64. Acute Shock – Mechanical Circulatory Support- Clinical Scenarios

Daniel Ryan Ziazadeh, MD, Clauden Louis, MD, Sunil Prasad, MD

Concept

  • Short term MCS
  • Cannulation options
  • Patient selection
  • Clinical Trials (MOMENTUM & ENDURANCE)
  • INTERMACS
  • Pitfalls that arise in of the above steps

AMBIOMED BVS 5000

This was the very first FDA device that was approved for use in the management of cardiogenic shock in the early 1990s. It is a pneumatically driven, pulsatile, extracorporeal, asynchronous ventricular assist device capable of providing cardiac outputs of 5 L/min to 6 L/min via univentricular or biventricular support.

Thoratec pVAD

The Thoratec pVAD is a pneumatically driven peripheral ventricular assist device that is designed to provide left, right, or biventricular support for short to medium term recovery

Centrimag

Similar to the pVAD, the Centrimag pump is also made by Thoratec. This short term paracorporeal device is magnetically levitated and can be used to provide left, right, and biventricular short-term support and can be attached to a membrane oxygenator for ECMO. In contrast to early generation short term devices, the Centrimag’s non-pulsatile continuous flow design mitigates several side effects that hampered its predecessors including hemolysis, thrombosis, inflammatory activation, and heat.

Tandem Heart

The Tandem Heart is another percutaneous ventricular assist device that can be used for left and right, but not biventricular support. In the LVAD configuration, the Tandem Heart uses a unique left atrial to femoral artery bypass system via a trans-septal cannula from the RA into the LA via the femoral vein.

Chief complaint

“A 56-year-old male presents to the Emergency Department with an anterolateral STEMI and is taken emergently to the Cath Lab for intervention. His hemodynamics decline during the time it takes to get to the Cath Lab. During interventional access he has an episode of ventricular fibrillation which is successfully defibrillated. He remains persistently hypotensive and you are consulted for emergent placement of VA ECMO.”

Differential

Cardiogenic shock

History and physical

Any patient requiring mechanical circulatory support needs to have a comprehensive systems-based history and physical to identify history of stroke, renal disease, coronary lesions, respiratory problems, bleeding disorders, or peripheral vascular disease. Often, this cannot be performed prior to initiation of mechanical circulatory support, however it is important to determine their neurological status or last known well.

Tests

  • Biochemical Profile (CMP, LFTs)
  • CBC
  • Cardiac Enzymes (Troponin, CK, LDH)
  • ABG (Base Deficit)
  • Lactate (Serial Arterial)
  • BNP
  • ECHO (TTE/TEE) to evaluate for Tamponade, Wall Rupture, Septal Defect, Ejection Fraction
  • CXR (Interstitial edema, Kerley B lines, cardiomegaly, bilateral effusions)
  • Coronary Angiography (Assess coronary vasculature to evaluate need for revascularization)
  • EKG (evaluate for STEMI, NSTEMI, life threatening arrhythmia)
  • Swan-Ganz catheterization

These tests allow for rapid diagnosis, identification of critical lesions that require immediate intervention, help guide resuscitation, and supportive therapies.

Index scenario (additional information)

“The patient has a normal neurological exam prior to entering the Cath Lab. Norepinephrine is immediately started, but the patient remains with refractory hypotension. Radial access is obtained for catheterization and diagnostic angiography demonstrates critical LM stenosis extending to the proximal LAD/LCX bifurcation. ABG demonstrates an arterial lactate of 6.”

Treatment/management

This patient will require initiation of mechanical circulatory support in the setting of cardiogenic shock. While Interventional Cardiology is performing PCI, femoral groin access should be obtained for tandem placement of venous and arterial cannulas and initiation of VA-ECMO. In the event of a cardiac arrest, one team member can perform compressions, while anesthesia manages the airway.  Another option in this scenario may include devices such as Impella.

Placing an individual on VA ECMO provides a bridge to definitive intervention. Patients in shock lack the oxygen carrying capacity of the heart to meet the demands of the body. The patient’s MAP should be kept at the upper range of normal to ensure adequate perfusion pressure to the end organs (renal, hepatic, and brain). ECMO RPMs should be titrated to allow for full support when initially placed with a goal cardiac index of 2.2 – 2.4 if at possible.

While other support therapies such as IABP may help reduce afterload, increase coronary perfusion pressure and augment blood pressure, they do not deliver direct cardiac output to end organs. The patient in this scenario has likely suffered significant myocardial injury. Emergent revascularization with PCI will be beneficial in the long term to provide the myocardium with more oxygen carrying capacity, but in the short term myocardial stunning, hibernation, or infarction has ensued to the point that the heart is unable to provide sufficient cardiac output.

Contraindications

Relative

  • DNR
  • Severe neurological event
  • Known PVD (distal aortic thrombus and severe aorta-iliac disease are specific to femoral access)

Operative steps

ACLS

  • Secure the airway
  • Assess for bilateral breath sounds
  • Maximize circulation via compression, fluids, inotropes

Cannulation

  • Determine access (Femoral, Central, Axillary).
  • Use ultrasound guidance if immediately available to avoid access complications.
  • For groin access, palpate the femoral artery for a pulse if present.
  • Alternatives include groin cut down for direct visualization and arterial cannula purse string sutures to aid in repair at time of ECMO explant.
  • If access to instruments are not available, perform a blind stick. Often, a femoral pulse is not present in cardiogenic shock.  Make sure to mark appropriate anatomy (inguinal ligament) to avoid a high stick. 
  • Once intraluminal access is obtained, pass a flexible J-tip guidewire into the artery and vein.
  • Access ipsilateral Superficial Femoral Artery via antegrade stick for placement of 6F reperfusion catheter & 15F or larger arterial ECMO cannula.
  • Give Heparin
  • Sequentially dilate the vessel via Seldinger technique.
  • Insert minimum 15F arterial and 25F venous ECMO cannulas and flush with heparinized saline and clamp with tubing clamps.
  • Always attempt to use the smallest size catheter for adequate cardiac output for a given BSA.
  • Connect ECMO tubing in air-free manner.  If saline is unavailable for de-airing, can use blood by carefully loosening tube clamps.
  • Y in 6F reperfusion catheter to arterial ECMO cannula. De-air via stopcock.
  • Check your lines to ensure no air bubbles. Release tubing clamps and initiate ECMO.
  • Alternative venous cannulas include central right atrial, right internal jugular, subclavian vein.

Initiation

  • Check your ACT and make sure you are > 250.
  • Ensure there is no obstruction in the pump.
  • Specify your temperature.

Maintenance

  • Check for pulsatility.
  • If chugging occurs, add volume.
  • Maintain MAPs (usually 65-75 mmHg) – use inotropes or fluids as needed.
  • Flow is usually 4.4-4.5 L/min, which is equal about Cardiac Index of 2 in most patients with 15F arterial cannula. Flow increases to 5.8L with a 17F arterial cannula.
  • Assess perfusion via arterial blood gas, lactate, venous saturation, urine output.
  • Increase or decrease Sweep to modulate pCO2.
  • Cooling to mild hypothermia (32-34°C) may allow a decrease of flow and MAPs when needed.
  • Check ECHO – heart should be fairly full, CVP and PAP should be normal or slightly elevated.
  • Check sats, ABG, oxygenation, visual inspection of arterial blood – should be bright red and there should be no clots in the circuit).
  • Check Doppler signals specifically DP/PT in the ipsilateral limb of the arterial ECMO cannula to evaluate for critical limb ischemia.
  • For Axillary/Subclavian cannulation, place pulse oximetry and radial arterial line to assess perfusion to the ipsilateral arm.
  • There are a variety of roller or centrifugal ECMO pumps that can be used. We prefer centrifugal (Centrimag, Rotaflow, CardioHelp, and Sarns) pumps as they are non-occlusive, provide passive displacement, and have less hemolysis.

The patient determines the course of VA ECMO. Goal is to maximize the mechanical flow of the machine at full RPMs to wean vasopressors and inotropes as able.

Potential questions/alternative scenarios

“After initiation of VA ECMO, arterial lactate begins to normalize. You obtain an ECHO and notice that the LV appears severely hypokinetic and distended. EF is estimated at ~5%. What do you do?”

The ventricle is not decompressed, and the heart is barely ejecting. Strong consideration should be made for an LV vent. Initial management should include maximizing drainage of the ECMO circuit. Evaluate for any signs of pulmonary edema or severe mitral regurgitation as the heart may not be able to overcome the regurgitant volume from the atrium. Medical optimization via inotropes should be attempted first. A mechanical circulatory vent such as an Impella can be placed across the LVOT and Aortic Valve to decompress the ventricle but be careful and watch out for signs of hemolysis. Alternatively, trans-septal atrial puncture can be performed, by going up the femoral vein into the IVC across the right atrium and into the left atrium to facilitate placement of a TandemHeart Cannula. Passive venting can also be achieved with an 8F suction catheter trans-apically across the aortic valve.

“Four days later, repeat ECHO shows significantly improved LV EF 50% compatible with myocardial recovery. The patient is hemodynamically stable and has developed a pulsatile waveform with MAP >65. What do you do?”

Weaning from ECMO

In general, you need to be warm, have pulsatility, stable rhythm and be ventilating in order to come off ECMO.

  • Confirm that myocardial and hemodynamic recovery has occurred as assessed by echocardiography (LV EF >25%, Aortic VTI >10cm, TDSa >6 vm/s)
  • Slowly wean speeds to decrease flow 0.5L/30 mins
  • Ensure patient is stable on minimal ECMO support (flow 2L/min)
  • Evaluate for resolution of metabolic disturbances (afebrile/euvolemic)
  • Confirm pulsatile waveform for >24 hours
  • Ensure MAPs acceptable (>65mmHg) in absence of pressor/inotrope
  INTERMACS Profiles 
Profile 1: Critical cardiogenic shock Life-threatening hypotension despite rapidly escalating inotropic support, critical organ hypoperfusion, often confirmed by worsening acidosis vs lactate levels. 
Profile 2: Progressive decline Declining function despite intravenous inotropic support, may be manifest by worsening renal function, nutritional depletion, inability to restore volume balance “Sliding on inotropes.” Also describes declining status in patients unable to tolerate inotropic therapy. 
Profile 3: Stable, inotrope dependent Stable blood pressure, organ function, nutrition, and symptoms on continuous intravenous inotropic support (or a temporary circulatory support device or both) but demonstrating repeated failure to wean from support due to recurrent symptomatic hypotension or renal dysfunction “Dependent stability.” 
Profile 4: Resting symptoms Stable close to normal volume status but experiences daily symptoms of congestion at rest or during ADL. Doses of diuretics generally fluctuate. More intensive management and surveillance strategies should be considered, which may in some cases reveal poor compliance that would compromise outcomes with any therapy.   
Profile 5: Exertion intolerant Comfortable at rest and with ADL but unable to engage in any other activity, living predominantly within the house. Patients are comfortable at rest without congestive symptoms, but may have underlying refractory elevated volume status, often with renal dysfunction. If underlying nutritional status and organ function are marginal, patient may be more at risk than INTERMACS 4, and require definitive intervention. 
Profile 6: Exertion limited Without evidence of fluid overload; comfortable at rest; fatigues after the first few minutes of any meaningful activity. Attribution to cardiac limitation requires careful measurement of peak oxygen consumption, in some cases with hemodynamic monitoring to confirm severity of cardiac impairment. 
Profile 7: Advanced NYHA III Without current or recent episodes of unstable fluid balance, living comfortably with meaningful activity limited to mild physical exertion. 
  • Confirm acceptable pulmonary function (clear CXR, PaO2 >100mmHg with FiO2 21%)
  • Wean sweep and adjust ventilator settings to maintain proper ventilation if still intubated

There is no single metric used to determine whether a patient is suitable for discontinuation from ECMO, rather it is a combination of clinical, radiographic, laboratory, and hemodynamic factors. Once the decision has been made to discontinue ECMO, venous return to the right heart will increase as ECMO flows decrease. The left heart will compensate if myocardial recovery has occurred and offset any effects from a reduction in ECMO flows. The patient should be decannulated as quickly as possible to avoid risk of complications as the number of days on VA ECMO increases. The cardiovascular surgery team should be mobilized to the operating room or interventional suite to remove the cannulas via open cut down or with percutaneous closure devices. If the patient is still intubated, transesophageal echocardiography should be used to monitor cardiac function in real time. Electrolytes and volume status should be optimized. Inotropes can be restarted as needed to assist with cardiac output post decannulation. Serial arterial blood gases can be drawn to monitor for any cardiopulmonary dysfunction.

Potential questions/alternative scenarios

“40 y.o. female with no previous past medical history who endorses fatigue and dyspnea on exertion that has progressively worsened over the last several months however has not sought previous care. She does not have children however does endorse a history of a tubal pregnancy requiring surgery several months ago. She undergoes an echocardiogram this admission with global hypokinesis and EF to 15%. She is brought to the cardiac cath lab for further evaluation and management of her heart failure with consideration for advanced therapies. Her coronary cath is nonrevealing and her bedside hemodynamics display a CVP of 17, CI of 1.2, and SvO2 of 40%.  Additionally, she has decreased urine output and elevated LFTs. While in the cardiac catheterization lab, angiographic evaluation of her femoral arteries reveals 4 mm femoral vessel and her BSA is 2.1.” What support would you recommend, and concerns do you have if any?

Several therapeutics exist from chemical to mechanical. Given her very limited cardiac function and cardiogenic shock state, chemical therapeutics alone may not be suffice. She should be considered for a mechanical support of which several modalities and routes of administration exist. Coronary augmented perfusion alone will not improve her state thus IABP is not considered. Given the size of her vessels she is unable to be supported by Impella CP (14Fr sheath) and ultimately Cardiac surgery should be considered for surgical placement of Impella device with cutdown for proximal and distal vessel control. Also, placement in the axillary vessel allows for ambulation as oppose to the immobility that follows placement in the femoral vessels. In this patient given the current devices at the time of writing of this text she can be considered for Impella 5.0 placement (or 5.5) through a tunneled right axillary approach with graft.

“Should she be considered for peripheral VA ECMO of the lower extremities?”

For the same reason the Impella will not be placed in the femoral vessels VA-ECMO should not be considered at this site. The arterial cannula for this patient should be a 15 French cannula or 17 French optimally based on her BSA, but her femoral vessels are disproportionally smaller. The 15 French cannula has a 5 mm outer diameter. There is likely a combination of her vessels being clamped down in her shock state as well as small vessels intrinsic to this patient. Although vessels are much more compliant in younger patients that older/calcified vessels issues with distal perfusion will remain with small vessels.

Pearls/pitfalls

  • Always use ultrasound if available, vessel injury is devastating to the shock patient
  • Always place distal reperfusion catheter in ipsilateral superficial femoral artery as, limb loss increases mortality of the patient to near 100% in some series
  • If possible, artery and vein in contralateral leg, however in the emergent settings access whatever vessels you can
  • 15 Fr arterial and 25 Fr venous are nearly universal sizes for the adult.

Suggested readings

  • John R, Long JW, Massey HT. Outcomes of a multicenter trial of the Levitronix CentriMag ventricular assist system for short-term circulatory support. The Journal of Thoracic and Cardiovascular Surgery, 2011:141(4), 932–939.
  • Sultan I, Kilic A, Kilic A. Short-Term Circulatory and Right Ventricle Support in Cardiogenic Shock: Extracorporeal Membrane Oxygenation, Tandem Heart, CentriMag, and Impella. Heart Failure Clinics, 2018:14(4), 579–583.
  • Deshpande A, Kar B, Paniagua D. Tandem Heart, percutaneous left ventricular assist device treatment for severe refractory cardiogenic shock: The Debakey VA experience. Journal of the American College of Cardiology, 2014:63(12), A1854.
  • Kar B, Adkins LE, Civitello AB. Clinical experience with the Tandem Heart percutaneous ventricular assist device. Texas Heart Institute Journal, 2006:33(2), 111–115.
  • Kurihara C, Kawabori M, Critsinelis A. Impact of Tandem Heart Use for Heart Failure Patients as a Bridged to Long-term Continuous Flow Left Ventricular Assist Devices. The Journal of Heart and Lung Transplantation, 2018:37(4), S321–S322.
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