What are the effects on hemodynamics of support mechanisms such as Extracorporeal Life Support (ECLS), aortic balloon pump (Intra-Aortic Balloon Pump, IABP), Intravascular Oxygenation (IVOX), and Ventricular Assist Device (VAD) in critically ill adult or pediatric patients with severe cardiac or respiratory failure?

Hemodynamic Effects of Mechanical Circulatory Support Devices

Extracorporeal Life Support (ECLS/ECMO)

ECLS provides complete or near-complete cardiopulmonary support by draining venous blood, oxygenating it externally, and returning it to either the venous (VV-ECMO) or arterial (VA-ECMO) circulation, with fundamentally different hemodynamic profiles depending on configuration. 1

Venovenous (VV) ECMO Hemodynamics

• Provides isolated respiratory support without direct hemodynamic effects since oxygenated blood returns to the venous system, requiring the native heart to maintain all cardiac output and systemic perfusion 1
• Preserves normal cardiac physiology and pulsatile flow 1
• May indirectly improve hemodynamics by correcting hypoxemia and reducing pulmonary vascular resistance 1
• Does not increase left ventricular afterload 2

Venoarterial (VA) ECMO Hemodynamics

• Provides both respiratory support and direct hemodynamic augmentation by actively pumping oxygenated blood into the arterial circulation, bypassing the heart entirely 1
• At 90% ECMO flow, the circuit provides 90% of total cardiac output with the native heart contributing only 10%, indicating near-complete cardiac failure 3
• Significantly increases left ventricular afterload by retrograde arterial perfusion, which can cause LV distension, pulmonary edema, and myocardial ischemia 4
• Creates risk of differential hypoxemia (Harlequin syndrome) where poorly oxygenated blood from the native heart perfuses the upper body while ECMO-oxygenated blood perfuses the lower body 3
• Reduces preload to the right ventricle by draining venous return 2
• Mean pulmonary artery pressure decreases significantly within 48 hours (from 32-34 mmHg to 21-22 mmHg) 5
• Eliminates or severely reduces pulsatile flow, which may contribute to complications 2

Critical Hemodynamic Monitoring for VA-ECMO

• Right radial arterial blood gas sampling is essential to assess cerebral oxygenation, as this site best represents what the brain receives 3
• Continuous monitoring of arterial blood pressure, ECMO flow, and pulse pressure from right radial line provides real-time indication of mixing point location 3
• Repeated echocardiography is mandatory to assess native cardiac function and detect LV distension 3, 1

Management of VA-ECMO Complications

• Immediate intervention required if upper body hypoxemia develops: increase ECMO flow to move mixing point proximally, optimize mechanical ventilation to improve native lung oxygenation 3
• Consider V-AV ECMO configuration (adding jugular venous return cannula) if differential hypoxemia persists despite maximal interventions 3
• LV venting mechanisms are often required to prevent LV distension: options include IABP, Impella device, pulmonary artery cannulation, or surgical LV venting 4

Intra-Aortic Balloon Pump (IABP)

The IABP provides modest hemodynamic support through counterpulsation—inflating during diastole to augment coronary perfusion and deflating before systole to reduce afterload—but does not significantly improve survival in cardiogenic shock. 4

Hemodynamic Effects

• Increases diastolic blood pressure by 10-20% through balloon inflation during diastole, augmenting coronary and systemic perfusion 2
• Reduces systolic afterload by 10-15% through rapid deflation before systole, decreasing myocardial oxygen demand 2
• Modestly increases cardiac output (typically 0.3-0.5 L/min) 2
• Improves coronary perfusion pressure during diastole 2
• Does not provide direct circulatory support or oxygenation 4

Clinical Evidence and Limitations

• The IABP-SHOCK II trial demonstrated no mortality benefit when IABP was used routinely in acute MI with cardiogenic shock (39.7% vs 41.3% mortality, p=0.69) 4
• No improvement in time to hemodynamic stabilization, ICU length of stay, renal function, or serum lactate levels 4
• Routine use of IABP cannot be recommended based on current evidence 4
• When combined with VA-ECMO, IABP effectively reduces pulmonary artery pressure (32 mmHg to 21 mmHg at 48 hours) and improves LV function 5
• IABP has lower complication rates than percutaneous VADs when used with ECMO (no bleeding at insertion site vs 22% with PVAD, no hemolysis vs 18% with PVAD) 5

Current Role

• May be considered as an LV venting mechanism during VA-ECMO to prevent LV distension 4
• Limited to larger children, adolescents, and adults due to size constraints 6
• Should not delay definitive coronary revascularization in acute MI 4

Ventricular Assist Devices (VADs)

VADs provide direct mechanical unloading and circulatory support by actively pumping blood from the ventricle to the systemic or pulmonary circulation, with hemodynamic effects varying by device type, flow rate, and configuration. 4

Left Ventricular Assist Device (LVAD) Hemodynamics

• Directly unloads the left ventricle by draining blood from the LV apex and pumping it into the ascending aorta or descending aorta 4
• Reduces LV preload, end-diastolic volume, and wall stress 2
• Decreases myocardial oxygen consumption 2
• Increases systemic cardiac output and mean arterial pressure 2
• Continuous-flow devices eliminate pulsatile flow, which may complicate pulse assessment and blood pressure measurement 4
• Improves end-organ perfusion as evidenced by decreased lactate and improved renal function 4

Percutaneous VAD (PVAD) Hemodynamics

• Provides superior hemodynamic support compared to IABP with greater increases in cardiac output and mean arterial pressure 4
• Meta-analysis showed improved hemodynamics with PVAD vs IABP but no difference in outcomes 4
• When combined with ECLS, effectively reduces pulmonary artery pressure (34 mmHg to 22 mmHg at 48 hours) 5
• Improves LV ejection fraction (16±7% to 22±10%) and reduces LV end-diastolic dimension (61±12 mm to 54±12 mm) 5

Right Ventricular Assist Device (RVAD) Hemodynamics

• Unloads the right ventricle by draining blood from the right atrium or RV and pumping it into the pulmonary artery 4
• Reduces RV preload and wall stress 2
• Maintains pulmonary blood flow in right ventricular failure 4
• Options include Impella RP and TandemHeart Protek-Duo 4

Clinical Outcomes and Monitoring

• Approximately 20% of LVAD patients develop atrial arrhythmias, most commonly within the first 60 days, associated with worse quality of life and decreased functional improvement 4
• Ventricular arrhythmias occur in about one-third of continuous-flow LVAD patients but may not be life-threatening 4
• Continuous electrocardiographic monitoring is standard of care for all hospitalized VAD patients due to difficult pulse assessment and arrhythmia risk 4
• REMATCH trial showed 2-year survival of 23% with LVAD vs 8% with medical therapy in non-transplant-eligible patients 4
• Device-related complications include bleeding, infection, thromboembolism, and device failure 4

Hemodynamic Recovery Potential

• Prolonged mechanical unloading may occasionally allow myocardial recovery sufficient for device explantation, though this is rare except in acute-onset heart failure without coronary disease 4
• Improvements in ventricular mechanics, myocardial energetics, histology, and cell signaling have been documented with LVAD support 4

Intravascular Oxygenation (IVOX)

IVOX is an obsolete technology with limited historical use and no current clinical role. The device consisted of hollow fiber membranes placed in the vena cava to provide supplemental oxygenation without extracorporeal circulation, but it provided insufficient gas exchange and is no longer used in clinical practice. 6

Device Selection Algorithm

Device selection requires multidisciplinary shock team input with consideration of the following hierarchy: 4, 7

1. Assess primary pathophysiology:

   • Isolated respiratory failure → VV-ECMO 1
   • Cardiogenic shock with adequate respiratory function → LVAD/PVAD 4
   • Combined cardiopulmonary failure → VA-ECMO 1
   • Right ventricular failure → RVAD 4
   • Biventricular failure → Bilateral VADs or VA-ECMO with LV venting 4

2. Evaluate severity and reversibility:

   • Refractory shock (SCAI stage D or E) despite maximal medical therapy → Consider VA-ECMO or PVAD 7
   • Potentially reversible condition → Short-term MCS as bridge to recovery 7
   • Irreversible failure → Long-term VAD as destination therapy or bridge to transplant 4

3. Consider institutional expertise:

   • ECMO should only be performed at centers with ≥20-25 cases annually with 24/7 multidisciplinary teams 3, 1
   • Lower-volume centers should establish transfer protocols with ECMO-capable institutions 1

Critical Pitfalls to Avoid

• Do not delay coronary revascularization to place mechanical support devices in acute MI—revascularization remains definitive therapy 7
• Do not use VA-ECMO without monitoring for LV distension—have LV venting strategy ready 4
• Do not ignore upper body oxygenation during VA-ECMO—right radial arterial monitoring is mandatory 3
• Do not continue mechanical support indefinitely without clear exit strategy (recovery, durable device, or transplant) 7
• Do not use IABP routinely in cardiogenic shock—reserve for specific indications like LV venting during ECMO 4