One patient required surgical correction for stenosis of the iVAS graft site. One patient had distal arm ischemia immediately after implant that was treated medically and resolved. There were no embolic events distal to the iVAS pump. Two patients who refused blood products were implanted for cardiogenic shock, renal failure, and low hemoglobin. They both recovered on iVAS but were not good transplant patients. They were successfully bridged to CF-LVAD after stabilization and rehabilitation.
| Type of Adverse Event | No. of Patients Early Within 30 Days | No. of Events Early Within 30 Days | No. of Patients Late 30–180 Days | No. of Events Late 30–180 Days |
|---|---|---|---|---|
| Cardiac arrhythmias | 3 | 3 | 0 | 0 |
| Heart failure | 1 | 1 | 0 | 0 |
| Hypertension | 1 | 1 | 0 | 0 |
| Major infection (device related) | 1 | 1 | 2 | 3 |
| Neurological dysfunction | 3 | 3 | 0 | 0 |
| Disabling or permanent | 2 | 2 | 0 | 0 |
| Device failure | 5 | 6 | 2 | 2 |
| iVAS balloon rupture | 2 | 3 | 0 | 0 |
| Driveline adjustment; SID issues | 3 | 3 | 2 | 2 |
| Venous thromboembolism | 1 | 1 | 0 | 0 |
| Arterial thromboembolism (graft site) | 1 | 0 | 0 | 0 |
| Limb ischemia treated medically | 1 | 0 | 0 | 0 |
Functional Testing and Quality of Life
Results of paired functional testing and the Kansas City Cardiomyopathy Questionnaire scores are shown in Figure 2. Six-minute walk test distance increased significantly from baseline to week 4 (N=28, 291±112 to 348±124 m; P=0.006; Figure 2A). Two-minute step test did not change significantly from baseline to week 4 (N=23, 55±20 to 64±22 times; P=0.065; Figure 2B). On the Kansas City Cardiomyopathy Questionnaire score (N=33), there were no statistically significant changes in the total symptom score, the overall summary, and the clinical summary score from baseline to week 4 (P=0.055, P=0.10, and P=0.078, respectively; Figure 2C).
Discussion
In this prospective, single-arm, multicenter FT, we assessed the efficacy and safety of the iVAS therapy in 45 advanced patients with HF potentially eligible for heart transplantation followed for up to 180 days. Our main findings are as follows: (1) 89% and 80% of patients successfully met the primary end point at 30 and 180 days, respectively. (2) Exercise capacity and quality of life improved during iVAS support. (3) There was a high transplant rate of 67%. (4) Low infection rate, no nonsurgical bleeding, and no device thrombosis were noted during the first 6 months.
Supporting advanced patients with HF with IABP as a bridge to transplant has become more common in recent years, as the use of subclavian or axillary implantation evolved.7,8 However, the large IABP console and need to keep patients in the intensive care unit limits the widespread use of the technology. Recently, we reported the FIH use of the iVAS, demonstrating a high implantation success rate and an acceptable safety profile,5 leading to the initiation of the FT, in which a larger cohort was enrolled from 6 academic centers in the United States.
In this study, there was a very high procedural success rate. All patients underwent minimally invasive surgery, including implantation of the subclavian graft via a small infra-clavicular incision and femoral artery access for an 8Fr vascular snare. The SID was implanted superficially. No thoracotomy or sternotomy was required, and there was no need for cardiopulmonary bypass.
iVAS is a promising device that can serve as an alternative therapy for short-term mechanical circulatory support, including bridge to transplantation or bridge to recovery. By avoiding invasive surgery required for CF-LVAD (sternotomy or thoracotomy), the recovery time is brief, and heart transplantation can occur within a short period of time. Lack of transfusions obviates the creation of percent reactive antibodies. The design of the iVAS system allows it to be replaced or removed without requiring access to the heart, mediastinum, or pleural space. This forward compatibility allows escalation to the next level of therapy, such as transplantation or LVAD insertion, with minimal trauma to the patient.
The current study is an early feasibility experience and incurred a significant learning curve on implantation techniques, patient selection, and patient management. For instance, the obstruction to airflow and SID/electrode issues requiring reoperation have been addressed by modifying the surgical techniques after the first 24 patients.
In the current study, 2 patients experienced pump rupture. One had a very aneurysmal descending aorta and the pump due to buoyancy migrated upward and folded on itself. The other patient had severe calcific atherosclerosis and curvature of the descending aorta which could have contributed to the rupture. Any intravascular pneumatic device can rupture. The iVAS was designed to address any air leaks by prevention, detection, and easy exchangeability: Prevention—the pump itself is made from a very durable material that has passed over 2.5 years of life testing. The pump is also seamless, obviating failure at any joint; Detection—in contrast to conventional IABPs, pneumatic actuation is obtained by a bellows mechanism. This allows precise insufflation of air, and leaks can be detected down to 2cc, resulting in immediate discontinuation of system operation; Exchangeability—if a leak is detected, the pump can easily be replaced via the subclavian graft. A plug is used to maintain the lumen of the graft, allowing for quick replacement. The internal SID and electrodes are kept intact and do not need to be replaced. As expected the air leaks were detected in all 3 incidents, and the system shut down immediately. One patient had neurological changes that resolved into a nondisabling, small visual field cut. The other patient did not exhibit any neurological changes.
Despite the inclusion of the FIH experience, the current results demonstrate an encouraging safety profile with most complications occurring within the first 30 days. Only 2 patients experienced disabling neurological dysfunction. Both strokes were adjudicated to patient management and not due to the iVAS being the sources of emboli. This is the very first implants of iVAS and as management protocols improve, the number of stroke is expected to decrease. There were 2 deaths in the 180 days of support. The adverse events profile of the device seems to be very encouraging, there were only 3 patients with 4 episodes of device-related infections. Although the infection rate is low, we believe that the incidence of device-related infection could be decreased further with revised implantation techniques using short-term suction drainage and modified fixation to decrease stress in the epidermal layer. Furthermore, there were no gastrointestinal bleeding, pump thrombosis, nonsurgical bleeding, or device-related aortic thromboembolic events (despite almost all patients having periods of the device being off). Escalation of iVAS therapy occurred either due to atrial fibrillation or air pathway obstruction. These adverse events have been obviated by requiring atrio-ventricular node ablation and pacing for A-FIB patients and improved surgical technique for internal driveline placement.
The minimally invasive procedure, combined with the low complication profile and improvements in quality of life and exercise capacity, brings back optimism for use of mechanical circulatory support, such as iVAS, in a less sick patient population. Although CF-LVAD in a less sick cohort has previously been considered, the high rate of complications resulted in a lack of clinical equipoise and the closure of the Randomized Evaluation of VAD Intervention before Inotropic Therapy study.3 A partial answer was obtained through the nonrandomized Risk Assessment and Comparative Effectiveness of Left Ventricular Assist Device and Medical Management in Ambulatory Heart Failure Patients study,4 in which patients and providers chose medical therapy or early initiation of CF-LVAD support based on preference. In this study, the CF-LVAD group had more adverse events, but both groups had overall similar outcomes; however, a significant number of patients from the medical arm crossed over to the CF-LVAD group.
In this study, we expanded the indication of iVAS therapy to include bridge to decision patients. In a previous sub-analysis, we demonstrated that iVAS support improved biventricular function as assessed by echocardiography,9 probably due to the reduction in afterload for both ventricles and increases in coronary flow.10 The iVAS allows for the degree of recovery to be fully assessed before potential explantation. The frequency of support can be adjusted on-demand, and the pump can be turned off for an extended period of time. If full recovery is achieved, the intravascular component can be removed, leaving a blank plug in the graft. This permits the lumen of the graft and the SID to be maintained, allowing for easy reimplantation of the pump if necessary. If recovery status remains stable after an extended period of time, all the components can be removed through a simple operation involving only subcutaneous tissue.
Finally, iVAS therapy may have an indication for the prolonged care for inotrope-dependent patients. They may achieve independence from inotropes with a better quality of life during long-term iVAS support. In addition to short-term use, the benefits of iVAS as a long-term device are also appealing. iVAS patients may avoid major complications such as gastrointestinal bleeding, infection, and death.11 The need for long-term outcomes is crucial to assess whether iVAS can be a viable option as destination therapy for less sick patients.
Limitations and Future Directions
This study is a single-arm study with the majority of the patients being recruited from one site. In this FT, we focused on learning the safety profile of the device, understanding patient selection and management, and building the foundation for an expansion of this device into longer-term use. These encouraging results call for a larger multicenter study with longer time on support. A late feasibility study enrolling advanced patients with HF regardless of eligibility for transplant is ongoing. Upon completion of that phase, a multicenter pivotal study will be initiated.
Based on our previous study showing significant reverse remodeling during iVAS support, we also believe that a sub-study of patients who may recover cardiac function is warranted. In this study, we did not measure any molecular, biological, or pathological parameters to assess myocardial recovery during iVAS support. These measurements and further evaluation of patients who received iVAS with preserved/moderate ejection fraction are needed.
Conclusions
This study demonstrated encouraging short-term outcomes with iVAS therapy with improved functional capacity and quality of life during therapy. Late FT and pivotal trials for all advanced patients with HF are warranted.
| CF-LVAD |
continuous-flow left ventricular assist device |
| FIH |
first-in-human |
| HF |
heart failure |
| IABP |
intraaortic balloon pump |
| iVAS |
intravascular ventricular assist system |
| SID |
skin interface device |
Sources of Funding
NuPulseCV provided research funding for the clinical trial and provided access to the data.
Disclosures
C. Juricek and T. Lammy are consultants for NuPulseCV. Drs Patel-Raman and Woolley are employees of NuPulseCV. The other authors report no conflicts.
Footnotes
References
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