Utilizing Percutaneous Ventricular Assist Devices in Acute Myocardial Infarction Complicated by Cardiogenic Shock

Summary

Percutaneous ventricular assist devices are increasingly being utilized in patients with acute myocardial infarction and cardiogenic shock. Herein, we discuss the mechanism of action and hemodynamic effects of such devices. We also review algorithms and best practices for the implantation, management and weaning of these complex devices.

Abstract

Cardiogenic shock is defined as persistent hypotension, accompanied by evidence of end organ hypo-perfusion. Percutaneous ventricular assist devices (PVADs) are used for the treatment of cardiogenic shock in an effort to improve hemodynamics. Impella is currently the most common PVAD and actively pumps blood from the left ventricle into the aorta. PVADs unload the left ventricle, increase cardiac output and improve coronary perfusion. PVADs are typically placed in the cardiac catheterization laboratory under fluoroscopic guidance via the femoral artery when feasible. In cases of severe peripheral arterial disease, PVADs can be implanted through an alternative access. In this article, we summarize the mechanism of action of PVAD and the data supporting their use in the treatment of cardiogenic shock.

Introduction

Cardiogenic shock (CS) is defined as persistent hypotension (systolic blood pressure <90 mmHg for >30 minutes, or the need for vasopressors or inotropes), end-organ hypo-perfusion (urine output <30 mL/h, cool extremities or lactate > 2 mmol/L), pulmonary congestion (pulmonary capillary wedge pressure (PCWP) ≥ 15 mmHg) and decrease cardiac performance (cardiac index <2.2 )^1,2 due to a primary cardiac disorder. Acute myocardial infarction (AMI) is the most common cause of CS³. CS occurs in 5-10% of AMI and historically has been associated with significant mortality^3,4. Mechanical circulatory support (MCS) devices such as intra-aortic balloon pump (IABP), percutaneous ventricular assist devices (PVAD), extracorporeal membrane oxygenation (ECMO) and percutaneous left atrial to aortic devices are frequently used in patients with CS⁵. Routine use of IABP has demonstrated no improvement in clinical outcomes or survival in AMI-CS¹. Given the poor outcomes associated with AMI-CS, the difficulties in conducting trials in AMI-CS, and the negative results of IABP use in AMI-CS, clinicians are increasingly looking to other forms of MCS.

PVADs are increasingly utilized in patients with AMI-CS⁶. In this article, we will focus our discussion primarily on the Impella CP, which is the most common PVAD used currently⁶. This device utilizes an axial flow Archimedes-screw pump which actively and continuously propels blood from the left ventricle (LV) into the ascending aorta (Figure 1). The device is most frequently placed in the cardiac catheterization laboratory under fluoroscopic guidance via the femoral artery. Alternatively, it can be implanted through an axillary or transcaval access when necessary^7,8.

Protocol

This protocol is the standard of care in our institution.

1. Insertion of the PVAD (e.g., Impella CP)

1. Obtain common femoral access over the lower half of the femoral head under fluoroscopic and ultrasound guidance using a micro-puncture needle^9,10. Position the micro-puncture sheath and obtain an angiogram of the femoral artery to confirm appropriate arteriotomy location¹¹.
2. Insert a 6 Fr sheath in the femoral artery.
3. If there is concern for ilio-femoral disease, insert a pigtail catheter in the inferior portion of the abdominal aorta and perform an angiogram of the iliofemoral system to ensure there is no significant peripheral artery disease (PAD) that may preclude PVAD insertion. If there is moderate disease or calcification of the iliac arteries consider using a longer 25 cm 14 French sheath so that the tip of the sheath is in a relatively healthy segment of the abdominal aorta.
4. Serially dilate the arteriotomy site over a stiff .035" wire using 8, 10 and 12 Fr dilators sequentially. Then, insert the 14 Fr peel away sheath under fluoroscopic guidance, ensuring the tip advances without resistance.
5. Administer heparin bolus (~100 U/kg body weight) for an ACT goal of 250 to 300 s. Alternative anticoagulation include bivalirudin and argatroban.
6. Use a pigtail catheter to cross into the LV using a .035" J tipped wire. Remove the J wire and check an LVEDP.
7. Shape the tip of the exchange length 0.018" wire included in the kit and insert it into the LV so that it forms a stable curve at the LV apex.
8. Make sure ACT is at goal (250 to 300 s) before insertion^12,13.
9. Remove the pigtail catheter and insert the pump by loading the wire on the pre-assembled loading red lumen (e.g., EasyGuide) until it exits near the label.
10. Remove the loading red lumen by gently pulling on the label while holding the catheter.
11. Advance the device in small increments under fluoroscopic guidance into the LV over the 0.018" wire.
12. Position the pump in the LV with its inlet 4 cm below the aortic valve and make sure it is free from the mitral chordae. Being too close to the apex can cause PVCs and trigger "suction alarms". Remove the .018" wire and once removed, start the pump. Remove excess slack so the pump rests against the lesser curvature of the aorta.
13. Monitor the console to make sure the motor current is pulsatile and aortic waveform is displayed. If a ventricular waveform is displayed, the pump may need to be pulled back.
14. If the device needs to be left in situ, remove the peal-away sheath and insert the repositioning sheath pre-loaded on the device.
15. Check the device position on fluoroscopy and the waveforms on the console again.
16. Palpate (or sense with Doppler) the distal lower extremity arterial pulses including dorsalis pedis and posterior tibial prior to and after insertion of the device. Document this appropriately in the patient's medical record.
17. If pulses or dopplers cannot be obtained, consider taking a lower extremity angiogram using the wire re-introducing port located on the side of the device or using another access to ensure non-obstructive flow to the lower limb.
18. If flow is obstructed, place a reperfusion sheath prior to transferring the patient to the CCU. In patients with PAD who are at high risk for obstructive flow, strongly consider inserting the reperfusion sheath prior to placement of the 14 Fr sheath (i.e., after step 1.4 listed above).
19. Monitor patients treated with a PVAD in the critical care unit (CCU) by personnel trained in its use.

2. Post-procedural care

1. Apply sterile dressing.
2. Position the device at a 45° angle when entering the skin (gauze underneath the repositioning sheath can be helpful to maintain this angle). Failure to do so may result in the arteriotomy oozing, leading to formation of a hematoma. It is also helpful to place sutures with forward pressure to avoid device migration and to prevent bleeding.
   NOTE: Securing the lower extremity with a knee immobilizer can also limit device migration as a reminder to patient not to bend/move the effected limb. This should not be fastened too tightly so as not to compromise circulation.
3. Continue to perform routine pulse checks (palpable or Doppler).

3. Positioning

1. Use bedside transthoracic echocardiogram to confirm appropriate device position either prior to transfer or immediately on arrival to the cardiac ICU, depending on availability of a point of care ultrasound.
2. Use a parasternal long axis view to assess device position. A subxyphoid view may also be used if parasternal long axis view is not obtainable. A measurement from aortic valve to the device inlet should ideally be 3-4 cm for proper positioning of the device.
3. Use echocardiograms to note the position of the device as it relates to the mitral valve.
4. When a device needs to be repositioned, turn down the device to P2, unscrew the locking mechanism on the sterile cover to advance or retract the device. One can torque as advancing or retracting if the pigtail or inlet is too close to the mitral valve.
5. Lock the device in the new position and document the new position.
6. Following this, increase the device to the desired level of support.
7. After increasing the level of support, reevaluate the device position as the device can jump forward when speed increases.
   NOTE: If the device has been pulled back across the aortic valve, repositioning is better done in the cath lab under fluoroscopy guidance.

4. Weaning

1. Consider weaning when vasopressors/inotropes are at low doses or completely weaned off. Hemodynamics should be continuously monitored to maintain a CPO > 0.6 W. Carefully monitor right ventricular (RV) hemodynamics with a goal to maintain right atrial pressure (RAP) <12 mmHg and pulmonary artery pulsatility index (PAPI) >1.0¹⁴. Also consider obtaining pH, mixed venous saturations and lactate every 2-6 hours to monitor cardiac work and end-organ perfusion.
2. Decrease power by 1-2 levels over 2 hours, noting CPO, PAPI, RAP, MAP and urine output. If CPO drops <0.6 W, RAP begins to increase, urine output drops > 20 mL/h or MAP <60 mmHg, increase power to previous level.

5. Removal¹²

1. Use vascular closure devices to close the arteriotomy access site with complete deployment of the device performed when the large bore sheath is removed¹⁴. Temporary endovascular balloon tamponade or "dry field closure technique" is an effective and safe way to ensure hemostasis of the large bore access site¹⁵.
2. Dial down to P1 and pull back the device into the aorta followed by change to P0 and disconnect the device from the console as the catheter is pulled out of the body.
   1. Note that the device should not be left across the aortic valve at P0 due to the risk of aortic regurgitation.
3. If considering manual hemostasis, wait until ACT <150 and hold 3 minutes of pressure per French size.

Results

Table 1 shows the safety and efficacy of PVAD implantation^{35,36,37,38,39,40}.

Optimizing PVAD Outcomes
PVADs are a resource-heavy intervention that requires significant experience and expertise to optimize outcomes. The following best practices should be consi...

Discussion

Minimizing the Risks and Complications of PVAD (Table 2)
The hemodynamic benefits of PVAD can be significantly neutralized if complications from large-bore access occur, such as major bleeding and acute limb ischemia^28,29. It is thus essential to minimize the risk and complications of the device.

In order to decrease access site complications and reduce the number of access attempts, ultrasound and fluoroscopic g...

Materials

Name	Company	Catalog Number	Comments
4 Fr-018-10 cm Silhouette Stiffened Micropuncture Set	Cook	G48002	Microvascular access
5 Fr Infiniti Pigtail Catheter	Cordis	524-550S	pigtail catheter
Impella CP Intra-cardiac Assist Catheter	ABIOMED	0048-0003	Impella catheter kit