The step forward for VA ECMO: left ventricular unloading!

Left Ventricular Assist Devices for Acute Myocardial Infarct Size Reduction: Meta-analysis

We conducted a meta-analysis of preclinical studies that tested left ventricular assist device (LVAD) therapy for reducing myocardial infarct size in experimental acute myocardial infarction (AMI). Twenty-six articles were included with a total of 488 experimental animal subjects. The meta-analysis showed that infarct size was significantly decreased by LVAD support compared to control animals (SDM, - 2.19; 95% CI, - 2.70 to - 1.69; P < 0.001). The meta-regression analysis demonstrated a high degree of heterogeneity associated with time from coronary artery occlusion to LVAD support, which correlated positively with infarct size. Subgroup analysis suggested smaller infarct size in LVAD therapies that withdrew blood from left heart than those from right heart. The proportion of left ventricular support relative to total cardiac output was positively correlated with infarct size reduction in Impella studies. Thus, early initiation of LVAD after ischemia and effective left ventricular venting may be important factors to reduce infarct size in AMI.

Escalation and de-escalation of mechanical circulatory support in cardiogenic shock

Cardiogenic shock (CS) is a clinical entity that includes a wide spectrum of different scenarios. Mechanical circulatory support (MCS) plays a fundamental role in the contemporary treatment of CS, and device selection is a key element in determining optimal treatment in this complex population. Cardiac support with mechanical devices should allow reduction and complete weaning from inotropes. Persistence of elevated left ventricular (LV) filling pressures, pulmonary congestion, metabolic decompensation, and end-organ damage during current MCS are criteria for MCS escalation. Precise diagnosis of the underlying cause of right ventricular (RV) failure is fundamental for undertaking the correct escalation strategy. In the setting of both MCS escalation and de-escalation, it is important to select a strategy in relation to long-term perspectives (bridge-to-recovery, bridge-to-LV assist device, or bridge-to-heart transplantation). Small retrospective studies have demonstrated that the BiPella approach is feasible, reduces cardiac filling pressures and improves cardiac output across a range of causes of CS. Simultaneous LV and RV device implantation and lower RV afterload may be associated with better outcomes in biventricular CS, but prospective studies are still required.

Balanced Biventricular Assist Versus Extracorporeal Membrane Oxygenation in Cardiac Arrest

Mechanical assist devices in refractory cardiac arrest are increasingly employed. We compared the hemodynamics and organ perfusion during cardiac arrest with either veno-arterial extracorporeal membrane oxygenation (ECMO) or biventricular assisted circulation combining left- and right-sided impeller devices (BiPella) in an acute experimental setting. Twenty pigs were randomized in two equal groups receiving circulatory support either by ECMO or by BiPella during 40 minutes of ventricular fibrillation (VF) followed by three attempts of cardioversion, and if successful, 60 minute observation with spontaneous, unsupported circulation. Hemodynamic variables were continuously recorded. Tissue perfusion was evaluated by fluorescent microsphere injections. Cardiac function was visualized by intracardiac echocardiography. During VF device output, carotid flow, kidney perfusion, mean aortic pressure (AOPmean), and mean left ventricular pressure (LVPmean) were all significantly higher in the ECMO group, and serum-lactate values were lower compared with the BiPella group. No difference in myocardial or cerebral perfusion was observed between groups. In 15 animals with sustained cardiac function for 60 minutes after return of spontaneous circulation, left ventricular subendocardial blood flow rate averaged 0.59 ± 0.05 ml/min/gm during VF compared with 0.31 ± 0.07 ml/min/gm in five animals with circulatory collapse (p = 0.005). Corresponding values for the midmyocardium was 0.91 ± 0.06 vs. 0.65 ± 0.15 ml/min/gm (p = 0.085). Both BiPella and ECMO could sustain vital organ function. ECMO provided a more optimal systemic circulatory support related to near physiologic output. Myocardial tissue perfusion and sustained cardiac function were related to coronary perfusion pressure during VF, irrespective of mode of circulatory support.

Comparison of Hemodynamic Support by Impella vs. Peripheral Extra-Corporeal Membrane Oxygenation: A Porcine Model of Acute Myocardial Infarction

Objectives: Several mechanical circulatory assist devices are used to treat critically ill patients requiring hemodynamic support during post-myocardial infarction or cardiogenic shock. However, little guidance is available to choose an appropriate device to match a particular patient's needs. An increased understanding of hemodynamic effects of the pump systems and their impact on myocardial pre-/afterload might help to better understand their behavior in different clinical settings. Methods: This was an open-labeled, randomized acute animal experiment. A model of acute univentricular myocardial injury by temporary balloon occlusion was used. The experiment was carried out in 10 juveniles female Piétrain pigs. The animals were randomized to mechanical hemodynamic support either by peripheral veno-arterial (VA-)ECMO or Impella CP. Results: While both devices were able to provide flows above 3 L/min and maintain sufficient end-organ perfusion, support by Impella resulted in a significantly more pronounced immediate effect on myocardial unloading: At the onset of device support, the remaining native cardiac output was reduced by 23.5 ± 15.3% ECMO vs. 66.2 ± 36.2% (Impella, p = 0.021). Native stroke volume was significantly decreased by Impella support compared to ECMO, indicating less mechanical work being conducted by the Impella-supported hearts despite similar total assisted cardiac output. Conclusions: Peripheral VA-ECMO and the transaortic Impella pump resulted in contrasting hemodynamic fingerprints. Both devices provided sufficient hemodynamic support and reduce left ventricular end-diastolic pressure in the acute setting. Treatment with the Impella device resulted in a more effective volume unloading of the left ventricle. A significant reduction in myocardial oxygen consumption equivalent was achieved by both devices: The Impella device resulted in a left-shift of the pressure-volume loop and a decreased pressure-volume-area (PVA), while VA-ECMO increased PVA but decreased heart rate. These data highlight the importance of specifically targeting heart rate in the management of AMI patients on hemodynamic support.

Determining the impacts of venoarterial extracorporeal membrane oxygenation on cerebral oxygenation using a one-dimensional blood flow simulator

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) is a mechanical system that provides rapid and short-term support for patients with cardiac failure. In many patients, pulmonary function is also impaired, resulting in poorly-oxygenated cardiac outflow competing against well-oxygenated VA-ECMO outflow, a condition known as North-South syndrome. North-South syndrome is a primary concern because of its potential to cause cerebral hypoxia, which has a critical influence on neurological complications often seen in this patient population. In order to reduce ischemic neurological complications, it is important to understand how clinical decisions regarding VA-ECMO parameters influence blood oxygenation. Here, we studied the impacts of flow rate and cannulation site on oxygenation using a one-dimensional (1D) model to simulate blood flow. Our model was initially tested by comparing blood flow results to those observed from experimental work in VA-ECMO patients. The 1D model was combined with a two-phase flow model to simulate oxygenation. Additionally, the influence of various other clinician-tunable parameters on oxygenation in the common carotid arteries (CCAs) were tested, including, blood viscosity, cannula position within the insertion artery, heart rate, and systemic vascular resistance (SVR), as well as geometrical changes such as arterial radius and length. Our results indicated that blood oxygenation to the brain strongly depended on the cannula insertion site and the VA-ECMO flow rate with a weaker but potentially significant dependence on arterial radius. During femoral cannulation, VA-ECMO flow rates greater than ~4.9L/min were needed to perfuse the CCAs. However, axillary and central cannulation began to perfuse the CCAs at significantly lower flow (~1L/min). These results may help explain the incidence of cerebral hypoxia in this patient population and the common need to change cannulation strategies during treatment to address this clinical problem. While this work describes patient-averaged results, determining these relationships between VA-ECMO parameters and cerebral hypoxia is an important step towards future work to develop patient-specific models that clinicians can use to improve outcomes.

Left ventricular unloading during extracorporeal membrane oxygenation – Impella versus atrial septal defect: A simulation study

Background:

Atrial septal defect and Impella have been proposed for left ventricular unloading in venoarterial extracorporeal membrane oxygenation patients. This work aims at evaluating the haemodynamic changes in venoarterial extracorporeal membrane oxygenation patients after Impella implantation or atrial septal defect realization by a simulation study.

Methods:

A lumped parameter model of the cardiovascular system was adapted to this study. Atrial septal defect was modelled as a resistance between the two atria. Venoarterial extracorporeal membrane oxygenation and Impella were modelled starting from their pressure-flow characteristics. The baseline condition of a patient undergoing venoarterial extracorporeal membrane oxygenation was reproduced starting from haemodynamic and echocardiographic data. The effects of different atrial septal defect size, Impella and venoarterial extracorporeal membrane oxygenation support were simulated.

Results:

Impella caused an increment of mean arterial pressure up to 67%, a decrement in mean pulmonary arterial pressure up to 8%, a decrement in left ventricular end systolic volume up to 11% with a reduction up to 97% of left ventricular cardiac output. Atrial septal defect reduces left atrial pressure (19%), increases right atrial pressure (22%), increases mean arterial pressure (18%), decreases left ventricular end systolic volume (11%), increases right ventricular volume (33%) and decreases left ventricular cardiac output (55%).

Conclusion:

Impella has a higher capability in left ventricular unloading during venoarterial extracorporeal membrane oxygenation in comparison to atrial septal defect with a lower right ventricular overload.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Transaortic Left Ventricular Unloading in VA-ECMO: The Transsubclavian Route

Left ventricular unloading during extracorporeal life support aims to minimize potential side effects of increased left ventricular afterload. A transaortic catheter vent implanted through a subclavian approach was used in 2 patients. Patient 1 was a 48-year-old man with a recent history of ST-elevation myocardial infarction who developed refractory cardiogenic shock due to severe biventricular dysfunction. Patient 2 was a 56-year-old man admitted for severe flu. The unloading procedure was successful in both patients, with bridge to heart transplantation in the first case and bridge to recovery in the other.

Efficacy of left heart decompression during extracorporeal membrane oxygenation: a case-control study

Background

Veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) is used in various cardiogenic shocks. In severe myocardial dysfunction, left heart (LH) distension may occur and aggravate pulmonary edema. Despite the recent case reports on various venting catheter insertion methods for LH decompression, the necessity and efficacy of LH venting procedure are still controversial. Therefore, we focused on evaluating efficacy of LH venting catheter insertion for LH decompression.

Methods

In total, 373 patients received VA ECMO at our institution from May 2012 to January 2016. Of these, 25 patients underwent LH venting catheter insertion. Indication for the procedure included pulmonary congestion observed on chest radiogram, with arterial pulse pressure ≤10 mmHg. The control group comprised of 45 patients with peripheral VA ECMO having arterial pulse pressure ≤ for ≥24 hours during the same study period who did not undergo LH venting procedure. Finally, 70 patients were compared and analyzed.

Results

Mean age of the patients was 52.6±17.1 years. The ECMO running time in each group was 7.2±7.1 days in the vent (-) group and 9.2±8.5 days in the vent (+) group. Successful weaning rate was higher in the LH vent (+) group (P=0.08). Moreover, LH venting catheter insertion was identified as a predictor of weaning success with marginal significance (OR =2.47; 95% CI: 0.90-6.72; P=0.07).

Conclusions

LH decompression by venting catheter insertion in patients on VA ECMO may be more effective and helpful for successful ECMO weaning than conventional medical management without survival benefit.

ECMO for Adults with Severe Respiratory Failure

The technology to provide Extracorporeal Life Support (ELS) has existed for over four decades. Its use has increased markedly in the last decade, initially in response to severe Acute Respiratory Distress Syndrome (ARDS) in adults during the 2009 H1N1 influenza epidemic and continuing with the increasing acceptance of Extracorporeal Membrane Oxygenation (ECMO) for the treatment of severe respiratory failure in adults from other causes.1 We highlight the use of ECMO, particularly at our institution.

Clinical complications during veno-arterial extracorporeal membrane oxigenation in post-cardiotomy and non post-cardiotomy shock: still the achille's heel

Extracorporeal membrane oxygenation (ECMO) is life-saving for potentially reversible heart failure and respiratory injuries not responsive to conventional therapies. Technological innovations have produced over the years significant improvements in ECMO devices (pump, cannula design and oxygenator) and have allowed a better risk/benefit profile. Alongside with recognized advantages in the treatment of very sick patients, ECMO remains an invasive procedure for mechanical circulatory support (MCS) and it is associated with complications that strongly influence the prognosis. Current review was designed to provide a comprehensive outline on ECMO complications, analyzing risk factors and strategies of management, focusing on adult population undergoing veno-arterial ECMO (VA-ECMO) therapy.