Comparing Hemodynamics of Contemporary Mechanical Circulatory Support

JACC: CARDIOVASCULAR INTERVENTIONS

VOL.

ª 2016 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION

-, NO. -, 2016

ISSN 1936-8798/$36.00

PUBLISHED BY ELSEVIER

http://dx.doi.org/10.1016/j.jcin.2016.09.012

EDITORIAL COMMENT

Comparing Hemodynamics of Contemporary Mechanical Circulatory Support Moving from In Silico to In Vivo Results* Morton J. Kern, MD, MSCAI, Arnold H. Seto, MD, MPA

T

he degree of myocardial recovery determines

involving LV unloading and other performance

the function and ultimately the survival of a

characteristics. To review, the intra-aortic balloon

patient in cardiogenic shock. Therapeutic

pump inflates in diastole, generating an augmented

efforts to improve myocardial function include inten-

pressure pulse and deflates abruptly in systole

sive pharmacotherapy (inotropes, vasopressors), and

reducing LV afterload. The net hemodynamic effects

use of mechanical circulatory support (MCS) devices,

of intra-aortic balloon pump produce (to variable

including the intra-aortic balloon pump, the left ven-

degrees) an increase in mean arterial pressure, coro-

tricular (LV)-to-aorta axial pump catheter (Impella CP

nary perfusion, and mild decrease in myocardial

[IMP]) and the left atrial (LA)-to-femoral artery pump

work. The magnitude of these effects is smaller than

(TandemHeart [TH]). All act through different mecha-

those of either the IMP or TH and requires a contracting

nisms, and to different degrees, to unload the heart,

heart to function effectively. The IMP works through a

increase blood pressure, cardiac output and systemic

catheter-mounted axial pump, drawing blood from the

perfusion, while reducing myocardial work and oxy-

LV and expelling it into the ascending aorta. The TH

gen consumption.

pulls blood from the left atrium through a trans-septal

The hemodynamics of MCS devices are known to

inserted large (22-F) inflow cannula to an external

us predominately from computer simulations (“in

centrifugal pump, returning the blood to the arterial

silico” models) (1,2), in vivo animal studies (3,4), and

circulation through the femoral artery. Both IMP and

series of cardiogenic shock patients (5,6). In practice,

TH substantially reduce LV stroke volume, LV loading,

a specific device is selected based both on its pre-

and myocardial work, and increase cardiac output and

sumed hemodynamic power as well as the patient’s

systemic pressure. Although the hemodynamics of

clinical features (e.g., status of the aortic valve, pe-

IMP and TH have been explored extensively by com-

ripheral vascular disease, etc.) and technical chal-

puter simulations (1,2), it remains largely unknown to

lenges of device implantation (e.g., cannula size, ease

what degree the MCS devices perform under in vivo

and speed of insertion, and availability of a trained

conditions, in the same subject with the same flow

team on call).

rates. Moreover, hemodynamic differences from

Because of the different mechanisms of action, we

computer simulations would be anticipated since any

can expect unique hemodynamic profiles, especially

in silico model cannot not completely replicate the more complex behavior of the intact, in vivo animal cardiovascular system (7).

*Editorials published in JACC: Cardiovascular Interventions reflect the

Moving from in silico to in vivo, Weil et al. (8)

views of the authors and do not necessarily represent the views of JACC:

compared the hemodynamics of the IMP and TH

Cardiovascular Interventions or the American College of Cardiology.

from a closed chest animal model of myocardial

From the Veterans Administration Long Beach Health Care System,

infarction.

University of California, Long Beach, California. Dr. Kern is a speaker for

catheter, PV loops were obtained before and after a

Abiomed Inc., St. Jude Medical, Volcano Therapeutics, Acist Medical,

Using

a

LV

pressure–volume

(PV)

Opsens Inc., and Heartflow Inc. Dr. Seto has reported that he has no

moderate-sized myocardial infarction was induced

relationships relevant to the contents of this article to disclose.

with a 2-h circumflex coronary artery occlusion.

2

Kern and Seto

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Hemodynamics of Contemporary Mechanical Circulatory Support

T A B L E 1 Comparative Hemodynamic Effects of Percutaneous Ventricular

Assist Devices

more effective decreases in myocardial oxygen demand would lead to greater myocardial recovery after infarction, or more support during cardiogenic shock.

IMP

Heart rate (beats/min)

TH

¼

¼

This well-performed study, comparing 2 commonly used MCS devices head to head for the first time in

Mean aortic pressure (mm Hg)

¼

¼

Aortic pulse pressure (mm Hg), control to device activation

34  2 to 27  4

34  2 to 14  1*†

LV end-diastolic pressure (mm Hg)

15  1 to 11  1*

15  2 to 7  4*†

whether blood is withdrawn directly from the LA or

Pulmonary capillary wedge pressure (mm Hg)

15  2 to 13  2

15  2 to 9  1*

the LV. The IMP draws blood from the LV and

End-systolic elastance (mm Hg/ml)

¼

¼

LV stiffness constant (b)

þ

þ

diastolic pressure and maintained arterial pressure,

LV dP/dtmax reduction

-

þþ

but in this study did not affect PV loop-derived

LV stroke work reduction

þ

þþþ

indices of myocardial work significantly. In contrast,

LV pressure volume area reduction

þ

þþþ

TH withdrawal of blood from the LA also reduced LV

LV preload recruitable stroke work reduction

-

þ

end-diastolic volume and LV end-diastolic pressure,

Values are mean  SEM. *p < 0.05 vs. post-MI; †p < 0.05 vs. Impella CP (IMP). Adapted from Weil et al. (8). þ ¼ improved compared with control MI state; ¼ ¼ equivalent change between devices; - ¼ no improvement compared to control; LV ¼ left ventricular; TH ¼ TandemHeart.

this way, suggests that, at comparable device flow rates, the degree of LV unloading depends on

decreased LV end-diastolic volume and LV end-

and maintained arterial pressure while also reducing native LV stroke volume, stroke work, dP/dtmax, PV area, and preload-recruitable stroke work consistent with enhanced LV unloading. Why should the findings of Weil et al. (8) differ from prior studies? Although neither a computer

Although frank cardiogenic shock was not produced,

model nor the induced animal infarction model

myocardial infarction shifted the PV loop to the right

exactly duplicates the human cardiogenic shock

due to an increased LV end-diastolic pressure

state, the in vivo conditions incorporate a number of

accompanied by reduced systolic pressure with

influences on myocardial function, arterial imped-

mildly reduced stroke volume. Both MCS devices

ance and afterload, and peripheral resistance that can

were then sequentially placed, with the order ran-

only be estimated in a more rudimentary fashion in

domized and the goal flow rates matched.

computer simulations. In contrast, the present study

Both MCS devices maintained the aortic pressure

did not truly induce a state of cardiogenic shock.

but, compared to IMP, the TH had a greater reduction

Because unloading with IMP occurs most effectively

in LV end-diastolic pressure (but not volume), native

when cardiac output is low and LV end-diastolic

LV stroke volume, dP/dt max , stroke work, PV area,

pressure and volume are increased (and poorly

and preload stroke work slope (Table 1). In short and

when these states are not present), the present model

at odds with some prior reports (2–5), TH unloaded

may have unfairly tilted the scale against IMP.

and rested the heart to a greater degree than IMP. Of

Why aspiration of similar flow rates from the left

particular interest and unique to this study was that

atrium compared with the LV would have such

the hemodynamics and PV loops of the 2 MCS devices

different hemodynamic effects remains unclear.

were not only different from each other but also diff-

Potentially, this result reflects the greater capacitance

erent from the computer model predictions (Figure 1).

of the LA (compared with the LV) to release volume to

The investigators deserve our compliments for their

the MCS device, particularly in euvolemic, nonshock

rigorous experimental methods. The greater decrease

states, but this would presumably have been evident

in native stroke work by TH suggests a more powerful

from the flow rates measured. Alternatively, the au-

volume unloading of the heart occurs despite the

thors suggest that, by decreasing the LV end-diastolic

relative increase in native end-systolic volume

pressure to a greater extent, LA withdrawal may

compared with IMP as demonstrated by the different

improve coronary blood flow. However, coronary

shapes of the in vivo PV loops (Figure 1). The IMP

blood flow was not measured in this study and would

maintained end-systolic pressure, reduced stroke

not explain how LV end-diastolic pressure is reduced

volume and shifted the PV loop leftward, whereas the

more effectively.

TH increased end-systolic pressure with a pronounced

The IMP and TH are powerful MCS devices that are

reduction in stroke volume and preload. As a result,

frequently used for high-risk percutaneous coronary

the TH produced a greater decrease in PV area (a well-

interventions and cardiogenic shock. In clinical prac-

validated index of myocardial oxygen consumption)

tice, the selection of a percutaneous MCS device de-

than the IMP in the animal model, a contrasting

pends not only on the hemodynamic power of the

observation from the computer models. Conceivably,

device, but also and more important on the specific

JACC: CARDIOVASCULAR INTERVENTIONS VOL.

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Kern and Seto

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Hemodynamics of Contemporary Mechanical Circulatory Support

F I G U R E 1 Ventricular Effects of LA-to-Arterial MCS and LV-to-Aorta MCS

(Top) Computer simulation of ventricular effects of left atrial (LA)-to-arterial mechanical circulatory support (MCS; TH; left) and left ventricular (LV)-to-aorta MCS (IMP; right) showing flow-dependent changes in pressure–volume loops, reductions in end-diastolic pressures, increased end-systolic volume, and decreased LV stroke volume (from Burkhoff et al. [9]). (Bottom) PV loops for TH and IMP from the in vivo animal model of Weil BR et al. (8) (IMP in blue and TH in green) compared with the corresponding unassisted post-myocardial infarction baseline time-point (red). Both devices shifted the PV loop to the left and decreased LV end-diastolic pressure, but TH produced a greater reduction in native LV stroke volume. Ao ¼ aorta; CGS ¼ cardiogenic shock; LVD ¼ left ventricular assist device.

clinical scenario. The TH takes an average of 45 to 60

patient in need of LV mechanical support, the operator

min to insert, compared with <10 min for the IMP,

must choose the device that is most clinically and he-

making the TH less useful in patients with unstable

modynamically appropriate.

cardiogenic shock (9). The risk of major bleeding with the TH is also higher than IMP (25% vs. 6%) (4). The

REPRINT REQUESTS AND CORRESPONDENCE: Dr.

carefully measured hemodynamic in vivo differences

Morton J. Kern, Department of Medicine, Veterans

of LV performance by Weil et al. (8) shift conventional

Administration Long Beach Health Care System,

wisdom about the MCS device power order and should

Building 1, 5901 East 7th Street, Long Beach,

bring new attention to the TH. Nonetheless, for each

California 90822. E-mail: [email protected].

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KEY WORDS cardiac output, hemodynamics, ventricular assist device