Physiology of the Assisted Circulation in Cardiogenic Shock: A State-of-the-Art Perspective

The association between introduction of the micro-axial flow pump Impella in hospitals and in-hospital mortality in patients treated with extracorporeal membrane oxygenation: interrupted time-series analyses

BACKGROUND

The micro-axial flow pump Impella, a new mechanical circulatory device for cardiogenic shock, is still only available in a limited number of hospitals, due to the facility certification requirements and insufficient evidence of the benefit of introducing Impella in hospitals. This study aimed to evaluate the impact of introducing Impella in hospitals on in-hospital mortality of patients treated with extracorporeal membrane oxygenation (ECMO).

METHODS

Using a nationwide Japanese inpatient database, we identified patients who received ECMO during hospitalization between 1 April 2014 and 31 March 2021. A hospital-level propensity score-matched cohort was created matching hospitals that introduced Impella (exposure group) to those that did not introduce Impella (control group). The inclusion period in each hospital was divided into two time periods according to the time of Impella introduction in the exposure group and the corresponding hospital in the control group (before and after exposure). The primary outcome was in-hospital mortality. Uncontrolled and controlled interrupted time-series analyses involved before-after exposure comparison and exposure-control comparison.

RESULTS

Out of 34,379 eligible patients, we created a matched cohort of 8351 patients from 86 hospitals with Impella introduction (exposure group) and 7230 patients from 86 hospitals without Impella introduction (control group). In-hospital mortality before and after exposure was 62.5% and 59.3, respectively, in the exposure group; and 66.8% and 63.7%, respectively, in the control group. Uncontrolled interrupted time-series analysis showed no significant level change or trend change in the before-after exposure comparison in both the exposure and the control groups. Controlled interrupted time-series analysis also showed no significant level change (-0.01%; 95% confidence intervals -5.36% to + 5.33%) or trend change (+ 0.10%, -0.30% to + 0.40%) after exposure in the exposure-control comparison.

CONCLUSIONS

This nationwide inpatient database study showed no association between Impella introduction in hospitals and in-hospital mortality of patients who underwent ECMO. Because this study confined itself to analze of the impact of the introduction of Impella solely at the hospital level, further detailed studies are warranted to assess its efficacy at the patient level.

Non-invasive assessment of left ventricular contractility by myocardial work index in veno-arterial membrane oxygenation patients: rationale and design of the MIX-ECMO multicentre observational study

Introduction and aims

Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is an increasingly utilized therapeutic choice in patients with cardiogenic shock, however, high complication rate often counteracts with its beneficial cardiopulmonary effects. The assessment of left ventricular (LV) function in key in the management of this population, however, the most commonly used measures of LV performance are substantially load-dependent. Non-invasive myocardial work is a novel LV functional measure which may overcome this limitation and estimate LV function independent of the significantly altered loading conditions of VA-ECMO therapy. The Usefulness of Myocardial Work IndeX in ExtraCorporeal Membrane Oxygenation Patients (MIX-ECMO) study aims to examine the prognostic role of non-invasive myocardial work in VA-ECMO-supported patients.

Methods

The MIX-ECMO is a multicentric, prospective, observational study. We aim to enroll 110 patients 48-72 h after the initiation of VA-ECMO support. The patients will undergo a detailed echocardiographic examination and a central echocardiography core laboratory will quantify conventional LV functional measures and non-invasive myocardial work parameters. The primary endpoint will be failure to wean at 30 days as a composite of cardiovascular mortality, need for long-term mechanical circulatory support or heart transplantation at 30 days, and besides that other secondary objectives will also be investigated. Detailed clinical data will also be collected to compare LV functional measures to parameters with established prognostic role and also to the Survival After Veno-arterial-ECMO (SAVE) score.

Conclusions

The MIX-ECMO study will be the first to determine if non-invasive myocardial work has added prognostic value in patients receiving VA-ECMO support.

The Effect of Artificial Pulsatility on the Peripheral Vasculature in Patients with A Continuous-Flow Ventricular Assist Device

BACKGROUND

Implantation of left ventricular assist systems (LVASs) has become the standard of care for advanced heart failure (HF). The absence of pulsatility in previous devices contributes to vascular and endothelial dysfunction, related to atherosclerotic or vascular complications. We hypothesized that the artificial pulsatility provided by the HeartMate 3 (HM3) LVAS would exert a favorable effect on the vasculature.

METHODS

In 32 patients implanted with HM3 (5 females; mean age 55±13.6 years), the reactive hyperemia index (RHI) and peripheral augmentation index (AI), markers of endothelial function and arterial stiffness, were measured with an Endo-PAT2000 prior to and in the 3^rd and 6^th months after implantation. RHI and AI data from 30 HeartMate II (HM II) recipients in the 3^rd and 6^th months after implantation, from 15 advanced HF patients without LVASs, and from 13 healthy volunteers were also analyzed.

RESULTS

In HM3 recipients, the mean RHI significantly decreased at 3^rd and 6^th months after implantation. The RHI was substantially lower at baseline than that of healthy or HF reference group. Increasing AI values, indicating worsening arterial stiffness, were also observed. Similar trends were observed in HM II recipients between the 3^rd and 6^th months, but with higher absolute values of RHI and AI.

CONCLUSIONS

We detected impaired vascular function in HM3 patients and provided additional evidence on the negative effect of low pulsatility on vascular function after LVAS implantation. The results suggest that the artificial pulsatility of the HM3 does not avert the progression of endothelial dysfunction.

Watershed phenomena during extracorporeal life support and their clinical impact: a systematic in vitro investigation

Aims

Extracorporeal life support (ECLS) during acute cardiac failure restores haemodynamic stability and provides life‐saving cardiopulmonary support. Unfortunately, all common cannulation strategies and remaining pulmonary blood flow increase left‐ventricular afterload and may favour pulmonary congestion. The resulting disturbed pulmonary gas exchange and a residual left‐ventricular action can contribute to an inhomogeneous distribution of oxygenated blood into end organs. These complex flow interactions between native and artificial circulation cannot be investigated at the bedside: only an in vitro simulation can reveal the underlying activities. Using an in vitro mock circulation loop, we systematically investigated the impact of heart failure, extracorporeal support, and cannulation routes on the formation of flow phenomena and flow distribution in the arterial tree.

Methods and results

The mock circulation loop consisted of two flexible life‐sized vascular models (aorta and vena cava) driven by two paracorporeal assist devices, resistance elements, and compliance reservoirs to mimic the circulatory system. Several large‐bore antegrade and retrograde access ports allowed connection to an ECLS system for extracorporeal support. With four degrees of extracorporeal support—that for cardiac failure, early recovery, late recovery, and weaning—we investigated aortic blood flow velocity, blood flow, and mixing zones using colour‐coded Doppler ultrasound in the aorta and its corresponding branches. Full retrograde extracorporeal support (3–4 L/min) perfused major portions of the aorta but did not reach the supra‐aortic branches and ascending aorta, resulting in an area in the thoracic aorta demonstrating nearly stagnant blood flow velocities during cardiogenic shock and early recovery (0 ± 4 cm/s; −10 ± 15 cm/s, respectively) confined by two watersheds at the aortic isthmus and renal artery origin. Even increased ECLS flow was unable to shift the watershed towards the aortic arch. Antegrade support resulted in homogeneous flow distribution during all stages of cardiac failure but created a markedly negative flow vector in the ascending aorta during cardiogenic shock and early recovery with increased afterload.

Conclusions

Our systematic fluid‐mechanical analysis confirms the clinical assumption that despite restoring haemodynamic stability, extracorporeal support generates an inhomogeneous distribution of oxygenated blood with an inadequate supply to end organs and increased left‐ventricular afterload with absent ventricular unloading. End‐organ supply may be monitored by near‐infrared spectroscopy, but an obviously non‐controllable watershed emphasizes the need for additional measures: pre‐pulmonary oxygenation with a veno‐arterial‐venous ECLS configuration can allow a transpulmonary passage of oxygenated blood, providing improved end‐organ supply.