Dr. Shah received no payment for his participation in this discussion. Sponsored content Impella CP vs. IABP in CS: The IMPRESS Trial Atman P. Shah, MD, is currently the Clinical Director of the Section of Cardiology, the Co-Director of the Adult Cardiac Catheterization Laboratory, and an Associate Professor of Medicine at the University of Chicago. Dr. Shah’s research efforts focus on improving survival rates in patients who have experienced a cardiac arrest or an acute myocardial infarction (heart attack) and novel therapies that can help save heart muscle during a heart attack. He specializes in caring for patients with complex structural heart disease and has innovated a number of new techniques to treat patients with challenging clinical conditions. Dr. Shah is the primary investigator on a number of large multicenter clinical trials investigating novel medications and devices designed to improve the quality of life in patients with coronary artery and structural heart disease. In this Conversation with the Expert, Dr. Shah shares with readers the results of the IMPRESS trial, which sought to compare mechanical circulatory support and intra-aortic balloon pump therapy for patients with AMI and CS. Describe the IMPRESS trial and its main objectives. The IMPRESS trial, published by Dr. Ouwaneel et al in the Journal of the American College of Cardiology last year, tries to answer the question of whether a more potent mechanical cardiopulmonary support device—in this case the Impella® CP mechanical circulatory support—offers an advantage to intra-aortic balloon pump (IABP) therapy in patients who’ve had an acute myocardial infarction (AMI) and who are in cardiogenic shock (CS). It is built on a number of different trials that we’ve had in the past about how to treat patients in AMI and CS. The main mechanical support therapy for decades has been the IABP; however, in recent trials, IABP use failed to demonstrate a mortality benefit compared to medical therapy in patients with acute myocardial infarction and shock. IABP therapy increases the cardiac output by approximatley 1L/minute, primarily by decreasing the systemic vascular resistance and by increasing coronary flow during diastole. The difference between an IABP and the Impella® CP is that the Impella® CP sits in the left ventricle and a rotating motor will pull blood out of the left ventricle and return the blood in the aorta. Unlike the IABP, it physically drains the left ventricle and gives help to the left ventricle to acquire more favorable geometry for contraction. It can decrease the amount of work that the left ventricle has to do in the setting of coronary ischemia. The Impella ® 2.5 can get up to two and a half liters of augmented flow, and the Impella® CP can give you up to four liters of flow. The thought process is that the heart has impaired contractility in the setting of a myocardial infarction, a percutaneous left ventricular assist device (pVAD) may improve cardiac output and enhance myocardial healing by unloading the left ventricle and providing a return to a favorable geometry on the Starling curve. And in theory, these effects can potentially improve clinical outcomes by increasing flow. Given the recent ISAR-SHOCK II trial, which failed to show a mortality benefit in patients treated with IABP compared to Impella® 2.5 in the setting of AMI and shock, there is a lot of interest in assessing whether pVADs may be able to offer more to these patients than IABP. The IMPRESS trial tried to answer the question looking at patients who had an AMI and were in CS and who were mechanically ventilated and were randomized either to receive the Impella® CP or IABP. The definition of CS was a systolic blood pressure of less than 90 mmHg for at least 30 minutes or patients who were treated with intravenous pressors to achieve a systolic BP of 90 mmHg. All patients had to be intubated and they were excluded if they had severe peripheral arterial disease, valvular disease, or if their life expectancy was less than 12 months. The primary endpoint was all cause mortality at 30 days with the secondary endpoint being mortality at 6 months. What do you contribute to the fact that the study showed that increased flow did not necessarily equate to an improvement in outcomes? Flow may not be everything. Even though we may be getting more flow with the Impella®, that extra flow may not be enough and that we either need even more flow than what the Impella® has given— maybe we need a device that gives us five or six liters of flow. Moreover, these patients were very sick. They were mechanically ventilated and 100% of the patients in the Impella® arm and 83% of the patients in the IABP arm suffered a cardiac arrest. Perhaps flow isn’t the only issue—oxygenation may be very important as well. While the Impella® CP unloads the left ventricle, it does not oxygenate blood. Furthermore, while the Impella® CP device may have given the patients in the IMPRESS trial more flow and a greater cardiac output, this wasn’t evidenced by a decrease in lactate. And there is the possibility that there may have been a benefit to increased flow that may have been offset by the increased risk of bleeding and vascular complications to the patients who had the Impella® CP. A subset of patients demonstrated a mortality benefit when mechanical support was initiated prior to revascularization however, but the majority of patients had the device placed after PCI. What do you think are the factors that contribute to the decision of insertion devices post-procedure? In the IMPRESS trial, the majority of patients had a cardiac arrest and had to be resuscitated. So these patients are really, really sick and they need immediate support. In this particular trial, it was up to the discretion of the operator of when to place either the IABP or the Impella®, so a number of different things can come into play. We know that, at the moment of PCI, once the artery is opened up, a patient can be at risk for reperfusion injury or ventricular tachycardia. A patient who has just suffered a cardiac arrest and an acute myocardial infarction may be ill prepared to suffer additional ischemic insults. If the device is placed prior to revascularization, the patient may be able to tolerate reperfusion injury or VT to a better degree than if the device is placed after the fact. Do you think the timing of initiation of therapy is more crucial than device selection? Timing is really critical because, the earlier we can put the patients on support, we can help support the heart and the rest of the patient, and it can allow for a more controlled coronary intervention. In many cases, a patient with AMI and CS may present and the provider’s first instinct is to initiate intravenous dopamine. However, dopamine neither revascularizes the occluded artery nor does it improve oxygenation. And if the patient deteriorates, a second agent is often added. As the patient’s clinical situation deteriorates, mechanically supporting the heart with an IABP or a pVAD becomes an option, but in a much sicker patient. We need to be very aggressive in treating and assessing the patient. Clinical parameters such as heart rate and blood pressure should be aggressively managed. As the patient develops significant cardiogenic shock, they will no longer be able to oxygenate, which will only further increase systemic vasoconstriction and worsen shock. So we need to intervene quickly. In addition, laboratory parameters such as serum lactate may provide earlier insight into a deteriorating patient. As the first-line providers, early identification of these critically ill patients is paramount. Now, whether the timing is more important than device selection is half-dozen in one hand and six in the other. As far as device selection, each device has its benefits and disadvantages. The IABP is a tool that every cath lab in the world is comfortable with and can be inserted in a few minutes. In addition, the lower profile of the catheter allows its insertion in smaller patients or those with mild peripheral arterial disease. The Impella® may provide more flow, but may require more time and expertise to insert and does require minimal peripheral arterial disease for insertion. We have to determine, faced with the individual patient we are treating, which particular device is best suited for that particular patient. In theory, the increased flow provided by the Impella ® should result in improved clinical benefits. I think many of us were surprised that the IMPRESS trial failed to show those benefits with the Impella® compared to the IABP. How important is the risk-to-benefit ratio when determining device selection? In this particular trial, the risk of insertion is not the same with both devices. The Impella® CP has a 14 French (Fr) pump motor, compared to the 7.5 Fr balloon pump. In the trial, there were more bleeding complications with Impella® CP compared with IABP, so patients who received the Impella were at higher risk of bleeding and vascular trauma. In addition, the Impella® may require more effort to position and reposition in the LV. The IABP, while giving less flow, is associated with less vascular injury and does not need repositioning. One of the critical parts of the IMPRESS trial was showing that not only was there no difference in mortality betweeen the two devices but one of the markers of flow was not different between the two groups. Our putative conclusion is that the Impella® CP should have more benefit than the balloon pump because it generates more flow and, therefore, the lactate, which is a broad marker for overall patient viability or overall patient function. If the lactate is high, the patient is not doing very well, and there is significant heart failure. If the lactate is going down, the patient’s heart failure is getting better. But the lactate was no different between the two groups, leading us to believe that perhaps flow isn’t as important. So risk benefit—making sure that that device has more benefit than a device that maybe has less risk—is absolutely critical, especially in a really sick patient who may not be able to give informed consent, especially if they are intubated or having cardiac arrest. The interventional cardiologist has to carefully weigh the clinical risks and benefits to each of these devices in critically ill patients within the context of the published trials. What can cardiologists do today that could impact patient outcomes in a setting of cardiogenic shock? The best thing is to identify that patient in CS early, either through clinical or laboratory parameters— and then do something about it. Simply treating the patient with escalating doses of intravenous pressors and then thinking rapid revascularization without hemodynamic support may not be in the best clinical interest of the patient. We need to assess these patients and then make a decision on early initiation of mechanical ventricular support. Choosing the right device would allow greater support of the patient and will allow the interventional cardiologist to proceed with effective revascularization. We know patients who’ve had cardiac arrest have a higher likelihood of having a repeat cardiac arrest. And it is a lot better to have a mechanical cardiopulmonary support device in place if that patient were to arrest again, because then you can bridge that patient with that device. In summary, the IABP-SHOCK II trial did not show a benefit of IABP over medical therapy in patients with AMI and CS and the IMPRESS trial did not show a benefit to Impella® over IABP in a CS patient population. Neither trial mandated device placement prior to revascularization and the most important aspect of these trials is that, no matter what the device, early identification and treatment of the shock patient may be critical to survival. Atman P. Shah, MD, received no payment for his particpation in this discussion. DISCLOSURES: This material was sponsored by Getinge.
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