Coronary hemodynamics and myocardial oxygen consumption during support with rotary blood pumps.
ABSTRACT Mechanical support offered by rotary pumps is increasingly used to assist the failing heart, although several questions concerning physiology remain. In this study, we sought to evaluate the effect of left-ventricular assist device (VAD) therapy on coronary hemodynamics, myocardial oxygen consumption, and pulmonary blood flow in sheep. We performed an acute experiment in 10 sheep to obtain invasively measured coronary perfusion data, as well as pressure and flow conditions under cardiovascular assistance. A DeBakey VAD (MicroMed Cardiovascular, Inc., Houston, TX, USA) was implanted, and systemic and coronary hemodynamic measurements were performed at defined baseline conditions and at five levels of assistance. Data were measured when the pump was clamped, as well as under minimum, maximum, and moderate levels of assistance, and in a pump-off condition where backflow occurs. Coronary flow at the different levels of support showed no significant impact of pump activity. The change from baseline ranged from -10.8% to +4.6% (not significant [n.s.]). In the pulmonary artery, we observed a consistent increase in flow up to +4.5% (n.s.) and a decrease in the pulmonary artery pressure down to -14.4% (P = 0.004). Myocardial oxygen consumption fell with increasing pump support down to -34.6% (P = 0.008). Left-ventricular pressure fell about 52.2% (P = 0.016) as support was increased. These results show that blood flow in the coronary arteries is not affected by flow changes imposed by rotary blood pumps. An undiminished coronary perfusion at falling oxygen consumption might contribute to cardiac recovery.
Coronary Hemodynamics and Myocardial
Oxygen Consumption During Support
With Rotary Blood Pumps
*Peter Voitl, †‡Michael Vollkron,
‡§Helga Bergmeister, †‡Georg Wieselthaler,
and *†‡Heinrich Schima
*Center for Biomedical Engineering and Physics;
†Department for Cardiothoracic Surgery; ‡Ludwig
Boltzmann-Cluster for Cardiovascular Research; and
§Center for Biomedical Research, Medical
University of Vienna,Vienna,Austria
Abstract: Mechanical support offered by rotary pumps
is increasingly used to assist the failing heart, although
several questions concerning physiology remain. In this
study, we sought to evaluate the effect of left-ventricular
assist device (VAD) therapy on coronary hemodynamics,
myocardial oxygen consumption, and pulmonary blood
flow in sheep. We performed an acute experiment in 10
sheep to obtain invasively measured coronary perfusion
data, as well as pressure and flow conditions under cardio-
vascular assistance. A DeBakey VAD (MicroMed Cardio-
vascular, Inc., Houston, TX, USA) was implanted, and
systemic and coronary hemodynamic measurements were
performed at defined baseline conditions and at five levels
of assistance. Data were measured when the pump was
clamped, as well as under minimum, maximum, and mod-
erate levels of assistance, and in a pump-off condition
where backflow occurs. Coronary flow at the different
levels of support showed no significant impact of pump
activity.The change from baseline ranged from -10.8% to
+4.6% (not significant [n.s.]). In the pulmonary artery, we
observed a consistent increase in flow up to +4.5% (n.s.)
and a decrease in the pulmonary artery pressure down to
-14.4% (P = 0.004). Myocardial oxygen consumption fell
with increasing pump support down to -34.6% (P = 0.008).
Left-ventricular pressure fell about 52.2% (P = 0.016) as
support was increased. These results show that blood flow
in the coronary arteries is not affected by flow changes
imposed by rotary blood pumps. An undiminished coro-
nary perfusion at falling oxygen consumption might con-
tribute to cardiac recovery.
Key Words: Left-ventricular
The prevalence of cardiovascular disease is on the
increase and is currently the most frequent cause of
death.For many patients with advanced heart failure,
the final treatment option is heart transplantation.
However, donor hearts are scarce and frequently
unavailable when required. Implantable cardiac-
support systems allow some of these patients to live
and experience an acceptable quality of life over a
long period of time. The spectrum of application of
these systems is changing as technical improvements
are being made and miniature systems are produced.
Some of the systems are specifically designed as des-
tination therapy (1,2).
The use of rotary blood pumps has gained wide-
spread acceptance. Rotary blood pumps are small
and clinically applicable systems capable of long-
term support. They are well-suited as an interim
therapy for left-ventricular insufficiency,as well as an
end-stage treatment for patients who cannot undergo
transplantation for a variety of reasons (3,4). Over
the last few years, these systems have emerged as a
feasible alternative to conventional pulsatile pumps,
although several questions concerning physiology
are still being addressed in a number of studies
(5–9), including computer models (10). Aspects of
the hemodynamic basis of ventricular assist devices
(VADs) have been discussed particularly with
respect to arterial blood flow pulsatility and histo-
logic changes. The effects of rotary blood pumps on
coronary blood flow have not been adequately docu-
mented;one study showed a decrease in the coronary
flow in pigs with and without a surgically created
coronary stenosis (11). Improved perfusion has been
previously registered with the use of pulsatile pump
systems (12). New information about coronary
perfusion and myocardial oxygen consumption is
Received August 2007; revised February 2008.
Address correspondence and reprint requests to Dr.PeterVoitl,
Medical University of Vienna, Center for Biomedical Engineering
and Physics, Waehringer Guertel 18-20, 1090 Vienna, Austria.
THOUGHTS AND PROGRESS77
Artif Organs,Vol. 33, No. 1, 2009
needed to design strategies for optimal unloading
and/or training of the heart and to model coronary
perfusion during cardiac assist. The purpose of the
present study was to investigate the effect of pump
flows oncoronary parameters
implanted left VAD (LVAD) (DeBakey VAD,
We performed an in vivo investigation during an
acute experiment in 10 sheep to determine invasively
measured coronary perfusion data, as well as pres-
sure and flow conditions under cardiovascular assis-
tance by means of rotary blood pump support of the
beating heart. Ten sheep (96 ? 19 kg) were anesthe-
tized with isofluorane, fentanyl, and propofol.A left-
sided thoracotomy with resection of the fifth rib was
performed,and a DeBakeyVAD (MicroMed Cardio-
vascular,Inc.) was implanted between the apex of the
left ventricle and the descending aorta. The specific
cannulation technique used in these experiments
restricts the results to this type of cannulation, and
VADs connected to the ascending aorta might have
a different impact on vascular hemodynamics. An
external pacemaker (atrial and ventricular) was used
to fix the heart rate and central-venous pressure.The
study protocol was approved by the ethics committee
of the Medical University of Vienna.
Within these 10 acute animal experiments, 51 h of
data were recorded.The program for data acquisition
was developed in Matlab/Simulink and was imple-
mented with a dSpace DS1103 board (dSPACE
GmbH, Paderborn, Germany). The analog-input
channels had a resolution of 16 bits and the sampling
rate was 100 Hz. For each of the baseline conditions
shown in Table 1, up to five levels of assistance were
tested. First, the pump was clamped (simulating no
pump), then, minimum, maximum, and moderate
levels of assistance were applied,and finally,a pump-
off condition, where backflow occurs, was imposed.
The amount of backflow in the pump-off condition
was 1.5–2 L per min.
As it is very difficult to establish a stable model of
heart failure, different baseline settings were used to
assure identical starting points for the data collection.
When the natural heart rate exceeded the fixed pace-
maker rate, a certain degree of variation of the heart
rate or the central-venous pressure occurred. The
predefined baseline conditions for the measurements
are shown in Table 1.
Blood samples were taken from central-venous-
and arterial catheters,and also from a catheter in the
coronary sinus which was implanted through the
azygos vein. Systemic and coronary hemodynamic
measurements were performed at the baseline con-
ditions defined in Table 1. Due to the poor general
condition of some sheep,data could not be elicited at
all steps in all sheep.
Coronary flow at the different levels of support
showed no significant impact of pump activity on the
measured flow values in the coronary arteries. Coro-
nary blood flow hardly changed at the different levels
of left-ventricular support. As shown in Fig. 1, coro-
nary flow was largely unaffected by the various base-
line conditions for central-venous pressure and heart
rate.Data from the moderate level of assistance have
been excluded in the figures as these measurements
could not be obtained in all animals.The flow in the
pulmonary artery showed a constant increase.
Myocardial oxygen consumption fell as expected
with increasing levels of pump support. Both
left-ventricular pressure and left-atrial pressure
decreased as support was increased, suggesting that
wall tension was reduced (Fig. 2).
Cardiac-support systems are implanted essentially
for two reasons: on the one hand to ensure sufficient
blood pressure and organ perfusion,and on the other
hand to reduce the load on the left ventricle and
allow the heart to recover (2,9).
It has been shown that an ischemic area can be
reduced by improved myocardial blood flow (13).
Furthermore, it has been suspected that one of the
major effects of a pump on coronary hemodynamics
is the reduction of ventricular load in combination
with reduced oxygen consumption (14). Finally, it
has been observed that pulmonary hypertension in
cardiac-transplant candidates can be lowered using
In fact, very few data are available to show the
effect of these pump systems on perfusion param-
eters in the coronary arteries. Such information are
TABLE 1. Predefined baseline conditions
pressure (mm Hg)
THOUGHTS AND PROGRESS78
Artif Organs,Vol. 33, No. 1, 2009
especially important to devise strategies to determine
pump settings that optimize perfusion conditions in
the left ventricle.
The present experiment showed that blood flow in
the coronary arteries is not affected by changes in
pump flow,whereas the myocardial oxygen consump-
tion can be reduced by increased levels of mechanical
assistance. Alterations in myocardial vascular pres-
sure resulting from changes in myocardial wall
tension might be compensated by autoregulatory
mechanisms, although these are not documented in
this series, possibly due to changes in endocardial
volume under pump support (8).
Falling myocardial oxygen consumption might be
explained by the reduced wall tension during
enhanced assistance,but constant coronary perfusion
could be explained by increased diastolic perfusion
pressure.Given the elevated mean pressure and dias-
tolic pressure in the aorta during support, the second
effect may possibly act as an additional factor in this
setting. Finally, one notes that unaltered coronary
FIG. 1. Coronary blood flow (A) and pulmonary artery flow (B) at various pump settings, changes from baseline at level 1a: central-
venous pressure = 10 mm Hg; Heart Rate (HR) = 100 bpm. Qcor, coronary artery flow; Qpulm, pulmonary artery flow.
FIG. 2. Myocardial oxygen consumption (A) and left-ventricular pressure (B), changes from baseline at level 1a: central-venous
pressure = 10 mm Hg; Heart Rate (HR) = 100 bpm. LVP, left-ventricular pressure.
THOUGHTS AND PROGRESS79
Artif Organs,Vol. 33, No. 1, 2009
perfusion at falling oxygen consumption might con-
tribute significantly to cardiac recovery.
The measured systemic responses at the different
settings show that the pump reduces the load on the
left ventricle and is fully capable of maintaining mean
aortic pressure. Furthermore, a decreased left-
ventricular pressure was observed with increasing
By nature, changes in the pulmonary artery reflect
enhanced LVAD support with increasing flow and
reduced pressure. However, this may also be inter-
preted as a drop in pulmonary vascular resistance:an
effect that can help stabilize the right ventricle.
These results reflect, on the one hand, the known
hemodynamic effects of rotary blood pumps on pres-
sure conditions in the heart and the large vessels,and
on the other hand, signal the reduced oxygen con-
sumption of the myocardium. The results could be
indicative of cardiac recovery. No effect on myocar-
dial flow was registered in the present experiment.
The reduced left-atrial pressure and increased pul-
monary flow that was observed might be indicative of
decreased vascular resistance. The pressure–flow
relationship of the coronary arteries showed no evi-
dence of an autoregulatory effect.
The limitations of the study were the frequent
alterations of pump support and the absence of pre-
vious left-heart failure. Investigations of myocardial
flow itself would be desirable. Likewise, further
studies in hearts with chronic left-heart failure should
be performed. A further limitation of the present
study was the small number of sheep used and the
diverse baseline conditions of the animals. Neverthe-
less,homogenous data were obtained within the indi-
This study shows, in acute experiments, that mean
coronary flow does not necessarily correlate with
changes in pump flows imposed by rotary blood
pumps. Unaltered coronary perfusion at falling
oxygen consumption during ventricular unloading
was observed and might contribute to cardiac
recovery.The obtained results are primarily valid for
a descending aorta VAD cannulation technique, and
VADs connected to the ascending aorta might reveal
Acknowledgments: We thank Edward Leonard
from the Department of Chemical Engineering,
Columbia University, New York, NY, for his assis-
tance in preparing the manuscript.
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Peter K Voitl