Understanding Cardiogenic Shock and Advanced Mechanical Circulatory Support: VA ECMO + Impella = ECPELLA

Nathan Stewart BSN, RN, CCRN and Brian Chapman BS, RRT-ACCS-NPS

Cardiogenic shock is a life-threatening condition where the heart is unable to pump sufficient blood to meet the body’s needs, leading to severe end-organ hypoperfusion and failure. This condition often results from acute myocardial infarction, severe heart failure, or other cardiac disorders. Timely intervention and advanced mechanical circulatory support are crucial in managing cardiogenic shock effectively. This article explores the pathophysiology of cardiogenic shock, the role of Veno-Arterial Extracorporeal Membrane Oxygenation (VA ECMO), and the use of the Impella device for left ventricular unloading.

Pathophysiology of Cardiogenic Shock

Cardiogenic shock occurs when the heart's pumping ability is severely compromised, leading to inadequate tissue perfusion and oxygen delivery. The primary causes include:

- Acute Myocardial Infarction: Reduced myocardial contractility due to ischemic damage.

- Severe Heart Failure: Progression of chronic heart failure leading to acute decompensation.

- Arrhythmias: Life-threatening arrhythmias such as ventricular tachycardia or fibrillation.

- Cardiomyopathy: Structural and functional abnormalities of the myocardium.

Clinical presentation includes hypotension, tachycardia, altered mental status, oliguria, and cold, clammy skin. Laboratory findings often show elevated lactate levels, indicating anaerobic metabolism due to poor perfusion.

Initiating VA ECMO for Cardiogenic Shock

When conventional therapies (inotropes, vasopressors, and mechanical ventilation) fail to stabilize the patient, VA ECMO is considered. VA ECMO provides both cardiac and respiratory support by oxygenating blood outside the body and returning it to the systemic circulation, thus bypassing the failing heart and lungs.

Process of Initiating VA ECMO:

1. Cannulation: Typically involves femoral artery and vein cannulation using large bore multistage venous drainage cannulas and single stage arterial return cannulas (French Sizes and Lengths dependent on patient size and anatomy). Ultrasound guidance is often used to ensure proper placement.

2. Circuit Setup: The ECMO circuit includes a pump, oxygenator, and heat exchanger. Blood is drained from the venous system, oxygenated, and returned to the arterial system.

3. Management: Continuous monitoring of hemodynamics, oxygenation, and coagulation parameters is essential. Anticoagulation with heparin is typically required to prevent circuit thrombosis.

VA ECMO serves as a bridge to recovery, heart transplantation, or other long-term mechanical support.

The Role of Impella for Left Ventricular Unloading

While VA ECMO provides essential circulatory support, it can increase afterload on the left ventricle (LV), potentially worsening myocardial injury and delaying recovery. The Impella device, a percutaneous left ventricular assist device (LVAD), helps address this issue by unloading the LV.

Using Impella for LV Unloading:

1. Device Insertion: The Impella is inserted via the femoral artery and advanced into the left ventricle under fluoroscopic guidance.

2. Function: The Impella draws blood in the left ventricle through the inlet and then pushes the blood outward into the aorta through the outlet, reducing LV pressure and volume, which decreases myocardial oxygen demand and helps improve coronary perfusion.

3. Management: Similar to ECMO, continuous monitoring of hemodynamics and device function is crucial. The combination of VA ECMO and Impella provides both systemic perfusion and myocardial protection.

Utilizing a Dual Reperfusion Catheter Technique

The dual reperfusion catheter technique for patients on ECPELLA (Impella CP) ensures adequate blood flow to both legs by inserting catheters typically into the superficial femoral arteries. However, the posterior tibial, dorsalis pedis and popliteal arteries are all alternative options to the superficial femoral artery. This method prevents ischemia in the limbs used for ECPELLA access by maintaining distal limb perfusion. By directing blood flow around the occlusion caused by the large bore catheter, the technique reduces the risk of complications such as: limb ischemia, promoting better overall patient outcomes and ensuring sufficient blood supply to both legs during mechanical circulatory support. 

Fig 1: Arterial Cannula in Right Femoral Artery and Venous Cannula in Right Femoral Vein with First Reperfusion Catheter in Superficial Femoral Artery

Fig 2: Impella Catheter in Left Femoral Artery with 2nd Reperfusion Catheter in Superficial Femoral Artery

Case Study

A 55-year-old male presented with acute myocardial infarction, leading to cardiogenic shock. Despite maximal medical therapy, including high doses of inotropes (Dobutamine 15 mcg/kg/min and Epinephrine 0.06 mcg/kg/min) and vasopressors (Norepinephrine 0.3 mcg/kg/min), the patient's hemodynamics remained unstable with a mean arterial pressure (MAP) of 55 mmHg, SVO2 of 38%, CI of 1.4, and lactate levels rising to 7 mmol/L.

Phase 1: VA ECMO Initiation

- Cannulation: 23 Fr Drainage cannula in the right femoral vein and an 18 Fr Return cannula in the right femoral artery. 

- Hemodynamics: MAP improved to 65-70 mmHg; lactate levels began to decrease. While simultaneously coming down on vasopressor and inotropic support. 

- Observation: Persistent high left ventricular end-diastolic pressure (LVEDP) suggested inadequate unloading. 

Phase 2: Impella Placement

- Device Insertion: Left femoral artery to the Left Ventricle - Inlet Placement and Aorta - Outlet of Impella.

- Hemodynamics: Significant improvement in LV unloading, LVEDP reduced, and MAP stabilized at 75-80 mmHg.

- Outcome: Lactate levels normalized (<2 mmol/L), SVO2 improved to 58, CI improved to 2.4, patient on very low doses of inotropes and pressors and the patient's overall condition improved, allowing time for myocardial recovery and eventual weaning off ECMO.

Conclusion

Managing cardiogenic shock requires a multidisciplinary approach and the integration of advanced mechanical circulatory support technologies. VA ECMO and Impella provide critical support, improving the chances of recovery and survival for patients with severe cardiac failure. Understanding and effectively implementing these therapies is vital in providing the best possible care for patients.

References

- Alfred ECMO Guideline. (n.d.). Distal perfusion cannula.

- American College of Cardiology. (n.d.). Indications and Complications for VA-ECMO for Cardiac Failure.

- American College of Cardiology. (n.d.). Use of Impella in Cardiogenic Shock. Retrieved from [ACC](https://www.acc.org)

- Critical Care Medicine. (n.d.). VA ECMO and Impella in Cardiogenic Shock. Retrieved from [Critical Care Medicine](https://ccforum.biomedcentral.com)

- Dove Medical Press. (n.d.). Distal perfusion catheters during VA-ECMO.

- Extracorporeal Life Support Organization (ELSO). (n.d.). Guidelines for ECMO. Retrieved from [ELSO](https://www.elso.org)

- Perfusion.com. (n.d.). Cannulation Strategies in Adult V-A and V-V ECMO.