Left Ventricular Assist for High-Risk Percutaneous Coronary Intervention

Abstract: As percutaneous coronary intervention (PCI) is being applied to higher-risk patients, ie, those with unprotected left main, multi-vessel disease, last remaining vessel, compromised left ventricular function, and ongoing ischemia, interventional cardiologists have used different percutaneous assist devices in an attempt to reduce procedure risk. The definition of high risk has varied among trials. There is no definitive evidence for superiority of the more invasive devices over the intra-aortic balloon pump (IABP); furthermore, a prophylactic strategy of IABP insertion has not proven superior to a provisional strategy. The purpose of this report is to review the physiologic mechanism of action of the devices and discuss indications, limitations, and clinical outcomes during high-risk PCI.

J INVASIVE CARDIOL 2012;24(10):544-550

Key words: LV assist, assist devices, high-risk PCI, Impella, IABP

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As percutaneous coronary intervention (PCI) has matured, it is being applied to higher-risk patients (Table 1).¹ Thus, patients with ongoing ischemia, unprotected left main, multi-vessel coronary artery disease, complex lesions, last remaining coronary vessel, and severely depressed left ventricular (LV) function are being treated with PCI. In order to improve safety, percutaneous support devices have been placed. The purpose of this report is to review these devices and discuss their role in the management of patients at high risk for PCI.

In particular, we will review the role of intra-aortic balloon counter-pulsation, the axial flow pump (Impella), left atrial femoral bypass (Tandem Heart), and extracorporeal membrane oxygenation (ECMO) in patients deemed to be at high risk.

Intra-aortic balloon pump (IABP)

The IABP has been used in clinical practice for 50 years, and is the most commonly used device to provide coronary and systemic circulatory support. The National Center for Health Statistics estimated that an IABP was used in 42,000 patients in the USA in 2002, the last remaining year for which data are available.

The intra-aortic balloon is placed in the proximal descending aorta. The physiologic effects are listed in Table 2.¹

Input and removal of helium gas causes inflation and deflation of the balloon. The timing of balloon inflation and deflation is based upon the aortic pressure waveform and the electrocardiogram. The effectiveness of the IABP results from synchronized counter-pulsation, the core principle of IABP therapy. The balloon inflation occurs immediately after aortic valve closure and balloon deflation just before opening of the aortic value. Inflation and deflation of the balloon have two major effects: inflation during diastole causes blood displacement into the proximal aorta resulting in increased coronary blood flow, while deflation during systole reduces aortic volume and afterload through a vacuum effect (Figure 1).

IABP counter-pulsation rapidly stabilizes patients in cardiogenic shock. The greatest improvement in cardiac index and pulmonary capillary wedge pressure occurs in patients with mechanical defects complicating acute myocardial infarction (MI), ie, mitral regurgitation or ventricular septal defect.¹

IABP is not a stand-alone therapy for cardiogenic shock and should only be used in conjunction with definitive therapy, ie, myocardial revascularization or correction of mechanical defects. Despite its ability to stabilize patients, the IABP has not been shown to decrease mortality in patients with ST-elevation MI except in those treated with fibrinolytic agents. However, the observational data of decreased mortality observed with fibrinolysis are limited due to selection bias and the lack of randomized trials.^2-4

High-risk PCI. Several observational studies have suggested that mortality and major complications after high-risk PCI can be reduced by elective insertion of an intra-aortic balloon pump.^5,6 The Balloon Pump Assisted Coronary Intervention Study (BCIS-1) is the only prospective, randomized trial that addresses the hypothesis that elective IABP insertion before high-risk PCI reduces major adverse cardiac and cerebrovascular events.⁷ This study compared prophylactic placement of an IABP to provisional use (if emergently needed for hemodynamic compromise during high-risk PCI). High-risk PCI was defined as the presence of impaired LV function (ejection fraction <30%) and extensive multivessel coronary disease, critical left main stenosis, or a target vessel that provides collateral supply to an occluded second vessel that in turn supplies >40% of myocardium. No difference was found in the composite primary endpoint, which consisted of death, acute MI, cerebrovascular event, or repeat revascularization. Of note, 12% of the patients assigned to the provisional strategy required “bail-out” IABP insertion due to hemodynamic instability. While the results of this study do not support routine prophylactic IABP placement, the cross-over rate in the provisional arm suggests that the operator be prepared for emergency placement. In our laboratory, we frequently place a 4 Fr sheath in the contralateral femoral artery to deal with this possibility.

Refractory myocardial ischemia. Clinical investigation has shown varying effects on coronary blood flow during IABP counter-pulsation, from no change to significant augmentation.^8-11 One study directly measured coronary blood flow during IABP counter-pulsation in patients with cardiogenic shock and unstable angina. IABP was found to augment proximal coronary blood flow velocity, nearly doubling the coronary flow velocity integral.¹¹ Furthermore, the IABP has been shown to be beneficial in patients with acute coronary syndromes with rapid reduction in electrocardiographic indices of myocardial ischemia and relief of refractory angina.^12,13

Complications. A review of nearly 17,000 patients who had an IABP inserted from 1996 to 2000 reported a 2.8% rate of major complications (Table 3).¹⁴

Axial flow pump: The Impella 2.5 device

The Impella 2.5 is a minimally invasive, catheter-based cardiac assist device that is delivered through a 13 Fr sheath via the common femoral artery, and is placed retrograde across the aortic valve into the LV. A revolving pump rotates at a maximum speed of 51000 rpm, drawing blood out of the LV and ejecting it into the ascending aorta beyond the end of the pump (Figure 2). The 13 Fr Impella device provides up to 2.5 L/min of forward flow from the LV into the systemic circulation. A larger 22 Fr catheter device, the Impella 5.0, results in cardiac output up to 5.0 L/min. The Impella reduces myocardial workload and myocardial oxygen consumption, with concomitant increases in cardiac output, coronary perfusion, and end-organ perfusion.

In order to understand the physiologic effects of the Impella, we will use pressure-volume (PV) loops to demonstrate ventricular hemodynamics and compare those with the effects seen in the IABP. PV loops are often used to characterize ventricular hemodynamics during a complete cardiac cycle. As the ventricle is unloaded by reduction in the left ventricular end diastolic pressure and volume, the area of the PV loop diminishes, resulting in a reduction in left ventricular work (Figures 3A and 3B).

High-risk PCI. Several clinical studies demonstrate the feasibility of the Impella 2.5 for cardiogenic shock secondary to acute MI and for support during high-risk PCI.^15-17

The Protect II trial was a randomized comparison evaluating the effectiveness of the Impella versus IABP for use during high-risk PCI.¹⁸ The criteria for high-risk PCI were the presence of unprotected left main disease, last patent conduit, and LVEF ≤35% or 3-vessel disease and LVEF ≤30%. The primary endpoint was a composite and included death, acute MI, stroke, repeat revascularization, severe hypotension, cardiopulmonary resuscitation/ventricular tachycardia, limb ischemia, increase in aortic insufficiency, and acute renal failure. There was no statistically significant difference in the primary endpoint for patients who received IABP vs the Impella at 30 and 90 days (Figure 4). Of note, subgroup analysis revealed higher rotational atherectomy use in the Impella arm with fewer repeat revascularization procedures. Moreover, cardiac power, which is a measurement of cardiac pump function, was utilized to assess the hemodynamic effectiveness. The Impella was shown to provide superior hemodynamic support as measured by cardiac power output. The results of this study demonstrate the non-inferiority of the Impella 2.5 to IABP for high-risk PCI. The use of the Impella should be considered when greater hemodynamic support is anticipated.

The ISAR-SHOCK trial compared the Impella 2.5 with the IABP in 26 patients with cardiogenic shock due to acute MI.¹⁹ The primary endpoint was the change in cardiac index from baseline to 30 minutes after implantation. The Impella 2.5 resulted in a greater increase in cardiac index compared to the IABP at 30 minutes (Impella: ΔCI = 0.49 ± 0.46 L/min/m²; IABP: ΔCI = 0.11 ± 0.31 L/min/m²; P=.02). However, at all other time points up to 30 hours, cardiac index was similar in the two groups. Although underpowered for clinical outcomes, 30-day mortality was the same in both groups. The results of this study demonstrate that the Impella will provide more rapid stabilization in patients with cardiogenic shock secondary to acute MI, but the effects are not sustained.

Contraindications. Contraindications for Impella use include aortic regurgitation, prosthetic aortic valve, aortic dissection, severe aortic or peripheral vascular disease, left ventricular or left atrial thrombi, bleeding diathesis, and uncontrolled sepsis.

Tandem Heart

The Tandem Heart is a left atrial-to-femoral artery bypass system, which utilizes a 21 Fr transseptal cannula, a 15-17 Fr arterial cannula, and a centrifugal blood pump. A venous catheter is inserted into the femoral vein and into the left atrium using the transseptal approach. Another cannula is inserted via the femoral artery and placed into the iliac artery. A centrifugal pump delivers flow rates up to 4.0 L/min at a maximum speed of 7500 rpm. The LV is unloaded by diverting blood from the left atrium to the systemic circulation (Figure 5).

High-risk PCI. The use of Tandem Heart in high-risk patients with unprotected left main artery and severely compromised LV function was evaluated in small observational studies, which demonstrated feasibility of use.^20-22 However, clinical benefit has not been clearly established.

A randomized trial compared the IABP with the Tandem Heart in patients undergoing revascularization for acute MI complicated by cardiogenic shock.²³ The primary endpoint was defined as hemodynamic improvement, as measured by cardiac index 2 hours after device implantation. Although there was a greater improvement in hemodynamic parameters with the left atrial femoral bypass, there were more bleeding and vascular complications. To date, there are no convincing clinical data to suggest improved clinical outcome using Tandem Heart compared to IABP in cardiogenic shock patients, despite superior hemodynamic support.

Contraindications. Contraindications to using the Tandem Heart device include aortic regurgitation, aortic dissection, severe peripheral vascular disease, bleeding diathesis, and uncontrolled sepsis.

Extracorporeal membrane oxygenation (ECMO)

The percutaneous cardiopulmonary support (CPS) provides full cardiovascular and pulmonary support analogous to that provided by bypass during cardiac surgery. With newer ECMO systems, patients may receive complete circulatory support for days to weeks.

Veno-arterial ECMO involves femoral insertion of two large-bore catheters. One is positioned in the aorta and the other in the right atrium. Blood from the venous catheter is pumped through a heat exchanger and oxygenator, and then returned to the systemic arterial circulation via the arterial cannula. ECMO removes carbon dioxide from and adds oxygen to venous blood via an artificial membrane, thus bypassing the pulmonary circulation. Oxygenated blood returns to the patient via an arterial route. ECMO can be instituted prophylactically, or used as standby during high-risk PCI. One analysis of 23 national registries investigated 569 patients comparing prophylactic versus standby percutaneous CPS in high-risk PCI. There were 389 patients in the prophylactic CPS group (catheters inserted and bypass initiated prior to PCI), and 180 patients in the standby group (preparations made, but bypass not initiated prior to PCI). High-risk PCI was defined as LVEF <25% or an angioplasty target vessel supplying >50% of viable myocardium or both. There were significantly higher femoral access-site complications and requirement of blood transfusions in the prophylactic CPS group compared with the standby group. Procedural success was not different between the groups. Of note, among patients with an LVEF <20%, procedural mortality was higher in the standby group. Thus, standby CPS affords comparable procedural success with a lower morbidity from access-site related issues. In patients with extremely depressed left ventricular function (LVEF <20%), prophylactic CPS may reduce mortality.

Contraindications. Contraindications to ECMO include significant aortic regurgitation, severe peripheral artery disease, bleeding diathesis, recent stroke or head trauma, and uncontrolled sepsis.

Representative case. A 76-year-old female with end-stage renal disease, hypertension, history of a transient ischemic attack, coronary artery bypass grafting 6 weeks ago (left internal mammary [LIMA] to left anterior descending [LAD]), presented with congestive heart failure and recurrent ventricular tachycardia in the setting of a non-ST elevation MI with dynamic ST changes.

Coronary angiography revealed severe calcified distal left main (LM) stenosis with multiple severely calcified lesions throughout the LAD (Figure 6A). The left circumflex and right coronary arteries had proximal chronic total occlusions filling via collaterals (Figures 6A and 6B). The recent LIMA to LAD was found to be 100% occluded (Figure 6C). Right heart catheterization showed significant pulmonary hypertension with pulmonary artery pressure of 66/30 mm Hg with a mean of 46 mm Hg. A left ventriculogram showed LVEF of 45% with significant mitral regurgitation (Figure 6D). Peripheral angiogram revealed severe left iliac artery disease (Figure 7A).

Because of the presence of complex, calcified LM/LAD lesions, occluded circumflex and right coronary artery in conjunction with LV systolic dysfunction and severe mitral regurgitation, we elected to use the Impella axial flow pump. In order to deal with the severe iliac disease, we performed a left iliac reconstruction with excellent results (Figure 7B). After preclosure of the femoral artery using percutaneous suture, we were able to advance a 13 Fr sheath for placement of an Impella 2.5 (Figure 8A), followed by rotational atherectomy and placement of stents in the LAD and LM coronaries (Figure 8B). The patient recovered nicely and was discharged in stable condition.

Summary

As PCI is being extended to a select group of very high-risk patients, support devices have been utilized in order to increase the safety and effectiveness of the revascularization procedure. Of note, the definition of ‘high-risk PCI’ has varied across the various studies. It should be emphasized that there are no compelling data to suggest the superiority of the more invasive devices over the IABP. Furthermore, a provisional strategy appears to be equally efficacious to prophylactic insertion of the IABP. In our experience, the vast majority of interventions can be safely performed without support; however, the operator should be familiar with the two most commonly used devices, the IABP and the Impella axial flow pump, and be prepared for their use based on the specific clinical and anatomic scenario of each patient.

Therefore, we recommend:

1. Careful assessment of coronary anatomy and anticipation of difficulties that may be encountered during the procedure. Heavy lesion calcification, bifurcation disease may require vessel preparation with rotational atherectomy and the use of multiple stents. Circulatory support is especially helpful in such circumstances.
2. Assessment of LV function. Patients with depressed LV function (EF<35%) and/or significant mitral regurgitation may require the substantial augmentation in cardiac output provided by the Impella axial flow pump.
3. Assessment of peripheral vasculature for stenosis, calcification or tortuosity with consideration of peripheral reconstruction if needed.
4. Placement of a contralateral femoral sheath if a provisional strategy is employed.
5. Selection of IABP or Impella depending on the need for ischemia control (IABP) versus augmentation of cardiac output (Impella).
6. Development of a strategy for rapid removal of the devices after the procedure is completed. In general, especially with the larger Impella, we favor the suture-mediated closure strategy for effective hemostasis.

References

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From the Department of Cardiovascular Medicine, Hahnemann University Hospital, Philadelphia, Pennsylvania.
Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.
Manuscript submitted April 24, 2012, provisional acceptance given May 4, 2012, final version accepted May 21, 2012
Address for correspondence: Sheldon Goldberg MD, Cardiology Consultants of Philadelphia, Hahnemann University Hospital, 230 North Broad MS108, Philadelphia, PA 19102. Email: sheldongoldberg66@gmail.com