Extracorporeal Circulatory Support in the Cath Lab: The TandemHeart Percutaneous Ventricular Assist Device

Two cannulae are inserted: one long, 21F cannula in the left atrium, and one (15 or 17F and sometimes two 12F arterial cannulae) in the femoral artery. The cannulae are connected to the pump, which is driven by an electromagnetic motor. The pump is connected to a microprocessor-based controller that provides operating power, provides controlled flow of lubricant (heparinized saline), and displays impeller speed and pump flow with automatic system monitoring and alarms. The device unloads the left side of the heart and thereby decreases cardiac workload and myocardial oxygen demand. The ventricle is able to rest during the period that the TandemHeart is providing circulatory support. How has the TandemHeart been utilized? It has been utilized in patients presenting with cardiogenic shock after myocardial infarction; in patients that are hemodynamically unstable after cardiac surgery; in patients with heart failure who are not responding to optimum pharmacological therapy and intra-aortic balloon pump (IABP) support. Worldwide, 752 implants have been done so far, and 32% of the implants have been for high-risk angioplasty. The device can be used as a bridge to recovery, but it is also useful as a bridge to definitive therapy, by which I mean that the TandemHeart can support patients till they are able to proceed to surgical ventricular assist device or occasionally even to cardiac transplantation. There have been two reported bridge-to-transplant cases, one at Vanderbilt University Medical center and one at Texas Heart Institute. Each patient had a TandemHeart implanted until cardiac transplantation surgery was performed. TandemHeart bridging to cardiac transplant is unusual because cardiac transplant is limited by availability of matching donors. If the patient is a candidate but there are no organs available, they will then go from the TandemHeart to a surgical ventricular assist device. The recommended maximum length of implantation for a TandemHeart is 14 days, although there are cases where it has been in place for a longer period. Beyond 14 days, a decision has to be made if the device needs to be removed due to adequate recovery or if the patient should move to a surgical ventricular assist device. Could you talk more about use of the device in cardiogenic shock? It is beneficial to have the TandemHeart implanted prophylactically prior to performing high-risk angioplasty, in order to be ready to support the cardiac function should the procedure be complicated by acute ventricular failure and cardiogenic shock. High-risk angioplasty would include patients with complex anatomy, with significant mass of myocardium at risk and often with left ventricular dysfunction. If the patient does develop cardiogenic shock, we now have a device in place that can help bail out the patient from potential death. For example, this device would be useful in high-risk cases such as unprotected left main coronary artery revascularization; a patient who has a single vessel supplying a large amount of myocardium; any intervention where the patient has no other options such as surgical revascularization and perhaps those patients with severe multi-vessel disease. The second, more emergent scenario is the patient that comes in with cardiogenic shock after suffering myocardial infarction. This device was initially used specifically for these types of patients. Early hemodynamic improvement can be seen as soon as the device is placed and significant improvement can be seen in just a few hours. Mortality in these patients is so high, however, that a device alone is often not the answer. These patients need a combination of early angioplasty in those with acute myocardial infarction, placement of either an IABP or a TandemHeart, and there is also a need for newer pharmacological and biological therapies. A combination treatment is most effective in decreasing the incidence of mortality in cardiogenic shock complicating myocardial infarction, which even with primary angioplasty, is still about 60 to 70%. The TandemHeart can be in use for up to 14 days. What are the typical lengths of time that various kinds of patients would utilize the device? For patients in whom we implant the device prophylactically for high-risk angioplasty, the device is generally removed the same day or the following day. For patients that come in with cardiogenic shock secondary to myocardial infarction, I suspect the average implantation time is between 4-5 days. We generally wait for the patient to demonstrate clinical and hemodynamic improvement, and then start weaning them off the device at that point. The patients in heart failure awaiting a cardiac transplant or a surgical ventricular assist device are the ones who need long-term implantation of the device. What are some of the medications utilized with the TandemHeart? Any device placed long-term is considered a foreign object by the body, triggering complement activation processes. A trial where the balloon pump was randomized to the TandemHeart showed overall mortality was not significantly reduced when compared to the balloon pump. A device as invasive as the TandemHeart may lead to more complications, such as vascular ischemia or complications that end up requiring blood transfusions. When a patient presents in cardiogenic shock after an MI, the body has activated the complement pathway and also develops and propagates the systemic inflammatory response system (SIRS). In these processes, there are several deleterious effects in progress, such as activation of inflammatory cytokines, which eventually leads to depression of myocardial function, pathological vasodilation of the peripheral vascular system, and down regulation of catecholamine response. Some of the mechanical and hemodynamic benefits that the TandemHeart provides may be offset by the response of the SIRS, triggered whenever the patient comes in acutely ill and gets a long-term support device. Clearly, anticoagulation is important. The company’s recommendation is to drip the anticoagulation (IV heparin) through the controller at a set rate to maintain ACT of 250 seconds during the intervention and more than 200 seconds during the prolonged support phase. We have used bivalirudin during device implantation in patients undergoing high-risk angioplasty. Then we use a standard protocol to stop the anticoagulation and remove the device. In our initial experience, the cannulae were removed surgically. Later, as we improved our understanding of groin management, we began using standard manual hemostasis and the placement of FemoStop. There are institutions that are also using percutaneous suture closure devices to achieve hemostasis after removal of the cannulae. Patients in shock generally are on one or more IV vasopressors. Some of the signs that the patient is doing better are that cardiac output starts to improve, the patient has increased urinary output and the hemodynamic indices obtained from the right heart hemodynamic monitoring catheter demonstrate improvement. At that point, we start weaning the IV vasopressors off. As the pressors are discontinued, then we start weaning the device off. How are patients weaned off the device? In patients that received the TandemHeart prophylactically for high-risk intervention, and if the procedure was uncomplicated, then the cannulae are removed within few hours post procedure, once the ACT has trended towards 150 seconds. In these patients, as the ACT decreases below 180 seconds, the controller is turned off and the left atrial cannula is withdrawn into the inferior vena cava, and then the cannulae are removed as mentioned. For patients where the device was implanted for longer periods to provide circulatory support, a stepwise reduction of pump output by 500 ml/minutes every hour is performed. The clinical and hemodynamic data are carefully monitored during the weaning process. Generally, in such patients, a 4- to 8-hour weaning period is required. How much of the cardiac workload is typically taken over by the TandemHeart? How does it compare to how an IABP helps the patient? The IABP is a standard device that is fairly effective in the population with intrinsically reasonable ventricular function. However, it doesn’t provide active cardiac support. The TandemHeart, unlike the IABP, is not entirely dependent on the residual left ventricular function and provides active cardiac support. We generally run the device at a speed that would give us a cardiac output of 2.5 to 3 liters per minute. If the patient is in cardiogenic shock, where there is very little innate cardiac output or stroke volume coming out of the left ventricle, then they would be fully dependent on this device. If the patient has prophylactic implantation of the device as part of high-risk angioplasty protocol, then we do not run the device at its maximum speed. On average, we maintain cardiac output of between 2.5 to 3 liters/minute. It really depends on how depressed the left ventricular function is and how much clinical and hemodynamic compromise is present. This determines the speed at which we run the device. It is important to note that the TandemHeart is dependent on a reasonable amount of blood volume being pumped from the right ventricle to the left atrium. In patients with severe chronic right ventricular dysfunction, this device is not likely to be effective, because there is not adequate preload. If the device is not receiving enough blood volume to fill the left atrium, it will not draw sufficient blood out of the left atrium. In patients that have acute right ventricular infarction, this device has been used as an RVAD device. I have discussed its use as an LVAD system, but there are patients that have had the device implanted as an RVAD device, with one cannula placed in the right atrium and one placed in the pulmonary artery. In this way, the right ventricle can be rested. What are device contraindications? One of the contraindications is coagulopathy. If a patient has bleeding diathesis, then other options should be explored. Long-term implantation of the TandemHeart generally has been associated with an increased likelihood for blood transfusions. We had one patient who needed the device support for more than ten days, but who did proceed successfully to a surgical ventricular assist device. This patient was not doing well on optimum pharmacological therapy in the transplant unit and her kidneys started failing. She was not a candidate for a surgical ventricular assist device at that period in time, so this device was placed to bridge her to a surgical ventricular assist device. She developed thrombocytopenia on IV heparin, which was changed to IV argatroban, a direct thrombin inhibitor. She is still alive and waiting for heart and renal transplant. Other contraindications include advanced age. In the beginning we focused mainly on patients that were from a middle-aged or lower population group, because the concern with elderly patients regarding the potential for long-term placement of the device. What would we do beyond 14 days if they were unable to be weaned off the device? It would leave everybody involved with very difficult choices. The elderly are not candidates for cardiac transplantation because of age restrictions and they are not generally good candidates for surgical ventricular assist devices for similar reasons. However, we have recently started to broaden our age criteria to include elderly people undergoing high-risk angioplasty after a thorough discussion about the device with the patients and their families. Another potential disqualification that generally comes up is severe peripheral vascular disease. If it is focal disease, say an iliac stenosis, then that can easily be overcome with stenting and then implantation of this device. However, if the ilieofemoral arteries cannot be revascularized percutaneously, if they are very tortuous or if the patient has significant runoff issues in the peripheral vasculature, then this device could lead to limb ischemia particularly if it is required for prolonged period. Therefore, it is important to screen the patient’s vasculature before implanting the device. If a patient has a severely diseased superficial femoral artery (SFA), but their iliac arteries are patent, we would implant the device and then remove it as soon as clinically possible after the procedure. However, if patients have lesions amenable to angioplasty and stenting, then we perform the necessary peripheral revascularization prior to placement of the device. If there is a bilateral total occlusion of iliac arteries or if there is aortic occlusion that cannot be revascularized prior to placement of the femoral arterial cannula, then the device cannot be used. How long have you been using the TandemHeart? We started using this device in December 2005, and we have done 10 implantations. Part of the reason for our slow rate of adoption of this device has been the difficulty in spreading the word to our physician community, which includes the state of Alabama and surrounding areas. I perform a number of complex procedures at University of Alabama at Birmingham (UAB) Hospital and hence my referral population is skewed toward an extremely high-risk patient population. A significant proportion of my patients are referred by interventional cardiologists in the state of Alabama, the Florida panhandle, East Mississippi, and West Georgia. My hope is to send a message out to the community at large that our center does have this technology available for patients that may be considered high-risk for angioplasty, those that are doing poorly after myocardial infarction or for some patients with unique medical problems where this device may be beneficial. My interventional cardiovascular training was at Vanderbilt University Medical Center. UAB has an excellent interventional cardiovascular program, and is the main tertiary referral center for the state of Alabama and surrounding regions. As a result, our program is heavily loaded with patients that have complex co-morbidities and need high-risk interventions. We are well-supported by the University Hospital System in terms of providing advanced and newer technologies for performing these complex procedures, and have an excellent cath lab and pre/post procedure unit staff that really are the backbone of successful outcomes and high patient satisfaction. Besides coronary and graft interventions, our program has been performing extracranial and intracranial cerebrovascular interventions for more than a decade. We have a rapidly growing volume of valvuloplasty (mitral/aortic/ pulmonary) procedures, ASD and PFO closures, and alcohol septal ablation procedures. We perform variety of peripheral vascular interventions and also offer interventions for unique problems, such as coiling of coronary fistulae, placement of vascular plugs, thrombectomy of cerebrovascular venous system, etc. UAB has a large population of transplant patients. We are the cardiac transplant center for our state. Cardiac transplant patients can develop very aggressive coronary and peripheral vasculopathy, sometimes requiring multiple revascularization procedures. On any given day, there is a wide mix of procedures in our lab. Recently, we successfully stented coarctation of aorta in a young adult patient. Our program participates in multiple multi-center research protocols and we are enhancing our abstract and publication productivity. I cannot emphasize enough that you need high-quality staff in order to do these complex procedures, both in the cath lab and in the peri-operative areas. We have senior staff that has been with UAB for many years, and their valuable experience is transferred to many of our younger staff. Is there a high learning curve for the TandemHeart? The limitation of the TandemHeart is the need for transseptal experience. Experienced interventional operators who perform transseptal procedures on a regular basis should not have a problem. The number of patients necessary to become comfortable with the device would be approximately 5 over a 1- to 2-month period, particularly for emergent or urgent medical conditions where you need an efficient team to prepare and assist in the implantation of the TandemHeart. To train the team, it would be beneficial to begin the program in patients undergoing planned implantation of the device, such as those in whom it is implanted prophylactically for high-risk coronary intervention. For physicians that have not had experience doing transseptals, they should learn implantation of this device only after they have become comfortable performing transseptal procedures. Just as important as physician training is the need for trained staff in the cath lab as well as in the post procedure units, generally the CCU (Cardiac Intensive Care Unit) or the heart transplant unit in some centers, such as UAB. The team makes a major difference. The operator needs experienced staff in order for implantation of the device to move in a smooth and coordinated fashion. You mentioned a clinical trial that randomized the TandemHeart with the intra-aortic balloon pump. This was a trial published in the January 2005 issue of European Heart Journal by Dr. Thiele’s group in Germany. They performed a small trial randomizing patients who presented after acute myocardial infarction and cardiogenic shock to either the TandemHeart or an IABP. Twenty-one patients received the TandemHeart and 20 patients received IABP. The primary endpoint of the trial was met, in the sense that use of the TandemHeart led to improvement in the cardiac power index (CPI, a risk stratification index for acute and chronic heart failure), significantly better than the IABP. The secondary endpoints, such as overall 30-day mortality, were not different between the IABP and the TandemHeart. As we discussed, this may have to do with the activation of complement pathway and the SIRS activation that we have to deal with when placing long-term devices. Are there any plans to create a registry? At the last meeting with company personnel, there was discussion about a plan to collect and track all experiences in a more centralized fashion in order to gain a better understanding of when to use the device and in whom it should be placed. We haven’t started the registry process yet; the company is working with internal advisors on how best to move forward. Where do you think the TandemHeart will prove most beneficial? First, I think patients undergoing high-risk angioplasty would benefit from this device. Second, patients who are in cardiogenic shock either after or despite successful coronary angioplasty for myocardial infarction would benefit from device placement for a medium-term duration, meaning about five days. Third, patients who will be undergoing complex cardiac procedures such as percutaneous aortic valve implantation, as is being done in Canada by Dr. Raoul Bonan in Montreal. At his center, they are percutaneously implanting stented valves in the aortic position while using TandemHeart to support the procedure. It is very likely that there will be an expansion in the use of this technology such as for an RVAD and also for unique problems, such as the implantation of this device in a patient that underwent complex ventricular tachycardia ablation at Mayo Clinic, as well as similar support devices, some in development stages and others currently undergoing trials. Dr. Misra can be contacted at vmisra@cardmail.dom.uab.edu

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